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TECHNICAL APPENDICES
CEDAR RIVER SECTION 205 STUDY
Seattle District, Army Corps of Engineers
March, 1997
APPENDIX A
SPONSOR CORRESPONDENCE
a&
CITY OF RENTON
Mayor
Earl Clymer
February 4, 1993
Colonel Walter Cunningham, District Engineer
U. S. Army Engineer District, Seattle
P. O. Box C-3755
Seattle, WA 98124-2255
SUBJECT: APPLICATION FOR SECTION 205 ASSISTANCE FOR THE LOWER CEDAR
RIVER SEDIMENT MANAGEMENT PROJECT
Dear Colonel Cunningham:
This letter is to seek the assistance of the U. S. Army Corps of Engineers under Section 205
of the 1948 Flood Control Act, as amended, in reducing flood damages along the Cedar
River within the City of Renton, King County, State of Washington.
In November, 1990, the Cedar River flooded its banks and caused in excess of $6.6 million
in damages in the City of Renton. In addition, the flooding shut down the Renton Municipal
Airport, threatened bridges, flooded the jail beneath City Hall, and prompted the evacuation
of nearby residents. The current channel capacity to carry flood flows is limited due to
significant sedimentation over the past twenty years.
The rating curve for the Lower Cedar River Channel has shifted upwards by approximately
five feet in the period between November, 1966 and November, 1990. As sedimentation
continues in the channel, further reductions in channel capacity will result in more frequent
occurrences of damaging flows. At current rates of sedimentation, even nearly annual flood
events result in water -surface elevations high enough to impact the airport and other
structures. A recent study prepared under contract to the Boeing Company (Permit
Engineering, 1991) estimated that flood waters would begin to inundate adjacent Boeing
aircraft storage areas at approximately the five year frequency. This points out the
increasing vulnerability to less frequent and more catastrophic storm events.
The City recently completed re -survey and hydraulic evaluation of the lower two miles of the
Cedar River through Renton. In the study a HEC-2 model was used to 1) identify locations
where flow can overtop existing channel banks, 2) determine; the bank fill capacities at those
sites, and 3) several potential flood relief alternatives were: evaluated. The results of the
HEC-2 study, conducted for the City by Northwest Hydraulic: Consultants, Inc. indicated that
the study reach can only safely pass the 2-year event. As identified by the study, the most
significant problem area is along the west bank of the lower river channel near the Renton
lnn Xrii Ave-mie Routh - Renton_ Washington 98055 - (206) 235-2580
4
Colonel Walter Cunningham
U. S' Army Engineer District, Seattle
Page 2
Municipal Airport where water would overtop during events having a return period of about 2
years.
Renton understands the cost sharing requirements for the feasibility phase and the
construction phase as described in the Water Resources Development Act of 1986. The
City would be willing to enter into a cost sharing agreement if the reconnaissance phase
study is favorable and acceptable.
Your consideration of the request would be appreciated. Please contact David Jennings,
Project Manager, Renton Surface Water Utility at (206) 277-6205.
Sincerely,
t& "-\�
Earl Clymer
Mayor
C:DOCS: 93-102:EC: DEJ:ps
CC: Lynn Guttmann
David Jennings
The Boeing Company
P.O. Box 3707
Seattle. WA 98124-2207
February 26, 1993
Colonel Walter J. Cunningham
Commander, Seattle District Office
U.S. Army Corps of Engineers
Federal Center South
4735 E. Marginal Way South
Seattle, WA 98134-3495
Dear Colonel Cunningham:
TOE/NG Subject: City of Renton Correspondence to the U.S.
Corps Requesting a Section 205 Flood Control
Study of the Lower Cedar River.
The Boeing Company strongly supports the efforts of the
City of Renton flood damage reduction through section
205 program. Current proposal is to dredge the lower
portion of the Cedar River. This program application
is of particular interest to The Boeing Company.
Flooding in the past and the immediate potential for
future flooding imperils Boeing's day to day commerce.
The Boeing company delivers a commercial jet aircraft,
from Renton, nearly every business day. If this
schedule is delayed there are substantial monetary
penalties. But even more severe is the dissatisfied
customer, the airline, upon which future business for
the company depends. The revenue generated by the
Boeing Company sales of jet aircraft to foreign firms
makes up a significant part of the United States
balance of trade against a world wide U.S. trade
deficit. Boeing's net exports of commercial airplanes
reduced the 1991 U.S. trade deficit by 18% or $ 14.2
billion dollars. The enclosed brochure "Jets and Jobs,
Boeing: America's Leading Exporter" discusses this in
more detail. Boeing's Renton plant delivered (317) 737
and 757 jet aircraft in 1992 which represented
approximately $14 billion in sales. Of these jet
aircraft, (178) were exported represented approximately
$7.3 billion in sales. Of the two jet aircraft, the
737 and 757 currently produced at the Renton Plant, the
737 is the most popular. With 3,000 orders, the 737 is
the best selling commercial aircraft ever produced.
Currently there is a large backlog of orders for both
jet aircraft produced at Renton.
Page 2
Colonel W. J. Cunningham
The enclosed "Factory Layout Guide" illustrates the
complex manufacturing process required in producing
large commercial jet aircraft. The critical "pinch
points" in this operation are the two bridges that span
the Cedar River, one at the mouth`hnd one approximately
one-half mile up river from the mouth. It is across
these bridges every 757 twin jet must travel to gain
access to the Renton Municipal Airport for its maiden
flight and delivery to the airline customer.
6T,p'E//YG During the November 25 and 26, 1990, flood of the Cedar
River these referenced bridges were in danger of
imminent loss. If The Boeing Company were to lose
these bridges, even just one, all aircraft delivery and
most production would shut down. The effects of this
upon Boeing, its workers, families, the U.S. economy,
and airline customers would be devastating until new
bridges could be constructed. When the next flooding
event occurs, we expect the effect to be even more
severe. Damages to the aprons where the aircraft are
prepared for takeoff and delivery, the adjaceht
manufacturing building, and the plant utilities
infrastructure would be extensive. For example, the
1990 flood occurred on a non -production weekend,
resulting in damages of $ 6,600,000. We anticipate
that the next event will cause even greater monetary
loss.
As a result of the 1990 flood the sediment load on this
stretch of the Cedar River dramatically increased.
Studies done, post-1990 flood, compared to data on pre
1990 flood conditions, show this significant increase
to be an increase of four feet of additional bedload in
the Cedar River Channel. Prior to the 1990 flood, what
would be termed a fifty year event would now be a ten
year event. Given the atypical fall storm events and
the spring snow runoff occurrence, a sustained rainfall
in the spring or fall would produce a flood equal to or
greater than the 1990 flood event. Every year there is
a continual build up of sediment on the previous years
river bed despite the typical scouring of the river bed
that occurs during fast flows.
rE/NG
Page 3
Colonel W. J. Cunningham
The Boeing Company has prepared emergency plans in the
almost certain possibility that a flood will occur
again. This preparedness is an additional cost to the
company. In the event of a flood,. sadbagging may delay
waters for a short time until critical items can be
transported out of the way. Other than moving items
there is nothing else we can do to prevent damaging
flood waters from entering Boeing's manufacturing
facilities. There is nothing we can do to protect the
bridges from loss in the event of a major flood event.
The cost to replace these bridges would be
approximately three million dollars each. This figure
does not include plant closure, the unforeseeable
permitting costs, lost wages, penalties from airlines
and other penalties as previously referenced.
It is critical to The Boeing Company,
Renton, its residents and the local,
national economy that the Cedar River
occur as expeditiously as possible.
----Sincerely,
Del Rowan
Manager, Corporate Public Affairs
the City of
regional and
Channel dredging
cc: Mayor Earl Clymer
Enclosure: BCAG How to Build an Airplane
BCAG First Family Commercial Jet Airplanes
BCAG Factory Layout Guide
BCAG Jets and Jobs
APPENDIX B
HYDROLOGIC APPENDIX
CEDAR RIVER AT RENTON FLOOD DAMAGE REDUCTION
SECTION 205 FEASIBILITY STUDY
TABLE OF CONTENTS
Paragraph
SECTION 1: HYDROLOGY
1.01 WATERSHED
Page
a.
Drainage Basin
1
b.
Principal Tributaries
3
C.
Reservoir and Storage Projects
4
1.02 CLIMATOLOGY
a.
Climate
8
b.
Climatological Records
8
C.
Temperature
9
d.
Precipitation
9
e.
Snowfall
10
f.
Storm Analysis
11
g.
December 1933 Storm
11
z.
December 1975 Storm
12
i.
December 1977 Storm
13
1.03 STREAMFLOW CHARACTERISTICS
a. Discharge Records 14
b. Runoff Characteristics 15
C. Flood Characteristics 16
d. Flood History 17
1.04 FLOOD FLOW ANALYSIS
a. Previous Studies 20
b. Routing Model 20
C. Cedar River at Renton Frequency and Flow
Duration Curve 22
d. Design Floods 23
1.05 REFERENCES 27
LIST OF TABLES
Table
No.
Title
Page
1
Cedar River Basin Summary of Temperature Data
28
2
Cedar River Basin Normal Monthly Temperatures
29
3
Cedar River Basin Summary of Precipitation Data
30
4
Lake Washington Basin Normal Monthly Precipitation
31
5
Cedar River Basin Ten Largest Peaks of Record
32
6
Peak Flows at Renton for 5, 10, 20 and 100 Year
33
Return Periods
7
Peak Flows at Renton for 200 and 500 Year
33
Return Periods
LIST OF EXHIBITS
Exhibit
No.
Title
Page
1
Cedar River Basin Map
34
2
Cedar River at Renton Frequency Curve
35
3
Cedar River at Renton Flow Duration Curve
36
4
5 Year Cedar River at Renton Hypothetical Hydrograph
37
5
10 Year Cedar River at Renton Hypothetical Hydrograph
38
6
20 Year Cedar River at Renton Hypothetical Hydrograph
39
7
100 Year Cedar River at Renton Hypothetical Hydrograph
40
8
200 Year Chester Morse Lake and Masonry Pool
41
9
200 Year Cedar River at Renton Hypothetical Hydrograph
42
10
500 Year Chester Morse Lake and Masonry Pool
43
11
500 Year Cedar River at Renton Hypothetical Hydrograph
44
SECTION 1. HYDROLOGY
1.01 WATERSHED
a. Drainage Basin The 188 square mile Cedar River Basin is located
southeast of the city of Seattle and is a major tributary to the 606 square
mile Lake Washington Basin (Exhibit 1). The Cedar River originates in the
Cascade Mountains just south of the Snoqualmie Pass and flows in a westerly
direction until it enters Lake Washington at the city of Renton. Lake
Washington empties into Puget Sound at Seattle through the Lake Washington
Ship Canal and the Hiram M. Chittenden Locks. The river itself is one of the
main sources of supply for Lake Washington which replenishes water lost in the
lake every year through evaporation and operation of locks. The Cedar River
watershed is bounded by the Snohomish and Sammamish River Basins in the north
and Green River Basin in the south. The environment within the basin ranges
from wilderness to heavy industrial. The Cedar River is used for recreation,
hydropower, and municipal water supply. The entire basin above Landsburg is
within the city of Seattle watershed which is closed to development and
recreational activities. The river below Landsburg provides good steelhead
fishing during the winter months and is also a major salmon -spawning area.
Currently, 67 percent of Seattle's municipal water supply is drawn from the
Cedar River at Landsburg. Chester Morse Lake (Cedar Lake) effectively divides
the basin into upper and lower subbasins.
The upper Cedar subbasin has a drainage area of about 81 square miles. This
area is rough and mountainous with a stream gradient averaging about 300 feet
per mile. Elevations range from 5,500 feet (National Geodetic Vertical Datum
- NGVD) at the crest of the Cascade range to about 1,600 feet near the outlet
1
of Chester Morse Lake. Two dams built by the city of Seattle for water supply
and hydropower control the level of Chester Morse Lake which is about 3-1/2
miles long and 1/2 mile wide.
The lower Cedar subbasin is about 107 square miles in area with elevations
ranging between 20 and 4,100 feet. This subbasin includes some high elevation
hills in the upper reach and relatively flat plateau areas in the lower reach.
The Cedar River in the upper reach of this subbasin flows generally westward
through a relatively narrow valley ending a few miles below Landsburg. Stream
gradients through this reach average around 200 feet per mile for the first 3
miles and about 35 feet per mile for the last 14 miles. From this point the
river flows northwesterly for 19 miles before emptying into Lake Washington.
Stream gradients in this lower reach average about 21 feet per mile. The
river in this reach occupies a braided channel in a widening flood plain with
streambanks that are easily eroded during high -flow conditions. The lower 5
miles of the Cedar River through the city of Renton has been channelized and
stabilized to some extent.
In the past, much of the flood plain below Landsburg was farmland, but
urbanization is now occurring in much of this area. As a result, an increase
in flood damages will likely occur in the coming years.
The natural vegetation pattern within the basin has been considerably modified
by man. Most of the areas along mountain slopes were formerly covered with
dense stands of conifers. The areas downstream of Chester Morse Lake were
logged in the early 1900's and are now covered with second -growth timber.
Logging now takes place above Chester Morse Lake, and the only remaining,
2
untouched timber stands are above 3,000 feet in the headwaters area. Most of
the flood plain has been logged, and this has eliminated or altered the
natural vegetation in this area. Undeveloped land has been disappearing
gradually in recent years under the pressure of urbanization and development.
b. Principal Tributaries The major tributaries to Chester Morse Lake
are the Cedar River itself and the Rex River. The Cedar River enters the lake
from the southeastern extremity and has a drainage area of approximately 41
square miles. The Rex River which flows in a northwesterly direction has a
drainage area of 13.4 square miles and drains the southern part of the basin
above the lake. There are also several small creeks that empty directly into
Chester Morse Lake.
Taylor Creek, a major tributary between Landsburg and Chester Morse Lake flows
northward to join the Cedar River near Selleck. Taylor Creek has a drainage
area of 17.2 square miles and is located in the southeastern portion of the
Cedar River. On the opposite or north side of the river, Rock Creek (drainage
area 11.1 sq. mi.) drains the area around Walsh Lake. For water quality
reasons, this creek has been diverted by the Seattle Water Department so that
it now enters the Cedar River below Landsburg during normal flow conditions.
From this point downstream to Lake Washington, the only tributaries are some
minor creeks and storm drain outlets except for Rock Creek near Maple Valley
(drainage area 12.6 sq. mi.) located on the south side of the Cedar River.
The geology of the basin causes some unique hydrologic behavior. The Cedar
River basin, from Chester Morse Lake downstream, contains glacial deposits.
This material can be highly permeable to groundwater. The right abutment of
3
the Masonry Dam, just downstream from the Crib Dam at Chester Morse Lake, is
an ancient, glacial moraine formed from these deposits. Whenever the pool
rises behind the Masonry Dam, seepage into the abutment occurs; and the amount
of seepage seems to be related to the Masonry Pool elevation. This resulting
groundwater splits the seepage and some of it eventually finds its way back to
the Cedar River above Landsburg and some of it into the Snoqualmie River. The
timing of the groundwater travel to the Cedar River above Landsburg results in
a substantial increase in the river's base flow during the summer months.
c. Reservoir and Storage Projects The principal storage reservoir in
the Cedar River basin is Chester Morse Lake, a water supply and power project
owned and operated by the city of Seattle Water Department and Seattle City
Light. Two other storage impoundments, Lake Washington and Lake Youngs,
effect flows on the Cedar River but to a much lesser extent. Considerable
pressure to increase the municipal and industrial (M&I) water supply storage
in the Cedar River Basin is expected in the future to cope with an
unprecedented amount of population growth in the region.
Lake Washington, located at the mouth of the Cedar River, is regulated by the
Corps of Engineers principally to supply water for operating a set of
navigation locks. A 2-foot draft limit of the lake between 20 and 22 ft
(Corps of Engineers' datum) or about 13.2 and 15.2 feet NGVD, respectively,
during the winter provides some erosion protection around the shoreline of the
lake. About 217 million gallons per day (m.g.d.) or 335 cubic feet per second
(c.f.s.) is required on an average annual basis to operate the locks without
drawing the lake below the authorized limits. The discharge capacity of the
spillway at the Locks is 18,200 c.f.s.. The fish ladder and saltwater return
4
systems have a combined discharge capability of approximately 385 c.f.s.
During periods of high runoff, Lake Washington can produce a backwater effect
on Cedar River streamflows below Renton which must be considered in hydraulic
computer model studies. Historically, regulation of Cedar River flood flows
has not significantly affected Lake Washington in an adverse manner.
Lake Youngs, located in the Cedar River Basin southeast of Renton, has a
capacity of 11,000 AF and is used as an equalization reservoir in the city of
Seattle's water supply system. Water from a diversion facility at Landsburg,
which averages about 113 m.g.d. or 175 c.f.s. on an average annual basis, may
either enter directly into Seattle's water supply or into Lake Youngs. During
floodflow conditions on the Cedar, the Landsburg diversion is shut off and all
of Seattle's water is drawn from Lake Youngs.
Seattle's development of the Chester Morse Lake project initially began in
1905 with the first hydroelectric power delivered to the city of Seattle from
the Cedar River. The head required for this plant was provided by a Crib Dam
constructed about 1904 just downstream of the natural outlet to Chester Morse
Lake. This raised the natural level of the lake 18 feet to elevation 1,548
feet (approximately NGVD datum). The Crib Dam spillway crest (top of
flashboards) was lowered after a failure in 1911 and maintained at varying
elevations between 1,546 and 1,548 feet until about 1936 at which time it was
permanently held at elevation 1,546 during the non -conservation period. Width
of the Crib Dam spillway crest was constructed to a length of about 108 feet.
Reconstruction of the Crib Dam occurred in 1988 with the new facility called
the overflow dike (described later in this section).
61
Construction of the Masonry Dam was initiated by Seattle in 1913 and completed
in 1914. The initial design called for the top of dam to be at 1,615 feet and
the spillway crest to be at 1,605 feet. An ungated notch 39.5 feet wide with
a bottom elevation of 1,554.5 feet was left in the dam pending construction of
a retaining dike near the northeast end of the dam. Because of the serious
seepage problems that were later encountered, this dike was never constructed
and the notch (service spillway) served as the permanent spillway for the
Masonry Dam until 1988 when the emergency and service spillways were
constructed (described later in this section). The current asbuilt top of dam
is at elevation 1,600 feet. Stoplogs were installed in the notch at varying
heights to 6 feet on a year round basis between 1922 and 1957. Between 1957
and 1988, stoplogs were removed during the winter flood season.
In order to minimize seepage, especially during the summer and fall
conservation period, the Masonry pool (between Masonry dam and overflow dike)
is drafted once the lake recedes below elevation 1,546 where Chester Morse
Lake becomes independent of Masonry Pool and can be controlled by the overflow
dike exclusively.
The principal low level outlets for Masonry Dam are the powerhouse penstocks
which have a maximum combined discharge capacity of 750 c.f.s. at pool
elevation 1,570 feet and an invert elevation at about 1,500 feet. The
powerhouse has a tailwater elevation of about 930 feet and discharges to the
Cedar River above the Cedar River at Cedar Falls streamgage. A single Howell-
Bunger valve through Masonry Dam at approximately elevation 1,498 feet, with a
discharge capacity of about 600 c.f.s. at pool elevation 1,570 feet is used to
evacuate water during operation and maintenance activities.
R
In 1988, the Masonry Dam was reconstructed to provide a second and much larger
emergency spillway on the north side of the dam primarily to improve dam
safety. Reconstruction also resulted in some modification of the service
spillway. The new emergency spillway has three 40-foot bays with radial
gates. The crest elevation of the emergency spillway is at elevation 1,538
feet and top of the gate is at elevation 1,570 feet. Total discharge capacity
of the emergency spillway at elevation 1,570 feet is 70,000 c.f.s. The
service spillway crest was raised to elevation 1,557 feet and a 13 foot gate
added with a top elevation at 1,570 feet. Maximum discharge capacity of the
service spillway at elevation 1,570 feet is 4,400 c.f.s. The combination of
the emergency and service spillway was designed to pass the spillway design
flood.
Additionally, during this reconstruction, the upstream Crib Dam was removed
and replaced with a concrete Overflow Dike. The spillway section in the
Overflow Dike has a crest elevation of 1,546 feet (same as the top of the
original Crib Dam)and a width of 100 feet. Top of the Overflow Dike was built
to elevation 1,550 feet. Two low level outlets are provided in the Overflow
Dike: the original 69-inch diameter woodstove conduit with an invert
elevation of roughly 1,524 feet and discharge capacity of about 420 c.f.s.;
and a new 78-foot diameter conduit with an invert elevation of 1,526 feet and
discharge capacity of about 800 c.f.s. Flow from Chester Morse Lake to the
Overflow Dike is limited by the approach channel which has a bottom elevation
of about 1,528 feet.
7
1.02 CLIMATOLOGY
a. Climate The climate of the Puget Sound area is quite mild when
compared to other regions at the same latitude because of the moderating
influence of the prevailing circulation from the Pacific Ocean. The Cedar
River Basin climate is characterized by heavy rainfall, particularly at higher
elevations, moderate humidity, wet winters, dry summers, and a comparatively
narrow temperature range.
b. Climatological Records Only two climatological stations are
located within the Cedar River drainage basin: the Landsburg station at
elevation 535 feet and the Cedar Lake station at elevation 1,560 feet. Each
station has accumulated over 75 years of independent temperature and
precipitation records and reflects the climatologic conditions occurring in
the middle segment of the basin. Stampede Pass, a National Weather Service
(NWS) station with about 50 years of record, is located near the head of the
adjoining Green River Basin and is considered to be reflective of conditions
near the headlands of the Cedar River basin. The NWS station Seattle -Tacoma
WSO-AP located about 5 miles southwest of Renton has nearly 50 years of record
and is considered to be representative of conditions in the lower segment of
the Cedar River Basin near the mouth.
c. Temperature The mean annual temperature of the Cedar River Basin
ranges from 390F at the upper elevations to 490F near the mouth. Summertime
temperatures within the basin average between 45OF at night to 70OF in the
afternoon; wintertime temperatures average between 240F at night to 350F in
the afternoons. Temperature extremes recorded in or near the Cedar River
Basin are 101OF at Landsburg and -21OF at Stampede Pass. A summary of
8
temperature averages and extremes and normal monthly temperatures for stations
in or near the Cedar River Basin are shown in Tables 1 and 2, respectively.
d. Precipitation Orographic lifting and cooling as the air mass moves
inland from the Pacific Ocean and results in persistent cloudiness and
widespread precipitation patterns in the Puget Sound area. Precipitation is
generally light in summer, increasing in the fall, reaching a peak in winter,
and then decreasing in spring.
Generally, 50 percent of the annual precipitation falls in the 4-month period
from October through January, 75 percent occurs in the 6 months from October
through March, and less than 5 percent during July and August. In the Cedar
River Basin, annual precipitation averages about 86 inches, ranging from
approximately 66 inches in the lower Cedar basin to about 111 inches in the
upper Cedar basin.
Normal monthly precipitation at stations in or near the basin ranges from 14.3
inches in December at Stampede Pass to only 0.7 inch in July at Seattle -Tacoma
WSO-AP. Maximum recorded monthly precipitation was 46.80 inches at Cedar Lake
in December 1917. A maximum 24-hour precipitation of 7.94 inches was recorded
at Stampede Pass in November 1962, and the maximum 1-hour precipitation
recorded during this period was 0.61 inch. A summary of precipitation
averages and extremes and normal monthly precipitation for stations in or near
the Cedar River Basin are provided in Tables 3 and 4.
e. Snowfall The percent of precipitation that falls as snow depends
largely upon elevation. Mean annual snowfall varies from about 13 inches near
9
the mouth of the basin to almost 450 inches in the higher elevations. Snow
surveys are routinely made at 9 snow courses in or near the Cedar River Basin.
f. Storm Analyses The Cedar River Basin on the western slopes and
foothills of the Cascade range lies directly in the path of cyclonic
disturbances rising inland from the Pacific Ocean from October through March.
Nearly all major floods in the basin are produced by severe storms which occur
mainly during the winter months and produce gale force winds and heavy
precipitation. Storm precipitation varies over the basin, with greatest
amounts falling at the highest elevations in the upper Cedar River basin where
precipitation is generally orographic in nature. It is not unusual for a
major storm to occur in the upper Cedar River Basin with only moderate
precipitation falling in the lower basin as in December 1977. The reverse
situation can also occur but usually produces less severe flooding due to the
attenuating effect of Chester Morse Lake on reservoir inflows.
The most common pattern of winter precipitation is a period of steady rain and
warm temperatures for 8 to 12 hours followed by a cooler showery period.
These storms often occur as a series of waves passing in rapid succession at
intervals of 24 to 36 hours and can produce large volumes of precipitation and
significant flooding as in December 1975. A critical storm situation from a
reservoir regulation standpoint can occur when several major events occur
within 7 to 12 days of one another potentially preventing storage evacuation
between events, such as in December 1933. Freezing levels during major storm
events typically rise above 8,000 feet as the first storm approaches and
remains high until the last of the series of storms passes through the area.
Snowmelt resulting from warm temperatures can average more than 5 to 10
10
percent of the total storm precipitation and as much as 50 percent of the
daily total for some events.
The storms of December 1933, 1975 and 1977, discussed further in the following
paragraphs are characteristic of the different meteorological conditions
producing major flood events.
g. December 1933 Storm The month of December 1933 was one of
unprecedented rainfall over western Washington, including the entire Cascade
Mountains. The total monthly precipitation was greater than for any month of
record at the majority of stations. A pronounced high pressure cell of polar
air stagnated in a position from central Alaska southeastward over Canada
during the entire month, forcing the low pressure storms from the Gulf of
Alaska to go southward and progress across British Columbia and Washington.
Moderate precipitation was general over western Washington, starting on the 2d
and increasing in intensity as a storm center developed in the Gulf of Alaska
on the 4th, increasing in magnitude and starting a southward movement on the
7th. After 8 December, this storm center stagnated with only minor shiftings
off the Washington coast, and secondary lows with frontal waves moved eastward
over Washington or southern British Columbia. This situation resulted in
steady rains over the western portion of the State for about 28 days with two
distinct storm fronts and periods of concentrated rain occurring about 12 days
apart.
Due to a lack of snow measurement stations in the Cedar River or adjacent
basins in 1933, little is known about the actual contribution of snowmelt to
this flood event. However, based on a study of snow depths at climatological
11
stations in the White River Basin about 20 miles south, snowmelt may have been
only a small portion of the total runoff volume. The study indicates that at
the beginning of the storm the snow line was at approximately 2,000 feet,
which indicates that 60 percent of the basin was snow-covered. During the
storm, however, the snow line apparently receded only a few hundred feet, as
the stations at Parkway (elevation 2,628 feet) and Longmire (elevation 2,762
feet) were still snow-covered at the end of the storm. The snow depth at
Parkway decreased from 13.5 inches on the 7th to 2.1 inches on the llth, and
at Longmire from 9.0 inches on the 8th to 1.0 inch on the llth. Perhaps 5 to
10 percent of the flood volume was the result of snow melt.
h. December 1975 Storm By 29 November, the high-pressure ridge
protecting the Pacific Northwest from more intense storms had flattened out
and moved eastward to be replaced by a strong inflow of warm, saturated air.
Heavy rain began over western Washington late on the 29th and early 30
November. It did not moderate at most stations until near midnight on 30
November, after which the rate of fall became increasingly heavy as the warmer
air arrived. Snowfall in the mountains had changed to heavy rain by the
afternoon of 30 November. Precipitation at Stampede Pass began early on 30
November, with more than half the 4 inches of rain on that day falling as
snow. Much of the rain was retained within the snowpack. As the warm air
mass arrived at Stampede Pass, the temperature rose about 25OF in a few hours
to near 40°F. The wet snowpack was estimated to be completely conditioned and
yielding runoff by the end of 30 November. During the next 24 hours to
midnight on 1 December, a near -record 6.9 inches of rain fell at Stampede
Pass. This was augmented by about 2 inches of snow melt for an estimated
combined 24-hour contribution to runoff of 8 inches. Rainfall and snowmelt
12
continued through 3 December. Precipitation diminished the morning of 4
December, and the temperature dropped to below freezing, reducing snowmelt.
Rainfall and snowmelt contributed to a total storm runoff at Stampede Pass
estimated at 21.6 inches. The storm period from 0000 hours on 30 November to
0600 hours on 4 December included three distinct storms following each other
in close succession.
i. December 1977 Storm For several days prior to the onset of the
heavy precipitation in western Washington, a protective ridge of high pressure
shunted the more intense Pacific storms to the north of Washington. By the
morning of 1 December 1977, the high-pressure ridge had flattened sufficiently
to allow the Pacific storm track to be depressed south, bringing a series of
intense short -wave storm systems into Washington and northern Oregon. Very
heavy rains were encountered on the westerly orographic slopes of the Cascade
and Olympic Mountains. Temperatures rose 100 to 15OF following the passage of
the first warm wave, and the freezing level remained between 5,000 and 10,000
feet during the first and second days of the storm period. Snowmelt estimated
in excess of 5.9 inches, the majority of which occurred between 2 and 3
December after the flood had peaked, added to the total storm runoff.
Stampede Pass recorded over 13 inches of precipitation during the 3-day storm,
5.93 inches of which was recorded in one 24-hour period.
13
1.03 STREAMFLOW CHARACTERISTICS
a. Discharge Records Most of the major streams and tributaries within
the Cedar River Basin have one or more recording streamgages. The Landsburg
and Cedar at Cedar Falls gages on the Cedar River have the longest records of
any station in the Puget Sound area with streamflow records dating back to
1895 and 1914, respectively. Records for most of the remaining gage stations
date back to 1946. Streamgage records for the Cedar River stations below
Chester Morse Lake are significantly affected by project regulation. Records
of daily (and some limited hourly) Chester Morse Lake elevations, power
production, and other pertinent project data have been maintained by City
Light since about 1905 and Chester Morse Lake elevations have been published
by the USGS since 1977. The Corps of Engineers has maintained a record of Lake
Washington elevations since 1901.
The streamgage location at Renton has a tendency to aggrade which affects the
observed flow rate during periods of high runoff on the river. During the
December 1975 flood, the rating at Renton shifted by 0.15 foot or 170 c.f.s.
The average shift in the rating or loss in channel capacity since 4 December
1968 when the rating began to shift has been about 0.22 feet or 350 c.f.s. per
year. The continued aggredation is causing a loss in channel capacity and is
significantly affecting the flood situation at Renton.
b. Runoff Characteristics Streamflows typically follow the general
rainfall pattern in the area, with highest runoff occurring in the rainy fall
and winter months. Winter flows are characterized by frequent rises resulting
from storms or series of storms; however, not all rises reach flood
proportions. Runoff gradually decreases as rainfall diminishes in the spring
14
and summer dry months. Lowest flows occur in August and September, although
low flow conditions can extend into November or December. Occasionally,
above -normal spring precipitation from a heavy storm in March or April will
produce periods of high runoff and cause the annual peak to occur during this
period (e.g., March 1972). The seasonal rise in temperatures during the
spring and early summer months frequently produces a period of high snowmelt
runoff from the upper Cedar basin. This snowmelt runoff is not as significant
in the lower Cedar basin where snowpack is generally light and does not last
long into the spring months. Snowmelt runoff into Chester Morse Lake during
the spring period is typically stored for summer conservation.
Inflow to Chester Morse Lake is affected by seepage from the reservoir, which
can range from about 50 c.f.s. to over 400 c.f.s. during low and high
reservoir levels, respectively. Return flow from reservoir seepage causes the
streamgages Cedar River at Cedar Falls and at Landsburg to show a somewhat
higher base flow during late summer and early fall than other nearby streams.
This flow augmentation from seepage return to the river above Landsburg is
estimated to be roughly 75 percent of the reservoir seepage lagged 60 days.
Flow augmentation at Renton is not as obvious since streamflows are reduced
because of Seattle Water Department's diversion below Landsburg which averages
about 159 m.g.d. or 245 c.f.s during July and August and 92 m.g.d. or 142
c.f.s. during the winter. A high base flow condition is also noticeable on
Taylor Creek, a tributary to the Cedar above Landsburg, but the source is
unknown. All three streamgages on the Cedar River below Chester Morse Lake
are affected by project regulation and releases for power production which can
be as great as 750 c.f.s.
15
c. Flood Characteristics Flood flows of significant magnitude on the
Cedar River are caused by concentrated 2-to 5-day rainstorms or series of
storms with intense periods of rainfall that usually last less than 24 hours.
Flood runoff to Chester Morse Lake is characterized by sharply rising
hydrographs with peak discharges maintained for only a few hours and followed
by recessions almost as rapid. The natural rate of rise in the inflow to
Chester Morse Lake is estimated at approximately 560 c.f.s. per hour and the
rate of fall above the base flow inflection point at about 480 c.f.s. per hour
based on the December 1977 flood which is representative of most large flood
events. Air temperature during these storms is usually warm enough to melt a
significant amount of the snowpack as the freezing level will typically rise
above 8-10,000 feet. Flood flows below the dam are generally a result of
spill from Masonry Dam combined with local runoff. Induced storage in Chester
Morse Lake and the small dimensions of the service spillway significantly
dampens the reservoir inflow and resulting spill thereby diminishing the flood
impact in the downstream reach. In rare instances these storms occur in a
critical sequence such that the timing of the local runoff and dam release
combine to produce the most severe level of flood damage in the lower basin as
in December 1933 and December 1975. These long duration, high volume floods,
rather than those with higher peaks but less volume, produce the most critical
runoff sequences for downstream flood control. Local runoff from the flatter
terrain of the lower elevation subbasins below Masonry Dam is characterized by
a relatively slow rise and long flow duration. On the average, local runoff
will peak about 5 hours after Chester Morse Lake inflow peaks, although this
can vary significantly depending on the regional extent of the storm and
meteorologic conditions. In addition, considerable variation can exist in the
relative magnitudes of the local runoff peak and reservoir inflow peak from
16
event to event. The effect of Lake Washington on flood flows in the Cedar
River below Renton has not been a significant problem historically.
d. Flood History Reports of flooding along the Cedar River in the
reach below Landsburg can be traced through newspaper articles back to 1850.
Flood damages prior to construction of the Masonry Dam were primarily
concentrated in the Renton area. Since that time, channelization work in the
lower 1 mile of the Cedar River around 1912 and development upstream of Renton
has been such that the upstream area now experiences flood damage before
Renton. The current Corps of Engineers zero damage level at Renton is 4,000
c.f.s., although this can vary with the amount of aggradation (see Section
1.03a). The National Weather Service in December 1983 established flood stage
for the lower valley based on the Landsburg gage at 5 feet or about 3,500
c.f.s. (NWS flood stage is usually set lower than USACE zero damage stage to
provide a warning period). The maximum recorded level of Lake Washington
during the winter due to high inflow occurred in December 1975 and was 20.6
feet (COE datum) which is 1.4 feet below the normal maximum lake level. The
level of Lake Washington during the December 1977 flood was 20.1 feet but this
was forced due to project operations. No significant damage was incurred or
induced around the lake at Renton from the December 1975 event.
The greatest floods of record on the Cedar River from a damage standpoint
occurred in December 1933, December 1975 and November 1990. All of these
floods were large volume events, with the December 1933 flood having the
greatest volume and longest duration. A tabulation of the ten greatest
observed and natural (deregulated) discharges at the Renton and Landsburg
17
gages and inflows to Chester Morse Lake are provided in table 5. The
following paragraphs provide a general description of the flooding associated
with several of the largest events of record in the Cedar River Basin.
(1) The flood of December 1933 was the result of a combination of
heavy precipitation and snowmelt. This particular flood affected the entire
basin. Some inundation occurred in the town of Renton, and severe flooding
occurred along the river between Landsburg and Renton. Reported logjams that
formed in the channel during this flood may have induced some of the damage.
(2) The flood peak in February 1951 was the result of some very heavy
rains that occurred from 8 to 11 February. Flooding occurred in the river
valley upstream of Renton, but no inundation took place within the city
itself.
(3) The high water of March 1972 was the result of some very heavy
rainfall that occurred mostly on 5 March. Local inflow between Cedar Falls
and Renton was particularly high.
(4) The flood peak in December 1975 was similar to that which occurred
in 1933 but of slightly higher magnitude and shorter duration. A ripe
snowpack, combined with heavy rainfall, produced optimum yield which
aggravated flood conditions. At Renton, the river was above the major -damage
level for 79 hours. Many residential areas had between 3 and 4 feet of
floodwaters. An estimated $2,350,000 of damage at 1975 prices and conditions
was experienced by this flood in the Cedar Valley.
18
(5) The high flows of December 1977 were the result of high -
intensity precipitation falling on the Cascades above about 1,500 feet. Flows
at Renton were relatively low because of a lack of significant local flow
between Cedar Falls and Renton and flood peak storage in Chester Morse Lake.
(6) The storms of November 1990 produced two large flood events;
the first occurring around Veterans Day and the second just after
Thanksgiving. Continuous warm heavy rainfall along with a melting snowpack
characterized the weather conditions throughout November. Flooding on the
Cedar River on November 24-26 was a new record maximum and lead to the closure
of the Renton Municipal Airport adjacent to a Boeing Company complex that
includes the 737 and 757 jet factories. The recurrence interval of the
Thanksgiving flood has been estimated from gages on the Cedar River at about a
50-year event.
19
1.04 FLOOD FLOW ANALYSIS
a. Previous Studies Much of the work described in this section was
based on the Corps of Engineers, Seattle District, 1988 Cedar River Flood
Control Study. The work performed in the 19.88 study was used to construct the
previously adopted Cedar River at Renton frequency curve dated July 1989. The
1989 Cedar River at Renton frequency curve was developed using the Corps of
Engineers SSARR (Streamflow Synthesis and Reservoir Regulation) flood routing
model. It was preferred to route Chester Morse Lake inflow using SSARR as
opposed to using observed gage readings at Renton when producing the frequency
curve. This would produce somewhat different flows at Renton than the
observed gage record, but would provide a common reservoir operating scheme
for the entire period of record.
b. Routing Model The SSARR computer model was used to route observed
flood hydrographs from Chester Morse Lake to Renton and develop coincident
local inflows for each historic flood event analyzed. The model was
calibrated to the December 1975 and 1977 floods by routing project inflows
through Chester Morse Lake to the downstream streamgages at Cedar Falls,
Landsburg and Renton and adding an estimate of the local inflow between the
gage. Routing parameters (time of storage and routing phases) were adjusted
for each routing reach until the timing and attenuation of the routed
hydrograph reconstituted the observed hydrograph. Project releases and
downstream flows in the calibration effort were adjusted to include an
estimate of the powerhouse discharge, seepage from the Masonry pool, and
seepage return flows above Cedar Falls and Landsburg. Landsburg M&I
diversions were reduced to zero when the flow at Landsburg exceeded about
2,000 c.f.s. as agreed to by the Seattle Water Department.
20
Observed flow data from 30 large flood events from 1906-1986 was applied to
SSARR to obtain the peak flow at Renton under current City of Seattle flood
regulation procedures (City of Seattle, Chester Morse Lake Operation and
Maintenance Manual). Historical inflows to Chester Morse Lake were calculated
by several methods depending on the availability of hourly streamflow and
reservoir elevation data. For each method, the inflow was calculated using
the continuity equation from an estimate of the dam outflow including spill,
powerhouse discharge and seepage from the Masonry pool and change in reservoir
storage. In some cases where hourly streamflow data but not reservoir
elevations were available and spill was known to have occurred, the hourly
reservoir levels were back -calculated from the spillway rating curve. If
hourly data was limited, the computed inflow hydrographs were reshaped to more
accurately define the timing and magnitude of the flows using regression and
other transfer techniques and comparison with tributary streams.
Local inflow hydrographs below the dam for each historic event were determined
by subtracting the routed observed hydrograph at an upstream gage from the
observed hydrograph at a downstream gage. The Landsburg local was adjusted to
exclude seepage return flow. The Renton local was adjusted to include M&I
diversion at Landsburg. Cedar Falls local (between the dam and the gage at
Cedar Falls) was estimated to be 10 percent of the Landsburg local based on a
ratio of the drainage areas. Renton local inflow prior to 1945 was estimated
as 60 percent of the Landsburg local based on regression analysis of the peak
discharges between the Renton and Landsburg locals and routings of
hypothetical floods.
21
Initial reservoir elevations were set at either the historic elevation if no
spill occurred for a period of time prior to onset of the flood or at an
elevation commensurate with the service spillway crest if spill had occurred
on the beginning of the flood. In cases where bulkheads were installed in the
service spillway (prior to 1957), an appropriate adjustment was made in the
starting reservoir elevation based on the volume of inflow. Outflow from
Chester Morse Lake was modeled through level pool routing and was determined
by a rating table that included discharge from the power tunnel and flow over
the service spillway. The outlet rating was adjusted to reflect maximum power
release even through the peak of each flood event which is the historical
practice to limit the pool rise. Seepage and seepage return were assumed to
be equal which produces a slight but acceptable increase in Cedar River flows
of less than 200 c.f.s.
C. Cedar River at Renton Frequency and Flow Duration Curves Computed
peak flows obtained by SSARR were used to develop the Cedar River at Renton
frequency curve (Exhibit 2) following the methodology discussed in U.S. Army
Corps of Engineers (1993), and U.S. Department of the Interior (1981). The
frequency curve was produced using median plotting positions and assuming a
zero skew which is consistent with skew values for similar natural watersheds
in the region. Graphical curve fitting methods were applied to the peak flows
since analytic fitting methods are not recommended for developing regulated
flow frequency curves (U.S. Army Corps of Engineers, 1993).
To update the 1989 frequency curve, data from the November 1990 flood was
routed through SSARR to produce a peak flow at Renton. The computed peak flow
was found to be 9,520 cfs and this was applied to the output of the previous
22
30 SSARR runs to produce a new frequency curve. When comparing the 1989 curve
with the new curve it was discovered that the November 1990 event increased
the 100 year peak flow by less than 596. Due to model and gage inaccuracies it
was deemed unnecessary to abandon the 1989 frequency curve. It should be
noted that the flow gages at Cedar Falls, Landsburg and Renton were all known
to have failed during various periods on the 24th and 25th of November 1990.
An additional frequency curve was developed to reflect future development in
Renton (see Exhibit 2). Future condition flows were taken to be an additional
8% over present condition flows as stated by King County Department of Public
Works (1993). A summary of peak flow values at Renton for various return
periods is given in Tables 6 and 7.
A Cedar River at Renton flow duration curve (Exhibit 3) was developed using
USGS mean daily flow data and the STATS (HEC, 1987) computer program. The
period of record for the flow duration curve is from water year 1946 to 1993.
d. Design Floods Hypothetical hydrographs of local inflow below the
dam and reservoir inflow were constructed based on observed floods and
regression analysis between peak discharges and coincident 1-, 3-, and 5-day
maximum average flows. Reservoir inflow was determined by regression analysis
between the peak at Renton and the 3-day (critical duration) inflow to Chester
Morse Lake. Coincident local inflow hydrographs below the dam were developed
based on regression between the peak at Renton and the peak of the local
inflows for Renton and Landsburg. The local inflow was adjusted within
acceptable limits in the SSARR routing model to reproduce the design flood at
Renton. For inflows with 100 years return period or less, the discharge from
the Masonry Dam consists of flow through the powerhouse and flow over the
service spillway. Outflow from the dam was modeled through level pool routing
23
and was determined by a discharge rating table in the SSARR model. Starting
lake levels for the 5, 10 and 20 year events were taken to be the normal
winter flood control pool (elevation 1546 ft). For events 100 years or
greater the initial lake elevation was taken to be 1560 ft based on the
assumption that antecedent conditions would cause the higher elevation. The
5, 10, 20 and 100 year hypothetical hydrographs for Renton are displayed in
Exhibits 4 to 7, respectively.
Hypothetical hydrographs for the 200 and 500 year floods were developed
through SSARR runs and simulate the opening of the 3 emergency gates.
According to the Chester Morse Lake Operations and Maintenance Handbook, the
current plan of operation for Chester Morse Lake with the emergency spillway
gates requires these gates to remain closed at all times except in the case
where an inflow greater than a 100-year event would cause the reservoir to
exceed the maximum flood pool at elevation 1,570 ft. A 100-year inflow is
defined when the flow exceeds 15,000 c.f.s. which is indicated by a specified
rate of rise in pool elevation. Emergency gate openings were determined
according to a rate -of -rise table and emergency gate schedule given in the
handbook. Opening of the emergency gates can occur at any elevation beyond
1560 ft as long as the rate of rise is satisfied, but must be opened at
elevation 1568 ft. This procedure allows for a considerable amount of
latitude in emergency gate operation. For the purpose of this analysis, a
conservative operation was chosen to estimate the maximum discharge from
Chester Morse Lake. Other flood control operations are possible which could
produce lower maximum outflows from Chester Morse Lake. For example, an
operation designed to optimize available storage could reduce outflows by up
to 26 and 14 percent respectively for the 200 and 500 year floods. However,
since the actual operation for a given flood event is unknown, this analysis
assumed a conservative operation in that the rate -of -rise criteria and gate
schedule would be rigidly adhered to.
24
For both the 200 and 500 year floods, the following operational assumptions
were made:
1. The emergency gates will not be opened until the rate of rise
in pool elevation equal or exceeds the values in the rate of
rise table. For the 200 and 500 year floods analyzed in this
study, the rate -of -rise did not necessitate opening the
emergency gates until elevation 1567 ft.
2. Gate openings are made in accords with the Masonry Dam
emergency gate schedule while adhering to an opening constraint
of 2 ft/hour.
3. The emergency gates will not pass more than current inflow on
the climbing side of the inflow hydrograph.
4. It was assumed that all three emergency gates would be utilized
and opened in unison.
Evacuation of the Masonry Pool can be performed in many different manners and
is not prescribed in the Operation and Maintenance Handbook. Both the 200
year and 500 year floods were evacuated using the following procedure:
1. As the reservoir pool falls below elevation 1568 ft, the
emergency gates are closed to 4.0 ft and maintained until
elevation 1562 ft with the goal of attaining 1560 ft (the
initial pool elevation)by the end of the 6-day simulation.
2. At elevation 1562 ft, outflows are gradually ramped down to
begin a transition back to the service spillway at elevation
1560 ft.
The reservoir regulation applied to the 200 and 500 year floods rigidly
followed the emergency gate schedule and made all the specified gate changes
according to pool elevation. An exception was taken for the specified gate
opening of 5.6 ft when the pool elevation reached 1568 ft. A 5.6 ft gate
opening would discharge roughly 19,400 cfs which is more than the peak inflow
for both the 200 and 500 year floods. Therefore, the gates were only opened
enough to pass the current inflow while also adhering to the 2.0 ft/hour gate
opening constraint. The gate opening was then increased or held depending on
25
whether inflows were climbing or falling. Evacuation of the reservoir was
performed as described above.
For the 200 year flood (Exhibits 8 and 9), a first emergency gate opening of
2.0 ft was made at 14:00 on Day 2 producing a discharge of 7,440 cfs by
elevation 1567.5 ft. Two hours later, at elevation 1568 feet, the emergency
gates were opened to 4.0 ft producing a discharge of 14,300 cfs. On Day 2,
17:00 it was observed that the inflow had peaked two hours earlier at 16,100
cfs and was receding. Therefore, the gates were only opened enough to pass
the current inflow of 15,600 and were held at that gate setting until the pool
fell below 1568 ft.
The 500 year flood (Exhibits 10 and 11) was regulated similar to the 200 year
flood. An initial emergency gate opening of 2.0 ft was made at elevation
1567.5 (Day 2, 12:00) producing a discharge of 7,440 cfs. Two hours later, at
elevation 1568 ft, the emergency gates were opened an additional 2.0 ft
yielding 14,300 cfs. At 15:00 hours the emergency gates were opened to pass
the current inflow of 17,900 cfs. The following hour it was observed that
inflows had peaked at 17,900 cfs, therefore the gate opening from the previous
hour was maintained until the pool elevation reached 1568 ft.
26
1.05 REFERENCES
City of Seattle, Seattle City Light, Seattle Water Department (1986), Cedar
Falls Improvement Project, Final Environmental Impact Statement, pg 2-12, 3-8,
3-9.
City of Seattle, Seattle City Light, Seattle Water Department (unknown date),
Operations and Maintenance Handbook, Cedar Falls Headworks and Overflow Dike.
Hydrologic Engineering Center (1975), Hydrologic Frequency Analysis, U.S. Army
Corps of Engineers, 609 Second Street, Davis, CA 95616, pg 4-28.
Hydrologic Engineering Center (1987), Statistical Analysis of Time Series Data
(STATS), U.S. Army Corps of Engineers, U.S. Army, 609 Second Street, Davis,
CA 95616, pg 4-28.
King County Dept. of Public Works Surface Water Management Division (1993),
Cedar River Current and Future Conditions, pg 3-35.
U.S. Army Corps of Engineers (1988), Cedar River Flood Control Study 1988
(Hydrol), Wrap-up Rpt and Draft Hydrol App. Report # 1110-2-1403b, Lk Wash R.
Basin - Invest, Seattle District.
U.S. Army Corps of Engineers (1993), Hydrologic Frequency Analysis,
Engineering Manual 1110-2-1415
U.S. Department of the Interior (1981), Guidelines For Determining Flood Flow
Frequency, Bulletin #17B, U.S. Department of the Interior, Geological Survey,
Office of Water Data Coordination, Reston, Virginia.
27
TABLE 1
CEDAR RIVER BASIN
SUMMARY OF TEMPERATURE DATA
(THROUGH 1994)
Climatological
Elevation
Station
(Feet)
Bothell 2N
100
Cedar Lake
1,560
Kent
30
Landsburg
535
Seattle -Tacoma WSCMO
AP 400
Seattle WBAP
14
Seattle WB City
14
Stampede Pass WSCMO
3,958
Temperature (OF)
Period
of
Mean
Record
Extreme
Extreme
Record
Annual
Years
Maximum
Minimum
1931-1959
49.9
29
100
-10
1912-
47.6
83
98
-16
1913-
51.06
82
101
- 5
1916-
49.04
79
101
0
1945-
52.0
50
100
0
1928-1964
52.3
33
100
0
1878-1971
52.4
81
100
3
1944-
39.3
51
91
-21
Station
Cedar Lake
Landsburg
Seattle -Tacoma
WSOAP
Stampede Pass
WSMO
TABLE 2
CEDAR RIVER BASIN
NORMAL MONTHLY TEMPERATURES (OF)
(1961-1990)
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
34.4
37.0
39.9
45.8
51.7
55.6
60.7
60.2
56.7
49.9
41.7
37.6
47.6
36.9
39.8
43.3
48.4
53.8
57.9
61.9
61.3
57.4
50.3
42.6
39.3
49.4
40.1
43.5
45.6
49.2
55.1
60.9
65.2
65.5
60.6
52.8
45.3
40.5
52.0
24.1
28.1
30.1
35.3
42.5
49.2
56.1
55.6
51.1
42.1
30.9
26.5
39.3
Station
Bothell 2N
Elevation
(Feet)
100
TABLE 3
CEDAR RIVER BASIN
SUMMARY OF PRECIPITATION DATA
(Through 1994)
Precipitation (Inches)
Period
of Mean Record Greatest 1-Day Greatest 1Mo
Record Annual Years Amount Date Amount Date
1931-1959 39.46
29
2.80 Dec 37 14.35 Dec 33
Cedar Lake
1,560
1899-
102.50
80
6.16
Nov
06
46.80
Dec
17
Kent
30
1912-
38.48
62
3.00
Jan
35
16.99
Dec
33
Landsburg
535
1903-
56.37
77
4.05
Feb
51
22.63
Dec
33
Seattle -Tacoma WSCMO
AP 400
1944-
37.19
44
3.74
Sep
91
12.92
Jan
53
Seattle WBAP1/
14
1928-1964
36.08
34
3.02
Feb
45
10.93
Jan
53
Seattle WB Cityl/
14
1878-1971
34.01
94
3.52
Dec
21
29.06
Jan
53
Stampede Pass WSCMO
3,958
1944-
92.57
45
7.94
Nov
62
30.42
Jan
69
V Record included for extension of Seattle -Tacoma WSOAP
TABLE 4
LAKE WASHINGTON BASIN
NORMAL MONTHLY PRECIPITATION (INCHES)
Stations
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Cedar Lake
13.31
10.55
10.04
8.38
5.82
5.51
2.12
2.89
5.63
10.29
13.46
14.50
102.50
Landsburg
7.24
5.66
5.20
4.46
3.31
3.14
1.33
1.82
3.32
5.53
7.45
7.91
56.37
Seattle -Tacoma
5.38
3.99
3.54
2.33
1.70
1.50
0.76
1.14
1.88
3.23
5.83
5.91
37.19
WSCMO AP
Stampede Pass
14.59
10.19
8.88
6.28
3.97
3.84
1.56
2.85
4.65
7.74
12.14
15.88
92.57
WSCMO
TABLE 5
CEDAR RIVER BASIN
TEN LARGEST PEAKS OF RECORD (C.F.S.)
CHESTER MORSE LAKE
RENTON (1933, 1945-1993)
LANDSBURG
(1903-1993)
(1906-1993)
Recorded
Natural
(deregulated)!/
Recorded
Natural
(deregulated)!/
Date
Discharge/
Date
Discharge
Date
Discharge
Date
Discharge
Date
Discharge
Nov
1990
10,600
Nov
1990
15,300
Nov
1911
14,2003/
Dec
1977
13,900
Dec
1977
13,500
Dec
1975
8,5004/
Dec
1977
13,800
Nov
1906
12,400
Nov
1990
13,700
Jan
1923
12,800
Dec
1933
8,100 (est)
Jan
1984
13,700
Nov
1990
10,800
Jan
1923
13,400
Nov
1990
12,500
Feb
1951
7,100
Nov
1959
11,900
Jan
1903
10,400
Feb
1924
13,400
Nov
1911
12,000
Mar
1972
6,200
Dec
1975
11,800
Nov
1909
8,370
Dec
1917
13,300
Dec
1917
11,700
Dec
1977
5,700
Mar
1972
11,700
Dec
1917
8,150
Jan
1984
12,600
Nov
1959
11,700
Nov
1959
5,600
Feb
1951
11,600
Dec
1975
8,000
Nov
1906
12,100
Dec
1943
11,300
Jan
1984
5,600
Nov
1959
11,400
Dec
1933
7,520
Nov
1959
12,100
Dec
1975
10,600
Dec
1946
5,500
Dec
1933
11,120(est)
Feb
1951
6,100
Dec
1943
11,700
Jan
1984
10,500
Jan
1965
5,250
Dec
1955
11,100
Dec
1921
5,960
Nov
1911
11,400
Dec
1924
10,350
!/ Flows developed from SSARR routing model. Natural flows are without Cedar Lake.
2/ Does not include floods of 1906 and 1911 with an estimated peak at Renton of 13,000 cfs
and 11,100 cfs respectively. These two events were used to construct the frequency curve.
3/ Landsburg November 1911 high flow caused by failure of flashboards. The estimated flow without
flashboard failure is 8,740 c.f.s.
4/ The USGS estimated the December 1975 peak at 8800 c.f.s. USACE used 8,500 c.f.s based on routing
and backwater studies.
TABLE 6 "
PEAK FLOWS AT RENTON FOR
5, 10, 20 and 100 YEAR RETURN PERIODS
Return Period
Peak Flow
(years)
(cfs)
5
4,900
10
6,300
20
7,900
100
12,000
1/ The regulation for up to a 100 year event assumes:
a. all inflows will pass through the power tunnel and over the service
spillway.
b. the gates for the service spillway will be at full open.
TABLE 7 i/
PEAK FLOWS AT RENTON FOR
200 AND 500 YEAR RETURN PERIODS
Return Period Peak Flow
(years) (cfs)
200 18,200
500 21,500
1/ For the 200 and 500 year floods analyzed in this study, the following
operational assumptions were made:
a. rate -of -rise did not necessitate opening the emergency gates until
elevation 1567 ft.
b. Gate openings are made in accords with the Masonry Dam emergency
gate schedule while adhering to an opening constraint of 2 ft/hour.
C. The emergency gates will not pass more than current inflow on the
climbing side of the inflow hydrograph.
d. It was assumed that all three emergency gates would be utilized and
opened in unison.
.M
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VICINITY 14AP
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4-49
M o
1. Hydrologic and c5matolodc paging statlorta are tocsted on the map
to the latt according to the symbol Identification In the legend beiaw. C
Z Streamgaging stations that show as numbered
rs isted in table 4-1. " ns'. aay a the
map
-Hydrologic Gaging Statiom of rite Lake
Washin,goC Ship Canal Watr Control Manual by index rxaribm.
station .—a. drainage was, and period-of-r�
3. Pradpttsdon stations that show as named cirdes are Ostad In table
4-2, "C mAnologlc Gaging Ststions", of the manual by station name,
elarathri, and pariod-of�ecord.
4. Soon' Courses and prows Me show as named diamonds are listed
in tablo 4-7, -Snow Courses% of the manual by stsbon nrne.
eievetfa.t, and periodof-record.
LEGEND
:T,e..r tA.e.. TTSTIp. _ reaaw • O
`1 ,-�` •: O ►'�-�+ rwrvwTaTxT. uo tn.a,t„rc AW- -0-
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I.AaI staKTON AND cr DPI arvrj
r�DRyO..0 Ar 11l..ATDLot.0
tally. TTATIO.
e
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r A , LOG --S
WE KEUFFEL & ESSER CO. It4or 14 us 4 1 468043
too 9.99 99.999.8 99 98 95 90 80 70 60 50 40 30 20 10 5 2 1 0.5 0.2 0.1 ().05 0.01
9
Exceedance Frequency in Percent 11 Mki I ITM ;T1
NO�F`S:
1. This curve was originally developed for the 1988 Cedar River Flood Control Study. The
November 1990 stomi was applied to this curve and it was found that the 100 year peak differed by less
A A A- .1- 19 ..
5
CD
CD
0
0 Cr
'D
ian c to mo c an gage naccurac CS L Was come unnecessary to re aw e curve.
2. Peak flows were generated with the computer model SSARR so that all events would have a conunon
regulation plan.
3. The regulation for up to a 100 year event assumes:
a- all inflows will pass through the power tunnel and over the service spillway. H.
b. the gates for the service spillway will be at full open.
4 Ilic regulation far events larger than 100 years assume:i 1 _j ' . { _ _.__..:_ .. - _ __ — -
& The emergency gates will not be opened until the rate of rise in pool elevation equal or exceeds
the values in the rate of rise tabOl. For the 200 and 500 year floods analyzed in this study, the
rate -of -rise did not necessitate opening the emergency gates until elevation 1567 fl-
b. Gate openings are made in accords with the Masonry Dam emergency gate scheduler while adhering
to an opening constraint of ft/hour.
c. The emergency gates will not pass more thancurrent inflow on the climbing side of the inflow hydrograph.
d. It was assumed that all three emergency gates would be utilized and opened in unison.
5. Median plotting positions were determined using an N value representing the period of record. The N
value used was 81 years (1906-1986).
6. Future condition flows were taken to be 8% greater than present condition flows as stated by King County
Department of Public Works "]. Existing and future condition curves appear to converge at roughly the 1.25
percent cxccedance frequency (80 year return period).
Ell City of Seattle, Seattle City Light, Seattle Water Department (unknown date), Operations and
Maintenance Handbook Cedar fi'alls Headworks and Overflow Dike.i.
King County l3cpartnient of Public Works, Surface Water Management Division (1993), Cedar River Current and Future Conditions Report.
11-41 -L�ALIL[t
- LJ1
FREQUENCY STATISTICS
-I--- Mir"
_Li+ 11Li1.� (.- I l i I j I i
Log Transform of Flow, cfs
Mean 3.4908
Variance 0.0572
Standard Deviation 0.2392
G Median Plotting Positions
Existing Conditions
Future Conditions
5% and 95% ConfidenoeIntavals 71
5 in
j 1il
.I
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T!
i}ar
CUMULATIVE FREQUENCY CURVE
Maximum
Annual Peak Rainflood Events
(Including the November 24-26, 1990 Flood)
CEDAR FJVr,,R AT RENTON
USGS Station Nwnber 12119000
Drainage Area = 186 sq. ini.
90 3n 4 n Fin 60 7n
Computed by: K. Yokoyan-la 01 March 1995
i i I - Checked by: G. Singleton
D. Harvey
Rn qn 95 ^v n(I
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lop
1
5
44
m
10
0.01 0.05 0.1 0.2 0.5 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 99.8 99.9 99.99
Exhibit 3
Cedar River at Renton Flow Duration Curve
PROBABIL I I X .' ( 01, t V I I. I.
KEUFFFL & PSY f? co - - 1 1 46 8043
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CEDAR RIVER AT RENTON
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Based on USGS observed data from 1947-1992
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K Yokoyarna 12 December 1994
5000
4500
4000
3500
a 3000
u
2500
0
M
2000
1500
1000
500
O
O
O
CEDAR RIVER AT RENTON
5 Year Hypothetical Hydrograph
0 O O O 0 O O 0 O 0 0 0 O O 0 0 0 O O 0 0 0 O O
O o o O o 0 o O o o O O O o o O o 0 0 0 0 o O O
0 N CO O 0 (V w O 0 N CO O 0 N 00 O (0 N m O t0 N OD O
DAY 1 DAY 2DAY 3 DAY 4 DAY 5 DAY 6
Exhibit 4
5 Year Cedar River at Renton Hypothetical Hydrograph
7000
6000
5000
in 4000
r—
U
3
O
UL 3000
2000
1000
0
0
0
O
CEDAR RIVER AT RENTON
10 Year Hypothetical Hydrograph
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
W N co O W N a0 O (D N 00 O w N 00 O cD N 00 O t0 N c0 O
DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6
Exhibit 5
10 Year Cedar River at Renton Hypothetical Hydrograph
9000
8000
7000
6000
5000
c.�
4000
3000
2000
1000
0
CEDAR RIVER AT RENTON
20 Year Hypothetical Hydrograph
0 0 0 0 0 O 0 0 0 0 0 0 0 0 o O 0 0 0 O o
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 cD N 00 O 0 N w O 0 N w O 0 N w O 0 N w O
DAY 1 DAY 2 DAY 3 DAY 4 DAY 5
Exhibit 6
20 Year Cedar River at Renton Hypothetical Hydrograph
0 0 0 0
0 0 0 0
tD N 00 O
DAY 6
CEDAR RIVER AT RENTON
100 Year Hypothetical Hydrograph
13000 --
12000 -- — —
11000
10000
9000
_ 8000
N
c 7000
30 6000
iL
5000
4000 —
3000 —
2000
1000
0 — — --
O O O O O 0 O O 0 O O O 0 O O 0 O O 0 O O O 0 O 0
0 0 0 0 0 0 0 o O O o 0 0 0 0 0 0 0 0 0 0 0 0 0 0
O (O N W O �D N 00 O fD N m O (Li w O cD m O N co O
DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6
Exhibit 7
100 Year Cedar River at Renton Hypothetical Hydrograph
CHESTER MORSE LAKE AND MASONRY POOL
200 Year Flood
18000
16000
14000
12000
.� 10000
U
3
0 8000
6000
4000
2000
0
1572.00
1570.00
1568.00
1566.00 >
a�
LLI
1564.00
1562.00
1560.00
O O O O o O O O
O O O O O
O O O
O O O O O O O O O
0 o O o 0 o O o
0 o O o 0
0 0 o
O o 0 o O o O o 0
p tU N 00 O to iV 00
O t0 N 00 O
co N 00
O to N 00 O to N 00 O
DAY 1 DAY 2
DAY 3
DAY 4
DAY 5 DAY 6
-CIVIL Inflow
CIVIL Outflow
----•-•-•- CIVIL Elev
Exhibit 8
200 Year Chester Morse Lake and Masonry Pool
CEDAR RIVER AT RENTON
200 Year Hypothetical Hydrograph
22000
20000
18000
16"
14000
U 12000
0 10000 -
8000
6000
4000
2000
0 p p p p p p p p p p p p p p p p
8 O 8 o S O O O O O O O O O O O O O S
O fD N GO O fp N CO O 0 <4 CO O 6 N 60 O 40 N
DAY 1 DAY 2 DAY 3 DAY 4 DAY 6
Exhibit 9
200 Year Cedar River at Renton Hypothetical Hydrograph
8 8 8 8 8 8
GO O 6 N GD O
DAY 6
20000
18000
16000
14000
12000
y
U
3 10000
0
EL 8000
6000
4000
2000
0
CHESTER MORSE LAKE AND MASONRY POOL
500 Year Flood
i
i�
1572
1570
1568
1566 >
a>
LLI
1564
1562
1560
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
O t0 N 00 O tD N 00 O to N 00 O CD N 00 O tD N 00 O tD N 00 O
DAY 1 DAY 2 DAY 3 DAY 4 DAY 5 DAY 6
-CIVIL Inflow CIVIL Outflow - -•- -•-•- CIVIL Elev
Exhibit 10
500 Year Chester Morse Lake and Masonry Pool
CEDAR RIVER AT RENTON
500 Year Hypothetical Hydrograph
24000
22000
20000 —
18000
16000
w 14000
C.1
3 12000
0
EL 10000 —
8000
6000
4000
2000
0
$ 8 S 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
O e6 N 6 6 6 N DO O 6 N CO O 6 N i6 O 6 N
DAY 1 DAY 2 DAY 3 DAY 4 DAY 5
Exhibit 11
500 Year Cedar River at Renton Hypothetical Hydrograph
8 8 8 8 8 8
cU O 6 N aD O
DAY 6
APPENDIX C
HYDRAULIC DESIGN
APPENDIX C
HYDRAULIC DESIGN APPENDIX
SECTION 1. HYDRAULIC DESIGN
1.01 SUMMARY
The original scope of this project as proposed in the
reconnaissance phase included a sediment capture basin located within
the study reach, combined with initial dredging to establish the desired
channel bed elevation. Proposed hydraulic evaluation included the
assembly and application of a sediment transport computer model (HEC-6)
to assess dredging and sediment trap success, and a steady state, one
dimensional water surface profile computer model (HEC-2) to evaluate
flood water surface profile reduction with the proposed project.
During the course of the study, the ground and channel survey
data was converted to HECRAS (a windows -based one-dimensional water
surface profile computer model) format to facilitate project evaluation
and organization of alternatives. Additionally, the SAM sediment
computer model was applied at the preliminary evaluation stage to
improve the assumptions taken in the HEC-6 model.
1.02 General Description of study reach
The study reach of the Cedar River is about 9000 ft in length,
extending from the I-405 freeway overpass in Renton, Washington at the
upstream end to Lake Washington at the downstream end. The
prehistorical Cedar River channel did not flow into Lake Washington at
the time settlers of European descent arrived at what is now the city of
Renton. The lake was at that time nine feet higher in elevation, and
flowed out through the Black River into the Duwamish, then into Puget
Sound near present day Harbor Island. The Black River was a sluggish,
deep, slow -moving slough with a fairly stable channel. The Cedar River
is a steep gradient, gravel bed stream flowing from a fairly confined
narrow valley. The present day city of Renton is founded on an
historical alluvial fan at the mouth of the Cedar. At times the Cedar
River may have alternately flowed into the lake or into the Black River,
or into both. Flood flows historically inundated large portions of the
active alluvial fan.
In the early 1900's, an artificial channel was dredged from
about the location of the present day I-405 overpass to the lake, and
the Cedar was permanently diverted into Lake Washington. Early accounts
of flooding prior to the construction of the artificial channel indicate
that the river overflowed its banks frequently and floodwaters flowed
down randon channels over the area now occupied by the city of Renton
(Ref #1). Around the same time period the Hiram Chittendon Locks and
the Lake Washington Ship Canal were constructed, and the level of the
lake was permanently lowered nine feet. The dredged channel was
extended, and the left bank area was developed into the present day
Renton airfield. Extensive manufacturing facilities were constructed on
the right bank by the Boeing company to support production of aircraft.
1.02 Available data
The City of Renton provided a copy of the study report
documenting Northwest Hydraulic Consultants' (NHC) limited flood
analysis study of the lower two miles of the Cedar River completed in
1991 (Ref #2). NHC provided electronic copies of the HEC-2 input and
output files for the subject report as well. The report compared the
channel conditions from 1986 to 1991, and calibrated the model to the
recent estimated 50-year recurrence interval flood event in 1990. Cross
sections for part of the historically dredged channel were evaluated as
well, including a limited set from 1954, and several limited sets from
the 1960's and 1970's.
Observed high water marks were available for the November 1990
flood event (an estimated 50 yr recurrence interval event), and the
December 1995 and February 1996 flood events (both about 15 to 20 yr
recurrence interval events). Calibration of the study hydraulic models
was made with the 1995 and 1996 events only, since historical bed
elevation changes suggest that any other than the most recent data are
not applicable for calibration purposes.
The City of Renton provided estimates of total past expenditures
on delta and channel dredging activities. Dredging volume records were
not available, though. Anecdotal information regarding the average
annual volume of sediment extracted from the river just upstream of the
study reach was obtained from the Stoneway sand and gravel mining
company. The Stoneway company mined gravel from the river bed upstream
of the study reach for many years, up until the 1960's.
Little observed sediment transport data is available for the
Cedar River. King County has performed a fairly extensive literature
search as part of their comprehensive plan for flood damage reduction
throughout the entire Cedar River basin, and have cited what little
observed data is available (Ref #3). The Corps of Engineers, as part of
this study, conducted a very limited sampling program to determine
preliminary bedload transport estimates within the study reach.
glover-MITT-W-W0 - . . . 1 . .. -
The NHC HEC-2 model was used to establish general cross section
locations so that results could be compared to those provided in the
1991 NHC report. Cross sections were surveyed in 1994 of the channel
and overbanks, and channel bed sections were surveyed again at the
accessible bridge locations following the December 1995 flood event. An
HEC-2 model was developed for the study reach from the I-405 overpass to
the mouth of the river and beyond to the extent of the delta formation
in the lake. The HEC-2 model format was modified thereafter to HECRAS
N
format to facilitate the presentation of data and results. Because the
flow characteristics of the channel and overbanks varies significantly
between relatively low flows and higher out -of -bank flows, model flow
data input was primarily separated into low flow and high flow
computation runs.
Manning's n values for the channel and overbanks were selected
by calibration to the December 1995 and February 1996 flood events, and
compared with those used in the NHC study several years prior. The
selected n values compared favorably with those used in the previous
model and were generally within the expected range for channels similar
to the study reach. Channel n values ranged from 0.022 to 0.040
throughout the study reach, with a value of 0.03 to 0.035 for most cross
sections. Overbank n values were much more difficult to assign, and
generally ranged from about 0.045 to about 0.12, with a value of about
0.05 to 0.06 for most left bank sections along the Renton airfield, and
0.075 to 0.12 for left bank sections where structures and vegetation
restricted conveyance. Right bank n values varied from about 0.045 to
about 0.1, with most sections including the Boeing manufacturing plant
using n values from 0.045 to 0.06 and sections with heavier vegetation
along the city park upstream of the Boeing plant using n values from
0.07 to 0.1. Upstream of the Logan Street bridge, overbank n values
ranged from 0.05 to 0.085, depending on the vegetation and obstruction
density.
Manning's n value selection for the overbanks was difficult, and
probably does not accurately represent the true roughness
characteristics of these areas. They were selected in order that the
amount of flow in the channel and along the left and right banks could
be properly distributed. The nature of flood overflows along the left
bank through the Renton airfield is such that a one dimensional steady
state model is difficult to apply. Flood overflows do not pond on the
airfield or flow downstream uniformly with the channel flow, rather they
flow downstream and away from the river channel under rapidly varied
conditions. The left bank upstream and downstream of the South Boeing
bridge behaves as an overflow weir, with overflows flowing along the
landing strip or across the strip centerline. Flow passing over the
centerline of the strip is lost directly to the lake without returning
to the river, while flow along the right side of the strip returns to
the river downstream of the South Boeing bridge. Observed water surface
elevations are not uniform across the cross sections.
Bridge flow characteristics were similar for all spans crossing
the Cedar River upstream of and including the Logan Street bridge.
Bridges at Logan Street, Wells Avenue, Williams Avenue, Bronson Way, and
Houser Way all have abutments supporting the left bank bridge deck and
intermediate near -bank piers and abutments supporting the right bank
bridge deck. Logan Street has both left and right bank abutments and an
intermediate pier near each abutment. Houser Way has a right bank
abutment and left bank abutment and intermediate pier near the left
bank. The Renton City Library is constructed over the river and is
supported by two conrete pile bents (multiple piles aligned parallel to
flow direction) centered roughly near the low water line along each
3
bank. Upstream bridges were analyzed with pressure flow and weir
overflow for higher discharges.
The South Boeing bridge is supported by left and right bank
abutments and intermediate piers located near each bank. Riverbank
elevations upstream of the bridge are lower than the top of bridge deck
elevation. Some left bank locations upstream are as low as the bottom
chord steel on the bridge. The South Boeing bridge was analyzed with
pressure flow, and approach roads were analyzed with weir flow for
higher discharges. Head loss coefficient for the bridge and piers are
in reality highly variable, since debris blockage greatly varies the
characteristics of flow under the bridge, as observed during past flood
events.
The North Boeing bridge is supported by two pile bents (row of
piles aligned parallel to flow direction) at each end of the span,
located near the bank. It was analyzed with pressure and weir flow for
higher discharges.
To duplicate the varied flow observed in the overflow area on
the left bank required an iterative process of adjusting model discharge
distribution values at each cross section and corresponding computation
of weir flow over the centerline of the airstrip to account for that
portion of flood discharge lost directly to the lake without returning
to the channel. Each run of the model was compared to the observed
field data and to a best guess estimate of flow distribution based on
engineering judgement and cursory computation, then the process was
repeated until satisfactory agreement between observed conditions and
computed results was reached. The calibrated model was used as the base
input file for all project alternatives analysis and for the HEC-6
sediment transport analysis.
The sediment modeling analysis was conducted with the HEC-6
computer model, developed by the Waterways Experiment Station (WES). We
used a recently upgraded version prepared by WES hydraulic modeling
group staff to address gravel bed rivers like the Cedar with
improvements in computational methods over the version released by the
Hydrologic Engineering Center (HEC), the more widely used Corps
standard.
Prior to application of the HEC-6 sediment model, a
preliminary assessment of the sediment transport characteristics of the
river was conducted with the SAM computer model developed by WES. SAM
computes the sediment transport capacity of the river using any one of
about nineteen transport equations. Input data includes the annual flow
duration curve, the bed material sediment gradation at the cross section
of interest, the river channel cross section water depth, width,
discharge, and water velocity, the energy slope at various discharges,
and the sediment inflow load curves developed from observed bed load and
suspended load data, and the roughness coefficients for the channel as
El
provided in the calibrated HEC-6 model. SAM aids the engineer in
selecting the most appropriate transport equation, the most appropriate
sediment inflow load curve, and the most appropriate sediment inflow
gradation curves for application in the HEC-6 model.
Observed sediment transport data for the Cedar River is not
extensive. Some data has been collected in the past by King County's
Surface Water Management division, and is documented in a literature
review presented in the County's Current and Future Conditions Report
for the Cedar River Basin (Ref #3). Most sediment transport capacity
estimates have been made by indirect means, such as bed elevation
surveys, channel meander analysis, discharge capacity changes, specific
gage analysis for the lower basin flow gage, previous lower channel
dredging records, and other methods. Northwest Hydraulic Consultants
Inc. (NHC), under contract to the City of Renton, collected suspended
load and bedload transport measurements during the course of this study
(Ref #4). NHC collected additional sediment data during the December
1995 and February 1996 flood events (Ref #5). Both of these events were
of about 15 to 20 year recurrence interval. The Corps and NHC also
extracted a number of bed material samples from the channel at low flow
throughout the length of the study reach (Figure #1). Gradation
analysis of the samples (Figures #2-#12) was conducted by NHC and by
staff at Seattle District in the District's geotechnical laboratory
(also in Ref #4). Observed suspended and bed load transport data are
very limited throughout the basin, with no observed data available for
large flood events. In addition, the unstable, aggrading nature of the
channel bed in the study reach did not provide a means of accurately
calibrating the sediment transport model for application within the
study reach.
SAM was also used in this study to determine the average annual
sediment yield, to develop the sediment discharge rating curve (sediment
discharge vs. water discharge), to develop the most appropriate sediment
inflow gradation curve, and to determine the most appropriate sediment
transport equation to be used in the HEC-6 model. Observed bed load and
suspended load data was analyzed and an approximate sediment transport
relationship was developed, which is shown below.
Qsediment-total = ( 0 .00000864 ) x Qwater2 163 + (0.00000257)x QWater2 37 (1. 03 -b. 1)
where Qbedload is the first term in the right hand side of the
equation, and Qsuspended load is the second term.
This relationship was compared to predicted sediment transport
in the SAM model using four of the most appropriate transport equations,
given the channel geometry, bed material gradation, flow conditions, and
sediment inflow gradation. None of the four equations provided clear
agreement with the observed data and derived equation at lower
discharges (below about 7500 cfs). However, minor manipulation of
sediment inflow load curve and inflow load gradations in the SAM input
provided the best fit between the sediment rating curve and sediment
inflow gradations predicted by the Meyer -Peter Muller equation (MPM) and
the curve derived from observed data. Shown below are the sediment
5
transport rating curves predicted by the four transport relationships
plotted along with the curve derived from the observed data (Equation
1.03-b.1 above).
&dnMtM d8W Rfirgav
Oom R 1-m7483
-� u.W �6JlaG'�QnQ
-ff- Kbi6 RhY MJ
-� a -Elm
Rrk2r
1 10D 1= 1C1SLID
Vdter(cfs)
Although the Schocklitsch formula more closely matches the
observed data curve, we felt that it might lead to less conservative
design conclusions by under -predicting sediment accumulation in the
project reach. The MPM formula, although over -predicting transport
capacity at lower discharges, predicts more reasonable transport
capacity at higher discharges than the other two applicable formulas
(Einstein and Parker). The MPM formula is also perhaps more applicable
in this case because it predicts transport capacity based on excess bed
shear stress, rather than excess bed velocity exposure above critical
bed velocity as in the Schocklitsch formula. In gravel bed rivers such
as the Cedar, bedload transport increases as discharge increases at a
greater rate than in sand bed streams. Shear stress -based transport
relationships more accurately predict transport capacity than critical
bed velocity -based transport relationships.
The sediment discharge rating curve predicted by the MPM method
was separated into particle size classes and plotted with the observed
sediment load data. In this way, the MPM-predicted sediment inflow
could be compared to observed data by particle size gradation to assess
the ability of the MPM method to predict which grain sizes would be
transported at the appropriate discharges. The figures below show
comparative sediment inflow curves by particle size gradation for the
observed data and for the predicted sediment inflow.
0
m
0
3
0
0
c
m
c
m
w
�a
E
0
U
V
R
0
3
0
0
c
m
d
a
m
m
E
0
U
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
100.00
90.00
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
0 2000 4000 6000 8000
Discharge (cfs)
Sediment Inflow by Size Gradation
Predicted (MPM) (Cumulative fraction)
0 5000 10000 15000 20000 25000
Discharge (cfs)
Sediment Inflow by Size Gradation
Observed data (Cumulative fraction)
.09375 mm Very Fine Sand
.1875 mm Fine Sand
.375 mm Medium Sand
.75 mm Coarse Sand
1.5 mm Very Coarse Sand
+_ 3 mm Very Fine Gravel
�— 6 mm Fine Gravel
)K 12 mm Medium Gravel
24 mm Coarse Gravel
48 mm Very Coarse Gravel
�— 96 mm Small Cobble
192 mm Large Cobble
.09375 mm Very Fine Sand
.1875 mm Fine Sand
— .375 mm Medium Sand
75 mm Coarse Sand
1.5 mm Very Coarse Sand
—� 3 mm Very Fine Gravel
6 mm Fine Gravel
—12 mm Medium Gravel
— 24 mm Coarse Gravel
48 mm Very Coarse Gravel j
—� 96 mm Small Cobble
j 192 mm Large Cobble
7
Using the annual flow duration curve (shown below) developed
from historical hydrologic data, a fair estimate of the average annual
sediment yield was predicted with SAM.
25000
20000
15000
N
m
lQ
L
V
—p 10000
4110111
0
0.0001
Annual Flow Duration
Cedar River
0.001 0.01 0.1 1 10 100
Percent of Time Equaled or Exceeded)
d_
'�j
Predicted annual yield was compared to data collected for other
Puget Sound and Pacific Northwest area streams with similar watershed
characteristics and was determined through engineering judgement to be
an adequate representation of the actual yield. The table shown below
tabulates annual yield figures for several similar basins (Ref #7-12).
Basin Name
Drainage Area
Annual bedload
Annual total
(mil)
sediment yield
sediment yield
(tons /Mi2
tons/mil )
tons/mil )
(tons /Mi2
Cedar River, WA
110 (below
50 (estimated)
500 (estimated)
(estimated)
Masonry Dam)
Cedar River
110
--200
2174
(predicted MPM)
White River, WA
400 (above Mud
50 to 125
1250 to 3125
Mtn. Dam)
(glacially fed,
high suspended
load)
Snohomish River,
-
20 to 100
200 to 1000
WA (various
(various
(various
tributaries)
tributaries)
tributaries)
Bogachiel River,
287
55 (approx.)
1390
WA
Soleduck River,
226
21 (approx.)
531
WA
Quillayute
629
33
635
River, WA
By manipulating slightly the sediment inflow load curve and the
inflowing load gradation curve and selecting from the two or three
different transport equations most appropriate for gravel bed rivers, a
fair estimate of annual yield was obtained with the MPM method. MPM
predicted more reasonable annual sediment yield than the other three
formulas, all of which significantly overpredicted yield by as much as
an order of magnitude. Additionaly, the MPM formula provided the better
channel bed response when utilized as developed in the HEC-6 model
simulation, as discussed in Section 1.03.b.2 below. Agreement with
annual yield estimates between the predictive method and the observed
data and data for similar watersheds was considered to be more important
in this study than other comparative measures, since the primary focus
would be estimation of future dredging requirements.
b.2 HEC-6 Model
The HEC-6 model used the HEC-2 cross sections and n-values
calibrated for the December 1995 and February 1996 flood events. Some
closely spaced cross sections were removed from the input file upon
evaluation of model stability. Ideally, application of the HEC-6
computer model requires that the cross sections be spaced some distance
apart, based on channel width, slope, and velocities. The decision to
remove a cross section is made by engineering judgement and experience.
Bridge cross sections also are not analyzed as in HEC-2. No pressure
flow condition is allowed in HEC-6. To compensate for this the channel
9
`n, values for the bridge section are artificially raised to reflect
appropriate bridge head losses.
HEC-6 application requires first the calibration of the steady
state hydraulics of the model. No sediment inflow load curve or
gradations are input to the model during this phase. In this case, the
model was calibrated to the HECRAS model for bankfull flows in the lower
reach of the study area (about 3500 cfs) and for the February 1996 flood
event (about 8000 cfs). As discussed above, n-values were increased as
appropriate for the cross sections representing bridges, to reflect the
observed head loss through the bridge (measured during February 96
event).
Following satisfactory calibration of the steady state
hydraulics, the sediment inflow load curve and gradations were added.
The Meyer -Peter Muller sediment transport relationship was selected for
use in this HEC-6 simulation, based on evaluation of transport
characteristics with the SAM computer model. As a test of sediment
transport calibration, the historical hydrologic data from the period
from 1991 to 1994 were parsed and input with proper time step. Minor
modifications to the sediment inflow load curve and inflow gradations
were made until the model predicted with some agreement the observed bed
elevation changes over that time period (final values shown below).
Additionally, the model was run with the historical hydrologic data for
the week or so surrounding the December 1995 flood event, using 1994
cross section geometry and the above -developed sediment inflow load
curve and gradations. Field surveys of the bridge cross sections
immediately following the December 1995 event were compared against the
predicted bed elevation changes from the HEC-6 model and found to be in
fair agreement.
10
100001
i[#I6I8hh]
m 10000
N
C
O
1000
f0
t
100
0
c
d
E 10
=5
d
V)
1
1.00
0.90
0 0.80
e 0.70
0 0.60
0.50
c 0.40
CD
0.30
v
0.20
E
v 0.10
0.00
0
Selected Sediment Inflow Load
0_ Selected Sediment Inflow Load
10 100 1000 10000 100000
Water Discharge (cfs)
Sediment Inflow by Size Gradation
Selected Values (Cumulative fraction)
.09375 mm Very Fine Sand
.1875 mm Fine Sand
_ .375 mrn Medium Sand
75 mm Coarse Sand
1.5 mm Very Coarse Sand
-�_ 3 mm Very Fine Gravel
{_ 6 rrm Fine Gravel
)K_ 12 mm Medium Gravel
— 24 rrm Coarse Gravel
48 mm Very Coarse Gravel
96 mn Small Cobble
192 mm Large Cobble
5000 10000 15000 20000 25000
Discharge (cfs)
The calibrated sediment transport model was then used to predict
the future condition of the channel for the no -action alternative.
Usually, good results are obtained with the HEC-6 model when predicting
future sedimentation by stepping the computations through a
"computational hydrograph" represented by the annual flow duration
11
curve. The computational hydrograph in this case was developed by
partioning the annual flow duration curve into a series of discrete
steady flows, each having a specified duration. For example, by
selecting all flows between 6000 and 6500 cfs, we see from the flow
duration curve that a flow of 6000 cfs will occur approximately .0475
days in any given year, and a flow of 6500 cfs will occur approximately
.0365 days in any given year. Therefore, one time step on the rising
limb of the computational hydrograph consists of a flow of 6250 cfs (the
mean of upper and lower limits of selected flow range) occurring
(.0475+.0365)/2 =.042 days per year. The same time step is repeated on
the falling limb of the computational hydrograph. For a 20 year
simulation, this computational hydrograph is repeated 20 times. The
annual computational hydrograph is shown below.
100000
10000
1000
N
V
10
Annual Computational Hydrograph
Cedar River
0 50 100 150 200 250 300 350 400
Duration (days)
In this application, the HEC-6 model run aborted at about 20
years in the future during a 50 year simulation because the predicted
channel bed had aggraded to such a degree that insufficient effective
flow capacity remained within the channel boundary. The future without -
project condition assumed, then, that the channel was no longer viable
at 20 years in the future if no action is taken. The predicted bed
elevation was input into the HECRAS hydraulic model and used to predict
water surface profiles for the without -project condition.
12
Several channel dredging scenarios were evaluated with the HEC-6
model. Detailed description of the various alternatives studied are
discussed in Section 1.04 below. In general, the HEC-6 model results
provided conservative estimates of average dredge volumes and dredge
cycle frequency required to maintain the desired channel flow capacity
within the study reach. Maintenance dredging intervals of from two to
five years were evaluated for the alternatives by simulating a 20 year
series of computational hydrographs and developing average maintenance
dredge volumes over the period of simulation.
1.04. Alternatives Analysis
Alternatives consisted of levees and/or floodwalls, dredging to
various depths, narrowed low flow channels, sediment trap, raising the
South Boeing bridge, widening the existing channel, and constructing an
overflow channel, as well as combinations thereof. The no -action
alternative was also evaluated to show the potential reduction in
channel capacity if nothing is done to alleviate the continuing
aggradation of the channel bed. Hydraulic analysis of water surface
profiles for a range of anticipated discharges was performed for each
alternative using HECRAS. Sediment transport analysis using HEC-6 was
performed for alternatives requiring initial and/or maintenance dredging
to provide desired level of flood protection to the project study area.
The selected alternative was based on the NED plan determination, using
Corps economic guidelines, with some minor changes to accommodate the
desires of the local sponsor.
The no -action alternative was first analyzed with the
sediment transport model to determine the extent of future aggradation
and its effects on channel capacity. Simulation of future aggradation
with the sediment model was performed for a fifty year period. However,
the predicted bed aggradation apparently reduced the channel capacity
within about 20 years to such a degree that the flow distribution
between overbanks and channel no longer met computational criteria for
the HEC-6 model and the computation aborted each time the run was made.
The future condition HECRAS input file represents the anticipated bed
geometry 20 years in the future. This predicted estimate can be
compared to the aggradational trend shown in a specific gage analysis of
the U.S.G.S. gage at Bronson Way (shown below).
13
•
34
32
30
j 28
C9
z
26
m
24
22
20
18
Rating Curve @ USGS gage site
Cross Section 7483 nhc 1991 model
0 2000 4000 6000 8000 10000 12000
Discharge (cfs)
OJILETI! _ 9_ - 9 #GV WV MkKzIWvFUF
-�— L4-IVOV-t5b
-�_ 14-Dec-94
_ A. 18-Feb-82
+. 1-Oct-79
16-Jan-74
- 23-Sep-70
This alternative included a diversion structure to carry
discharges in excess of the existing channel capacity to Lake Washington
through an artificial channel. Upon cursory examination it became
obvious that there existed no shorter or more efficient route to the
lake than the existing channel, and that any such bypass channel sized
to carry even the discharge in excess of channel capacity for a 100 yr
flood would have to be very large. Such a channel would require large
real estate investment and high construction costs, and cause disruption
to the operation of the airfield. FAA restrictions would very likely
also require that the bypass channel be covered at least partially
throughout the entire length.
Preliminary investigation of a constructed bypass channel
showed that an overflow weir would have to be constructed along the left
bank of the existing channel over about 1000 ft of length, which would
pass flow directly into the bypass channel. The overflow channel would
be designed to carry up to about 8500 cfs (100 yr flow of 12,000 cfs
minus existing river channel capacity of about 3500 cfs) about 4000 ft
to the lake, roughly alongside the existing river channel. Assuming a
concrete lined channel with slope approximately equal to the river (So =
.0023) and a maximum depth of about 8 ft, design width would be at least
200 ft. The high construction costs and failure of this alternative to
address the aggradation problem in the existing river channel eliminated
it from further consideration. A system of closed conduits of similar
capacity would require higher construction costs and thus was also
eliminated from further consideration.
14
c. Sediment trap alternative
This alternative, originally selected during the reconnaissance
phase, considered several locations for a trap, or overexcavation,
within the existing river channel. Primary concerns with this
alternative focused on the potential for reduced maintenance dredge
requirements for portions of the channel not within the trap area. Most
sections of the river upstream of the study reach were eliminated from
further consideration for trap locations due to environmental concerns
with disturbance of very productive sockeye spawning areas. Real estate
concerns favored trap siting within the study reach, as the entire
length of the artificial channel from I-405 to the mouth is wholly owned
by the City. Three sites were proposed as potential trap locations.
The old Stoneway plant extraction area is upstream of the study reach,
but would provide sufficient channel length and depth for as much as
10,000 cubic yards of sediment storage. The existing river channel from
the South Boeing bridge to Logan Street bridge provides sufficient
length and depth for as much as 25,000 cubic yards of sediment storage.
The existing river channel from the South Boeing bridge to the mouth
provides sufficient channel length and depth for as much as 70,000 cubic
yards of sediment storage. Construction access limitations and
construction equipment bridge clearance issues ruled out trap locations
from Logan Street bridge upstream to I-405.
Sediment transport analysis of the proposed Logan Street -to -
South Boeing bridge location showed that the trap could fill quickly
with smaller sized sediment particles that may have flushed out to the
delta if the trap were not constructed rather than depositing in the
channel. This effect would increase dredge requirements unnecessarily.
Periodic excavation of the trap area to the initial geometry would
provide renewed sediment storage capacity. Concerns with the sediment
trap concept were voiced by the local sponsor when results showed
possible filling of the sediment trap during a single large flood event
and subsequent loss of channel capacity for short term future flood
events during the same flood season. Should such a series of events
occur, it would not be possible to remove sediment from the trap area
safely between consecutive events during the flood season, and therefore
the project would not provide the design level of protection.
Environmental concerns with the channel bed configuration
upstream and downstream of the sediment trap resulted in less favorable
standing of this alternative. An effective sediment trap design would
result in significant modification of the existing character of the
river through the trap reach by making it deeper and slow moving.
Sediment transport analysis showed that regular dredging of the entire
project reach was more efficient at removing only those sediments which
would normally accumulate in the channel and would reduce the overall
annual dredging equivalent volume. Further consideration of the
sediment trap alternative was eliminated.
The existing 100 to 110 foot wide channel would be widened to
150 feet upstream of the South Boeing Bridge and to 250 feet from the
15
South Boeing bridge to the mouth. However, widening alternatives
seriously impacted the City of Renton's Riverside Park along the entire
right bank by removing most of the park area. High construction costs,
park impacts, and limited effective reduction in flood profiles
eliminated this alternative from further consideration. Additional
investigation included widening the channel to 250 feet from Logan
Street bridge to the mouth and adding an additional span to the South
Boeing bridge. Minimal reduction in flood water surface elevations were
provided by this alternative. In addition, this alternative did not
address continued channel bed aggradation.
Wingwalls or riprap would confine a narrow channel excavated six
feet below existing grade roughly in the center of the existing channel
bed from I-405 to the mouth of the river. This alternative was proposed
as a means of increasing bed shear and thus transport capacity for flows
below about 1000 cfs (the flow at which the most sediment is tranposrted
through the reach over long periods of time). However, simulation of
this alternative with HEC-6 over a 20 year period showed no significant
reduction in average maintenance dredging volumes for the study reach
over that provided by regular dredging of the entire width of the
existing channel. Additionally, large construction costs for this
alternative would also be required, therefore it was eliminated from
further consideration. Sediment transport analysis of this alternative
showed the following dredge quantities required to maintain the desired
channel geometry:
Alternative E: 6'd x 50'w low flow channel dredge into existing channel thalweg,
2 Year
3 Year
5 Year
Maint.
Maint.
Maint.
Dredge
Dredge
Dredge
Volumes
Volumes
Volumes
(cy)
(cy)
(cy)
Year
0
145362
145362
145386
(Beginning
1
of year)
2
115068
3
166405
4
118339
5
266100
6
120412
177168
7
8
123139
9
177870
10
123400
285484
11
12
123400
177852
13
14
123538
16
15 177769 307114
16 123298
17
18 123789 177755
19
20 123618 306965
21 177718
Channel and/or delta dredging alternatives were evaluated with
the HECRAS steady state hydraulic model and with the HEC-6 sediment
transport computer model. Reduction in flood water surface profiles
resulting from varying dredge depths were not necessarily directly
proportional to the variation in dredging depths. Dredge channel
configuration generally considered excavation of the entire width of the
existing channel bed down to the desired depth. Excavated side slopes
were assumed to be 1V:3H in all cases; a reasonable assumption for in -
water excavation of gravels with relatively stable slopes.
Interestingly, the hydraulic model predicted that critical depth control
for all alternatives except the deep dredge alternative occurred near
the downstream face of the North Boeing bridge. This was confirmed by
field visits during the December 1995 and February 1996 flood events.
The critical depth hydraulic control was clearly indicated by the two to
three foot head drop through and downstream of the North Boeing bridge.
Alternatives including delta and channel dredging were evaluated
against alternatives including only channel dredging. The additional
reduction in flood water surface profiles attributed to delta dredging
was not significant in all but the deep channel dredge alternative. For
this reason, delta dredging was not included in three of the four
channel dredging alternatives. The rate at which the delta builds is
dependent on the available sediment storage volume available in the lake
near the delta. Lake Washington is quite deep, well over 100 ft,
immediately outboard from the delta, with very large capacity for
additional sediment deposition. Thus the rate of outward delta growth
has been, and would be expected to remain, quite slow. With this
natural limit to delta growth, and consequent limit to delta subchannel
length increase, the effect of the delta on flood water surface profiles
would be expected to remain fairly constant over the expected life of
the project. However, significant coverage of the delta with permanent
vegetation would be expected to increase the potential for backwater
effects to extend into the project channel, superceding the critical
depth hydraulic control at the mouth.
E.• ._..- - .. -.
This alternative consisted of inital excavation of the
existing channel to a uniform width at the existing thalweg elevation,
and regular maintenance dredging every 2, 3, or 5 years thereafter.
17
Hydraulic analysis of this alternative showed that no significant
reduction in flood profiles would be realized (Figure #13).
Sediment transport analysis of this alternative showed the
following dredge quantities required to maintain the desired channel
geometry:
Alternative F.1:
Existing channel thalweg, maintain at existing channel bottom
2 Year
3 Year
5 Year
M aint.
M aint.
Maint.
Dredge
Dredge
Dredge
Volumes
Volumes
Volumes
(cy)
(cy)
(cy)
Year
0
31067
31067
31067
(Beginning
1
of year)
2
91943
3
114828
4
91278
5
133856
6
91139
111403
7
8
93870
9
113750
10
93684
109170
11
12
93999
114058
13
14
93950
15
113813
136548
16
93987
17
18
93885
114232
19
20
93710
137485
21
114335
f.2. FExistincr channel dredge 4 ft below exisi<inc7 thalw
This alternative consisted of initial excavation of the
existing channel bed approximately 4 feet below the existing channel
thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross
section 16.12, and to uniform elevation 8.0 from cross section 16.12 to
just downstream of the river mouth (cross section 0.08), and tapering up
to the existing thalweg elevation at cross section 65.01 (d/s face of
Wells Avenue bridge). Regular dredging to the initial bed profile every
2, 3, or 5 years thereafter would maintain the desired level of
protection within the study reach. Hydraulic analysis of this
18
alternative showed that a reduction in flood profiles would be realized
(Figure #14).
Sediment transport analysis of this alternative showed the
following dredge quantities required to maintain the desired channel
geometry:
Alternative F.2:
4 foot dredge below existing channel thalweg, maintain at 4 foot
2 Year
3 Year
5 Year
M aint.
M aint.
Maint.
Dredge
Dredge
Dredge
Volumes
Volumes
Volumes
(cy)
(cy)
(cy)
Year
0
158420
158420
158677
(Beginning
1
of year)
2
109415
3
154403
4
117006
5
243989
6
119637
171192
7
8
124258
9
172946
10
124480
264124
11
12
124435
173899
13
14
123941
15
173967
272486
16
124421
17
18
124278
174178
19
20
122996
270199
21
174140
f.3. Existincr channel dredge 6 ft below existing thalw
This alternative consisted of initial excavation of the
existing channel bed approximately 6 feet below the existing channel
thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross
section 25.32, and to uniform elevation 8.0 from cross section 25.32 to
just downstream of the river mouth (cross section 0.06), and tapering up
to the existing thalweg elevation at cross section 76.82 (d/s face of
Bronson Way bridge). Regular dredging to the initial bed profile every
2, 3, or 5 years thereafter would maintain the desired level of
protection within the study reach. Hydraulic analysis of this
19
alternative showed that a reduction in flood profiles would be realized
(Figure #15).
Sediment transport analysis of this alternative showed the
following dredge quantities required to maintain the desired channel
geometry:
Alternative F.3:
6 foot dredge below existing channel thalweg, maintain at 6 foot
2 Year
3 Year
5 Year
M aint.
M aint.
Maint.
Dredge
Dredge
Dredge
Volumes
Volumes
Volumes
(cy)
(cy)
(cy)
Year
0
194394
194394
195952
(Beginning
1
of year)
2
113774
3
159988
4
123099
5
252420
6
124262
176764
7
8
124634
9
178660
10
124769
279309
11
12
125119
179273
13
14
124879
15
180027
288229
16
124934
17
18
124932
179810
19
20
125062
288088
21
179884
f.4. Existing channel dredcae_ loft below existincr thalw
This alternative consisted of initial excavation of the
existing channel bed approximately 10 feet below the existing channel
thalweg from cross section 56.43 (d/s face Logan Street bridge) to cross
section 46.54, and to uniform elevation 7.0 from cross section 46.54 to
just downstream of the river mouth (cross section 0.08), and tapering up
to the existing thalweg elevation at cross section 76.82 (d/s face of
Wells Avenue bridge). This alternative approximately duplicates the
historical dredge profile the City of Renton maintained prior to the
1980's. Regular dredging to the initial bed profile every 2, 3, or 5
20
years thereafter would maintain the desired level of protection within
the study reach. Hydraulic analysis of this alternative showed that a
reduction in flood profiles would be realized (Figure #16).
Sediment transport analysis of this alternative showed the
following dredge quantities required to maintain the desired channel
geometry:
Alternative F.4:
10 foot dredge below existing channel thalweg, maintain at 10 foot
2 Year
3 Year
5 Year
M aint.
Maint.
M aint.
Dredge
Dredge
Dredge
Volumes
Volumes
Volumes
(cy)
(cy)
(cy)
Year
0
260462
260462
260235
(Beginning
1
of year)
2
119604
3
173731
4
124836
5
265879
6
126041
183964
7
8
127406
9
185209
10
127971
288400
11
12
128224
185602
13
14
128088
15
186339
291226
16
128024
17
18
127846
187600
19
20
127879
297554
21
190664
.._ I M:.-
This alternative considered raising the South Boeing bridge to
an elevation above the desired flood water surface. Permanent raising
of the bridge by more than just a few feet also required significant
regrading of the bridge approach roadways to accommodate the shallow
grades required to tow aircraft across the bridge. High costs and very
limited amount of elevation gain of the bridge afforded in this concept
eliminated it from further consideration. Temporary jacking systems for
lifting the bridge only during floods were evaluated instead. The
21
bridge structure would be lifted only during the flood event above the
flood water surface to sufficient height that debris would no longer
impact the low chord steel. Similar bridge jacking systems have been
designed by the District for flood protection, as in the Placer Creek
project in Wallace, Idaho, and for navigation clearance, as in the Grays
Harbor - Aberdeen railroad lift bridge design.
This alternative considered alone reduces debris impact damage
to the bridge deck during floods, but does not significantly reduce
overall flood damages within the study area. However, the bridge
jacking concept was used in combination with other alternatives to
provide reduction of debris impact damage, reduced levels of induced
flooding from bridge blockage by debris, and overall reduction in flood
water surface profiles. Temporary jacking systems for the bridge were
required for all levee alternatives to eliminate excessive levee height
requirements upstream of the bridge which would result if the bridge
were not raised.
This alternative considered levees and/or floodwalls to provide
the desired level of protection for the study area. However, this
alternative was not effective in significantly reducing flood damage
over the life of the project unless combined with a dredging program.
Without dredging, the initial level of protection would be reduced over
time as a result of continued aggradation of the channel bed. In
addition, without dredging, the bridges crossing the river throughout
the study reach would eventually be rendered impassable under all flow
conditions by sediment and debris deposition. HECRAS was utilized to
evaluate the height of levees necessary to contain events of various
recurrence intervals for each dredging depth scenario.
In addition, some alternatives included an intentional overflow
section levee designed to withstand overtopping for the duration of the
flood event during events larger than the design level of protection.
The purpose of the overflow section would be to limit flooding to an
area not seriously at risk of large damages, thereby preserving the rest
of the levee system intact and effective in preventing damage to higher
valued areas. However, during some very large events greater than the
design level of protection, the entire levee system would be overtopped.
1.05. Selected alternative
The selected alternative was one of four combination
alternatives, all of which included channel dredging to various depths,
a South Boeing bridge jacking system, levees/floodwalls on both banks
extending up to Williams Avenue, and an overflow levee/floodwall section
on the left bank from the South Boeing bridge to the mouth of the river.
These combination alternatives were analyzed in detail following the
first round of elimination during the early part of the study.
The selected alternative provided slightly less protection than
the NED-recommended plan, because the local sponsor chose not to
increase the level of protection for the upstream portion of the study
22
reach. It includes initial dredging of the channel to a depth of about
four feet below existing thalweg and maintenance dredging to the initial
dredge bed elevation every three years or as necessary to provide the
desired level of protection or greater, levees and floodwall sections
extending from the mouth up to the Williams Avenue bridge, a jacking
system for the South Boeing bridge, an overflow levee and floodwall
section extending from the South Boeing bridge to the mouth of the
river, and closure panels for the section•of levee on each end of the
South Boeing bridge.
A complicated procedure for determining required levee elevation
for the desired level of protection was used. The local sponsor
requested that the completed project provide sufficient level of
protection for FEMA to re -designate the protected area as outside the
100 year floodplain limits. This criteria required that the project
provide protection to at least the 100 year recurrence interval event
with 90 percent reliability. Recent COE guidance on the application of
risk and uncertainty analysis to levee projects was used to determine
the 90 percent reliability level of protection (Ref #6).
The 90 percent reliability water surface profiles were
determined by first establishing the 100 year profile with the
calibrated HECRAS model. Mannings n values for the calibrated model
were increased to the highest estimated upper limit of their possible
value for the future channel, based on engineering judgement. N values
were increased by 25 percent throughout the entire study reach to
reflect this upper limit. These values and the resulting 100 year water
surface profile computed with them represented one standard deviation
away from the mean (the calibrated model water surface profile, ie. 50%
reliability), which was assumed equivalent to the 67 percent reliability
profile. The difference in water surface, in feet, between the mean
(50o reliability profile) and the 67 percent reliability profile at each
cross section was then added to the 67 percent profile to arrive at the
estimated 90 percent reliability water surface profile (two standard
deviations from the mean).
The overflow levee section was designed to contain at least the
90 percent reliability water surface profile for the four foot dredge
channel with three years of predicted sediment accumulation, immediately
before a maintenance dredging cycle. Levees on the right bank
throughout the study reach and on the left bank upstream of the overflow
section were designed to provide a minimum of one foot of freeboard
above the 90 percent reliability overflow levee design profile. The
South Boeing bridge jacking system would be designed to lift the low
chord of the bridge at least one foot clear of the maximum water surface
elevation which could be contained by the overbuilt levees upstream of
the bridge. The recurrence interval of an event which would overtop the
overbuilt levees upstream of the bridge was determined to be in excess
of 100 years, and perhaps as much as 150 years. Overflow upstream of
the upstream end of the overbuilt levees (Williams Avenue) occurs during
events larger than 100 year recurrence interval (90 percent
reliability).
23
Cursory analysis of historical aggradation of the channel within
the study reach was conducted using cross section surveyed in 1986,
1991, and 1994. During that time period, no dredging activity within
the channel occurred, and no upstream extraction of sediment was
conducted at the Stoneway gravel mining site. Computation of channel
bed volume changes from the mouth to I-405 over that eight year period
from 1986 to 1994 showed an average sediment accumulation of about 5,150
cubic yards per year. Several moderate sized flood events occurred
during that period, including an estimated 50 year recurrence interval
event in November 1990, a 15 to 20 year recurrence interval event in
December 1995, and a 15 to 20 year recurrence interval event in February
1996. Based on the observed data, the predicted channel bed aggradation
and predicted maintenance dredge average annual volumes based on the
HEC-6 model simulation were considered to be conservative. Thus, the
design level of protection provided by the selected alternative was
considered to be adequate.
24
References
Reference #1 - "One Hundred Years on the Cedar". Margeret Slauson. 1967.
Reference #2 - Lower Cedar River HEC-2 Model and Evaluation of Flood
Relief Alternatives. Northwest Hydraulic Consultants Inc. February
1992.
Reference #3 - Current and Future Conditions Report - Cedar River,
Appendix B: Addendum to Bedload Analysis. King County Deptartment of
Public Works. Surface Water Management Division. November 1993.
Reference #4 - Cedar River Sediment Data Collection and Analysis.
Northwest Hydraulic Consultants. July 1995.
Reference #5 - NHC additional sediment data from December 1995 and
February 1996 events.
Reference #6 - Guidelines for risk and uncertainty analysis in water
resources planning, Vol. I and II. March 1992. IWR Report 92-R-2.
Reference #7 - Nelson, L.M., 1971, Sediment Transport By Streams in The
Snohomish River Basin, Washington, October 1967 - June 1969 U.S.
Geological Survey Open -file Report, 44p.
Reference #8 - Nelson, L.M., 1974, Sediment Transport By Streams in The
Deschutes and Nisqually River Basins, Washington, November 1971-june
1973 U.S. Geological Survey Open -file Report, 37p.
Reference #9 - Nelson, L.M., 1979, Sediment Transport By The White
River Into Mud Mountain Reservoir, Washington, June 1974-june 1976 U.S.
Geological Survey Water -resources Investigations 78-133, 26p.
Reference #10 - Nelson, L.M., 1982, Streamflow and Sediment Transport
in The Quillayute River Basin, Washington: U.S. Geological Survey Open -
file Report 82-627, 29p.
Reference #11 - Glancy, P.A., Sediment Transport By Streams in The
Chehalis River Basin, Washington, October 1961 - September 1965 U.S.
Geological Survey Water -supply Paper 1798-h, P.hi-h53, 1971.
Reference #12 - Sikonia, W.G., Sediment Transport in The Lower Puyallup,
White, and Carbon Rivers of Western Washington U.S. Geological Survey
Water Resources Investigations Report 89-4112, 2001990.
25
FIGURES
Figure #1 - Bed material sample location plan map
Figure #2 - Bed material gradation by distance from mouth
Figure #3 - Bed material sample gradation analysis (sample RP-0)
Figure #4 - Bed material sample gradation analysis (sample nhc 1-2)
Figure #5 - Bed material sample gradation analysis (sample nhc 3-4)
Figure #6 - Bed material sample gradation analysis (sample nhc 6)
Figure #7 - Bed material sample gradation analysis (sample RP-9)
Figure #8 - Bed material sample gradation analysis (sample RP-11)
Figure #9 - Bed material sample gradation analysis (sample RP-13)
Figure #10 - Bed material sample gradation analysis (sample RP-15)
Figure #11 - Bed material sample gradation analysis (sample RE-1)
Figure #12 - Bed material sample gradation analysis (sample RE-2)
Figure #13 - Existing channel dredge w/out delta dredge w.s. profiles
#13a Same but with delta dredge
Figure #14 - 4 ft dredge w/out delta dredge w.s. profiles
#14a Same but with delta dredge
Figure #15 - 6 ft dredge w/out delta dredge w.s. profiles
#15a Same but with delta dredge
Figure #16 - 10 ft dredge w/out delta dredge w.s. profiles
#16a Same but with delta dredge
Figure #17 - Cedar River Cross Section Locations (1994 COE Survey)
Figure #18 through #38 - Cedar River Section Survey Comparison
(1986,1991,1994)
Figures #39 through #59 - Cedar River Existing Condition and predicted
19.2 yr Sedimentation
Figures #60 through #87 - Cedar River Existing Condition and Dredge
Proposals
26
Figure I plan map
20743.1.1.1
4r- VVMM
low-
ul
MM
FoIF
&Auk
ZU
MV M—
Jz
214
NIL
.0 40
AA
'Aj
4.
.
t
-R U- B-0E-ING-BR'iD�6r-:-*
t
5
*T7
LIMW'
RENTON
RP -
Cedar River Sediment Analysis
Study Reach
N —7
and
Sample
—Site
Notes: I Prefix
NHC indicates sample collected by NHC.
Scale
Location
Map
2. Prefix
RP indicates COE sites; Samples collected by
feet
- COE at
3.
locations marked with an asterisk.
F- e CcP-
800
0 800 1600
northwest hydraulic
consultants
-
I --4e-s
-.L-
a]
27
1.0000
0.9000
0.8000
0.7000
v
0.6000
0
C H
O N
M
v U
N '�1! N 0.5000
00 _
i Fn
m .o
E 0.4000
U
0.3000
0.2000
0.1000
0.0000
Bed gradation variation upstream by distance upstream from mouth
Cedar River
=I
0 1000 2000 3000 4000 5000 6000 7000 8000
Distance upstream of Mouth
Very Coarse Gravel
+Coarse Gravel
—0— Medium Gravel
—K Fine Gravel
---X.- - Very Fine Gravel
Very Coarse Sand
— 0 Coarse Sand
Medium Sand
Fine Sand
Very Fine Sand
Figure #3
29
Figure 44
30
Figure #5
Bed Sediment Sample COE-nhc 3.4
125 ft d/s of 1991 nhc Cross Section 1665
31
CD
CD
N
M
3
3
Figure #6
Bed Sediment Sample COE-nhc 6
110 ft d/s of 1991 nhc Cross Section 2585
0
0
0
0
O
O
O
0 0 0
o 'o 0 0 0 c_*_ Average of samples
Percent Passing — _ Sample #2 3801 rd
mac. Sample #1 4131 ml
32
Figure #7
Bed Sediment Sample COE-ERS RP-9
300 ft dls of 1991 nhc Cross Section 3460
33
Figure #8
Bed Sediment Sample COE-ERS RP-11
80 ft d/s of 1991 nhc Cross Section 3975
3 �{
0
O
0
0
0
0
N
Co
sn
N
�D
O
O
O
Q
C>
0
Figure #9
Bed Sediment Sample COE-ERS RP-13
205 ft d/s of 1991 nhc Cross Section 4732
rrveraye of samples
Percent Passing — — Sample #2 4618 ml
Sample #1 4692 rd
35
Figure # 10
Bed Sediment Sample COE-ERS RP-15
95 ft d/s of 1991 nhc Cross Section 5332
3L
0
0
0
0
0
0
m
CA
N —�
W
O
O
O
J
Q
Q
Q
� Q
O
O
Figure # 11
Bed Sediment Sample COE RE-1
at 1991 nhc Cross Section 6931
N W A (n O v co c0 —�
O O O O O O O O O O
O O O O O O O O O
O O O O O O O O O O
O
Percent Passing
37
Figure #12
Bed Sediment Sample COE RE-2
at 1991 nhc Cross Section 8596
45
40
35
30
E 25
0
R
m 20
w
15
10
5
0
0
Figure #13
HECRAS WSEL's for alternatives Chart 59
Existing Thalweg Dredge no delta dredge 3 yr predredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
39
Page 1
—100 yr 3yr accumulation 90% ws profile
f Existing Right Bank
f Existing Left Bank
Existing Thalweg
45
40
35
30
E 25
c
0
m 20
w
15
10
5
0
0
Figure #13a
HECRAS WSEL's for alternatives Chart 60
Existing Thalweg Dredge incl. delta dredge 3 yr predredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
M
Page 1
-4 100 yr 3yr accumulation 90% ws profile
Existing Right Bank
—a— Existing Left Bank
Existing Thalweg
45
40
35
30
E 25
Z=
c
0
'm 20
w
15
10
5
0
0
Figure # 14
HECRAS WSEL's for alternatives Chart 61
4 Ft Dredge no delta dredge 3 yr predredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
41
Page 1
♦ 100 yr 3yr accumulation 90% ws profile
Existing Right Bank
�— Existing Left Bank
3 yr Predredge Thalweg
Existing Thalweg
4 Ft Dredge Channel Thalweg
45
40
35
30
U)
E 25
0
is
020
w
15
10
5
0
0
Figure #14a
HECRAS WSEL's for alternatives Chart 62.
4 Ft Dredge incl. delta dredge 3 yr predredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
42
Page 1
• 100 yr 3yr accumulation 90% ws profile
• Existing Right Bank
T Existing Left Bank
3 yr Predredge Thalweg
Existing Thalweg
e Gr n.oa .e f'k ,., 1
45
40
35
30
E 25
c
0
is
> 20
w
15
10
5
0
0
Figure # 15
HECRAS WSEL's for alternatives Chart 63
6 Ft Dredge 3 yr predredge no delta dredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
43
Page 1
—�-- 100 yr 3yr accumulation 90% ws profile
Existing Right Bank
�— Existing Left Bank
3 yr predredge thalweg
6 Ft Dredge Channel Thalweg
Existing Thalweg
w
45
40
35
30
E 25
c
0
R
D 20
w
15
10
5
0
0
Figure #15a
HECRAS WSEL's for alternatives Chart 64
6 Ft Dredge 3 yr predredge incl. delta dredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
Page 1
♦ 100 yr 3yr accumulation 90% ws profile
i
—T Existing Right Bank
—� Existing Left Bank
3 yr predredge thalweg
6 Ft Dredge Channel Thalweg
Existing Thalweg i
w
45
40
Figure #16
HECRASVVSEL's for alternatives Chart 14
1OFtDredge nodelta dredge 3yrpcmdredQe
80% Reliability (1'8SDabove calibration 1OOyr)
100 Year Water Surface Profile
`oVu 2000 u000 4000 s000 6000 7000 uooV e000
45
Existing Right Bank
Existing Left Bank
-Existing Thalweg
45
40
35
30
E 25
c
0
R
d 20
w
15
10
5
0
0
Figure # 16a
HECRAS WSEL's for alternatives Chart 65
10 Ft Dredge incl. delta dredge 3 yr predredge
90% Reliability (1.8SD above calibration 100 yr)
100 Year Water Surface Profile
1000 2000 3000 4000 5000 6000 7000 8000 9000
Distance upstream from mouth (ft)
.o
Page 1
100 year 90% ws profile
Left Bank Levee/Existing Bank
• Right Bank Levee/Existing Bank
Existing Thalweg
— 10 Ft Dredge Channel Thalweg
v
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41
45 —
40 —
35 -
-. O—
0
�25
z
4: �-)0
W15
10 -
5
0=
50
45 —
40 —
35
30 —
25 —
20 —
15—
EL
10
5-
0-
900
Figure #18 / #19
Cedar River Section Survey Comparison
Section 0.63, U/S N. Boeing Bridge
1994
1991
....... 1986
150 250ation ( }50 450 550
Cedar River Section Survey Comparison
Section 8.62
1000 1100 1200
Station (ft.)
19941
---1991
�u_. ........ 1986.
1300 1400
M.
Fiizure #20 / #21
Cedar River Section Survey Comparison
Section 16.12
45 —
40 —
35 —
0 30 —
0 25 —
z
4� 20
w 15
10
5-
0
1050 1150 1250 1350 1450 1550
Station (ft.)
45
40
35
30
25
20
EL15 t
10
5
0 —
1050
Cedar River Section Survey Comparison
Section 25.32
1150 1250 1350
Station (ft.)
1450 1550
1994
'____1991
....... 1986
1994
____ 1991
....... 1986
95
Figure #22 / 423
Cedar River Section Survey Comparison
Section 33.82
45 —
40 —
or_ '
Cedar River Section Survey Comparison
Section 39.01, D/S S. Boeing Bridge
45
40
35
� 30
1994
25
20 .... 1986
15
EL
10
5+
i
0
1200 1300 1400 1500 1600 1700
Station (ft.)
50
Figure #24 / 425
Cedar River Section Survey Comparison
Section 41.14
I
45 - I
40 -
35 -
0 30 - 1994
25 ____----1991
z------- 1986
$ 20
w 15 - y.
I
10 1
5�
T
0
1200 1300 1400 1500 1600 1700
Station (ft.)
Cedar River Section Survery Comparison
Section 46.54
45
40
35
30
25 �,'. - 1994
20 �'----1991
....... 1986
15
EL10
5
0'
1300 1400 1500 1600 1700 1800
Station (ft.)
5)
45 —
40
35 T
0 30
t7 25 T
z
J 20
w 15
10 r
5T'
i
0
700
45 —
40
35
30
25
20
EL15 t
10
5t
0-
600
Fieure #26 / #27
Cedar River Section Survey Comparison
Section 52.44
____ 1991
....... 1986
800 900 1000 1100 1200
Station (ft.)
Cedar River Section Survey Comparison
Section 56.43, D/S Logan Ave. Bridge
i
700 800 900 1000 1100
Station (ft.)
1994
___ 1991
..... 1986
57
45
40
35
.. 30
0
25 T
z
20�
J
w 15=
10 —
5
0-
200
45 —
40 T
35 T
30 =
25 -
20
15-
EL
10
5-
0-
250
Figure 928 / 429
Cedar River Section Survey Comparison
Section 60.12
300
` 1994
____ 1991
------- 1986
400 500
Station (ft.)
600 700
Cedar River Section Survey Comparison Section
65.01, D/S Williams Ave. Bridge
a
;i 1994
____ 1991
_______ 1986
350 450 550
Station (ft.)
650 750
53
45 -
40 -
35 -
30 -
0
25 -
z
1� 20 —
J
w 15 -=
10-
5-
0
200
#30 / #31
Cedar River Section Survey Comparison
Section 66.81
400 500
Station (ft.)
600 700
1994
____ 1991
------- 1986
Cedar River Section Survey Comparison
Section 69.31, D/S Wells Ave. Bridge
i
45 T
i
40 1
35 it
30
25 1994
____ 1991
20 i
1986
15
EL 10
1
5
0
300 400 500 600 700 800
Station (ft.)
5q
45 -
40
35
0 30
0 25
z
20 -
w 15 -
10 -
5-
0
300
Figure #32 / #33
Cedar River Section Survey Comparison
Section 74.83
400 500 600
Station (ft.)
700 800
1 a/ -T
____ 1991
....... 1986
Cedar River Section Survey Comparison
Section 76.82, D/S Bronson Wy. Bridge
45 -
40 = -t
35 - t
t
30 f tr
t
25 - t
20 -
15-
EL 10 -
5-
0
0 100 200 300
Station (ft.)
400 500
19941
_-__ 1991
_______ 1986,
5 y_
Figure #34 / #35
Cedar River Section Survey Comparison
Section 78.44 D/S Library
45 —
40
35
p 30
z 25
20 —
w 15 —
10 —
5-
0-
0 100 200 300
Station (ft.)
400 500
1994
____ 1991
_______ 1986
Cedar River Section Survey Comparison
Section 80.03, U/S Library
45 —
40
35
30
25
20 —
15 —
EL
10
51
0
0 100 200 300
Station (ft.)
400 500
1 .7.-Y '
____ 1991
.......1986.
5�
45 —
40 —
35 -
0 30 —
z 25
20 —
w 15 —
10 -
5-
0
0
45 —
40
35
30
25
20
15
EL
10 -
5-
0 —
Figure #36 / #37
Cedar River Section Survey Comparison
Section 80.92
100 200 300
Station (ft.)
400 500
1994
�____1991
------- 1986
Cedar River Section Survey Comparison
Section 84.01, D/S Houser Wy.
0 100
200 300
Station (ft.)
400 500
1 .d;J-?
____ 1991
_______ 1986
5-?
Figure #3 8
Cedar River Section Survey Comparison
Section 85.96,1-405
45 —
40
35
p 30
t� 25
z
20
w 15
ilk,
5�
0
0 100
200 300
Station (ft.)
400 500
I y7'i
____ 1991
------- 1986'
5�
Figure #39 / #40
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 0.63
40
35
> 30,
Z 25 Existing (1994)
,Z! 20 — _ .... _ . 19.2 yr. EL
w 15 -
10
5
0
0 100 200 300 400 500
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 Section 8.62
40
35
0 30
z
25 Existing (1994)
$ 20 19.2 yr. EL
w 15 --
i
10
i
5
I
0'
850 950 1050 1150 1250 1350
Station (ft.)
Figure #41 / #42
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 16.12
40 —
35 —
0 30 —
c:; 25 — Existing (1994)
z
20 —------- 19.2yr. EL
w 15 _ - -
10
5
0
1050 1150 1250 1350 1450 1550
Station (ft.)
0
z
J
W
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 25.32
40
35
30 t
25 T Existing (1994)
20 ....... 19.2yr. EL
15
10
5
0
1050 1150 1250 1350 1450 1550
Station (ft.)
6C
Fijzure 943 / #44
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 33.82
40 -
35 =
0 30 —
z
25 — Existing (1994)
20 — ........ ------- 19.2yr. EL
w 15-
10 —
5 —
0'
1050 1150 1250 1350 1450 1550
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 39.01
40 —
35 —
0 30 —
z 25 — —
20 —
w 15— —
10-
5-
0
1150 1250 1350 1450 1550 1650
Station (ft.)
Existing (1994)
...... 19.2yr. EL
6j
Figure #45 / #46
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 - Section 41.14
40 -
35 -
0
30 -
25 -
z Existing (1994)
- -
w 20 - ------- 19.2yr. EL
w 15
life
5-
0
1200 1300 1400 1500 1600 1700
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 - Section 46.54
40 -
35 -
0
30
z 25 -.. _.._-_____.___ Existing (1994)
20 - 19.2 yr. EL
w 15-
10-
5 -
0'
1300 1400 1500 1600 1700 1800
Station (ft.)
64
45
40 t
35 T
0 30 y
z 25
$ 20
..r
w 15
10
5
0 �-
750
45 -
40
35
0 30
z 25
20
w 15
10
5
0
550
Figure #47 / 448
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 52.44
Existing (1994)
------- 19.2yr. EL
850 950 1050 1150 1250 i
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 56.43
650 750 850 950 1050
Station (ft.)
Existing
(1994)
------- 19.2yr. EL.
6.3
45 —
40 —
35
0 30
z 25
4� 20
w 15
10
5
0
250
45 —
40 —
35
0 30
z 25
20
w 15
10
5
0
250
Figure #49 / #50
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 60.12
Existing (1994)
....... 19.2yr. EL
350 450 550 650 750
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 65.01
cxisting � i yy4�
....... 19.2yr. EL
350 450 550 650 750
Station (ft.)
6y
Fieure #51 / 452
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 - Section 66.81
40 -
35 -
0 30 -
z 25 -
$ 20 -
w 15-
10-
5-
0
250 350 450 550 650
Station (ft.)
Existing (1994)
------- 19.2yr. EL
750
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 - Section 69.31
40 -
35
0 30 -
z 25 -
$ 20 -
vr
w 15-
10
5-
0
250 350 450 550 650
Station (ft.)
Existing (1994)
------- 19.2yr. EL
750
E5-
Figure #53 / #54
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 74.83
40 —
35 T
0 30
0 25
w 20
w 15
10 T
5
0
250 350 450 550 650
45
40
35
0 30
z 25
20
w
15
10
N
Station (ft.)
Existing (1994)
------- 19.2yr. EL
750
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Rartinn 79 99
Existing (1994)
------- 19.2yr. EL
0 100 200 300 400 500
Station (ft.)
66
45 —
40 --n
35
0 30
Z 25
;:� 20
W 15
10
5
0
Figure #55 / #56
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 78.44
0 100 200 300 400 500
Station (ft.)
45 —
40
35
0 30
>
z 25
*� 20
—J 15
w
10
5
0
Existing
(1994)
.____.. 19.2yr. EL
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 80.03
►A
0 100 200 300 400 500
Station (ft.)
Existing
Y
19.24r. EL'
67
45 —
40
35 T
0 30
z 25
20
w 15
10
5
0
Figure #57 / #58
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
Section 80.92
Existing (1994)
------- 19.2yr. EL
0 100 200 300 400 500
Station (ft.)
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
45 — Section 84.01
40 —
35 —
0 30 —
z 25 -
20 —
w 15 —
10—
5=
0'
Existing
(1994)
------ 19.2yr. EL
0 100 200 300 400 500
Station (ft.)
G
U
Figure #59
Cedar River Existing Condition
and Predicted 19.2-yr. Sedimentation
I 45 _ Section 85.96
txisiing (-I VyK)
------- 19.2yr. EL
�y
45
40
35
45
40
35
— 30
0
a 25
z
$ 20
J
W15
I
10
5
0
Figure #60 / 461
Cedar River Existing Condition and Dredge
Proposals, Section 0.09
• Existing (1994)
_ 4 ft. Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 0.63
—.— Existing (1994)
4 ft. Dredge EL
X 6 ft. Dredge EL
_ . � _ _ 10 ft. Dredge EL
0 100 ?5�0P 400 500
ation (11.I
70
Figure #62 / #63
Cedar River Existing Condition and Dredge
Proposals, Section 8.62
45 —
40 —
35 —
- 30 —
z 25 y
= 20
W15 y
10 T ,
■��-� �■
01
850 950 V87i on 11�0 1250 1350
a
Existing (1994)
�• _ 4 ft. Dredge EL
* 6 ft. Dredge EL
10 ft. Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 16.12
45
• Existing (1994)
40
4 ft. Dredge EL
35
* 6 ft. Dredge EL
0
30
_ _ 10 ft. Dredge EL
0
25
z
20
w
15
10�
t
5
+
0'
i
1000
1100 1200 1300
1400 1500
Station (ft.)
71
Figure #64 / #65
Cedar River Existing Condition and Dredge
Proposals, Section 25.32
45 —
.l
35 —
0 30 —
�25CIO
—
z �
20r�-L
w15 — �ti�.-•� '
� a
10 —
i *�
5—
0
1100 1200 1300 1400 1500 1600
Station (ft.)
45 —
35 —
Existing (1994)
4 ft. Dredge EL
* 6 ft. Dredge EL
10 ft. Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 33.82
0 30-
Z25
20
w 15
f
10 Ms- W IF
)1�,XXX
Existing (1994)
4 ft. Dredge EL
* 6 ft. Dredge EL
10 ft. Dredge EL
0
1050 1150 1250 1350 1450 1550
Station (ft.)
72
Figure #66 / #67
Cedar River Existing Condition and Dredge
Proposals, Section 39.01
45 -
40 -
35 -
0 30 -
25
z
*i 20
w 15
10- *X XXK
5 f XX-X-
—♦— Existing (1994)
4 ft. Dredge EL
6 ft. Dredge EL
10ft. Dredge EL
0
1200 1300 1400 1500 1600 1700
Station (ft.)
Cedar River Existing Condition and Dredge
Proposals, Section 39.64
45 T
40
35
30 Existing (1994)
z25 1� __�---+� _ _ 4 ft. Dredge EL
$ 20 - 6 ft. Dredge EL
_.._10ft. Dredge EL
w15 -
10 x )Kx
0 1300 1400 19falion JAJO 1700 1800
VAI
45 —
40 —
35 -
0 30
iw
Figure #68 / #69
Cedar River Existing Condition and Dredge
Proposals, Section 41.14
Existing (1994)
17 A XL Pl__J-_ rl
Cedar River Existing Condition and Dredge
Proposals, Section 46.54
45
40 —
35 —
030
0 25 -
Z ---
*! 20 —
v
W15— ,
tea- a a
10 — )K)K* XAk
5 xt-x-X -;
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1300 1400 19fali on I IRT 1700
an
—�_ Existing (1994)
4 ft. Dredge
X 6 ft. Dredge EL
_ . * _ -10 ft. Dredge EL
1800
74
Figure #70 / #71
Cedar River Existing Condition and Dredge
Proposals, Section 52.44
30 T
25 -`-
rt
0 20�
>
a
Z 15 t
X XX
J 10 x -X-x -)OR
5
0 i
700 800 900 1000 1100
Station (ft.)
45
40 T
35
0 30
0 25
z
*i 20
w 15
10
5T
0
600
—T Existing (1994)
_ 4 ft. Dredge EL
6 ft. Dredge EL
10 ft. Dredge EL
1200
Cedar River Existing Condition and Dredge
Proposals, Section 56.43
700
800 900 1000 1100
Station (ft.)
Existing (1994)
4 ft. Dredge EL
* 6 ft. Dredge EL
10 ft. Dredge EL
75
Figure #72 / 473
Cedar River Existing Condition and Dredge
Proposals, Section 57.63
45 —
40 —
030� l
i
0 25 —
z
20 —
W 15
10
5=
I
01
—.— Existing (1994) i I
4ft Dredge EL
* 6 ft. Dredge EL
10 ft. Dredge EL
0 100 200 300 400 500
Station (ft.)
Cedar River Existing Condition and Dredge
Proposals, Section 60.12
45
I
40
35
- 30
z25 T
4� 20
w15
10 —
5-
0
200 300
:� - ? _;�- 17
Mation (W.
600 700
1994 EL
4 ft. Dredge
* 6 ft. Dredge
10 ft. Dredge
V197i
45 -
40 -
35 -
30 -
25 -
z
4� 20 -
w 15 -
10 -
5 -
0 —
200
Figure #76 / 477
Cedar River Existing Condition and Dredge
Proposals, Section 66.81
i
300 400 500 600 700
Station (ft.)
• Existing (1994)
4 ft. Dredge EL
6 ft. Dredge EL
10 ft. Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 69.31
45 -
40 t
35,E
030 -
0 25-
z
20 -
v
w15-
10-
5-
0
300 400 Motion (tt•)
--♦— Existing (1994)
_ 4 ft. Dredge EL
6 ft. Dredge EL
1Oft. Dredge EL.
700 800
45 —
40 -
35
0 30
z 25
$ 20
w 15
10
5
0,
300
45
40
35 -
30 -
z 25 -
I = 20 —
i J
1 w15
Figure #78 / #79
Cedar River Existing Condition and Dredge
Proposals, Section 69.74
m
500 600
Station (ft.)
700 800
• Existing (1994)
4 ft. Dredge EL
X 6 ft. Dredge EL
. _ 10 ft. Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 74.83
10 —
5
0 rt
300 400
Motion N
—� Existing EL
4 ft. Dredge EL
* 6 ft. Dredge EL
x _ _ 10 ft. Dredge EL'
700 800
79
45 —
40
35
- 30
0 25
z
20 1
w 15�
10 -
5—
0
0
45 —
40
35
- 30
C7 25
z
-1� 20
Lu 15
10 —
5-
0-
0
Figure #80 / #81
Cedar River Existing Condition and Dredge
Proposals, Section 76.82
• Existing (1994)
4ft Dredge EL
* 6ft Dredge EL
10 ft Dredge EL
100 200 300 400 500
Station (ft.)
Cedar River Existing Condition and Dredge
Proposals, Section 77.26
100 200 300
Station (ft.)
�— Existing (1994)
_ 4ft Dredge EL
* 6ft Dredge EL
_ . _ _ 10 ft Dredge EL
KIIIIIIIIIIIINWIN
80
45 —
45 T
40
35
0 30
025
z
20
J
w15 —
10 T
5-
0—
0
Figure #82 / #83
Cedar River Existing Condition and Dredge
Proposals, Section 78.44
Cedar River Existing Condition and Dredge
Proposals, Section 80.03
100
Existing (1994)
4ft Dredge EL j
6ft Dredge EL
_.._10ft Dredge EL
Oation (tt.) 400 500
81
45 -
40
35 -
0 30 -
z 25 -
.ij 20
J
i
W15
10
5
0
Figure #84 / 485
Cedar River Existing Condition and Dredge
Proposals, Section 80.92
0 100 Mation (10 400 500
45 —
40
35
- 30
z 25
20
w 15
10
5
0-
+_ Existing (1994)
4ft Dredge EL
* 6ft Dredge EL
X _ 10 ft Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 84.01
0 100 200 300
Station (ft.)
400 500
Existing (1994)
4ft Dredge EL
X 6ft Dredge EL
10 ft Dredge EL
82
45
40
35
0 30
025
z
w 20
r..
J
111 1 c
45 —
40
35
030
025
z
.1� 20
J
W15
10
5
0
Fieure #86 / #87
Cedar River Existing Condition and Dredge
Proposals, Section 84.38
�— Existing (1994)
4ft Dredge EL
6ft Dredge EL
_ 10 ft Dredge EL
Cedar River Existing Condition and Dredge
Proposals, Section 85.96
—� EAsting (1994)
4ft Dredge EL
X 6ft Dredge EL
�._10ftDredge EL
0 100Mation T
400 500
83
APPENDIX D
PROJECT FEATURES
`r
APPENDIX D
ANALYSIS OF DESIGN
TABLE OF CONTENTS
Paragraph Page
SECTION 1. DESIGN CONSIDERATIONS
1.01 Site Description D-1
a. Left Bank Description D-1
b. Right Bank Description D-2
1.02 Existing Condition D-2
SECTION 2. DESIGN FEATURES AND ANALYSIS OF THE RECOMMENDED PLAN
2.01
General
D-2
2.02
Proposed Project
D-2
2.03
Design Length and Layout
D-3
2.04
Final Variations Considered
D-3
2.05
Details of Flood Protection Features
D-4
a. Levees
D-4
b. Floodwalls
D-4
c. Closure Structures
D-7
d. Erosion Control
D-7
e. Utilities
D-7
2.06
Bridge Jacking Details
D-8
2.07
Operation and Maintenance
D-8
a. Operation
D-8
b. Maintenance
D-9
TABLES
TABLE D-1 Project Feature vs. Rivermile D-1
TABLE D-2 Levee Configuration D-4
FIGURES
FIGURE D-1
Typical Levee Sections
D-5
FIGURE D-2
Typical Floodwall Sections
D-6
FIGURE D-3
Site Plan 1
D-10
FIGURE D-4
Site Plan 2
D-11
FIGURE D-5
Site Plan 3
D-12
FIGURE D-6
Site Plan 4
D-13
FIGURE D-7
Site Plan 5
D-14
FIGURE D-8
Jacking Option Structural Plan
D-15
FIGURE D-9
Jacking Option Bridge Elevation
D-16
FIGURE D-10
Jacking Option Truss Elevation
D-17
FIGURE D-11
Jacking Option Upstream Pile Cap Plan
D-18
FIGURE D-12
Jacking Option Pile Cap Elevation
D-19
FIGURE D-13
Jacking Option Lifting Jack Collar Details
D-20
1. Design Considerations
1.01 Site Description. The Cedar River is located entirely within the boundaries of
King County Washington. The proposed project lies on the final 1 '/z miles of the Cedar
River before it empties into Lake Washington. Both banks of the river in the vicinity of
the proposed project are highly developed with The Boeing Company on the right bank
and the City of Renton's Municipal Airport on the left bank. A narrow riverside park
owned by the City of Renton runs along the lower 1+ miles of the right bank downstream
of the Logan Avenue bridge. Features along the river that will be referred to throughout
this report are listed below along with their corresponding rivermile.
TABLE D-1.
PROJECT FEATURE VS. RIVERMILE
PROJECT FEATURE
RIVERMILE
Mouth of Cedar River at Lake Washington
0.00
North Boeing Bridge
0.01
Boat Ramp on Right Bank
0.14
Gazebo on Right Bank
0.37
Hangars on Left Bank
0.41
Hangars on Left Bank
0.52
Park Access Via N. 6t' Street on Right Bank
0.60
Compass Rose on Left Bank
0.63
South Boeing Bridge
0.74
Logan Ave Bridge
1.07
Williams Ave Bridge
1.23
Wells Ave Bridge
1.31
City of Renton Public Library
1.50
Interstate Highway 405
1.64
a. Left Bank Description. The left bank project area begins at Williams Avenue
Bridge, the next bridge upstream of Logan Avenue. The area between Logan and
Williams Avenues is a city park which has a riverside trial and some trees planted along
the rivers edge. Adjacent to the park are a couple of buildings and parking lots.
Downstream of the Logan Avenue Bridge the left bank area is used for the airport and
related businesses including The Boeing Company operations. An airport perimeter road
begins just downstream of Logan Avenue and travels the length of the left bank to the
mouth of the river. The edge of this road generally stays within 15 feet of the river bank
until the small -plane hangars are reached where the road moves inland. Buildings,
hangars, and vehicle and airplane parking are scattered throughout this stretch until
downstream of the hangers where FAA restrictions prohibit objects in the safety zone of
the runway. Utilities include electrical (overhead and buried), natural gas, water, sanitary
sewer, and storm drainage lines.
D-1
b. Right Bank Description. The right bank project area also begins at Williams
Avenue. Two riverside trails at different elevations follow the river between Williams
Avenue and Logan Avenue. The two levels converge above Logan Avenue and traverse
a semi -circular path in front of the Renton Senior Center. Downstream of Logan Avenue
lies a riverside park that averages 200 feet wide and runs the remainder of the right bank
to the mouth. The park has a bike and pedestrian trail that meanders its length and is
landscaped with planted mounds and numerous trees. An access road leading off of
Logan Avenue at North 6th Street provides vehicle access to the northern end of the park.
Parking is provided along the access road and there is a ramp for non -motorized boats.
The park also has a covered gazebo and a public restroom. Utilities include trial side
lighting, underground irrigation, sanitary sewer, and storm drainage lines.
1.02 Existing Condition. The existing left bank profile averages several feet lower than
the corresponding location on the right bank. This allows for frequent overtopping of the
left bank (presently estimated at a 2 year event). The low spot along the left bank is
immediately downstream of the South Boeing Bridge. Water flowing out of the river
bank here travels north towards Lake Washington with the runway centerline preventing
further advancement west until it can spill back into the river just upstream of the North
Boeing Bridge. The low left bank prevents the right bank from having much inundation
and keeps the South Boeing Bridge from being threatened by flood waters. Inland areas
along both banks have interior runoff back flooding caused by clogged storm drainage
outfalls. Most of the storm drainage lines have become plugged with river sediments as
the river channel has filled in over the years when regular dredging of the channel was
stopped.
2. Design Features and Analysis of the Recommended Plan
2.01 General. This section presents features and analysis of constructing flood
protection measures along both banks of the lower Cedar River. Present conditions allow
for frequent flooding of the Renton Municipal Airport along the left bank causing
property damage, extensive cleanup, and delays for the users of the airport.
2.02 Proposed Project. The main design features of the project include: dredging of the
river channel to an average depth of 4 feet below the present river thalwag, construction
of flood control features along both banks to contain the 100 year flood event in the
present river channel, hydraulically jacking the South Boeing Bridge above the contained
flood water surface profiles, and providing closure structures to span the approach roads
to the bridge. Additionally the left bank will incorporate an overtopping section
downstream of the South Boeing Bridge. This and overbuilding the remaining levee and
floodwall sections by 1 foot will provide the right bank with something greater than 100
year flood protection. The recommended plan provides for federal construction and local
maintenance of all project features.
D-2
2.03 Design Length and Layout. The flood control features will include both earth
embankment levees and steel sheetpile floodwalls. In areas of the riverside park the bike
and pedestrian trail will be raised or realigned to accommodate the levees while
preserving the aspects of the original park. For the Left Bank beginning at the upstream
extent of the proposed project:
`The riverside trail between Williams Avenue and Logan Avenue will be raised in
its present alignment an average of 3 feet.
•A steel sheetpile floodwall will be erected along the rivers edge between Logan
Avenue and the South Boeing Bridge. Average height of this section is 8 feet
above the existing ground line.
*An 80 foot long removable closure structure will be provided to span the
approach road leading to the South Boeing Bridge.
•A steel sheetpile floodwall will be erected along the rivers edge between the
South Boeing Bridge and the downstream extent of the small -plane hangers.
This section of floodwall will be designed to overtop and averages 7 feet high.
•A levee 4 feet high will be constructed from the end of the flood wall to the
North Boeing Bridge and the end of the project.
The right bank project layout will be:
*The riverside trail between Williams Avenue and Logan Avenue will be raised in
its present alignment an average of 3 feet.
*The trail in the park will be realigned and raised and average of 3 feet between
Logan Avenue and the South Boeing Bridge.
*An 80 foot long removable closure structure will be provided to span the
approach road leading to the South Boeing Bridge.
*The trail in the park will be raised 4.5 feet to the top of the levee alignment from
the South Boeing Bridge to the park access road from North 6th street.
•A short floodwall section will be constructed where North 6th street enters and
space constraints do not allow for continuation of the levee.
•A series of short levee sections will be constructed to join existing areas of high
ground in the park. Sections of the park trail will be realigned and raised to
accommodate the levee. Levee height varies between 3 and 6 feet.
'An 80 foot long removable closure structure will be provided at the gazebo
location.
"The levee sections will continue through the park to the North Boeing Bridge
and the end of the project.
Various utilities will need to be relocated along both banks. Figures C-3 through C-7
show the levee and floodwall footprints for both banks.
2.04 Final Variations Considered. During the design process several alternatives were
considered. All alternatives were to contain the 100 year flood event through the
I -DID]
construction of levees and floodwalls, and all involved some dredging initially and as part
of a maintenance program. The different dredge depths were 10 feet, 6 feet, 4 feet, and 0
feet. Differing height levees were computed for each of these dredge depths.
Maintenance dredging frequency and quantities were also developed. (See Appendix A.
Hydrology and Hydraulics.) Cost comparisons were prepared and the alternatives
weighed against each other using environmental impacts and construction cost criteria as
well as the desires of the local sponsor.
2.05 Details of Flood Protection Features.
a. Levees. Several variations of levee configuration were necessary due to widely
differing uses of the land where the levees will be constructed. Generally all levees will
be constructed out of silty sandy gravel with a three foot top width and no steeper than
2H:1 V side slopes. The side slopes and top will be covered with a layer of topsoil and
seeded. Variations of this include; having one side of the levee slope at 4H:1 V to meet
FAA restrictions on slope, increasing both side slopes to 3H:1 V to allow for maintenance
mowing and pedestrian use in areas of the park, and constructing an 8 foot wide asphalt
trail on top of the levee in other areas of the park. The top elevation of the levee was
determined using the water surface profiles developed by Hydraulics (See Appendix A.
Hydrology and Hydraulics.) and adding a settlement allowance of 1 inch for every foot of
levee height. See figure D-1 for typical levee sections.
TABLE D-2
LEVEE CONFIGURATION
Levee Type Description
Type I 3' top width; 2H:1 V side slopes.
Type Ia 3' top width; 3H:1 V side slopes.
Type II 8' wide Asphalt trail on top of levee section; 3H:1 V side
slopes for maintenance mowing and use in park setting.
Type III 3' top width; landward side slope flattened to 4H:1 V to
meet FAA restrictions, levee designed to overtop when
flows in river are greater than 100 year event. Backside of
levee strengthened against scour with 18" layer of rock.
b. F000dwalls. Where the width of the alignment is restricted due to existing
development, roads, topographic features, or geotechnical concerns, a floodwall will be
constructed. The floodwall will be composed of interlocked steel sheetpile 18 to 26 feet
in length. The sheetpile joints will be sealed relatively watertight with a mastic joint
sealer. The sheetpile will be capped with a continuous steel channel section welded in
place. The floodwall height will be between 6 and 9 feet above the ground surface. The
steel sheetpile wall will be allowed to rust becoming a brownish -copper color. Areas of
sheetpile floodwall that are highly visible can be partially hidden using landscaping.
E ALIGNMENT
2' MIN. TOPSOIL
AND SEEDING
EXISTING GROUND �.,LEVEEERIAMBANKMENT--I
SURFACE MATL
2OR 3 I 2OR3
STRIP 6" AND REMOVE
UNSATISFACTORY MATERIAL
NOTE: LEVEE TYPE I HAS 2H:IV SIDE SLOPES. LEVEE TYPE la HAS 3H:IV SIDE SLOPES.
LEVEE TYPE I & TYPE la
NOT TO SCALE
If ALIGNMENT
1.5' 41 14
2" MIN. TOPSOIL
AND SEEDING
1 3" AC PAVEMENT
3
LEVEE EMBANKMENT 4" GRAVEL BASE
MATERIAL I L
_ 3
— — — — — — J — — — — — — — —
STRIP 6" AND REMOVE
UNSATISFACTORY MATERIAL
LEVEE TYPE II
NOT TO SCALE
C ALIGNMENT
1 18" MIN. ROCK
1.5' I1.5' SLOPE PROTECTION
4" MIN. TOPSOIL
RIVER SIDE �' + AND SEEDING AIRPORT SIDE
4
1� LEVEE EMBANKMENT
2 MATERIAL
----------- —
------------------------
------/Aduff
STRIP 6" AND REMOVE
UNSATISFACTORY MATERIAL
i
LEVEE TYPE III
NOT TO SCALE
D-5
---- ----------------------------
D-6
The sheetpile floodwall sections downstream of the South Boeing Bridge will be
designed to overtop when flows in the river exceed the 100 year event. These sections
will have a rock splash apron installed at the landward toe to prevent undermining.
Typical sections for the floodwall can be seen in figure D-2.
c. Closure Structures. Three removable closure structures are required along the
alignment, two at the South Boeing Bridge, and one at the gazebo location on the right
bank. The South Boeing Bridge closure structures had to be designed to pass aircraft
through with enough vertical and horizontal clearance. They will be 80 feet long and 3.5
feet high. The closure structure for the gazebo location will be 80 feet long and 6 feet
high. The closure structures will consist of a concrete bottom sill that has a rubber seal
and pre -formed slots that W8x15 structural steel sections can be inserted vertically into.
The slots will be spaced on 8 foot centers. The vertical steel sections allow for fabricated
treated wood sections to span the distance between them to form a wall. Seals along the
backside and between the wood sections will minimize leakage. The terminal ends of the
closure structures will have the same steel section formed into a concrete wall from which
the levee or floodwall will continue.
d. Erosion Control. The grassed side slopes of the proposed levees will provide
adequate erosion protection due to low in -channel water velocities. The outside of the
river bend downstream of the Logan Avenue bridge will be riprapped for approximately
400 feet. There is evidence of erosion along this portion of the river and some existing
rock is already in place. This the only location along the river within the limits of the
proposed project where additional erosion control protection is necessary. The riprap will
extend up to the base of the sheetpile floodwall to be constructed along this reach. A rock
splash apron will be provided on the landward side of the sheetpile floodwall where it is
part of the overtopping section. The overtopping portions of levee, downstream of the
small -plane hangers, will have a protective rock layer placed below the seeded topsoil
layer on the landward side to prevent scour of the levee material when it overtops.
e. Utilities. Several utilities will be impacted by construction of the proposed
project. The storm drainage system for the airport currently has outfalls that drain to the
river. The ends of the pipes have become plugged with river sediments since the river
was last dredged by the City of Renton. The proposed plan calls for exposing the ends of
the pipes by dredging or excavating and installing a backflow preventor. Where the pipes
must pass through the sheetpile floodwall the pipe will be exposed on both sides of the
alignment, shut off, and a section of the pipe removed so that the sheet pile maybe driven.
After the sheetpile has been driven a hole will be cut through the steel sheetpile centered
on the axis of the pipe. A 1'/z foot long steel sleeve with an inside diameter 2 inches
larger than the outside diameter of the existing pipe will be inserted into the hole and
welded to the sheetpile. The existing pipe will be passed through the sleeve and
reconnected to the ends of the existing pipe left in place. The space between the pipe and
the sleeve will be filled with an asphaltic mastic to provide a watertight seal. The
excavation will be backfilled with suitable material and properly compacted. The
existing storm drainage system on the right bank also drains to the river. The Boeing
D-7
Company has definite plans to install an interceptor that will take the flows from all but
one of the outfalls on the right bank and carry them to Lake Washington. The proposed
plan assumes that this work will be completed before construction of the proposed
project. The remaining outfall will be retrofitted with a backflow preventor. An existing
water line and an existing sewer line cross the river via the South Boeing Bridge. The
proposed jacking of the bridge will require that these lines be re-routed. Both lines will
be re-routed under the river 3 feet below the proposed dredge depth. The sewer line is a
pressure system so no siphon is required. The re-routed lines will be encased in concrete
to prevent accidental damage during subsequent maintenance dredging operations and to
prevent the lines from floating. Trail side overhead lights will be moved to new locations
in areas where the existing trail is re -aligned. The underground irrigation system for the
park will need to be modified after completion of levee construction.
2.06 Bridge Jacking Details. The south Boeing bridge will be jacked clear of the water
surface of the design flood event. The concept involves unbolting the existing bridge
from its current foundations and jacking the bridge intact to a sufficient height to prevent
debris in the river from snagging the under side if the bridge. Four hydraulic jacks of
approximately 175 tons capacity each will be positioned on new foundations at each of
the four corners of the bridge. The foundations will be concrete pile caps on nine to 12
deep piles. Based on the design of the original foundations, the new piles will be more
than 80 feet long. The pile caps will also serve as guides for the jacks and protection from
debris for the jacks. One new steel lifting truss, 66 feet long and 6 Meet deep, will be
installed at each end of the bridge and attached to the new hydraulic jacks. In order to
clear debris in the flood waters, the bridge will be jacked to a height of seven feet. Boeing
can expect to operate the bridge until the water reaches the bottom of the bridge, then the
bridge will be raised and the closures for the bridge approaches will be sealed. Figures
D-8 through D-13 show details of the bridge jacking plan.
2.07 Operation and Maintenance. Following construction, the completed project will be
transferred to the local sponsor for operation and maintenance (O&M). The Seattle
District will prepare an O&M manual and furnish copies to the local sponsor, who will
then be responsible for operating and maintaining the project as described in the O&M
manual to ensure serviceability against floods at all times. including levees, floodwalls,
closure structures, dredging, and bridge jacking operations
a. Operation. Operation of the project during flood events will require the
monitoring of river levels, placement of the closure structures, raising of the South
Boeing Bridge, and verification that the project is operating as designed. All equipment
and supplies required to operate the project will be stored close by. Flood exercises will
be required periodically to train local sponsor personnel in the proper operation of project
features. Removal of debris will be required throughout the year to ensure proper
operation of drain pipes, the South Boeing Bridge jacking mechanisms, and installation
of the closure structures.
M
b. Maintenance. Maintenance of the project is required to ensure that the project
will provide the designed protection during floods. The major maintenance feature of the
proposed project is the periodic redredging of the river channel. See Appendix A -
Hydrology and Hydraulics for a discussion of redredge frequency and amount. General
project maintenance will include mowing the grassed levees, removing undesirable
vegetation from the embankment side slopes, removal of debris from levee slopes and
structures, trimming and pruning of trees and shrubs along with monitoring survival of
planted materials, correction of all types of animal burrows and, if required, restoring the
embankment to the design grade and section. As the age of the project increases,
maintenance of the project will include replacing deteriorated and damaged equipment.
Particular attention to closure structures and jacking machinery will be required. The
local sponsor will prevent encroachment on the rights -of -way that would interfere with
project operation and maintenance. An inspection program will be developed by the local
sponsor to recognize and correct any conditions that could adversely affect the project.
M
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LEGEND
LEVEE FIGURE D-3
100' 50' 0 100, 200'
I " = 100'
FLOODWALL
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
SITE PLAN 1
CEDAR RIVER WASHINGTON
SIZE INVITATION NO. FILE NC. PLATE
B C1.1
oscN: BRANDY i CHK: SHEET D- I O
DATE AND TIME PLOTTED: 18-MAR-1997 13:04 DESIGN FILE: 1:00esigns0crfc0civ0cr_dprl.dgn SCALE! 1 = 100'
r n I .............. _- _ l —
x
.-
SMALL- PIaQ LANE HANG
..........._. .._...... «............... A S
Z
1
w
f-.:.''-
_..........
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UR
....R 35+00
CLOS
E STRUCTURE
- An.._..._ _
s.:
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s:y ..,.+...
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FIGURE D-4
100' 50' 0 100' 200'
r = i 0 C'
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
SITE PLAN 2
CEDAR RIVER WASHINGTON
PG
ZE INVITATION NO. FILE NO, PLATE
C1.2
N: BRANDT CHK: SHEET D- I
DATE AND TIME PLOTTED: 18-MAR-1997 13:04 DESIGN FILE: I:0designs0crfc0civ0cr_dpr2.dgn SCALE: 1 = 100•
....... .........
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------ . . . . . ...........
4-
CLOSURE STRVCTURE
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------------
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uj . . .............
----------- . ........ ....
f
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.. . .. ........ ... ...
.... . .....
— - ----------- . . . ...........
<I FLOOD AC TYPE L 50+00
L 45+00t FLOODWALL TYPE 11 L 40+00
SOLITH
C E D A R R I V E R BOEING
FLOW
BRIDGE
rl '4 +00
-LEVEE TYPE*
R 45+00
R 50+00 YPE 11
. ............ A E VI.E.E.—T.
"-I .... . ...... . .
........... .. :.".::
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7
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fn.
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. .. .. TURE
. a :z::
CL�JD..S U R E S T
RIJ
FIGURE D-5
100' 5 0' 0 100, 200'
100, 1 0 i�--
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
SITE PLAN 3
CEDAR RIVER WASHINGTON
SIZE I tNVITATION NO- FILE NO. PLATE
� B T CI.3
DSGN: BRAND D- 12
T SHEET I
DATE AND TWE PLOTTED: 18-MAR-1997 13:17 DESIGN FILF: J-0dpsian,%0crfcft-ivqorr ein,-3-cinn CrAi C. I Inn,
...I Z
. . .. ............ . ...... I <
......
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............
_ L 55+00 a
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:, •� . -.' - ••mil Wiz'..
`Y FIGURE D-6
.... ...... ::.
100, 50, 0 100, 200'
I" = 100'
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
SITE PLAN 4
CEDAR RIVER WASHINGTON
SIZE INVITATION N0. FILE N0. PLATE
[B C 1.4
DSGN: BRANDY I CHK: SHEET D-13
DATE AND TIME PLOTTED: 18-MAR-1997 13:05 DESIGN FILE: L•OdesiansArrfcOcivOcr dor4_dan cre, r. i - inn,
FIGURE D-7
•• • • 100, 200'
----�zi-------
U. S. ARMY ENGINEER DISTRICT, SEATTLE I
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
AND TIME PLOTTED: 18-MAR-1997 1
IL
Mn
SCAT F- I " = 100'
:
NEW LIFTING TRUSS
NEW 10'X I O'
PILE CAP
TYP
I
D> D c c c
EXISTING STEEL GIRDERS
> > c c c
I
I
I
I ,
I
I
I
� 1
> > c c c
D EXISTING PIER I c
> > > BRIDGE DECK c c c
> > > 0
p c c c
7P
�- 5 ILE,
12" DIAMETER
TYP
EXISTING ABUTMENT
7P
�- 5 ILE,
12" DIAMETER
TYP
EXISTING ABUTMENT
NEW 10'X 13' PILE CAP
SEE PLATES S3.4 & 53.5
i
TYP
I
I
FIGURE D —8
NOTES:
104 0 10, 20' 30,
1' - 0"
I. ONE HYDRAULIC
JACK WILL BE INSTALLED
._
ON EACH NEW PILE
CAP.
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
2. THE BRIDGE WILL
BE UNBOLTED FROM ITS
SEATTLE, WASHINGTON
CURRENT FOOTINGS.
JACKING OPTION
,
3. THE BRIDGE WILL
BE BOLTED TO THE NEW
STRUCTURAL PLAN
LIFTING TRUSSES.
CEDAR RIVER WASHINGTON
SIZE
INVITATION NO.
FILE NO.
PLATE
B
I
51.1
DESIGN FILE: I:6designsOcrfcfstrocrfcso0a.dgn
DSGN: SHAW
CHK:
SHEET D — 15
DATE AND TIME PLOTTED: 22-JAN-1997 16:03
DESIGN FILE: I:fdesignsfcrfcestrscrfcsoOa.dgn SCALE: %, -
ABUTMENT
EXISTING PIER
APPROXIMATE EXISTING GROUND -
LEVEL. EXCAVATE AS REQUIRED
FOR TRUSS, AND SHOTCRETE NEW
SURFACE UNDER BRIDGE.
i:Ode signsOcrfcOstrOcrfcsaOb.don
FIGURE D-9
10, 0 10, 20' 30'
I . _ 0„
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
JACKING OPTION
BRIDGE ELEVATION
CEDAR RIVR
SIZE INVITATION NO.
B
FILE NO.
WASHINGTOr
PLATE
SI.c
SHEET D-- ! 6
4,_6„
4,_6„ 6,_0„
TYP
FEW
8X40VERTICAL
LEMENT, TYP
I
-----------,----�----------------------
�W18X1751
--—- — -- —�
ATTACH T0---" --------
---- ------ ------
—-—-—-—-—-—-— - — - — -— — —
JACK COLLAR
AT EACH END
2L 5X3X I/2
W 18X 175 0
OF TRUSS
TYP
I
in
'
FIGURE D-10
NOTES:
I. THE EXISTING BRIDGE GIRDERS
WILL REST ON THE VERTICAL/e•�
-
- ,
5 0 5 Io 15
I, - 0„
TRUSS MEMBERS.
2. ALL STEEL IS A36.
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
sEArnE, WASHINGTON
3. THE ENTIRE TRUSS MUST BE PAINTED
OR GALVANIZED
FOR CORROSION PROTECTION.
JACKING OPTION
TRUSS ELEVATION
CEDAR
RIVER WASHINGTON
SIZE
INVITATION NO,
FILE NO.
PLATE
B
S1.3
DESIGN FILE:
i:odesignsocrfc*strOcrfcso0c.dan
DSGN: TMS
CHK:
SHEET D— 17
i
DATE AND TIME PLOTTED:
22-JAN-1997 16:07
DESIGN FILE: i:6designs$crfcostrocrfoso0c.dpn
SCALE: /e" = I-0
NOTE: EXACT LOCA
OF THESE TWO SURI
WILL BE DETERMINE
DESIGN OF GUIDE W
FOR THE JACKS. TI
SURFACES RESIST L
LOADS WHILE BRIDG
NOTE:
CONSTRUCTION OF DOWNSTREAM PILE CAP
SIMILAR. DOWNSTREAM PILE CAP IS 3'
SHORTER IN DIRECTION OF FLOW, BUT
OTHERWISE IS IDENTICAL.
OESIGN FILE: i:Odesignsmcrfc4strOcrfcsoOd.dgn
FIGURE D-11
„6„ 0 11 2' 3' 4' 5'
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
JACKING OPTION
UPSTREAM PILE CAP PLAN
CEDAR RIVER WASHINGTON
SIZE INVITATION NO. FILE NO. PLATE
B S 1.4
OSGN: TMS CHK: SHEET D - 18
13' - 0"
NOTE:
CONSTRUCTION OF DOWNS
SIMILAR. DOWNSTREAM PILE CAP IS 3'
SHORTER IN DIRECTION OF FLOW, BUT
OTHERWISE IS IDENTICAL.
RADIUS CORNER
FIGURE D -12
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
JACKING OPTION
PILE CAP ELEVATION
CEDAR RIVER WASHINGTON
SIZE INVITATION NO. FILE NO. PLATE
g 1 IS1.5
DSGN: TMS I CHK:
SHEET D- 19
ni
PON
COLLAR SECTION
SCALE: 3" = 1'-0"
ASSEMBLY NOTES:
i9/6" WELD
ATE
1 0 1 CCL I,ULLAt-t
I. BOLT THE WEB OF THE TOP W 18 OF THE LIFTING
TRUSS TO THE SHEAR PLATE SHOWN HERE.
2. WELD THE FLANGES OF THE W 18 TO THE WELD
PLATES SHOW HERE.
3. THE WHEELS SHOWN HERE ARE TO GUIDE THE
JACK ALONG THE NOTCH IN THE CONCRETE PILE
CAP.
A. THE WHEELS MUST SUPPORT A FORCE OF 12 KIPS.
" SHEAR PLATE
'CENTERLINE OF
W 18 MEMBER
& HYDRAULIC JACK
i q/ ii uir-LD
COLLAR ELEVATION
SCALE: 3" = 1'-0"
FIGURE D —13
•
AR PLATE
U. S. ARMY ENGINEER DISTRICT, SEATTLE
CORPS OF ENGINEERS
SEATTLE, WASHINGTON
JACKING OPTION
LIFTING JACK COLLAR DETAILS
CEDAR RIVER WASHINGTON
S;lZE INVITATION N0. FILE N0. PLATE
S1.6
oscN: TMS CHK: SHEET D -20
APPENDIX E
PROJECT COSTS
TOTAL - ALL CONTRACTS TOTAL PROJECT COST SUMMARY
PAGE 1 OF 2
BASED ON THE DETAILED PROJECT REPORT DATED MARCH 1997
PROJECT:
CEDAR RIVER SECTION 205 FLOOD DAMAGE REDUCTION STUDY
DISTRICT: SEATTLE
LOCATIO
RENTON, WASHINGTON
POC: OLTON SWANSON, CHIEF, COST
ENGINEERING
CURRENT MCACES ESTIMATE PREPARED:
25 Mar 97
AUTHORIZED/BUDGET YEAR:
FULLY FUNDED ESTIMATE
EFFECTIVE PRICING LEVEL:
Oct 1997
EFFECTIVE PRICING LEVEL:
ACCOUNT
COST CNTG
CNTG
TOTAL
COST CNTG TOTAL
COST
CNTG
FULL
NUMBER
FEATURE DESCRIPTION ($K) ($K)
(%)
($K)
($K) ($K) ($K)
($K)
($K)
($K)
9
CIiANNELS AND CANALS 5,095 1,019
20%
6,114
5,518
1,103
6,621
TOTAL CONSTRUCTION COST $5,095 $1,019
20%
$6,114
$5,518
$1,103
$6,621
01
LANDS AND DAMAGES 575 115
20%
690
599
120
719
30
PLANNING, ENGINEERING AND DESIGN 516 104
20%
620
543
109
652
31
CONSTRUCTION MANAGEMENT 408 82
20%
490
461
93
554
TOTAL PROJECT COSTS $6,594 $1,320
20%
$7,914
$7,121
$1,425
$8,546
TOTAL FEDERAL COSTS
THIS TPCS REFLECTS A PROJECT COST CHANGE OF
TOTAL NON-FEDERAL COSTS
DISTRICT APP VED:
THE MAXIMUM PROJECT COST IS
HIEF, COST ENGINEERING
CHIEF, REAL ESTATE
DIVISION APPROVED:
CHIEF, PLANNING
CHIEF, COST ENGINEERING
CHIEF, ENGINEERING
DIRECTOR, REAL ESTATE
CHIEF, CONSTRUCTION
CHIEF, PROGAMS MANAGEMENT
CHIEF, OPERATIONS
DIRECTOR OF PPMD
CHIEF, PROGRAMS MANAGEMENT
APPROVED DATE:
PROJECT MANAGER
DDE (PM)
FULLFUNO.XLS
3125/97
TOTAL CONTRACT COST SUMMARY PAGE 2 OF 2
BASED ON THE DETAILED PROJECT REPORT DATED MARCH 1997
PROJECT: CEDAR RIVER SECTION 205 FLOOD DAMAGE REDUCTION STUDY DISTRICT: SEATTLE
LOCATIO RENTON, WASHINGTON POC: OLTON SWANSON, CHIEF, COST ENGINEERING
CURRENT MCACES ESTIMATE PREPARED: 25 Mar 97 AUTHORIZED/BUDGET YEAR: FULLY FUNDED ESTIMATE
EFFECTIVE PRICING LEVEL: Oct 1997 EFFECTIVE PRICING LEVEL:
ACCOUNT COST CNTG CNTG TOTAL COST CNTG TOTAL FEATURE OMP COST CNTG FULL
NUMBER FEATURE DESCRIPTION ($K) ($K) N ($K) ($K) ($K) ($K) MIDPT (%) ($K) ($K) ($K)
9
CHANNELS AND CANALS
09.01
CHANNELS
09.01.01
MOB, DEMOB & PREPARATORY WORK
132
26
20%
158
OCT 99
8.3%
143
28
171
09.01.14
SIDECASTER/SPECIAL PURPOSE DREDGING
1,470
294
20%
1,764
OCT 99
8.3%
1,592
318
1,910
09.01.30
BANK STABILIZE, DIKES AND JETTIES
2,370
474
20%
2,844
OCT 99
8.30'o
2,567
513
3,080
09.01.99
ASSOCIATED GENERAL ITEMS
1,123
225
20%
1,348
OCT 99
8.3%
1,216
244
1,460
TOTAL CONSTRUCTION COST
$5,095
$1,019
20%
$6,114
$5,518
$1,103
$6,621
01
LANDS AND DAMAGES
575
115
20%
690
OCT 97
4.2%
599
120
719
30
PLANNING, ENGINEERING AND DESIGN
478
96
20%
574
OCT 97
4.2%
498
100
598
MONITORING
38
8
21%
46
OCT U1
17.9%
45
9
54
31
CONSTRUCTION MANAGEMENT
408
82
20%
490
OCI 99
13.1%
461
93
554
TOTAL PROJECT COSTS
$6,594
$1,320
20%
$7,914
$7,121
$1,425
$8,546
FULLFUND.XLS
3125/97
CEDAR RIVER SECTION 205
FLOOD DAMAGE REDUCTION STUDY
NARRATIVE
1. To reduce flood damages on the Cedar river in Renton several flood control measures will be
implemented. The flow capacity of the river will be increased by dredging to a depth of four feet below
existing conditions from the mouth of the river to the Logan Avenue bridge. Dredging will be
accomplished by dragline and the dredged materials will be disposed of near the intersection of
Interstate 5 and Highway 169. 3600 LF of levees will be constructed as space allows and 3620 LF
sheetpile floodwalls will be driven where space is limited. Temporary closure structures will be
provided for the south Boeing bridge and for the rest room at City park. The south Boeing bridge will
be modified to allow it to raise during a flood event. Hydraulic cylinders will jack the bridge evenly from
all four corners. Mitigation features include construction of a salmon spawning channel in the Cedar
River Regional Park and plantings along levees and in the Cedar River Trail Park.
2. The basis of the estimate is the 21etailed project report dated March 1997.
3a. The need for overtime for any of the construction activities has not yet been determined.
3b. The construction window for working in the river is June 15 through August 31.
4. The only assumed subcontractor identified at this time is for the truck hauling of the dredged
materials. Three separate contracts may be used for the major types of work which include bridge
jacking, dredging, and levee and floodwall construction.
5a. Site access will include City of Renton Parks parking lots and access roads, Renton Airport access
road and the Renton Boeing Plant access roads and bridges.
5b. The nearest borrow a,eas are located approximately 2 miles away in Renton, WA.
5c. All construction methods are assumed to be conventional at this time.
5d. Work interruptions including the potential for flooding and salmon migration periods are the only
factors anticipated to affect construction.
5e. Availability of labor and equipment is not foreseen as a problem. The project site is centrally
located in the Puget Sound urban corridor.
6. Contingencies are set at 20% for all features including construction and in-house labor. Inflation
factors used in full funded summary according to EC 1-2-169 dated March 31, 1996.
7. Labor rates are based on October 1997 King County union wages. Equipment rates are effective
October 1995 and material prices are effective October 1995. All MCACES database materials and
material quotes are effective October 1997.
3/27/97
Thu 20 Mar 1997
Eff. Date 10/01/97
Tri-Service Automated Coat Engineering System (TRACES)
PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205
DPR Estimate
Four Foot Dredge Alternative
Cedar River Section 205
Flood Damage Reduction Study
Detailed Project Report
Renton, Washington
Designed By: Seattle District Design Branch
Estimated By: U.S. Army Corps of Engineers
Prepared By: Cost Engineering Branch
William Garrott/Stephen Pierce
Preparation Date: 03/17/97
Effective Date of Pricing: 10/01/97
Eat Construction Time: 426 Days
Sales Tax: 8.20%
This report is not copyrighted, but the information
contained herein is For Official Use Only.
M C A C E S F O R W I N D O W S
Software Copyright (c) 1985-1996
by Building Systems Design, Inc.
Release 1.00
TIME 12:43:21
TITLE PAGE 1
LABOR ID: RING97 EQUIP ID: NAT95A Currency in DOLLARS CREW ID: NAT95A UPB ID: NAT95A
Thu 20 Mar 1997 Tri-Service Automated Cost Engineering System (TRACES) TIME 12:43:21
Eff. Date 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205
TABLE OF CONTENTS DPR Estimate CONTENTS PAGE 1
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SUMMARY REPORTS SUMMARY PAGE
PROJECT INDIRECT SUMMARY - system.........................................1
PROJECT DIRECT SUMMARY - System...........................................2
DETAILED ESTIMATE DETAIL PAGE
10. General Overhead
0. Overhead Items
A. Supervision and Management................................1
B. Administration Job Office.................................I
D. Engineering and Surveying.................................2
E. Quality Control and Testing...............................3
F. Safety, Trfc Cntrl, Fst Aid,Fire..........................3
G. Sanitation Fac.6 Temp Bldgs...............................4
I. Miscellaneous Project Expenses ............................4
09. Channels and Canals
O1. Channels
O1. Mob, Demob & Preparatory Work
01. Mobilization and Demobilization ...........................5
03. Preparatory Work..........................................5
14. Sidecaster/Special Purpose Dredg
02. Sitswork..................................................5
30. Bank Stabilize, Dikes & Jetties
02. Civil.....................................................6
04. Structural............................................11
06. Demolition...............................................11
08. Relocations..............................................12
99. Associated General Items
02. Structural...............................................14
99. Mitigation (Salmon Spawning..............................14
No Backup Reports...
• • • END TABLE OF CONTENTS • '
Thu 20 Mar 1997^ Tri-Service Automated Cost Engineering System (TRACES)
Eff. Date 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205
DPR Estimate
+• PROJECT INDIRECT SUMMARY - system +•
TIME 12:43:21
SUMMARY PAGE 1
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
QUANTITY UOM DIRECT OVERHEAD HOME OFC PROFIT INS/BOND B&O Tax TOTAL COST UNIT COST
----------------------------------------------------- -------------------------------
09 Channels and Canals
09U1 Channels
090101 Mob, Demob & Preparatory Work
090114 Sidecaster/Special Purpose Dredg 158500.00 CY
090130 Bank Stabilize, Dikes & Jetties 6920.00 LF
090g9 Associated General Items
TOTAL Channels
TOTAL Channels and Canals
TOTAL Four Foot Dredge Alternative
110,000
8,801
4,443
6,162
1,941
657
132,003
1,225,357
98,035
49,495
68,644
21,623
7,316
1,470,470 9.28
1,974,956
158,007
79,773
110,637
34,851
11,791
2,370,014 342.49
935,918
-----------
74,878
--------- ---------
37,004
52,430
16,515
5,588
1,123,133
4,246,231
-----------
339,721
---------
---------
171,515
---------
237,873
---------
74,930
25,351
-----------
5,095,621
4,246,231
-----------
339,721
---------
---------
171,515
------------------
237,873
---------
74,930
25,351
-----------
5,095,621
4,246,231
339,721
---------
171,515
--------- ---------
237,873
---------
74,930
25,351
-----------
5,095,621
LABOR ID: KING97 EQUIP ID: NAT95A Currency in DOLLARS _ CREW ID: NAT95A UPB ID: NAT95A
Thu 20 Mar 1997 Tri-Service Automated Coat Engineering System (TRACES)
Eff. Date 10/01/97 PROJECT CEDAR2: Four Foot Dredge Alternative - Cedar River Section 205
DPR Estimate
** PROJECT DIRECT SUMMARY - system '�•
TIME 12:43:21
SUMMARY PAGE 2
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
QUANTITY UOM MANHRS LABOR EQUIPMNT MATERIAL OTHER TOTAL COST UNIT COST
-------------------------------
09 Channels and Canals
0901 Channels
090101 Mob, Demob & Preparatory Work
090114 Sidecaster/Special Purpose Dredg 158500.00 CY
090130 Bank Stabilize, Dikes & Jetties 6920.00 LF
090199 Associated General Itoms
TOTAL Channels
TOTAL Channels and Canals
TOTAL Four Foot Dredge Alternative
OVERHEAD
SUBTOTAL
HOME OFC
SUBTOTAL
PROFIT
SUBTOTAL
BOND
SUBTOTAL
B&O Tax
TOTAL INCI. INDIRECTS
1,680 54,000 50,000 6,000 0 110,000
15,365 575,189 650,168 0 0 1,225,357
12,369 700,750 609,455 552,496 112,255 1,974,956
7,736 250,706 '15,552 469,621 0 935,918
37,151 1,580,645 1,525,215 1,028,116 112,255 4,246,231
------ ------------------ -----------------------------
37,151 1,580,645 1,525,215 1,028,116 112,255 4,246,231
------ ------------------ --------- --------- -----------
37,151 1,580,645 1,525,215 1,028,116 112,255 4,246,231
339,721
4,585,952
171,515
4,757,467
237,873
4,995,340
74,930
5,070,270
25,351
5,095,621
7.73
285.40
LABOR ID: KING97 EQUIP ID: NAT95A Currency in DOLLARS CREW ID: NAT95A UPB ID: NAT95A
APPENDIX F
FISH AND WILDLIFE COORDINATION ACT REPORT
CEDAR RIVER SECTION 205 DREDGING PROJECT
U. S. FISH AND WILDLIFE
COORDINATION ACT REPORT
U.S. Fish and Wildlife Service
North Pacific Coast Ecoregion
Western Washington Office
OIympia, Washington
February 1997
U.S. Fish and Wildlife
Final Coordination Act Report
CEDAR RIVER SECTION 205 DREDGING PROJECT
Prepared for
U.S. Army Corps Of Engineers
Seattle District
Prepared by
Gene Stagner, Biologist
U.S. Fish and Wildlife Service
North Pacific Coast Ecoregion
Western Washington Office
Olympia, Washington
February, 1997
TABLE OF CONTENTS
INTRODUCTION..........................................................I
AUTHORITY AND DOCUMENTATION ....................................... 1
PROJECT LOCATION AND DESCRIPTION ..................................... 2
Location .......... 2
..................................................
Project Alternatives Descriptions .......................................... 5
FISH AND WILDLIFE RESOURCES ........................................... 6
Wildlife Resources..................................................... 6
Fish Resources........................................................9
THREATENED AND ENDANGERED SPECIES ................................. 17
STUDY RESULTS.........................................................
18
Wildlife Study.......................................................18
PredatorStudy.......................................................19
Longfin Smelt Study..................................................20
Habitat Study/Survey..................................................
21
Sockeye Salmon Spawning Survey ........................................
22
Fish Utilization Studies ................................................
22
Aquatic Invertebrate Study ..............................................
22
FUTURE WITHOUT THE PROJECT .......................................... 23
POTENTIAL PROJECT IMPACTS TO FISH AND WILDLIFE RESOURCES ........... 24
Impacts to Wildlife ................................................... 24
Impacts to Aquatic Resources ........................................... 25
NoAction....................................................25
Alternative ...................................................25
Alternative2...................................................26
Alternative3...................................................27
Alternative 4...................................................27
RECOM%ffiNDATIONS..................................................... 28
Mitigation for Wildlife Impacts ........................................... 29
Proposed Mitigation for Aquatic Resource Impacts ........................... 30
LITERATURECITED......................................................33
LIST OF TABLES
Table...................................................................7
Birds observed in the vicinity of the lower Cedar River
Table2..................................................................10
Resident and anadromous fish species utilizing the Cedar River
Table..................................................................11
Sockeye Salmon redds observed in the lower Cedar River, 1994 and 1995
Table4..................................................................16
Smelt egg distribution in Lake Washington tributaries
LIST OF FIGURES
Figure...................................................................3
Lower Cedar River Section 205 Project Vicinity Map, City of Renton, King County,
Washington
Figure2...................................................................4
Lower Cedar River Section 205 Project Location
Figure..................................................................11
Cedar River Salmon and Steelhead Periodicity Chart
Figure4..................................................................13
Cedar River Sockeye Escapement
Figure..................................................................15
Anadromous Fish Returns to the Lake Washington Basin and Cedar River
INTRODUCTION
This is the final Fish and Wildlife Coordination Act Report (FWCAR) for the Lower Cedar River
Section 205 project. It fulfills the Scope of Work (SOW) for the U. S. Fish and Wildlife Service's
(Service) feasibility -level activities as described in the Army Corps of Engineers (Corps) Military
Interdepartmental Purchase Agreement (MIPR) 9 E-86- 97-3035. It has been prepared pursuant to
Section 2(b) of the Fish and Wildlife Coordination Act (48 Stat. 401, as amended; 16. U.S.C. 661
et seq.) and supersedes our draft FWCAR of October, 1996.
After reviewing all of the pertinent information, we support the shallow dredge alternative (discussed
in a later section as alternative 2). The impacts to fish and wildlife resource seem to be minimized
with this alternative. The flood control objective of the project should also be accomplished with this
alternative.
This report is being sent to the Corps, several state and local entities, and the Muckleshoot Indian
Tribe. The Service plans on being involved through the implementation of this project. We will be
available to support the Corps during the development of the mitigation and monitoring plans.
AUTHORITY AND DOCUMENTATION
Section 205 of the 1948 Flood Control Act as amended allows the Corps to construct small flood
control projects not specifically authorized by Congress. Each project is limited to a Federal cost of
not more than $5 million including studies, design, plans, specifications, and construction costs. The
costs for both the preliminary evaluation and the feasibility stage are cost shared with a local sponsor.
The City of Renton (the local sponsor) will bear the maintenance costs for the project.
This report is based on project plans and information provided by the Corps through January 29,
1996. It uses results from studies conducted by the Corps, private contractors, the Service, the
Washington Department of Fish and Wildlife (WDFW) and Muckleshoot Tribal biologists. The
Project Impact and Mitigation portions of this report are based on consultation with the above entities
as well as comments from agency and public meetings.
As a result of the initial appraisal, the Corps has determined that there is a federal interest in
participating in flood damage reduction measures along the lower Cedar River in the urban/industrial
area in the City of Renton, King County, Washington. Average annual flood damages for the lower
one mile of the Cedar River have been estimated at $670,000. In November 1990, flooding in this
area reached the highest level recorded at Renton since 1945 and caused an estimated $8 million in
damages to the Renton airport and Boeing manufacturing plant. The 1995/1996 floods also caused
significant damage to City and private property. The Corps has indicated that flood reduction
benefits exceed costs for a structural solution and has initiated feasibility level study.
Historically, the lower Cedar River was dredged periodically to a depth of >10 feet. This was
expensive and created a need to dredge the delta area. The delta created the control level for water
flow into the lake and therefore limited flow if it was not dredged to an equal depth as the channel.
Due to the recent flooding along the lower Cedar and the significant damage incurred, alternative
methods for flood control are being investigated by the City of Renton and the Corps of Engineers.
An interagency scoping meeting was conducted on June 12, 1996, to discuss the latest flood control
alternatives and solicit agency issues. These issues should be addressed in the Environmental Impact
Statement (EIS) and in the design report. The discussions focused on fish and wildlife resource
studies, and impacts of the projects on these resources. Sediment traps and transport were discussed
and five (5) alternatives were presented. The no action alternative will be evaluated in context during
the EIS. Consequent phone discussions with the Corps indicated that the sediment traps would not
significantly delay the frequency of lower channel dredging so that alternative will likely be dropped
from future consideration. The remaining alternatives with various permutations are discussed below.
PROJECT LOCATION AND DESCRIPTION
LOCATION
This proposed project involves the Cedar River from the mouth at Lake Washington upstream
approximately one mile. It is entirely within the city limits of Renton. The Cedar River watershed
is located about 16 miles southeast of Seattle entirely within King County (See Figure 1). The
headwaters begin within the boundaries of the Mt. Baker - Snoqualmie National Forest. The drainage
basin is about 50 miles long and encompasses an area of approximately 186 square miles. The Cedar
River cuts a canyon through steep mountain terrain from its source to Chester Morse Lake at about
rivermile (RM) 37.2. This relatively small reservoir angles west about 1.5 miles to Masonry Dam
(RM 35.9). From Masonry Dam, flow is diverted through penstocks to Seattle's Cedar Falls Power
Plant located about 3.5 miles west. At this point, the entire flow returns to the main Cedar River
channel. Downstream to Landsburg, the river channel initially occupies a steep, well-defined channel
that gradually widens and moderates in steepness.
At Landsburg, water is diverted into a pipeline which transports it to Lake Young Reservoir southeast
of Renton. The diversion dam at Landsburg (RM 21.8) blocks anadromous fish runs from using the
upper basin. A Habitat Conservation Plan (HCP) is currently being negotiated for lands owned by
the City of Seattle in the upper Cedar River. If this plan is implemented, Seattle has agreed to fund
fish passage around the Landsburg dam for chinook salmon, coho salmon, and steelhead trout.
Sockeye salmon will not be allowed passage above the dam due to a concern for water quality given
the larger number of adult fish. Steelhead trout were hauled around the dam historically but this has
not happened in the last few years.
2
The Cedar River from Landsburg to Maple Valley (RM 14.7) flows through a relatively shallow,
narrow valley with moderately steep hillsides. Stream gradient in the upper 2 miles of this section
is moderately steep with fast riffles and large rock and boulders. Downstream, the gradient decreases
and is moderate for the remainder of this section. Several steep gravel banks border the stream
throughout the upper 5 miles. Erosion from these contributes fine sediment as well as vital spawning
material to the river below.
Cr
May Creek
CeIv
ark
Creek
Evans Creek
c
Lakeamishm
From Maple Valley, downstream to Renton, the Cedar River winds through a broad, flat valley with
increasing rural and commercial development. The river maintains a moderate to gentle gradient in
91
this section with a few channel splits and bends with sand and gravel bars. Rural areas exist on both
sides of the river valley floor with higher urban densities nearer the population center of Renton. In
this section, river banks have received extensive bank protection work, primarily riprapping.
The lower 3 miles of the river flow through a heavily industrialized area of Renton. The last 1.25
miles of the river flow through a channelized segment before emptying into Lake Washington (See
Figure 2). The effects of development in the lower Cedar River are most apparent from the increased
rates and volume of storm water discharge caused by the extensive impervious surface areas of
buildings, highways, and parking lots. This has resulted in substantial bank erosion, increased
siltation, and frequent floods in the vicinity of Renton. Water quality and fish habitat have
deteriorated as a result.
Figure 2 Lower Cedar River Section 205 Project Location (Not to Scale)
11
Oceanic storms, usually lasting from 1-3 days, cause major floods on the Cedar River. Warming
temperatures from these storms are sufficient to melt a significant amount of the snowpack.
Successive storms can cause a series of floods which most commonly occur from October through
June during those periods of intense rainfall or rapid snowmelt.
The Cedar River supplies 54 percent of Lake Washington's water supply, which is important to the
operation of the Hiram Chittenden Locks for commerce, for ship passage, and control of salt water
intrusion. Lake levels of Lake Washington are maintained at +20 foot M.S.L. during winter and
increased to 22 feet for summer operation of the locks and fish ladder when precipitation and other
Lake Washington inflows are low.
PROJECT ALTERNATIVES DESCRIPTIONS
The Corps has considered several preliminary alternatives to control flood damage in the lower one
mile of the Cedar River. During feasibility stage planning, four action alternatives are being evaluated
by the Corps to establish which is the most cost effective and most environmentally acceptable. All
of the following alternatives include the addition of a hydraulic jack to the south Boeing bridge. The
latest action alternatives include:
1. Constructing levees along the right bank from Logan Avenue to the mouth and on the
left bank from Logan Avenue to a point 2,000 feet above the mouth. There would be
maintenance dredging every three years to maintain the existing channel bottom.
2. Dredging the lower mile of river a moderate amount (4 feet) to the Logan Avenue
bridge. From the Logan Avenue bridge the dredging would slope upstream for 400
yards to meet the present gradient. This alternative will include constructing a
levee/floodwall along the bank. The height would range from .58 - 6.92 feet, depending
on the existing bank height. Maintenance dredging of 171,000 yds3 would be required
every three years.
3. Dredging the lower mile of river a deeper amount (6 feet) to the Logan Avenue bridge.
From the Logan Avenue bridge the dredging would slope upstream for 700 yards to
meet the present gradient. This alternative will include constructing a levee/floodwall
along the bank. The height would range from 1.36 - 5.83 feet, depending on the existing
bank height_ Maintenance dredging of 176,000 yds3 would be required every three years.
4. Dredging the lower mile of river up to 10 feet deep to the Logan Avenue bridge. From
the Logan Avenue bridge the dredging would slope upstream for 700 yards to meet the
present gradient. This alternative will include constructing a levee/floodwall along the
bank. The height would range from .63 - 5.43 feet, depending on the existing bank
height. Maintenance dredging of 185,000 yds3 would be required every three years.
I
The proposed levees would consist of filling in between the existing mounds on the right bank. The
levees would not encroach on the river and would be set back from the river's edge to allow for
riparian zone planting. On the left bank (the airport side), sheet piling combined with raising the
roadway to form a berm would be used to protect the airport.
The south Boeing bridge creates a debris trap during floods and would require higher levees upstream
of the bridge to accommodate the backwater effect caused by debris blockage. The proposed
solution to this is to construct hydraulic jacks under the bridge and jack the bridge up during flood
events to reduce the potential for debris blockages. This feature is included with each alternative.
Two dredging methods have been proposed for this project. A barge mounted clamshell dredge
could be used since the water depth is adequate to float the barge. In conjunction with the clamshell
a barge mounted dragline could be used in the lower portion of the project area. The other method
considered is to divert the water by coffer dams and remove the gravel from the contained area by
excavator.
FISH AND WILDLIFE RESOURCES
WILDLIFE RESOURCES
Terrestrial wildlife species and wildlife habitat in the study area are limited due to the amount of
industrial and commercial development. However, many different wildlife species can adapt to these
environments. In fact, the diversity of bird species in the project area is significant. A narrow band
of riparian vegetation occurs discontinuously at the water's edge. Bird species are the most prevalent
wildlife using these areas. The lower Cedar River is used by several groups of bird species such as
songbirds, waterfowl, shorebirds, wading birds, gulls, hawks, and eagles. Gulls are probably the
most abundant group of birds in the area.
One of the reasons for dredging the Cedar River delta in 1994 was to reduce the risk of aircraft and
bird collisions at the Renton airport. The shallow gravel bar areas attract many birds, primarily
gulls. These birds were presumed to increase the risk of collision with aircraft landing or taking off
at the airport (COE 1993).
Sixty-four different bird species were recorded during surveys completed by Service, Corps and
Harza Northwest biologists (Table 1). These surveys were completed between March, 1992 and
September, 1995. Many of these birds were using the project area for breeding and rearing. Smaller
birds breeding in the area included bushtits, swallows, red -winged blackbirds and hairy woodpeckers.
A male woodpecker, accompanied by a female, was observed excavating a hole in one of the few
alder snags in the area. The number of broods and young of the year observed indicated that this area
is getting substantial use for nesting and/or rearing. Juvenile gulls, mallards, common mergansers,
and Canada geese were observed in the project during most of the spring and summer. Bushtits, hairy
I
woodpeckers, barn and rough -winged swallows, house sparrows, and red -winged blackbirds were
observed either nesting or with young of the year.
Riparian zone areas are extremely valuable to wildlife. Their value is due to their shape and proximity
to water. They provide large edge -to -area ratios from their linear nature and varying soil moisture
that support a greater diversity of plant species. Of the 480 species of wildlife in Washington, 291
are found in wooded riparian habitats. Of these, 68 species of mammals, birds, amphibians, and
reptiles require riparian areas to satisfy vital life requirements for all or part of the year.
Table 1. Birds observed in the vicinity of the lower Cedar River. (Brunner 1995) (USFWS 1995)
1993
199
Species Scientific Name 11 Species Scientific Name
Homed grebe
Western grebe
Double -crested cormorant
Great blue heron
Green heron
Canada goose
Green -winged teal
Mallard
Northern Shoveler
Gadwall
Canvasback
Redhead
Lesser Sca.up
Common goldeneye
Barrow's goldeneye
Buffiehead
Hooded merganser
Common merganser
Domestic ducks
Bald eagle
Cooper's hawk
American coot
Killdeer
Western sandpiper
Mew gull
Ring -billed gull
California gull
Herring gull
Thayer's gull
Glaucous -winged gull
Rock dove
ceps
Podiceps auritus
Aechmophorus
Phalacrocorax auritus
Ardea herodias
Butorides virescens
Branta canadensis
Anas crecca
Anas platyrhynchos
Anas clypeata
Anas strepera
Aythya valisineria
Aythya americana
Aythya aff:nis
Bucephala clangula
Bucephala islandica
Bucephala albeola
Lophodytes cucullatus
Mergus merganser
Spp. ?
Haliaeetus leucocephalus
Accipiter cooperii
Fulica americana
Charadrius vociferus
Calidris mauri
Larus canus
Larus delawarensis
Larus californicus
Larus argentatus
Larus thayen
Larus glaucescens
Columba livia
7
Downy woodpecker
Hairy woodpecker
Northern Flicker
Tree swallow
Violet -green swallow
N. Rough -winged swallow
Cliff swallow
Barn swallow
American crow
Northwest crow
Black -capped chickadee
Chestnut -backed chickadee
Bushtit
Bewick's wren
Winter wren
Ruby -crowned kinglet
American robin
European starling
Yellow warbler
Yellow-nunped warbler
Common yellow throat
Wilson's warbler
Spotted towhee
Song sparrow
Golden -crowned sparrow
White -crowned sparrow
Red -winged blackbird
Brewer's blackbird
House finch
House sparrow
Picoides pubescens
Picoides villosus
Colaptes auratus
Tachycineta bicolor
Tachycineta thalassina
Stelgidopteryx ruficollis
Hirundo pyrrhonota
Hirundo rustica
Corvus brachyrhynchos
Corvus caurinus
Parus atricapillus
Parus rufescens
Psaltriparus minimus
Thryomanes bewickii
Troglodytes troglodytes
Regulus calendula
Turdus migratorius
Sturnus vulgaris
Dendroica petechia
Dendroica coronata
Geothlypis trichas
Wilsonia pusilla
Pipilo maculatus
Melospiza melodia
Zonotrichia atricapilla
Zonotrichia leucophrys
Agelaius phoeniceus
Euphagus cyanocephalus
Carpodacus mexicanus
Passer domesticus
Riparian areas also maintain the health of the stream by providing large woody debris to the stream,
creating storage for overbank flood flows, trapping sediments and pollutants, moderating temperature
extremes, and providing organic material. Even small areas of riparian zone habitat are important
to a stream's health. This important habitat has been greatly reduced on many of the Lake
Washington basin rivers as the area becomes more urban. Pressure will continue to be exerted on
riparian zone habitat as the Cedar River basin is developed. Since the riparian zone in the project area
is greatly reduced from its historical extent, the remaining riparian zone is even more valuable.
Riparian vegetation in the project area is very limited on the west or left bank, especially adjacent
to the airport. Willows, a few short alders, and a mix of non-native weedy species, mainly blackberry,
account for most of the vegetation.
The east or right bank is more diverse with scattered overstory tree species such as alder, willow, and
cottonwood. Cultivated trees such as oaks, maples, and conifers have been planted along the trail
system. These trees provide perching, nesting and foraging habitat for birds. Many bird species were
observed foraging in the trees and shrubs near the river.
A few areas contained a mix of trees, shrubs and herbaceous vegetation. These areas provide the
greatest wildlife habitat value in the area. Overhanging vegetation is limited, but furnishes a small
amount of cover for duck broods and aquatic furbearers. Grazing habitat is provided to ducks and
geese in the form of cultivated and mowed grass associated with the trail/park system.
Neotropical migrants are land birds that breed in Washington yet migrate to the neotropics, like
Mexico and Greater Antilles, during the winter. Over one half of our breeding birds are neotropical
migrants (Morton and Greenberg 1989). Passerines (perching or songbirds) make up the largest
group of these birds and include birds like flycatchers, thrushes, sparrows, waxwings, and warblers.
Many of these birds rely on the riparian areas by the river for breeding. Fifty-three percent of all
neotropical migrants are associated with these riparian areas and 67 percent of the species with
known declines use these habitats.
A recent review of Washington's neotropical migrants by Andelman and Stock (1993), supports the
need to concentrate our efforts on preserving or restoring habitats for these birds. Riparian habitats
were identified as a priority habitat for species with known population declines. Sixty-eight of the
120 bird species breeding in Washington use riparian areas. Thirty-one percent of these species are
habitat specialists and depend on only one or two habitats for breeding.
Andelman and Stock (1993) found severe long-term population declines in several of these riparian
species that include the gray catbird; the Wilson's, yellow, and orange -crowned warblers; eastern
kingbird; solitary vireo; rufous hummingbird; barn swallow; and song sparrow. They also identified
several species that are habitat specialists (i.e., use two or fewer habitats) and have localized breeding
populations. The species that use the riparian zone heavily include Vaux's swift and MacGillivray's
warbler. Andelman and Stock (1993) identified riparian zone habitat as one of the highest priority
habitats to protect.
0
Many of the plant species present are on the State noxious weed list or are extremely invasive. These
include Japanese knotweed, Himalayan blackberry, Scotch broom, reed canary grass, and morning
glory. This vegetation provides brushy areas that are the preferred habitat for some species.
However, the nature of these species dictates that aggressive control is needed to avoid displacement
of native species that are more valuable to wildlife.
Snag habitat is almost non existent which severely limits primary excavators (woodpeckers) and the
dependent cavity nesters. The downy woodpecker and hairy woodpeckers seen during the survey
were utilizing one alder snag located in the park. During the spring of 1995, nesting bird boxes were
installed on posts along the riparian zone by the local Audubon Society. These will help provide
cavity nesting habitat but are a poor substitute for actual snags.
Mammal species were not as prevalent nor as obvious. This type of habitat in other areas has
supported mammals such as raccoons, skunks, opossum, mice, rats, eastern gray squirrels, and river
otter.
FISH RESOURCES
At least 20 species of resident and anadromous fish species utilize the Cedar River including chinook,
coho, and sockeye salmon and steelhead trout. The Cedar River contributes an estimated 40 percent
of the wild fall chinook salmon to the Lake Washington Basin, 12 to 25 percent of the wild coho,
and 25 percent of the wild winter -run steelhead trout. The largest sockeye salmon run in the lower
48 states spawns in the Cedar River, including the majority (80 - 90 percent) of Lake Washington
sockeye. One of only two landlocked longfin smelt populations in North America utilizes Lake
Washington and the Cedar River (Hart 1973). Sculpins, mountain whitefish, western brook lamprey,
speckled dace, and three -spine stickleback are also found (Wydoski and Whitney 1979).
Recent studies by the Service and Corps biologists have identified 30 species of fish using the south
end of Lake Washington, the delta or project area of the Cedar River. Fish species observed during
the studies associated with the Cedar River 205 project are shown on Table 2. These fish may be
residents in the Cedar River or may reside in Lake Washington and periodically use the project reach.
Sockeye salmon are the most valuable commercial species in the Cedar. Coho and chinook salmon
have become less predominant commercial species in the Cedar due to their limited numbers in
comparison to the size of the sockeye run. Steelhead trout is a highly valued game fish in the system.
Currently, the fisheries of the Cedar River basin are managed for natural production of salmonids.
E
Table 2. Resident and anadromous fish species utilizing the Cedar River or south end of
Lake Washington as observed by Service and Corp biologist in 1994 and 1995 studies
Mountain whitefish'
Yellow perch '
Bull trout
Longfin smelt '
Dolly Varden
Lar escale sucker '
Sockeye salmon'
Northern s uawfish
Kokanee
Longnose dace '
Coastal Cutthroat trout '
Torrent scul in '
Steelhead trout '
Coast range scul in '
Rainbow trout'
Reticulated scut in '
Coho salmon'
Prickly scul in '
Chinook salmon'
Blue ill
Peamouth chub
Brown bullhead '
Smallmouth bass'
Brook lamprey
Largemouth bass '
Atlantic salmon '
Pumpkinseed '
Tench
Three-s fined stickleback'
Warmouth
' These species were actually found in the Cedar River during studies for this*Sec. 205 project.
Sockeye salmon spend one year in Lake Washington as pre-smolts before migrating through the
Ballard Locks to the ocean. They spend two years in the ocean and then return as adults to spawn.
The adults enter Lake Washington as early as July and may begin spawning as early as August. Most
spawners, however, enter the Cedar beginning in early September and continue through mid -
December with peak spawning occurring in mid -October. A few fish may be found spawning as late
as February (See Figure 3). Escapement levels to the Cedar River have ranged from 107,000 to
383,000 adults, with an average of 226,827 between 1964 and 1989.
Stober and Graybill (1974) showed that the heaviest spawning activity on the river occurs in the
higher quality habitat of the upper and middle river reaches above RM 5.3. The largest
concentrations of spawners were consistently observed above RM 11.5. The lower reach below RM
5.3 was the least utilized section of the river. Stober (1975) found no spawners below RM 5.3 during
spawner counts of the same study area.
Stober and Graybill (1974) also discovered that the early spawners used the upper accessible reaches
of the Cedar while the later spawners used the middle and then the lower reach toward the end of the
spawning period. This trend seems to be apparent during the December 1994 spawning survey in
which twenty-eight (28) redds were located below the south Boeing bridge (See Table 3).
10
Sockeye
Spawning
Incubation
Emergence
Fall Chinook
Spawning
Spring Chinook
Holding
Spawning
Coho
Spawning
Winter Steelhead
Spawning
Holding
Summer Steelhead
Holding
Spawning
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
Shoulder LLLJ Peak
Figure 3 Cedar River Salmon and Steelhead Periodicity Chart (from Cedar River
IFIM, Seattle Water Department October 1991)
Table 3. Sockeye salmon redds observed in the lower Cedar River,
1994 and 1995
Segment
Nov. 1
Nov. 16
Dec. 12
Nov. 3
1994
1994
1994
1995
Wells Avenue bridge to William Avenue bridge
53
100
NS*
53
(RP 18)
William Avenue bridge to RP 16 (just below Logan
99
285
61
133
Avenue bridge)
.......... ...........__
.......
RP 16. 1 : 4 ;:.:;.>::::.:::::.::
,. _
__........
_ _ __ _
_
..._... ........_
_........... .....
.....
Re% ::m er �4 # S. B „' edge ..:�..:
<.
2
4Q ::
3
.... ......... ........... ....... _........ ......._ .
B d iv to the xn th ol€`Ic6wl Ri
_...._ ....:......_
11
.__ ................
1;
.
Total redds for surveys area
158
461
151
267
__..... ......... _.......................... ....... ......... _
T, r dds wiihtn ro t' 3aai z�rie
__. __._ .. .............
6
6
90
181
* Not Surveyed
Sockeye spawning surveys were completed by the Corps biologists in 1994 and 1995 from the mouth
of the Cedar River up to Wells Avenue. The highest single survey count for 1994 was the four
11
hundred thirty-two (432) redds located on November 16, 1994. Most of these redds were located
between the Wells Avenue bridge and just below the Logan Avenue bridge. Seventy six (76) of these
redds were located in the proposed project section below reference point (RP) 16 near the Logan
Avenue Bridge. Redds observed downstream of the Logan Avenue bridge were confined to the
rile -like areas along the left bank. Only one survey was completed in 1995 (November 3), due to
high water and poor observation conditions. In the 1995 survey, eighty-one (81) redds were within
the proposed dredging area located downstream of RP 16. The results of these two years indicate
a significant usage of the lower Cedar by sockeye salmon. A more extensive discussion of the
spawning surveys can be found under the Habitat Survey/Studies section.
The lower section, from RP 14 to the mouth, is characterized by deeper water and slower velocities.
This type of habitat was not being used by sockeye salmon for spawning. Upstream in the area where
spawning was concentrated, the water is faster and more shallow. Observations during the spawning
survey indicated that redds were being constructed in less than 2 feet of water with obvious velocity.
This corresponds to documented preferred spawning habitat for sockeye in streams. Reiser and
Bjornn, (1979) report sockeye salmon preferences for spawning velocities of 4 - 21 feet per second
(fps) and depths of Z6 inches. Velocities and depths in this range were measured over redds by
Chambers et al. (1955. cited in Reiser and Bjornn 1979). These measurements indicated a velocity
of 11 fps over each redd with depths from 12 - 18 inches. These values fall within the depth and
velocity preference curves developed by the Cedar River Committee Curve Report (Seattle Water
Department 1991).
In recent years there has been a significant downward trend of the sockeye salmon population. In
1988, the total run size to the Lake Washington/Cedar River basin was the largest on record with an
estimated 640,000 adult fish. About 376,000 adults escaped to spawn in the Cedar River that year.
Since 1988, escapement to the Cedar has declined dramatically with escapement estimates in the
range of 38 percent to 44 percent of the pre-1989 26-year historic average, and with no indications
that this trend will change. The 1992 Washington State salmon and steelhead stock inventory
(WDFW 1992) fisted this population as "depressed".
The escapement for 1996 was an exception to this downward trend and was large enough to support
a Lake Washington fishing season for sockeye (See Figure 4). Approximately 500,000 adult sockeye
returned to the Lake Washington basin during the summer of 1996. A combination of a high fry
count entering the lake and excellent ocean feeding conditions is credited with this record run. Over
28 million fry entered the lake from this year class. Whether this is an upward trend is very much
open for conjecture. With the exception of this year class, the overall trend is still downward. The
26,000 sockeye escapement in 1995 was the lowest since at least 1970. It is most likely that the 1996
escapement is an aberration common to anadromous fish populations. The escapement goal for the
Cedar River is 350,000 adult spawners.
12
Cedar River Sockeye Escapments
500000
400000
300000
0
0
E200000
z
100000
1990 1991 1992 1993 1994 1995 1996
Year
Figure 4
For the last several years, there have been emergency efforts to ensure that the sockeye salmon run
of the Cedar will not drop to critical levels. The emergency measures involve collecting sockeye
salmon eggs from captured brood stock in the fall, incubating the eggs to the emergent fry stage, and
releasing the newly emerged fry back to the Cedar River in the spring during the normal out -
migration period. Research to identify the cause of the sockeye decline has recently begun. In 1994,
the first of several multi -year studies of Lake Washington was initiated to test various hypotheses for
the decline. These studies are focused on Lake Washington because the smolt population that rears
in the lake has experienced dramatic declines.
The Lake Washington basin study program involves financial and/or other resource commitments
from many entities such as state and federal agencies, local and county governments, Lake
Washington municipalities, tribes, industry, and the University of Washington. Approximately $1.6
million will be spent to support this effort.
There are resident cutthroat trout populations in many of the tributaries of the Cedar as well as an
adfluvial (migratory lake population) spawning run. Although little is known about anadromous
cutthroat trout and Dolly Varden, these species probably use the project area for transportation to
higher quality spawning habitat upstream. Juvenile rearing may occur in the project reach, but is very
limited. Pfeifer(1993) indicated that there has been a marked increase in spawning cutthroat in Cedar
River tributaries in the past few years. With the exception of wild cutthroat trout however, all species
of wild anadromous salmonids returning to the entire Lake Washington basin have experienced record
low escapement levels since 1989 (Figure 5).
Adult chinook enter Lake Washington in June and continue entering through October (See Figure
3). Spawning in the Cedar River occurs from mid -September through mid -December. Intragravel
development extends into early March. Chinook rear in the Cedar until fingerling size and out
migrate from May through July. No known chinook spawning occurs in or near the project area.
13
Utilization of the project area is primarily for transportation with some possible, although limited,
rearing for juveniles.
Coho spawning occurs predominantly in the small tributaries of the Cedar River, although some
probably occurs in the mainstem, from mid -October through February. Coho rear in the Cedar River
one year before migrating out from March through June. Similar to chinook, use of the project area
is largely for transportation and limited rearing.
The wild winter run of adult steelhead enters Lake Washington between mid -December and mid -May
with a peak during late January through early February. Peak spawning in the river can vary from
year to year, but generally begins in mid -March and continues into mid -June with a peak during mid -
April to mid -May. Spawning of most wild steelhead in the Cedar occurs from RM 1.6 to 21.8 with
spawning densities being relatively uniform from RM 5.2 to 21.8. The project area is used by
steelhead primarily for transportation, although some limited rearing may occur. A stream -side
steelhead culture program using captured wild brood stock provides 40,000 to 80,000 fry that are
planted in the Cedar annually. Predation by California sea lions has caused an estimated 50 percent
mortality on the returning winter run of Lake Washington bound wild steelhead.
Healthy populations of bull trout, a federally listed candidate species, are known to occur in the upper
Cedar River watershed above Masonry Dam (RM 35.9). It is unknown whether bull trout reside in
the reach between Landsburg Dam (RM 21.8) and Masonry Dam (RM 35.9). A char was recently
caught off of the mouth of the Cedar in Lake Washington. This may have been a Dolly Varden or
a bull trout. Fluvial populations of bull trout are not uncommon in adjacent drainages. It is possible
that bull trout could use the project reach during their spawning migration. However, poor water
quality and habitat conditions in the lower river make it unlikely that the project reach is used
extensively by bull trout.
Longfin smelt are a key species in the Lake Washington fish community and the species which is
likely to be affected to the greatest extent by the proposed project. They may compete with juvenile
sockeye for the same food resources in the lake (Chigbu and Sibley 1992). This may have
contributed to the decline of the sockeye population. Other information shows a concurrent
population expansion of longfin smelt and sockeye during the mid 1960s (Edmondson and Abella
1988). This would indicate that at most, the competition causes an indirect effect on population.
However, longfin smelt may also serve to buffer predator effects on juvenile sockeye.
Longfin smelt have played an important role in the increase in water clarity in the lake (Edmondson
and Abella 1988). Daphnia, a small crustacean, eat small particles that make the water cloudy. The
major predator on Daphnia was another small crustacean, Neomysis. Neomysis is a major prey
species for longfin smelt. When smelt started to increase in abundance, the Daphnia population
increased. This caused a corresponding decrease in the particles that caused turbidity in the lake.
14
O
CL o
� � O
y
(0
O
0
9�
y
O
w �
(� tz
(D
CD �
CAD ]
� a
w
C
O C
�D CCD
W CL
Sockeye Escapement
Lake Washington
400000
350000
r 300000
250000
e
200000
E 150000
z 100000
50000
0
1970 1974 1978 1982 1986 1990 1994
Return Year
1400
1200
w 1000
LL
`0 800
600
E
400
z
200
0
1982
Steelhead Escapement
Cedar River
Steelhead
—x EsoapementGoal 257
1984 1 1988 1
1986 1990
Return Year
18000
14000
M 12000
F 10000
8000
e
Bon
Z 4000
2000
0
Chinook Escapement
Lake Washington
11 —0— EscapementO al5T200
1970 1974 1978 1982 1986 1990 1994
Return Year
Coho Escapement
Lake Washington
30000
Coho
L 25000 ♦ Escapment goal 15,000
LL 20000
G 15000
a
E 10000
z
5000 ----
1992 � °
1972 1 1976 1960 1 1984 1 1988 1 1992
1970 1974 1978 1982 1986 1990
Return Year
Approximately 98 percent (Sibley and Brocksmith 1996a) of Cedar River longfin smelt spawn within
0.6 kilometers (km) of the mouth of the Cedar River. This is completely within the proposed project
reach. The Sibley study found smelt beginning to spawn as early as January 13 in 1993 and as late
as May 18 in 1994. Distribution of smelt in the entire Lake Washington basin indicates that the
Cedar River is used as the main spawning area. Surveys for smelt in other Lake Washington
tributaries were completed in 1970 (Moulton 1970), 1995 (Sibley and Brocksmith 1996a), and 1996
(Martz et al 1996). Results are shown in Table 4.
Table 4. Smelt egg distribution in Lake Washington tributaries.
Year of
Survey
May
Creek
Coal
Creek
Juanita
Creek
Denny
Creek
Swamp
Creek
Lyon
Creek
McAleer
Creek
Thornton
Creek
1970
+
+
+
—
—
—
—
—
1995
+
+
1996
+
+
+
—
—
—
+
—
+ indicates presence of eggs, - indicates absence
Moulton (1974) observed that these fish exhibited a 2-year life cycle with even -numbered year classes
being more abundant and showing a lower growth rate than the odd. He also reported that the Cedar
River was the major spawning area and that the larger adults of the odd year -class spawn earlier in
the year than the smaller adults of the even year -class. Spawning by longfin smelt takes place in
freshwater over sandy -gravel substrates, rocks, and aquatic plants. Most longfin smelt die after
spawning but a few live to spawn a second year (McGinnis 1984). The accumulated substrate
materials of sand and gravel and relatively wide, weedy, shallow areas of the dredged channel in the
lower 1.6 miles of the Cedar River have created good spawning habitat for smelt.
Nishimoto (1973) reported that small numbers of peamouth chub spawn in Lake Washington
tributaries, although he found no direct evidence of peamouth spawning in the lower Cedar River.
Spawning likely occurs from late March through June when mature fish begin to migrate inshore
during spring. Spawning peamouth show greater preference for sandy or gravelly substrates. This
substrate constitutes most of the bottom materials in the project area. In June and July, Tabor (1996
personal communication) caught numerous peamouth in the lower river during studies in 1995.
Presumably these fish were spawning at that time.
Largescale suckers also feed or spawn within or near the project reach. They have been observed
congregating and spawning upstream of the Logan Avenue bridge. These fish usually move upstream
from lakes or impoundments into streams where they seek out gravel riffles with a strong current.
Sucker fry and fingerlings serve as important forage for many game fishes. On the other hand, the
dense populations of suckers characteristic of many impoundments can be detrimental to the
production of some salmonids. Largescale suckers have been observed in the project reach by
Service and Corps biologists.
16
Tabor (1996 personal communication) also observed several brook lamprey in the lower Cedar on
May 18, 1995. Two pair of these lampreys appeared to be actively spawning.
THREATENED AND ENDANGERED SPECIES
Bald eagles are known to occur in the vicinity of the project area. Prior to the 1994 dredging, they
used the Cedar River delta for foraging (primarily on waterfowl and possibly salmon carcasses). The
WDFW reported the occurrence of three adult and two juvenile bald eagles during mid -winter surveys
of the Cedar River in 1989. A bald eagle was observed in the Gene Coulan Park area in the
southeastern corner of Lake Washington in March of 1992. During October and November in 1991
and 1992, Service biologists observed an occasional bald eagle along the Cedar. In addition, over
several weeks of brood stock collection of adult sockeye during October and November in 1991 and
1992, Service biologists observed an occasional bald eagle along the Cedar. An adult bald eagle was
observed on September 19, 1995 flying upstream from the mouth of the Cedar River. The nearest
known nesting pair of bald eagles occurs about 3 miles from the project at Seward Park on the west
shoreline of Lake Washington.
The latest species list (USFWS 1996) obtained from the Service for this project was in August 1996.
As of that date no listed or proposed species occurred within the project area on a permanent basis.
Candidate species that may occur within the project area include the bull trout and the spotted frog.
Species of concern include three bat species (long-eared, long-legged, and Pacific western big -eared),
Northwestern pond turtles, olive -sided flycatchers and river lamprey.
Section 7(a)(2) of the Endangered Species Act of 1973, as amended, requires federal agencies to
consult with the Service when a federal action may affect a listed endangered or threatened species.
This is to ensure that any action authorized, funded, or carried out by the federal agency is not likely
to jeopardize the continued existence of listed species or result in the destruction or adverse
modification of critical habitat.
A biological assessment was written by the Corps on November 13, 1996. The determination was
that this project as proposed is "not likely to adversely affect" any listed species. The Service wrote
a letter of concurrence with that determination on December 11, 1996 through the informal
consultation process. If the project or conditions at the site change significantly, the Corps should
re -initiate Section 7 consultation through this office.
The northwestern pond turtle, Clemmys marmorata marmorata, is a federal species of concern and
has been found in Lake Washington historically. It is also listed as endangered by the State of
Washington. The WDFW has contracted with a private consultant to survey Lake Washington for
northwestern pond turtles (Slavin 1996). To date no northwestern pond turtles have been located.
However, only one small area of Lake Washington has been surveyed. The surveyed area is at the
Lakewood Marina and is several miles from the Cedar River. The turtles that have been found have
been exotics, probably dumped into the lake by pet owners. Surveys during future years may be
17
focused on the Cedar River and south Lake Washington. This will provide additional information
about the turtle population of the lake.
Service biologists, working on the predator study, observed turtles on several occasions in the project
reach of the river. They captured and photographed one of these turtles and tentatively identified it
as a red -eared slider, a non-native species that was probably a discarded pet. However, all of the
observed turtles were not identified to species. It is possible that there may have been northwestern
pond turtles in the project area.
STUDY RESULTS
Due to the significant fish and wildlife resources at risk, and the gaps in the information on how these
resources utilize the project reach, the Service recommended several studies to determine baseline
conditions of fish and wildlife resources, evaluate potential impacts, and identify potential mitigation
opportunities. In the following section, we will summarize the results of each study.
The concerns that were identified during the early scoping for this project primarily focused on the
potential impacts on the fishery resources of the Cedar River. The main concern was the potential
impacts of the project on spawning habitat and distribution of both sockeye and longfin smelt. Other
concerns included predation on sockeye salmon fry, migration delay due to slower water velocity, and
effects on macro invertebrates within the project reach.
The results in each of these studies are based on very limited data. The Service believes the studies
were not extended over a sufficient time span to yield definitive results. At most, three years of data
is available and in most cases only two years of data is available. Because of poor weather
conditions, problems with equipment, and problems with methods several of the important studies
were not completed as designed. The results and conclusions should therefore be used with caution.
WILDLIFE STUDY
The effect of the project on bird species was the main focus for wildlife studies. Bird surveys were
discussed above in the general section on Fish and Wildlife Resources. On February 1, 1996, Corps
biologists (Brunner 1996) completed a night avian predator study from the fry trap on the lower
Cedar River down to mouth and out into the lake just past the delta. The objective was to provide
some quantitative estimate of piscivorous birds that may be drawn to the area due to the emigration
of sockeye fry. This date was chosen to coincide with an earlier release of hatchery sockeye fry
which should have been reaching the delta at about the same time period as the surveys. Mallards,
coots, and gulls were roosting on the logs at the delta and grebes were widely scattered around the
lake when the survey began at 1915 hours. Grebes abruptly flew to the mouth just after 2000 hours
and were all actively feeding by 2005 hours. This was about 1 hour after the peak fry migration past
the fry trap which is about '/g mile upstream from the mouth. By about 2030 the grebes began
dispersing to other parts of the lake. It would be hard not to make some type of connection between
the out migrating sockeye fry and the abrupt feeding behavior of the western grebes. Although
predation on sockeye smelt is a normal part of the grebes feeding pattern, the migration to the mouth
during the out -planting of sockeye fry may have a significant impact on sockeye populations.
Additional surveys of this type, coincident with fry releases, should be considered to determine what
effects if any western grebes may have on sockeye releases.
Other bird species that were feeding in the area, including great blue heron and mergansers, did not
alter behavior in any noticeable way during this same time period. Herons were feeding on the delta
through this entire time period and were assumed to be feeding on longfin smelt. Mergansers were
in the area and were observed actively feeding during this period.
Artificial fight had been previously assumed to be much greater than normal due to the Boeing plant
and the Renton airport, thus providing predators better light conditions for hunting. Although there
did seem to be brighter conditions than normal along the river, the light dimmed beyond
approximately 100 feet from shore in the lake. This additional light did not seem to be influencing
where the birds were feeding. Western grebes have been observed feeding in situations with less light
than in the project area.
Mi:731f7:welicl1liJ-M
Potential impacts to sockeye salmon that were identified were mostly focused on increased predation
on sockeye fry during their downstream migration and a loss of spawning habitat within the project
reach. The first year of predator studies was completed by Service biologists and published in May
1996. The last year of this study was published in November 1996.
The 1995 data indicated that the highest density of piscivorous fish and the highest predation rates
occur in the lower 600 meters of the Cedar River (Tabor and Chan 1996a). Additional data from
1996 indicated that the vast majority of predation was occurring in the lower 440 meters (Tabor and
Chan 1996b). This section is generally backwater from Lake Washington. The only other location
where predation of fry was detected was in a backwater eddy near the south Boeing bridge.
Prickly sculpin appeared to be the most important predator of sockeye salmon fry because of their
abundance, their high consumption rate of fry, and their larger size. Torrent sculpin also had
relatively high consumption rates of fry but were less abundant than prickly sculpin. Prickly sculpin
have a strong preference for the areas of least velocity and greatest average depth. Several studies
(Tabor and Chan 1996b) confirm this preference for lower velocity and deeper water. This type of
habitat corresponds significantly with the post project habitat conditions anticipated by the dredging
alternatives.
In 1995, cutthroat trout seemed to be significant predators as indicated by the highest number of
salmonid fry recovered from stomach samples (Tabor and Chan 1996a). Rainbow trout, steelhead
smolts, coho salmon, and prickly sculpin also appear to be major predators of salmonid fry in the
19
lower Cedar River. The abundance of predators was relatively small until after the peak fry
emigration period. Predation in the littoral zone of southern Lake Washington was low. Cutthroat
once again exhibited the highest predation rate. In addition to the predators in the river, smallmouth
bass showed up as predators in the lake. In 1996, the salmonid populations in the lower river were
significantly lower than the previous year (Tabor and Chan 1996b). This was thought to be due to
the flooding earlier in the year.
Lonzarich and Quinn (1995, cited in Tabor and Chan 1996a) found that water depth seemed to be
more important than structure in determining the distribution of large age 1+ cutthroat and steelhead
trout while structure and depth were important for coho salmon smolt distribution. Since cutthroat
trout are the main predators in the river, the increase in depth by dredging would seem to favor an
increase in cutthroat. Obviously, other factors besides depth enter into the potential for predation.
Channel configuration, for example, might increase or decrease predator populations. Information
is not available to make this determination.
Predation rates appeared to be related to discharge levels. Low predation rates were observed at >
17m3s. Seiler and Kishimoto (1996, cited in Tabor and Chan 1996b) found that survival rates of
hatchery sockeye salmon fry were positively correlated with discharge. Survival rates for a discharge
of lOm3s would be predicted at around 23 percent, whereas a 17m3s discharge would show a survival
rate of around 44 percent. This correlation may be tied to the increased turbidity found during higher
discharges.
Difficulty with weather, equipment availability and performance limited the population estimates
somewhat. However, based on the 1995 data, there did not seem to be obvious movement by
predators to the mouth of the Cedar River during the sockeye fry emigration. The number of
piscivorous fish did seem to increase after the peak emigration season (May - June). This trend was
also seen in the data collected in 1996 (Tabor and Chan 1996b). Therefore any impacts would be
concentrated on the late -emerging part of the sockeye population.
LONGFIN SMELT STUDY
Smelt seem to occupy a "keystone" position in Lake Washington. The population size of the longfin
smelt and their interaction with other river and lake species seems to be implicated in water clarity,
zooplankton species diversity, competition with sockeye salmon for food resources, and as a prey
base for fish predators. Several investigators have looked at the feeding habits and interactions of
longfin smelt and sockeye salmon in Lake Washington (Chigbu and Sibley 1992) (Dryfoos 1965)
(Edmondson and Abella 1988) (Moulton 1970) (Moulton 1974). Concerns about possible effects
to smelt populations include changes in spawning substrate, changes to food sources, and increases
or decreases in actual populations. The smelt food base is also a concern as it is related to possible
competition with sockeye salmon.
An abbreviated study was conducted on Lake Washington for two years that included one high
population year and one low population year. Year one of a two year study was completed by Sibley
20
and Brocksmith in April of 1996. The first year study seemed to verify previous reports that indicate
that the even year classes are an order of magnitude larger than the odd year classes. Preferred
substrate experiments were conducted in artificial streams at the Fisheries Research Institute and
Seward Park hatchery. There seemed to be a slight correlation with sand sized particles but the
results in this test may have been biased due to the experimental design. Results from field testing
showed no apparent correlation with substrate size, water depth or water velocity. Harza (1994) also
showed no correlation between particle size, water depth or water velocity. These results are not
supported by other studies involving baitfish and substrate preference. Other smelt species have a
definite preference for a sand/gravel substrate (Fresh 1996). Longfin smelt in California use a
sand/gravel substrate in weedy areas for spawning.
Longfin smelt are poor swimmers and seem to avoid high velocities. This may be one of the reasons
smelt are found in diminishing numbers above the south Boeing bridge. There also seems to be an
inverse correlation to spawning smelt and distance from the mouth of the river. This could be
explained by one of several avoidance mechanisms. Larger substrate size, shallower water and higher
velocities are found in the reach above Logan Avenue. Smelt may be avoiding any one of or a
combination of these habitat components. Another explanation for the decrease in upstream numbers
could simply be distance from the lake. Harza (1994) implied this relationship in their report to the
Corps.
The second year of the two year study was completed by Corps personnel (Martz et al 1996). This
study showed a significant negative correlation between egg abundance and substrate size. It also
confirmed the negative correlations between egg abundance and velocity and distance upstream found
in previous studies.
Earlier reports indicated that the "majority" of smelt spawned in the lower Cedar River. Sibley and
Brocksmith (1996a) sampled 9 other tributaries in addition to the Cedar River to determine if smelt
eggs were present. Eggs were found in May Creek and Coal Creek in very small numbers (See Table
4). The Corps (raw data 1996) found eggs in these two tributaries and additionally in Juanita and
McAleer Creeks. Overall 98 percent of the eggs found in the Cedar were in the lower 600 meters
(Sibley and Brocksmith 1996a).
HABITAT STUDY/SURVEY
The second year of a habitat inventory to determine the quantity and quality of salmonid habitat
within the project reach has been completed using the State's Timber, Fish and Wildlife methodology
(Martz 1996). The percentage of riffle habitat in the lower one mile of Cedar River is quite high, as
expected. Around 77 percent is riffle, 2 percent is pool habitat and 20 percent is lake backwater.
Pools are largely bank scour pools along the banks near Logan Avenue and the south Boeing bridge.
Fine sediment is dominant along the bank areas. Gravel and cobble comprise most of the main
channel. This grades into small gravels towards the mouth with deposition of sand and silt during low
flow. Armoring occurs during the spring and summer, making many sections of the main channel
21
too hard for sockeye spawning. Overhanging vegetation is found on only 25 percent of the banks,
with several 15-20 year old cottonwoods and alders on each side above the south Boeing bridge.
Low flow water depth is shallow (<6 inches) in much of the reach between Logan Avenue and the
south Boeing bridge. This often causes the water to heat up significantly with estimates of water
temperature > 21 ° C. Warmer water and shallow depths may delay the upstream migration of
sockeye adults until the release of flows from the dam in early September.
SOCKEYE SALMON SPAWNING SURVEY
Two years of spawning surveys have been completed by Corps biologists. Service personnel assisted
in two of the surveys during the 1994 and 1995 spawning seasons. Results are summarized in Table
3 for 1994 and 1995. The high water and associated turbidity prevented complete surveys on several
days of both seasons but the remaining surveys were completed from the just above the Wells Avenue
bridge to the mouth. Combinations of visual wading surveys and snorkel surveys were used to gather
data over this entire reach. The majority of the redds were above reference point 15 (1,500 meters)
and concentrated along the bank edges. With exception of the December 12, 1995 survey, there were
never more than 4 redds downstream of the south Boeing bridge during any survey. Assuming that
all redds observed were distinct (with no double -counting between surveys) and had been spawned
in, a maximum of 1 percent of the overall sockeye run spawns in the project reach.
FISH UTILIZATION STUDIES
Daytime and night time snorkeling surveys were conducted to assess fish use of the project reach and
related side channels. Corps biologists completed several snorkel surveys from July to September
1995. In the lower mile of the river the only fish observed were rainbow and cutthroat trout, large-
scale suckers, mountain whitefish, sculpins, and yellow perch. By the last survey in September, adult
sockeye and chinook salmon were appearing in the river. Sculpin and mountain whitefish were the
most common. Yellow perch were only observed in the lake backwater and only in small numbers
(<10). Crayfish were also observed during the snorkle surveys.
An assessment of the impacts of the proposed project on downstream juvenile migration was
recommended by the Service. This assessment has not been initiated due to difficulty correlating
flows from upstream dams with the City of Seattle. This type of information is still needed to
compare the pre- and post -project migration rate for sockeye salmon. Impacts due to increased
migration times can not adequately be assessed without this type of information. This should be
considered in the mitigation planning for this project.
AQUATIC INVERTEBRATE STUDY
This study (Sibley and Brocksmith 1996b) was completed in 1996 from field work done in 1995. For
the most part, the aquatic invertebrate populations were found in the expected velocity and substrate
22
type. There were some exceptions but these could be explained by sampling size, sampling design,
or seasonal variation. Chironomids where the most abundant taxa at all sites during all seasons. They
did seem to show less abundance at the lower sites but were still more abundant than other taxa.
Ephemeroptera, Plecoptera, and Tricoptera overall were more abundant in the upper reaches in higher
velocity water as would be expected. Oligochaetes were more common in the lower reaches in lower
velocity water. There did seem to be a positive correlation between water velocity and both taxa
richness and taxa diversity although this correlation was not consistent. This is generally the situation
found in other studies.
The discussion of effects on the aquatic invertebrates concluded that dredging of the project area
would have an extensive effect. A similar project but with a shallower dredge showed that up to 92
percent of the bottom organisms were removed in the dredged area (Rees 1959 cited in Sibley and
Brocksmith 1996b). Recovery of all types of insects originally present occurred within 10 months.
Macro invertebrate population size may take much longer to rebound. In the Cedar River, the effect
due to a deeper proposed dredging will be greater but recolonization should still be fairly rapid. The
total impact to the food web in the Cedar River should be minimal due to the 14 miles of assessable
anadromous fish habitat above the project area.
FUTURE WITHOUT THE PROJECT
Based on sediment transport modeling completed by the Corps, the lower Cedar River is aggrading
at about 0.2 feet per year measured at the south Boeing bridge. This rate of deposition will fill the
channel within 20 years to such an extent that most winter flows will flood the Renton airport and
other low lying areas.
This deposition of sediment will create a wide very shallow stream with minimal habitat value for fish.
Longfin smelt spawning habitat will most likely be severely reduced compared to current conditions.
Sockeye spawning habitat may increase in the short term as the higher velocity shallow habitat moves
downstream. The quality of this habitat and its length of availability depends on the resultant depth
of water and the velocity over the gravel. Armoring of the substrate is likely to occur which would
cause any potential spawning gravels to be cemented and too compacted to be usable.
Due to the heavy urbanization and industrial base along the project reach, flooding on a yearly basis
would cause significant economic hardship. If the Corps would decide not to pursue this project it
is likely that other concerned entities would look into alternative solutions to the flooding problem.
As the local sponsor for this proposed project, the city of Renton would most likely be involved in
other alternatives.
23
POTENTIAL PROJECT IMPACTS TO FISH AND WILDLIFE RESOURCES
Under the proposed alternatives, direct project effects on fish and wildlife species and their habitats
may be both short-term and long-term. Short term impacts may be on the order of one or two
seasons and primarily the result of construction activities. An increase in turbidity and sediment will
occur during the actual dredging work. The actual dredging will be limited to between June 15 and
August 15. This will minimize the impact on sockeye salmon and other anadromous fish. Depending
on the severity of the sediment increase, fish and other aquatic dependent species could be displaced
from the project area.
Disturbances to the spawning gravels above Logan Avenue could cause scouring of redds during the
first winter storms. It could also cause deposition of sediment on top of these redds. Any impacts
on the fish populations in the project reach could cause a ripple effect within the food chain by
decreasing the food source or by increased predation on other species within the basin. The sloping
of the gradient above Logan Avenue should minimize this effect. But, there may be a significant
adjustment of the stream channel during the first winter high flows.
These changes may also cause impacts over an extended period. Effects to fish and wildlife resources
would vary in magnitude, primarily according to the sensitivity of the species impacted and how
important a role it serves in the function of the lake and lower river ecology. Shifts in species
distribution and use patterns may be expected from direct habitat modifications, which could cause
immediate or long-term ecological changes in the lower river.
Long term impacts may result due to permanent habitat losses or degradation. Depending on which
alternative is chosen these effects will vary in significance.
Each of the "dredge" alternatives and the "no -dredge" alternative have levees associated with them.
Short term impacts will be related to sediment from surface erosion on the newly constructed levees
and berms. Intensive revegetation should restrict this impact to one season. Long-term aquatic
effects from the levees should be minimal as long as best management practices are followed to
prevent sedimentation and other disturbances of the stream course.
IMPACTS TO WILDLIFE
Direct impacts to terrestrial wildlife species and habitats will be largely related to the loss of riparian
zone habitat and associated shallow water habitats along both shorelines. Loss of shallow water
habitats would directly affect foraging for wading birds such as great blue herons, and feeding
dabbling ducks such as mallards. Various gulls may also be displaced as well as fish -eating birds like
belted kingfishers, which generally forage in water that is less than 24 inches deep.
The loss of existing vegetation could also preclude duck nesting and rearing of duck broods,
particularly for mallards and common mergansers, which currently utilize herbaceous and overhanging
24
vegetation for nesting and cover, respectively. The current alternatives minimize streambank
disturbance. Plant materials will be salvaged from the left bank and reused as much as possible. This
will reduce the impact to the shrub layer but it will still take several years for a dense herbaceous layer
to develop.
River otter and raccoons are species that often forage among the stream side vegetation or along the
irregular and diverse shorelines of streams and creeks. These species could be displaced permanently
if riparian vegetation is eliminated or if the project results in decreased diversity in shoreline
configuration or a decrease in total edge habitat. With a change to a predominantly silt bottom in the
project reach, there will be fewer niches for prey species such as invertebrates and small fish. A
change in the prey base may indirectly affect small mammals.
The impacts to many of the neotropical bird species may be significant in all of the alternatives due
to the construction of levees on the river banks. These levees may eliminate much of the overstory
and shrub habitat currently being used for nesting and foraging by birds in the area. This riparian
zone habitat can be partially restored over time, but even with immediate revegetation, it will be
several decades before the overstory canopy is reestablished. Replanting by using a diverse mix of
native species should increase the habitat diversity of the area. A long-term benefit to terrestrial
wildlife should be realized due to the increased width of native vegetation along the stream. Removal
and control of the non-native invasive plant species adjacent to the river course should enhance this
benefit to native wildlife species.
IMPACTS TO AQUATIC RESOURCES
No Action
There is no dredging in this alternative and it should not change sockeye or longfin smelt spawning
habitat in the near term. However, with the continual deposition of sediment in this reach, spawning
may be precluded due to a lack of suitable habitat in the future. Sediment modeling done by the
Corps indicates that within 20 years, the lower reach will be so aggraded that most winter flows will
flood adjacent low-lying land. Within the Cedar River channel this may create more spawning habitat
for sockeye salmon if depths and velocities are within the preferred parameters. Longfin smelt habitat
may be reduced if preferred habitat parameters are lost.
Alternative 1 - Levee construction and maintenance dredging only.
There is minimal dredging with this alternative. Dredging will be only to create a uniform channel
to the depth of the present thalweg. Sockeye or longfin smelt spawning habitat should not be
significantly changed except for some minor channel adjustment which could degrade habitat
somewhat. Predation on sockeye fiy should not increase significantly with this alternative. Also the
impacts on aquatic invertebrates should be minor.
25
Alternative 2 - Shallow Dredging (<_ 4') The Service's preferred alternative.
We believe that this alternative best protects fish and wildlife resources while still providing flood
protection for the lower Cedar River corridor. The known impacts have been avoided or mitigated
as much as possible. Detailed mitigation plans have yet to be finalized but the Corps seems willing
to work cooperatively with the resource agencies to reach final resolution.
The dredging will slope the bottom gradient to meet the present gradient about 400 yards above
Logan Avenue. In this alternative, the potential spawning area for at least 90 pairs of sockeye salmon
will be disturbed (see Table 3). Most of this spawning habitat should be available after the dredging
but may be affected due to the adjustment of the stream channel during the first winter high flows.
With less depth to the dredging the gravel deposition in the lower reach should begin providing some
minimal sockeye spawning after the first major winter storm.
Other concerns within the dredged area include the potential for increased predation on sockeye fry
as they migrate downstream to the lake. The slower velocities resulting from this shallow dredging
will increase the time needed for the fry to move through the project area and will make them more
vulnerable to predation. Tabor and Chan (1996) documented several fish species that preyed on
sockeye fry during the outmigration period.
Assuming that longfin smelt actually have a preference for lower velocity as implied in the smelt
studies, then this alternative should increase available smelt spawning habitat. The first year after
dredging the habitat may have reduced value for smelt spawning due to channel readjustment. The
actual impact of this is unknown. Also it is expected that finer sediment may settle out below Logan
Avenue and create a sand and mud substrate. Winter flows should flush this finer material out but
with the increased depth of the channel, velocity will be slower. This may prevent this flushing action
and reduce the success of smelt spawning.
Aquatic invertebrates make up one of the major food sources for fish within the project reach. This
shallow dredge option will change the velocity and substrate that largely determine the invertebrate
populations. The dredging process will displace or kill most of the resident invertebrates and will
cause a zone depauperate of aquatic invertebrates for several weeks to months depending on the
species and the specific rate of recolonization. Species which prefer faster, more turbulent water such
as mayflies, stoneflies and caddisflies will be eliminated or greatly reduced. Recolonization by these
species may be delayed until velocity and substrate within the project reach return to pre -disturbance
level. In order to maintain flood control under this alternative, dredging will be more frequent and
it is unlikely that habitat for these macro invertebrates will be replaced to the same extent as present.
On the other hand, species that prefer slow velocity and fine substrate material, such as oligochaets
and most chironomids, should increase due to the increase in available habitat. Initially this group of
invertebrates will also be eliminated or reduced because of the dredging operation. Recolonization
should occur, assuming that these species exist upstream of the project area.
W
Alternative 3 - Moderate Dredging (6).
The moderate dredging depths proposed in alternative 3 may significantly change habitat values. The
impacts will be similar to those in alternative 2 but will vary in severity depending on the species
group under discussion.
The moderate dredging up to the south Boeing bridge will create the potential for greater movement
of the channel after the first major winter storm events. This may reduce habitat values for sockeye
in the project reach. Deeper water will reduce velocities and subsequently the substrate size. This will
reduce the suitability of the habitat for sockeye spawning. The effect on sockeye spawning will be
greater and will last longer. Gravel movement into the area will be gradual (depending on yearly high
flows) and will take several years to approach pre -project levels. The even slower velocities
expected with this alternative will increase the time the sockeye fry are exposed to predation in the
lower river and may decrease the number entering the lake compared to pre -project levels.
This alternative may create habitat more suitable for longfin smelt. The backwater, low velocity areas
preferred by the smelt for spawning should increase under this alternative.
Effects to aquatic invertebrates will be much like those in alternative 2. The recolonization of the
area by mayflies, stoneflies and caddisflies will take longer. Oligochaets and most chironomids should
increase due to the increase in available habitat.
Alternative 4
The deep dredging with this alternative has the potential for significant impacts to all species and
could affect habitat values even outside the immediate project area. The Corps' assessment of this
alternative indicates that the deep dredging would increase the rate of deposition and could cause
dredging to be necessary even more frequently than in alternatives 2 and 3.
Edmondson and Abella (1988) suggested that the increase in the longfin smelt population might have
been related to the cessation of dredging in the Cedar River. This was based on historic deep
dredging that exceeded 10 feet in depth, in contrast to alternatives 2 and 3, which would dredge to
a more moderate depth. Since the majority of the Lake Washington longfin smelt population spawn
within the project reach, the change in spawning habitat conditions caused by dredging may be so
profound that it could eliminate longfin smelt from any further spawning within the reach. Spawning
and egg incubation habitat could degrade significantly because the reach would change from a
relatively shallow bed profile to a lake backwater. Substrate material would change from
predominantly gravels and cobbles to primarily silts. Channel configuration and surface area would
become more uniform. Water temperatures and dissolved oxygen levels would decrease and flows
within the reach would decrease in mean velocities.
How longfin smelt would respond to these changes is unknown. They may compensate by moving
further upstream in the Cedar into better spawning habitat, if available, or expand to other Lake
27
Washington tributaries. It is also possible that smelt may increase beach spawning to a greater degree
than now exists. Nevertheless, the smelt population is considered a key, and perhaps the most
important, fish species in the Lake Washington ecosystem. Should this population decline or expand
dramatically, the cascading effects on the dynamics of the Lake Washington fish community and lake
ecology could be highly disruptive.
RECOMMENDATIONS
During coordination with other resource agencies, there have been concerns raised about constructing
this project at this time, given the current sensitivity of the Lake Washington/Cedar River system.
Significant efforts are underway to understand why the changes in the ecosystem are occurring.
Serious declines in sockeye salmon and steelhead are being observed in the Lake Washington
ecosystem. This project, which may have significant effects on the fish community, could be untimely
and damaging.
The newest alternatives being considered have much less impact on fish and wildlife resources than
the historic deep dredging projects. In discussions with the Corps, we have been encouraged by their
willingness to protect and mitigate for potential fishery habitat loss with this project. We welcome
the opportunity to work with the Corps and the local sponsor to plan the mitigation and any
enhancement projects connected with the lower Cedar River flood control project. The mitigation
measures recommended by the Service for wildlife have been accepted and incorporated into the
latest alternatives.
Mitigation will be required for natural resource losses resulting from project implementation.
Opportunities to enhance the values of the existing habitat beyond those that currently exist should
also be identified pursuant to the Fish and Wildlife Coordination Act. Mitigation involves a series of
actions (National Environmental Policy Act, as amended, 42 U.S.C., 4321 et. seq.). These include
the following:
1. Avoiding the effect all together;
2. Minimizing the effect;
3. Rectifying the effect;
4. Reducing or eliminating the effect over time; and,
5. Compensating for the effect.
The availability, extent, location, and uniqueness of a habitat dictates its value to its constituent fish
and wildlife populations. The goal of mitigation ranges from no loss of in -kind habitat values to
minimal loss of habitat value.
N:3
Habitat for terrestrial species has been severely reduced due to the heavy industrialization of the area,
parking lots, and manicured parks. Some species, however, can maintain populations in these
conditions. There are currently many bird species using the area for breeding and rearing young.
The aquatic habitat has also been significantly altered by human activity. The existing habitat within
the project reach provides spawning for a significant number of sockeye salmon and a substantial
portion of the longfin smelt population of Lake Washington. The Service has determined that the
project could result in adverse effects on existing habitat values. The degree of impact would depend
on the alternative that is selected.
The Service offers the following recommendations to help the Corps in project planning and to
protect, mitigate, and enhance fish and wildlife resources in the project vicinity. These
recommendations are based on current project alternatives as furnished by the Corps.
The Corps should develop a comprehensive mitigation plan in conjunction with State and Federal
agencies and the Tribes. This plan should include actions that avoid or minimize potential impacts
to fish and wildlife resources. It should include elements to address longfin smelt, sockeye salmon,
and wildlife species. Short-term and long-term monitoring of these resource should also be included.
A contingency plan should be developed and implemented if the results of the monitoring show
unacceptable impacts. The Corps could provide appropriate funding and participate in the on -going
Lake Washington basin studies that deal with sockeye and longfin smelt.
MITIGATION FOR WILDLIFE IMPACTS
1. Due to the high value of the riparian zone we recommend that this type of habitat be
replaced. Most bird species were observed using the narrow strip of shrub and tree
vegetation on the right bank. Tree and shrub planting for overstory cover should be
pursued. Plant large sized trees and shrubs to reduce recovery time. Retain all native
tree species along the bank where possible and only remove non-native invasive shrub
vegetation. Fast growing trees such as native black cottonwood and alders are
recommended for the bulk of the plantings. Native conifers such as Douglas fir, western
red cedar and hemlock should also be planted to help block light from Boeing at night
and to provide a long term vertical habitat component for bird species.
2. The levees, as proposed, will incorporate existing "islands" of higher elevation ground
and tie into these areas to create a continuous levee. Using these high points in the park
as part of the levee designs may increase the riparian zone diversity and width along the
lower river. We highly endorse this concept as well as leaving all trees along the banks
and only removing non-native shrubs.
3. Revegetation of disturbed areas should be completed immediately after construction. A
plan should be developed to monitor the success of these efforts. Creation of a terrace
or shelf associated with the new shoreline to provide shallow water habitat for fish and
wildlife should be investigated. Planting of native emergent submergent marsh plants in
OU11
the newly created shallow water habitat should be explored. Care should be taken to
avoid the invasion of Eurasian watermilfoil, particularly during construction. It is vital
to identify new colonies early in order to eradicate it. We recommend an extended
monitoring program in the area following construction to ensure watermilfoil is
controlled.
4. Due to the sighting of turtles in the project reach, we recommend that turtle surveys be
conducted to determine species. Species identification is important because one of the
two native turtle species that may occur in this location, the northwestern pond turtle,
is a species of concern to the Service.
PROPOSED MITIGATION FOR AQUATIC RESOURCE IMPACTS
If a dredging alternative is chosen, a monitoring program should be developed to test the
assumptions concerning habitat. Smelt could be monitored by looking at the resulting
substrate composition during the spawning run, looking at actual use in the dredged area
for spawning and by checking egg viability. Sockeye could be monitored by marking a
representative number of redds above the test site and looking at depositional rates, or
scour depth at each redd site. Potential head -cutting and channel configuration changes
should also be monitored after several significant storm events.
2. If this monitoring produces unacceptable results, we recommend that the Corps
reconsider the proposed three year dredging cycle. The Service believes that the
precarious situation of salmon and steelhead resources in the Lake Washington/Cedar
River basin and the potential of the proposed project to adversely affect these resources
warrants a cautious approach. Close monitoring as described above could provide early
detection of potential fish resource problems and possibly avoid catastrophic results to
the fish community in this system.
3. Before dredging, sediments should be tested for contaminants and a determination of
whether disturbance of any contaminants found could be toxic to fish and wildlife
resources. We are concerned about the possible presence of contaminants due to the
close proximity of two major industrial sites, and the heavy use of fuel, oil, solvents, and
other chemicals. Contaminated sediments should be isolated and stored away from
water, particularly rivers, creeks, and lakes. All new concrete structures should be sealed
during construction to contain runoff from the construction site until the concrete is fully
cured. Runoff should be collected and pumped to a settling basin or other treatment area
to remove contaminants before discharge into the Cedar River or other surface water
course. Fuels, oils, solvents, and other potentially toxic chemicals should be properly
stored and protected from accidental release into the river or lake.
4. Construction activities should take place between mid -June and mid -August. This timing
is necessary to miss most of the major fish migrations and minimize project impacts on
this part of the life cycle.
30
5. We recommend that gravel removal be accomplished by dewatering the stream as much
as possible and constructing coffer dams to exclude water flow. The actual removal can
then be completed in an area isolated from flowing water and should reduce the entry of
fine sediment and additional turbidity into Cedar River and downstream into Lake
Washington. The actual method could be dragline or front end loader. We recommend
using the method that creates the least disturbance to the terrestrial habitat while still
protecting the stream.
6. A detailed sediment and erosion control plan should be developed to protect water
quality in the project area during and following construction. All steps should be taken
to minimize turbidity and fine sediments from entering the river and lake. Sediment
retention structures, settling ponds, silt fences, or other measures to protect water quality
should be employed as needed during construction.
7. At the spoil disposal site, we recommend that a catch basin be constructed to contain all
runoff and prevent sediment from moving downslope into nearby rivers, or other water
bodies. The spoils should be covered during the rainy season to reduce erosion and
additional downstream sedimentation. Revegetation should be started as soon as
practical to provide long term erosion and sediment control.
8. Gravel and cobble removed from the lower river could be cleaned and stored for future
fish enhancement projects. These substrate materials may be appropriate in some cases
for restoration of fish habitat in upstream areas. This possibility should be investigated.
9. We recommend the Corps investigate onsite mitigation measures for fish impacts.
Development of off -channel or side -channel habitat for longfin smelt spawning or
salmonid spawning and rearing habitat within the project reach may be possible. Because
the existing channel is narrowly confined by development, the opportunities to widen the
channel or add additional fish habitat features appear to be limited mostly to the lower
river. Any fish habitat features developed for mitigation should be monitored to
determine their effectiveness.
10. We recommend the Corps explore the potential for off -site fish mitigation measures
similar to an investigation of on -site mitigation opportunities. There may be potential
fish mitigation/enhancement projects upstream of the project that are feasible to pursue.
We recommend that the Corps coordinate with King County Surface Water Management
Division who may have identified potential fish habitat restoration projects in the lower
Cedar River basin. A combination of on -site and off -site mitigation projects may
adequately serve to offset fish habitat losses.
11. The WDFW presently operates a fry trap near the mouth of the Cedar River. This
project as proposed would make this trap unusable and would jeopardize several years
of data in a long term study involving the Cedar River. For this reason we recommend
31
that a new location for a fry trap be found in cooperation with WDFW. This trap will
need to be installed at least two years in advance of the implementation of this project.
This will allow both traps to be fished for two years and a calibration curve to be
established.
The Service will remain involved in this project and will be available for advice and support as
needed. We intend to assist the Corps in the development of the mitigation and monitoring plans for
this project and expect that other appropriate resource agencies and the Muckleshoot Tribe will also
be involved.
32
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