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CITY OF D ENTON,
WASHINGTON , a W4 7
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KING COUNTY
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NOVEMBER 5, 1980
Ak federal emergency management agency
1, federal insurance administration
COMMUNITY NUMBER-530088
TABLE OF CONTENTS
Page
• 1.0 INTRODUCTION 1
1.1 Purpose of Study 1
1.2 Coordination 1
1.3 Authority and Acknowledgments 1
2.Q AREA STUDIED 1
2.1 Scope of Study 1
2.2 Community Description 3
2.3 Principal Flood Problems 6
2.4 Flood Protection Measures 17
3.0 ENGINEERING METHODS 8
3.1 Hydrologic Analyses 9
3.2 Hydraulic Analyses 10
4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS 12
4.1 Flood Boundaries 12
4.2 Floodways 13
5.0 INSURANCE APPLICATION. 19
5.1 Reach Determinations 19
5.2 Flood Hazard Factors 20
5.3 Flood Insurance Zones 20
5.4 Flood Insurance Rate Map Description 22
6.0 OTHER STUDIES 22
7.0 LOCATION OF DATA 23
8.0 BIBLIOGRAPHY AND REFERENCES 23
1
TABLE OF CONTENTS (Cont'd)
Page
FIGURES
Fig re 1 - Vicinity Map 2
FiglIre 2 - Floodway Schematic 19
TABLES
I
Tab e 1 - Summary of Discharges 11
Table 2 - Floodway Data 15
Tab e 3 - Flood Insurance Zone Data 21
EXHIBITS
Exh' it 1 - Flood Profiles
Green River Panel OlP
Cedar River Panels 02P-03P
May Creek Panels 04P-05P
Springbrook Creek Panels 06P-07P
Black River Panel 08P
Exhioit 2 - Flood Boundary and Floodway Map Index
Flood Boundary and Floodway Map
PUBLISHED SEPARATELY:
Flood Insurance Rate Map Index
Fl000 Insurance Rate Map
ii I
FLOOD INSURANCE STUDY
1.0 INTRODUCTION
1.1 Purpose of Study
The purpose of this Flood Insurance Study is to investigate the
existence and severity of flood hazards in the City of Renton,
King County, Washington, and to aid in the administration of the
National Flood Insurance Act of 1968 and the Flood Disaster Protection
Act of 1973. Initial use of this information will be to convert
Renton to the regular program of flood insurance by the Federal
Insurance Administration. Further use of the information will
be made by local and regional planners in their efforts to promote
sound land use and flood plain development.
1.2 Coordination
On April 8, 1976, streams selected for detailed analysis were
identified in a meeting attended by representatives of the com-
munity, the original study contractor, and the Federal Insurance
Administration.
On July 13, 1979, the results of the work were reviewed at an
intermediate coordination meeting attended by representatives
of the city, the study contractor, and the Federal Insurance Admin-
istration.
The results of this study were reviewed at a final community coordi-
nation meeting held on May 5, 1980. Attending the meeting were
representatives of the Federal Insurance Administration, the study
contractor, and the city. No problems were raised at the meeting.
1.3 Authority and Acknowledgments
The source of authority for this Flood Insurance Study is the
National Flood Insurance Act of 1968, as amended.
The hydrologic and hydraulic analyses for this study were performed
by Tudor Engineering Company, for the Federal Insurance Administra-
tion, under Contract No. H-4025. This work, which was completed '
in July 1979, covered all significant flooding sources affecting
the City of Renton.
2.0 AREA STUDIED
2.1 Scope of Study
This Flood Insurance Study covers the incorporated area of the
City of Renton, King County, Washington. The study area is shown
on the Vicinity Map (Figure 1) .
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.9-1 FEDERAL EMERGENCY MANAGEMENT AGENCY APPROXIMATE SCALE
Federal Insurance Administration 4 0 4 8 12 MILES
Wa
CITY OF RENTON, WA
"' [KING Co.) VICINITY MAP
Floods caused by overflow of Green River, Cedar River, May Creek,
and Springbrook Creek which includes the Black River were studied
in detail.
A small area of King County located north of State Highway 900
has not been included in this study.
Those areas studied by detailed methods were chosen with consider-
ation given to all proposed construction and forecasted development
through 1984.
2.2 Community Description
The City of Renton, in western King County in central-western
Washington is situated 11 miles southeast of Seattle on the south
shore of Lake Washington. It is bordered by the Cities of Kent
to the south and Tukwila to the west. The remaining area is bordered
by the unincorporated areas of King County.
Many Indians were living in this region before the arrival of
the settlers. Because of the abundance of food in the rivers
and the fertility of the delta, it had long been the home of the
Duwamish Tribe. They engaged in agriculture, fishing, and the
harvesting of wild berries which abounded in the region. In 1852,
the Oregon Territorial Legislature created King County and named
it in honor of William King, Vice President of the United States
from 1852 to 1856.
In 1853, Henry and Diana Tobin became the first residents of Renton.
They built a homestead on a donation land claim between the banks
of the Cedar and Black Rivers. Later, settlers chose to name
their town, Renton, after the founder of the first sawmill.
Coal mining played an important role in the development of Renton
The coal was discovered accidentally while land was being cleared
not far from the present site of Renton. At one time there were
16 profitably operating mines in the immediate vicinity. In 1918,�I
over 1.3 million tons of soft coal were mined and billions of
tons of proven deposits still remain. Lumber and milling were
important early industries, also.
The Town of Renton was platted in 1876, gained city incorporation
in 1901, and thereby became part of Washington Territory. World
• War II brought a tremendous change to the city. Production of
war planes at the Boeing plant in Renton reached six a day as
population swelled from 4,000 to 16,000 (Reference 1) . The popula-
' tion in 1976 was 27,800 (Reference 2) .
In 1962, damaging floodflows from Green River came under the control
of Howard A. Hanson Dam. At that time, Green River valley became
an attractive area for industrial development. The economy of
3
Renton includes a variety of industries, services, and businesses
but is dominated by the Boeing Airplane Company. In 1976, the
company employed nearly 11,000. Other major employers include
Pacific Car and Foundry Company (1,685) and the Renton School
District (1,096) (Reference 2) . • I
Renton was originally built in the lowlands between the Cedar
and Green Rivers, but has gradually spread into the surrounding '
hills. The elevations range from less than 10 feet to approxi-
mately 450 feet. The commercial center of the city is located
north and west of Interstate Highway 405, on both sides of Cedar
River. Residential development has spread primarily along the
ascending ground east of Cedar River, and includes extensive areas •
outside the corporate limits. The flood plain areas of Renton
were originally farmland, a use which predominated until the early '
1960s. Urban development has displaced agriculture to the extent •
that the Green River valley is among the fastest growing urban
employment centers in the Puget Sound region (Reference 3) . Agricultural
and noncommercial pastureland account for only 18 percent of the i
land use in the east Green River watershed. In King County, approxi-
mately 2640 acres of prime agricultural land have been industrialized
(Reference 4) , including land in the Renton area of the Green
River valley.
Land use throughout the May Creek watershed is primarily open
space with scattered houses, most of which have been built back
from the creek.
Land use in the Springbrook Creek basin is primarily residential
on the valley slopes, with major industrial development on the
flatlands adjacent to Green River.
Renton at one time was primarily in the Cedar River drainage basin.
It has since expanded into four watersheds; Green River, Cedar
River, May Creek, and Springbrook Creek.
Green River meanders from north to south and is extremely flat.
It varies in elevation from 23 feet to 27 feet over a distance
of approximately 2 miles.
Cedar River enters Lake Washington at Renton and drains approxi-
mately 186 square miles. The higher portions of the basin are
rugged and densely forested. Elevations within the basin range
from 14 feet at Renton to over 5000 feet at the headwaters. Major
tributaries to the north of Renton include Rex River, which flows
northwesterly into the upstream end of Morse Lake, and Taylor '
Creek, which flows northerly to join Cedar River near Selleck.
The slope of Cedar River within the study area is steep, approxi'
mately 19 feet per mile. Channel velocities generally range from
5 to 10 feet per second. '
4
May Creek flows through the northern portion of Renton into Lake
Washington, and drains approximately 13 square miles. The north
side of the watershed is forested, except near the mouth. The
south side is becoming increasingly urbanized. The drainage basin,
especially the southern section, has been significantly affected
by glaciation. Retreating glaciers have created bogs, lakes,
irregular channel slopes, and unusual drainage patterns. In the
middle of the creek, channelization has been used to improve drain-
age. Elevations throughout the basin range from 20 feet near
the mouth to approximately 1600 feet at the highest point. The
slope of the creek bed through the study reach is very steep,
• approximately 64 feet per mile. The 100-year flood plain varies
in width from 20 to 260 feet, with anticipated channel velocities
of up to 15 feet per second. May Creek drains both Lake Kathleen
and Lake Boren located to the west of Renton. The main tributary
is Honey Creek which enters from the west at River Mile 2.0.
Springbrook Creek drains the southwestern portion of Renton, and
enters Green River through Black River. Upstream from Renton,
Springbrook Creek is joined by Mill Creek and together they drain
approximately 22 square miles, including most of the City of Kent.
Elevations throughout the basin range from 13 feet near the mouth,
to over 450 feet at the headwaters.
Glacial activity dramatically influenced the terrain of the Puget
Sound region until recent times. The area has been repeatedly
occupied by glaciers advancing from British Columbia. The last
glaciation (Vashon) took place about 13,500 years ago. It is
estimated this glacier was approximately 3000 feet thick at Renton.
During this period, most west-trending valleys were filled with
glacial drift (jumbled boulders, gravel, and sand) while preexisting
north-trending valleys like Green River were scoured deeper.
As the ice retreated to the north, the Straits of Juan de Fuca
became ice-free, and the ocean once more covered the Green River
valley. This embayment slowly filled with alluvium carried by
the White, Green, and Cedar Rivers, creating a flood plain with
a series of bogs and swamps. These alluvial deposits vary from
a few feet thick near the hillsides to 400 to 500 feet thick in
the ,central lowland area. This alluvium forms some of the most
fertile soil in the Pacific Northwest. Glacial deposits from
the Vashon glaciation are the chief components of the uplands
and vary from 25 to 200 feet in thickness.
The climate of the region is predominantly a mid-latitude, west
coast, marine type, because most of the air masses that reach.
•
the Puget Sound area originate over the Pacific Ocean. In late
fall and winter these masses are moist and approximately the same
temperature as the ocean surface. Orographic lifting and cooling
as air masses move inland result in cloudiness and widespread
precipitation throughout King County. Renton experiences approxi-
mately 39 inches of annual rainfall, of which 50 percent of the
5
annual precipitation falls in the 4-month period, October through
January, and 75 percent occurs in the 6 months of October through
March. Average annual snowfall is 8.6 inches. During the warmest
summer months, afternoon temperatures are in the 73°F to 80°F
range. Temperatures reach 90°F on the average of 2 days per year.
In winter, afternoon temperatures range from 40°F to 50°F. The
Japan Current generally moderates winter temperatures but each
year temperatures below freezing occur on an average of 16 nights
(Reference 5) .
2.3 Principal Flood Problems
Minor flooding occurs almost annually, especially during the winter
months as a result of heavy rainfall. The flood impact is more
severe due to the effects of urbanization. Rapid increases in
construction of roads, housing, and parking lots accelerate the '
amount of runoff reaching the valley floor. Industrial landfills
in the valley are frequently located with little regard for natural
drainage patterns.
During periods of excessive precipitation, surface and subsurface
runoff from the steep valley walls cause significant rises in
groundwater elevations in the valley floor. This creates open I
ponding in topographically depressed areas. The condition is
further aggravated by floodflow and corresponding high elevations
on Green River, which prevents natural drainage of subsurface
water. In other areas, the overlying soils are relatively imperl-
meable and runoff collects in ponds perched above the water table.
Renton is not subject to flooding from Green River due to discharge
control at Howard A. Hanson Dam, diking, and other flood-control
measures. However, Springbrook Creek, a tributary to Black Rivelr
through the P-1 pumping station, does cause flooding problems
within the dikes to the east of Green River.
Cedar River is channelized through Renton and has the capacity
to convey the 100-year return flood for most of its length. The
lower 1-mile reach of the Cedar River channel was stabilized in
1912. Only minor overbank flows and negligible, flood damage were
experienced during the December 1933 flood in Renton. However, :
extensive flooding occurred upstream. Since that flood, King
County has provided extensive riprap bank protection, bulkheads;
cleanings, and snag removal upstream of Renton.
Flood damage on May Creek occurs mainly at the mouth where a lumber
mill has been built on the small delta there. Upstream of Inter-
state Highway 405, May Creek flows generally within a canyon.
Flooding problems in this reach are the result of surface runoff
and ground-water seepage from the steep canyon walls rather than
excessive overflow of May Creek.
6
Flooding from• Springbrook Creek within the corporate limits is
due in part to overburdened channels and ponding upstream of under-
sized culverts. However, large areas are inundated because of
ponding behind the P-1 pumping station. The station is limited
to a maximum discharge of 300 cfs when Green River is at flood
stage. Landfill for development in the area has reduced natural
storage capabilities and further aggravated this type of flooding
problem.
The most recent flood occurred on December 3, 1975. Discharges
and recurrence intervals for Green River, Cedar Creek and May
Creek were 12,100 cubic feet per second (cfs) , 10-, 500-year;
8,800 cfs, 50-year; and 510 cfs, 15 year, respectively.
2.4 Flood Protection Measures
The U.S. Army Corps of Engineers operates Howard A. Hanson Dam 1
at Eagle Gorge, north of King County, on upper Green River. Since
1962, the dam has provided approximately a 500-year level of protec-
tion against overbank flooding by Green River. The dam is a rockfill
embankment approximately 235 feet high with a gated spillway and
a maximum reservoir elevation of 1222 feet. Stored water is released
as soon as possible after a flood to prepare for the possibility '
of a second flood. When the Auburn gage (No. 12113000) is expected
to reach 12,000 cfs, dam operators allow runoff over the spillway.
At that point, they regulate further releases in order to maintain
no more than 12,000 cfs at Auburn. Protection of flood plain
lands is afforded by channelization and diking. Along Green River,
a total of 12 miles of levees have been constructed. The King
County Division of Hydraulics is responsible for dike maintenance.
Since the adoption of enabling legislation by the State of Washington
in 1945, the state and King County have combined to control river-
bank erosion.
The channelizing of Cedar River now allows it to convey the 100-
year return flood. Since the 1933 flood, King County has provided
Cedar River with extensive riprap bank protection, bulkheads,
cleanings, and snag removal upstream of Renton. Within the study
reach, most of the channel of May Creek is in its natural condition.
The lower 1000 feet have been channelized to alleviate flooding
problems at the mouth caused by excessive deposition.
Floodflows on Springbrook Creek are discharged into Black River ,
just upstream of the P-1 pumping station located approximately
1 mile downstream of Interstate Highway 405. This pumping station,
constructed in 1972, is operated and maintained by King County.
It performs the dual function of preventing Green River backwater
from entering and inundating the low-lying east valley lands.
Also, it pumps water from relatively low elevations on Black River
into Green River at higher elevations. The pumping station is
part of a 1965 Watershed Work Plan designed by the U.S. Soil Conser-
vation Service with the cooperation of King County. It includes
7
a system of integrated drainage channels known as P-channels.
It is expected that construction of these P-channels will continue
and extend as far south as Orillia.
Under Chapter 86.16 of the Revised Code of Washington, Green River
is in Flood Control Zone 2 and Cedar River is in Flood Control,
Zone 3. Pursuant to the statute, flood plain management in these
zones is administered by county and city authorities. Specific
provisions for flood plain management, designed to reduce flood,
damage to urban developments, have been formulated jointly by
King County, the City of Renton, and the other municipalities
located in the Green River valley. These provisions require all
new urban developments in flood-prone areas to floodproof against
100-year flood conditions. To meet these flood-proofing require-
ments, l developers must raise the ground surface to an elevation
1.0 foot above the predicted water surface caused by the 100-year
flood.
Flood forecasting and protection is facilitated by an agreement
between the U.S. Army Corps of Engineers, Seattle District, and
King County whereby the former will advise the King County Division
of Hydraulics when a flow of 10,000 cfs in Green River is expected
to reach Auburn. The Division of Hydraulics has agreed to monitor
river conditions and to be responsible for encroachments on th'e
safe carrying capacity of the existing levees.
3.0 ENGINEERING METHODS
For the flooding sources studied in detail in the community, standard
hydrologic and hydraulic study methods were used to determine the flood
hazard data required for this study. Flood events of a magnitude which
are expected to be equalled or exceeded once on the average during any
10-, 50-, 100-, or 500-year period (recurrence interval) have been selected
as having special significance for flood plain management and for flood
insurance premium rates. These events, commonly termed the 10-, 504,
100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance,
respectively, of being equalled or exceeded during any year. Although
the recurrence interval represents the long term -average period between
floods of a specific magnitude, rare floods could occur at short intervals
or even within the same year. The risk of experiencing a rare flood
increases when periods greater than 1 year are considered. For example,
the risk of having a flood which equals or exceeds the 100-year flood
(1 percent chance of annual occurrence) in any 50-year period is approxi-
mately 40 percent (4 in 10) , and, for any 90-year period, the risk increases
to approximately 60 percent (6 in 10) . The analyses reported here 'reflect
flooding potentials based on conditions existing in the community at
the time of completion of this study. Maps and flood elevations will
be amended periodically to reflect future changes.
8
3.1 Hydrologic Analysis
Hydrologic analyses were carried out to establish the peak dis-
charge-frequency relationships for floods of the selected recur-
rence intervals for each stream studied in detail in the community.
On Green River, releases are controlled by Howard A. Hanson Dam
engineers so as not to exceed a discharge of 12,000 cfs at the
City of Auburn for all recurrence floods up to the 500-year event
(Reference 6) .
The U.S. Army Corps of Engineers, Seattle District, had previously
carried out a hydrologic study to derive recurrence flood peaks
on Cedar River (Reference 4) . Historic streamflow data for this
river was obtained from two Cedar River gages, both operated and
• maintained by the U.S. Geological Survey. One gage at the mouth
in Renton (gage no. 12-1190) , has been in operation continually
since 1945. The other, (gage no. 12-1175) , near Landsburg, has
been in operation at its present site since 1948.
Flood-frequency data for May Creek was based on discharge records
at a U.S. Geological Survey streamflow gaging station at the mouth
of May Creek. The gage (no. 12-1196) , located at the Lake Washington
Boulevard bridge, has a period of record from 1964 to the present.
Analysis of streamflow data was performed in accordance with the !
standard log-Pearson Type III method outlined by the U.S. Water
Resources Council (Reference 7) .
There are no streamflow records available for Springbrook Creek
and Black River. Hydrologic analysis for this drainage basin
was performed by the U.S. Soil Conservation Service using synthetic
hydrograph methodology (Reference 8) and the TR-20 computer program
(Reference 9) . Results of this study were reviewed and incorpor
ated into a computerized runoff-routing model developed by the
study contractor to utilize the U.S. Soil Conservation Service
synthetic hydrograph method. Hydrographs representing the 10-
and 100-year return storms runoff were generated and routed through-
out the study reach. The 24-hour precipitation volume for the
expected 10- and 100-year return storm was obtained from the Natlional
Oceanic and Atmospheric Administration Precipitation-Frequency
Atlas (Reference 10) . It was compared with precipitation gage
records at Seattle-Tacoma International Airport. Intensity distri-
bution was also based on the Seattle-Tacoma International Airport
rainfall records. The 50- and 500-year floods are not within
the scope of this study, therefore, discharges were not computed
for these recurrence intervals.
The expected 8-day, 100-year return storm precipitation volume
was used to determine the extent of surface ponding in low-lying
areas.
9
Peak discharge-drainage area relationships for Green River, Cedar
River, May Creek, and Springbrook Creek are shown in Table 1.
3.2 Hydraulic Analyses
1
Analyses of the hydraulic characteristics of streams in the commu-
nity were carried out to provide estimates of the elevations of
floods of the selected recurrence intervals along each stream
studied in the community.
Water-surface elevations throughout the May Creek and Springbrook
Creek study reaches were computed using the U.S. Army Corps of
Engineers HEC-2 step-backwater computer program (Reference 11) .
The U.S. Army Corps of Engineers, Seattle District, had prleviously
developed 10- and 100-year water-surface elevations having' field
surveyed the physical data for Green and Cedar Rivers. Cross
section and bridge data for May and Springbrook Creeks were field
surveyed (References 4 and 6) .
Locations of selected cross sections used in the hydraulic, analyses
are shown on the Flood Profiles (Exhibit 1) . For stream segments
for which a floodway is computed (Section 4.2) , selected cross
section locations are also shown on the Flood Boundary and!Flood-
way Map (Exhibit 2) .
Channel- and overbank-roughness coefficients are based on field
inspection. Values used in this study are listed below:
1
Stream Channel Overbank
Green River 0.030 - 0.055 0.090 •- 0.150
Cedar River 0.026 - 0.054 0.035 - 0.099
May Creek 0.045 - 0.055 0.080 - 0.150
Springbrook Creek 0.038 - 0.045 0.100 - 0.150
The U.S. Army Corps of Engineers has previously determined the
starting water-surface elevations for Green River and Cedarl River
(References 4 and 6) .
Starting water-surface elevation for May Creek is controlled by
Lake Washington. On Springbrook Creek, starting water-surface
elevation is dependent on the storage-elevation curve upstream
from the P-1 pumping station (Black River) . In order to arrive
at an accurate estimate for the starting water-surface elevation,
the hydrograph at the mouth was routed through the pump station
using pumping criteria and a maximum discharge of 300 cfs. 'The
routing was done using an in-house computer program incorporating
the Modified Puls routing techniques.
10
Table 1. Summary of Discharges
Discharges
Flooding Source Drainage Area (Cubic Feet Per Second
and Location (Square Miles) 10-Year 50-Year 100-Year 500-Year
Green River
At Renton 450 12,0001 12,0001 12,0001 1
12,000
Cedar River
At Mouth 186 5,950 8,550 9,810 13,000
May Creek
At Mouth 12.7 480 795 870 1,015
Springbrook Creek
At Mouth 21.9 5852 N/A 1,1052 N/A
Downstream of Confluence With
r Mill Creek 16.0 680 N/A 1,020 N/A
H
2Discharges Constant Due to Controlled Release From Howard A. Hanson Dam
Decrease in Discharges Due to P-1 Pumping Plant Pumping 300 Cubic Feet Per Second Into Green River
During Flood Stages
Flood profiles were drawn showing computed water-surface elevations
to an accuracy of 0.5 foot for floods of the selected recurrence
intervals (Exhibit 1) . Only the 10-year and 100-year flood elevations
are shown for Springbrook Creek and Black River because of the
limited scope of this study.
The Black River profile, upstream to the P-1 station,
pumping on,
was developed by projecting the water-surface elevations taken
from the confluence with Green River, as flat backwater from Green
River (Reference 12) . The 10- and 100-year elevations atlEarlington
Golf and County Club Foot Bridge on Springbrook Creek were projected
downstream to the P-1 pumping station to complete the profile.
At the P-1 pumping station, the water from the Springbrook Creek-
Black River system is pumped up to the elevation of Green River.
Results of the Green River- study (Reference 6) show that the 10-,
50-, 100-, and 500-year water-surface elevations through Renton
are represented by a single water-surface profile of controlled-
discharge releases at Howard A. Hanson Dam. This profile was
taken from the Flood Insurance Study for King County (Reference
6) . Flood Hazard areas caused by high water on Green River, as
shown in this study, are based on the previously developed profile
and information from topographic maps obtained from Renton (Refer-
ence 13) .
The hydraulic analyses assumed unobstructed flow. The flood eleva-
tions are considered valid only if bridges and culverts remain
unobstructed.
II
Ponding elevations were derived using the runoff-routing computer
model described in Section 3.1, together with pumping criteria
and elevation-storage curves developed from field surveys, and
information from topographic maps (Reference 13) .
All elevations are referenced to the National Geodetic Vertical
Datum of 1929 (NGVD) . Elevation reference marks used in the study
are shown on the maps.
4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS
A prime purpose of the National Flood Insurance Program is to encourage
State and local governments to adopt sound flood plain management pro-
grams. Each Flood Insurance Study, therefore, includes a flood boundary
map designed to assist communities in developing sound flood plain' manage •
-
ment measures.
4.1 Flood Boundaries •
In order to provide a national standard without regional diserimi-
nation, the 100-year flood has been adopted by the Federal Insurance.
Administration as the base flood for purposes of flood plain manage-
12
ment measures. The 500-year flood is employed to indicate addition-
al areas of flood risk in the community. For each stream studied
in detail, the boundaries of the 100- and 500-year floods have
been delineated using the flood elevations determined at each
cross section; between cross sections, the boundaries were inter-
- polated using topographic maps at a scale of 1:2400, with a contour
interval of 5 feet (Reference 13) .
For the detailed study of Green River, the flood boundary delin-
eated is representative of the 10-, 50-, 100-, and 500-year floods.
For Springbrook Creek, only the 100-year flood boundary has been
delineated.
In cases where the 100- and 500-year flood boundaries are close
together, only the 100-year flood boundary has been shown.
Flood boundaries for the 100- and 500-year floods are shown on
the Flood Boundary and Floodway Map (Exhibit 2) .
Approximate flood boundaries in some portions of the study area
were taken from the Federal Insurance Administration's Flood Hazard
Boundary Map (Reference 14) .
Small areas within the flood boundaries may lie above the flood
elevations and, therefore, not be subject to flooding; owing to
limitations of the map scale, such areas are not shown.
Similarly, small areas which may be subject to shallow ponding
due to runoff or high ground-water elevations may not be shown.
4.2 Floodways
Encroachment on flood plains, such as artificial fill, reduces
the flood--carrying capacity and increases flood heights, thus
increasing flood hazards in areas beyond the encroachment itself.
One aspect of flood plain management involves balancing the economic
gain from flood plain development against the resulting increase
in flood hazard. For purposes of the National Flood Insurance
Program, the concept of a floodway is used as a tool to assist
local communities in this aspect of flood plain management. Under
this concept, the area of the 100-year flood is divided into a
floodway and a floodway fringe. The floodway is the channel of
a stream, plus any adjacent flood plain areas, that must be kept
free of encroachment in order that the 100-year flood be carried
without substantial increases in flood heights. As minimum standards,
the Federal Insurance Administration limits such increases in
flood heights to 1.0 foot, provided that hazardous velocities
are not produced.
13
The floodways developed in this study were initially computed
on the basis of equal-conveyance reduction from each side of the
flood plain. Further refinement was made using field observations,
hydraulic principles, and a topographic map (Reference 13) .
For Springbrook Creek, there were areas of backwater ponding up-
stream of roadway culverts where floodway requirements were com-
puted based on storage routing criteria. The 100-year pondi'ng
water-surface elevations were established using reservoir routing
by Modified Puls techniques. The floodway encroachment limits
were then determined by reducing the width of the flood plain
to obtain the required surcharge for each ponding area upstream
of the culvert. The flow with the increased elevation was then
routed through the culvert. No cross section widths, areas,lor
velocities are shown for these ponding areas.
No floodway was computed for Black River since the area upstream
from the P-1 pumping station to the confluence of Springbrook
Creek was considered a reservoir suitable to receive the overflow
from Springbrook Creek.
The results of these computations are tabulated at selected cross
sections for each stream segment for which a floodway is computed
(Table 2) .
As shown on the Flood Boundary and Floodway Map (Exhibit 2) , Ithe
floodway boundaries were determined at cross sections; betwedn
cross sections, the boundaries were interpolated. In cases where
the floodway and 100-year flood boundaries are close together;,
only the floodway boundary has been shown.
The area between the floodway and the boundary of the 100-year
flood is termed the floodway fringe. The floodway fringe thuls
encompasses the portion of the flood plain that could be completely
obstructed without increasing the water-surface elevation of the
100-year flood more than 1.0 foot at any point. Typical relation-
ships between the floodway and the floodway fringe and their signi-
ficance to flood plain development are shown in Figure 2.
I .
14
FLOODING SOURCE FLOODWAY BASE FLOOD
WATER SURFACE ELEVATION
__ _ --MEAN - — - I- WITHOUT I WITH
CROSS SECTION DISTANCE 1 WIDTH AREA VELOCITY REGULATORY FLOODWAY FLOOODWAY— INCREASE—
(FEET) (SQUARE _CFFET--P-ER
FEET) SECOND) (FEET NGVD)
Green River
A 11,845 160/1102 2609 4.6 27.1 27.1 27.1 0.0
B 13,100 185/140 2857 4.2 27.5 27.5 27.5 0.0
1 2
Feet Above Corporate Limits Width/Width Within Corporate Limits
FEDERAL EMERGENCY MANAGEMENT AGENCY nn
a —
Federal Insurance Administration F—OODWAY LJATA
CITY-OE-REHTOH-WA
rr' [KING CO.) GREEN RIVER
NJ
A. v
BASE FLOOD
FM-00a1N -SUAQE FLOODWAY WATER SURFACE ELEVATION
SECTION MEAN WITHOUT WITH
CROSS SECTION DISTANCE 1 WIDTH AREA VELOCITY REGULATORY FLOODWAY FLOODWAY INCREASE
(FEET) (SQUARE (FEET PER
FEET) SECOND) (FEET NGVD) ,
Cedar River
A 0.025 158 1280 7.7 15.0 15.0 15.0 0.0
B 0.462 144 180 10.0 18.9 18.9 18.9 0.0
C 0.767 157 1510 6.5 23.7 23.7 23.7 0.0
D 1.144 156 1020 9.6 25.7 25.7 25.7 0.0
E 1.261 120 950 10.3 27.5 27.5 27.5 0.0
F 1.337 135 1030 9.5 28.5 28.5 28.5 0.0
G 1.489 150 1110 8.8 30.6 30.6 30.6 0.0
H 1.679 114 950 10.3 32.5 32.5 32.5 0.0
I 1.830 135 1180 8.3 35.5 35.5 35.5 0.0
J 1.960 221 1360 7.2 37.3 37.3 37.3 0.0
K 2.038 135 1280 7.7 38.4 38.4 38.4 0.0
L 2.090 115 1210 8.1 39.5 39.5 39.5 0.0
M 2.160 103 1160 8.5 40.7 40.7 40.7 0.0
N 2.320 110 1490 6.6 43.4 43.4 43.4 0.0
O 2.470 142 1500 6.5 45.2 45.2 45.2 0.0
P 2.730 141 1210 8.1 49.5 49.5 49.5 0.0
Q 2.900 130 1310 7.5 52.6 52.6 52.6 0.0
R 2.960 140 1220 8.1 53.6 53.6 53.6 0.0
S 3.020 150 1070 9.1 55.4 55.4 55.4 0.0
T 3.250 210 1690 5.8 60.9 60.9 61.0 0.1
U 3.370 196 1310 7.5 62.8 62.8 62.9 0.1
- 1M-iles_Above Mouth
FEDERAL EMERGENCY MANAGEMENT AGENCY FLOODWAY DATA
--I Federal Insurance Administration
Xis
°° CITY OF RENTON, WA
rrl
N (KING CO.) CEDAR RIVER
BASE FLOOD
FLOODING SOURCE FLOODWAY
WATER SURFACE ELEVATION
-_ _ _-- - SECTION =-- MEAN- - - - ---- WITHOUT WITH -
CROSS SECTION DISTANCE- WIDTH AREA VELOCITY REGULATORY �I FLOODWAY LOODWAy __INCREASE
(FEET) __IEWARE_--WEE-T PER
FEET) SECOND) (FEET NGVD)
May Creek
A 0.14 34 158 5.5 21.0 21.0 21.5 0.5
B 0.16 60 239 3.6 21.8 21.8 22.2 0.4
C 0.24 42 99 8.8 23.3 23.3 23.3 0.0
D 0.25 42 110 7.9 25.7 25.7 25.7 0.0
E 0.31 31 121 7.2 29.0 29.0 29.2 0.2
F 0.39 40 150 5.8 32.5 32.5 33.0 - 0.5
G - 0.46 28 - 87 10.0 35.8 35.8 35.8 0.0
H 0.52 23 123 7.1 40.0 40.0 40.6 0.6
I 0.57 45 165 5.3 41.8 41.8 42.5 0.7
J 0.63 31 89 9.7 45.3 45.3 45.3 0.0
K 0.78 33 133 6.5 55.2 55.2 55.2 0.0
L 0.94 79 143 6.1 64.7 64.7 64.7 0.0
M 1.09 33 113 7.7 76.4 76.4 76.6 0.2
N 1.25 39 128 6.6 85.4 85.4 85.4 0.0
O 1.36 32 89 9.6 93.1 93.1 93.2 0.1
P 1.39 40 172 4.9 95.6 95.6 96.0 0.4
Q 1.41 33 90 9.5 95.8 95.8 95.8 0.0
R 1.42 33 111 7.7 96.4 96.4 96.4 0.0
S 1.46 30 95 8.9 99.8 99.8 99.9 0.1
T 1.54 22 91 9.3 106.8 106.8 106.9 0.1
U 1.56 8 68 12.5 112.2 112.2 112.2 0.0
✓ 1.61 43 283 2.9 114.2 114.2 115.1 0.9
W 1.74 27 81 9.9 120.9 120.9 120.9 0.0
X 1.83 38 170 4.8 125.0 125.0 125.7 0.7
Y 1.96 522 101 8.0 135.8 135.8 135.8 0.0
Z 2.02 42 130 6.3 140.4 140.4 140.5 0.1
1Miles Above Mouth 2Floodway Lies Entirely Outside Corporate Limits
FEDERAL EMERGENCY MANAGEMENT AGENCY - - - -
a
- - - Federal Insurance Administration F-L-0-ODMIRY DA-T-A
CITY OF RENTON, WA
N°
N (KING CO.) MAY CREEK
BASE FLOOD
FLOOD -cuReE - LOODWAY
WaTFR SURFACE ELEVATION
,SECTION MEAN WITHOUT WITH
AREA VELOCITY REGULATORY FLOODWAY FLOODWAY INCREASE
CROSS SECTION DISTANCEI WIDTH
(FEET) (SQUARE (FEET PER
FEET) SECOND) (FEET NGVD)
Springbrook Creek
A 0.238 81 616 2.1 14.9 14.9 14.9 0.0
B 0.587 150 706 1.8 15.0 15.0 15.1 0.1
C 0.737 68 472 2.7 15.1 15.1 15.4 0.3
D 0.787 68 482 2.6 15.2 15.2 15.5 0.3
E 0.859 58 467 2.7 15.4 15.4 15.8 0.4
F 1.254 50 439 2.9 15.8 15.8 16.3 0.5
G 1.487 83 638 2.0 16.0 16.0 16.6 0.6
H 1. 624 25 297 4.0 16.0 16.0 16.7 0.7
I 1.987 63 581 2.1 16.6 16.6 17.4 0.8
J 2.565 44 325 3.8 17.0 17.0 17.9 0.9
K 2.605 43 383 3.2 17.3 17.3 18.2 0.9
L 2.672 56 476 2.6 17.4 17.4 18.3 0.9
M 2.760 88 881 1.4 17.6 17.6 18.5 0.9
-- - --- - - - - -
1
Miles Above Mouth - - - -
FEDERAL EMERGENCY MANAGEMENT AGENCY
Federal Insurance Administration FLOODWAY DATA
,-
CITY OF RENTON, WA
rm
NJ (KING Co.) I SPRINGBROOK CREEK
•
I1[It 100-YEAR FLOOD PLAIN 1,1
FLOODWAY FLOODWAY�
FRINGE ID Q FLOODWAY. FRINGE
STREAM
-ArCHANNEL-D
• FLOOD ELEVATION WHEN
CONFINED WITHIN FLOODWAY
ENCROACHMENT ENCROACHMENT
S U R C H A R G E
AREA OF FLOOD PLAIN THAT COULD FLOOD ELEVATION
BE USED FOR DEVELOPMENT BY BEFORE ENCROACHMENT
RAISING GROUND ON FLOOD PLAIN
LINE AB IS THE FLOOD ELEVATION BEFORE ENCROACHMENT.
LINE CD IS THE FLOOD ELEVATION AFTER ENCROACHMENT.
•SURCHARGE IS NOT TO EXCEED 1.0 FOOT (FIA REQUIREMENT) OR LESSER AMOUNT IF SPECIFIED BY STATE.
Figure 2. Floodway Schematic
5.0 INSURANCE APPLICATION
II
n order to establish actuarial insurance rates, the Federal Insurance
dministration has developed a process to transform the data from the
engineering study into flood insurance criteria. This process includes
he determination of reaches, Flood Hazard Factors, and flood insurance
zone designations for each flooding source studied in detail affecting
Renton.
5.1 Reach Determinations
Reaches are defined as lengths of watercourses having relatively
the same flood hazard, based on the average weighted difference
in water-surface elevations between the 10- and 100-year floods.
This difference does not have a variation greater than that indica-
ted in the following table for more than 20 percent of the reach:
Average Difference Between
10- and 100-Year Floods Variation
Less than 2 feet 0.5 foot �I
2 to 7 feet 1.0 foot
• 7.1 to 12 feet 2.0 feet
More than 12 feet 3.0 feet
•
•
19
i I
The locations of the reaches determined for the flooding sources
of Renton are shown on the Flood Profiles (Exhibit 1) and summar-
ized in Table 3.
5.2 Flood Hazard Factors
The Flood Hazard Factor (FHF) is the Federal Insurance Administra-
tion device used to correlate flood information with insurance
rate tables. Correlations between property damage from floods
and their FHF are used to set actuarial insurance premium rate
tables based on FHFs from 005 to 200.
The FHF for a reach is the average weighted difference between
the 10- and 100-year flood water-surface elevations expressed;
to the nearest one-half foot, and shown as a three-digit code.
For example, if the difference between water-surface elevations •
of the 10- and 100-year floods is 0.7 foot, the FHF is 005; if
the difference is 1.4 feet, the FHF is 015; if the difference'
is 5.0 feet, the FHF is 050. When the difference between the
10- and 100-year water-surface elevations is greater than 10.0
feet, accuracy for the FHF is to the nearest foot.
5.3 Flood Insurance Zones
After the determination of reaches and their respective Flood
Hazard Factors, the entire incorporated area of the City of Renton
was divided into zones, each having a specific flood potential
or hazard. Each zone was assigned one of the following flood
insurance zone designations:
Zone A: Special Flood Hazard Areas inundated
by the 100-year flood, determined, by
approximate methods; no base floo,'d
elevations shown or Flood Hazard Factors
determined.
Zone AH: Special Flood Hazard Areas inundated
by types of 100-year shallow flooding
where depths are between 1.0 andr3.0
feet; base flood elevations are shown,
but no Flood Hazard, Factors are deter-
mined.
Zones Al, A2, A4, A5, Special Flood Hazard Areas inundated
and A7 by the 100-year flood, determined by
detailed methods; base flood elevations
shown, and zones subdivided according
to Flood Hazard Factors.
20
ELEVATION DIFFERENCE2
1 BETWEEN 1% (100-YEAR) FLOOD AND FLOOD BASE FLOOD
FLOODING SOURCE PANEL HAZARD ZONE ELEVATION 3
10% 2% 0.2% FACTOR _ =(-FEET NGVD) — -
(10-YEAR) _(50--YEAR)-(500-YEAR) = --- --
Green River
Reach 1 0004 0.0 0.0 0.0 005 Al Varies - See Map
Cedar River
Reach 1 0002 -2.3 -0.7 2.0 025 A5 Varies - See Map
Reach 2 0002,0003 -3.6 -0.9 1.9 035 A7 Varies - See Map
Reach 3 0003 _ -2.3 -0.9 1.2 025 A5 Varies - See Map
May Creek -
Reach 1 0001 -1.2 -0.18 1.59 010 A2 Varies - See Map
Springbrook Creek
Reach 1 0002,0004 -2.0 N/A N/A 020 A4 Varies - See Map
Ponding Area 0004 N/A N/A N/A N/A AH 16
Black River
Reach 1 0002 -2.0 N/A N/A 020 A4 Varies - See Map
•
lFlood 4
Insurance Rate Map Panel 2Weighted Average 3Rounded to Nearest Foot Data Based on Regulated Flow
From Howard A. Hanson Dam
..I FEDERAL EMERGENCY MANAGEMENT AGENCY -
Mon Federal Insurance Administration - FLQ.QD-JN-S-URANCEZONE D-ATA
CCP
GITY OF-RENT-ON-WA
rr.
�, (KING CO.) GREEN RIVER-CEDAR RIVER-MAY CREEK-SPRINGBROOK CREEK-BLACK RIVER
Zone B: Areas between the Special Flood Hazard
Areas and the limits of the 500-year
flood, including areas of the 500-year ;
flood plain that are protected from
the 100-year flood by dike, levee,
or other water control structure; also
areas subject to certain types of 100-,
year shallow flooding where depths
are less than 1.0 foot; and areas subject
to 100-year flooding from sources with'
drainage areas less than 1 square mile'.
Zone B is not subdivided.
Zone C: Areas of minimal flooding.
The flood elevati
on differences, Flood Hazard Factors, flood insur-
ance zones, and base flood elevations for each flooding source
studied in detail in the community are summarized in Table 3.
i
5 . , Flood Insurance Rate Map Description
The Flood Insurance Rate Map for Renton is, for insurance purposes,
the principal result of the Flood Insurance Study. This map (published
separately) contains the official delineation of flood insurance,
zones and base flood elevation lines. Base flood elevation lines
show the locations of the expected whole-foot water-surface eleva-
tions of the base (100-year) flood. This map is developed in
accordance with the latest flood insurance map preparation guide-
lines published by the Federal Insurance Administration.
r
6.0 •I HER STUDIES
he Federal Insurance Administration published a Flood Insurance Study
'Reference 6) in March 1976, which covered the unincorporated areas
of King County, including those areas affected by Green and Cedar Rivers
.djoining Renton.
the Federal Insurance Administration is conducting Flood Insurance Studies
for the adjacent Cities of Kent (Reference 15) and Tukwila (Reference 12) .
hese studies are in general agreement with this study.
fhe Federal Insurance Administration has previously published a Flood
azard Boundary Map for the City of Renton (Reference 16) . However,
this study represents a more detailed analysis.
he U.S. Army Corps of Engineers, Seattle District, also published a'
Flood Plain Information report (Reference 4) on Cedar River through
Renton in March 1969. Data from this report have been incorporated
into this study.
22
The U.S. Soil Conservation Service has conducted extensive studies (Refer-
ence 17) in the Green River valley. Its work has been directed primarily
toward determining criteria pertinent to the design of flood-control
drainage channels and associated structures. These studies have been
mainly concerned with the effects of future land use and development
of runoff patterns, rather than existing flood-hazard conditions.
This study is authoritative for the purposes of the National Flood Insur-
ance Program; data presented herein either supersede or are compatible
with all previous determinations.
7.0 LOCATION OF DATA
Survey, hydrologic, hydraulic, and other pertinent data used in this
study can be obtained by contacting the Insurance and Mitigation Division,
Federal Emergency Management Agency, Federal Regional Center, 1301228th
Street, SW. , Bothell, Washington 98011. "
8.0 BIBLIOGRAPHY AND REFERENCES
1. Greater Renton Chamber of Commerce, Renton History, unpublished
2. Greater Renton Chamber of Commerce, An Economic Profile of Renton,
Washington, 1976
3. Puget Sound Committee, "The Green River Valley Discussion Paper,"
presented at Puget Sound Governmental Conference, Seattle, Washington,
March 1975
4. U.S. Department of the Army, Corps of Engineers, Seattle District,
Flood Plain Information, Cedar River, Renton, Washington, Seattle,�
Washington, March 1969
5. U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, Climatography of the United States, No. 60-45,
Climate of Washington, Silver Spring, Maryland, February 1960,
Revised April 1965
6. U.S. Department of Housing and Urban Development, Federal Insurance
Administration, Flood Insurance Study, King County, Washington,
(Unincorporated Areas) , March 1976
7. U.S. Water Resources Council, Hydrology Committee, "Guidelines
for Determining Flood Flow Frequency," Bulletin 17, 1976
8. U.S. Department of Agriculture, Soil Conservation Service, Engineer-
ing Division, National Engineering Handbook, Section 4, Hydrology,
January 1971
9. U.S. Department of Agriculture, Soil Conservation Service, Engineer-
. ing Division, Technical Release 20, Computer Program For Hydrology
•
May 1975
23
10. U.S. Department of Commerce, National Oceanic and Atmospheric
P P
Administration, Atlas 2, Precipitation - Frequency Atlas of ,the
Western United States, vol. IX, 1973
11. U.S. Department of the Army, Corps of Engineers, Hydrologic Engi-
neering Center, No. 723-X6-L202A, HEC-2 Water-Surface Profiles,
Generalized Computer Program, Davis, California, November 1976
12. Federal Emergency Management Agency, Federal Insurance Administra-
tion, Flood Insurance Study, City of Tukwila, Washington, unpublished
I
13. Aerial Mapping Company, Topographic Map, 1:2400, Contour Interval
5 feet: Renton, Washington (1968)
14. U.S. Department of Housing and Urban Development, Federal Insurance
Administration, Flood Hazard Boundary Map, City of Renton, King
County, Washington, Scale 1:9600, June 7, 1974
15. Federal Emergency Management Agency, Federal Insurance Adminis-
tration, Flood Insurance Study, City of Kent, Washington, unpublished
16. U.S. Department of Housing and Urban Development, Federal Insur-
ance Administration, Flood Hazard Boundary Map, City of Renton,
Washington, June 7, 1974 (Revised November 7, 1975)
17. U.S. Department of Agriculture, Soil Conservation Service, Draft
Environmental Impact Statement, East Side Green River Watershed,
King County, Washington, Spokane, Washington, May 1977
I ,
24
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FEDERAL Federal Insurance Administration AGENCY
FLOOD PROFiILfS
CITY OF RENTON, WA
(KING co.) SPRINGBAOOR CREEK
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LOCATION o
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500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000
STREAM DISTANCE IN FEET ABOVE MOUTH
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*PANEL NOT PRINTED - AREA OF MINIMAL FLOOD HAZARDS
AL FLOOD INSURANCE PROGRAM
1ODWAY
BOUNDARY AND
IWAY MAP
IF
PON, WASHINGTON
COUNTY
P INDEX
SPRINTED: 1 - 4
COMMUNITY -PANEL NUMBERS
530088 0001-0005
EFFECTIVE DATE:
MAY 5, 1981
federal emergency management agency
federal insurance administration
1)
Elevation Reference Mark RM7X
River Mile • M 1 .5
NOTES TO USER
Boundaries of the floodways were computed at cross sections and
interpolated between cross sections. The floodways were based on
hydraulic considerations with regard to requirements of the
Federal Insurance Administration.
This map was prepared to support minimum flood plain manage-
ment regulations; it may not show all areas subject to flooding
in the community or all planimetric features outside special
flood hazard areas.
For adjoining map panels, see separately printed Index To Map
Panels.
Q
APPROXIMATE SCALE
500 0 500 FEET
NATIONAL FLOOD INSURANCE PROGRAM
FLOODWAY
FLOOD BOUNDARY AND
FLOODWAY MAP
CITY OF
RENTON, WASHINGTON
KING COUNTY
PANEL 1 OF 5
(SEE MAP INDEX FOR PANELS NOT PRINTED)
COMMUNITY -PANEL NUMBER
530088 0001 B
EFFECTIVE DATE:
MAY 5, 1981
federal emergency management agency
federal insurance administration
KEY TO MAP
4
APPROXIMATE SCALE
500 0 500 FEET
NATIONAL FLOOD INSURANCE PROGRAM
FLOOD BOUNDARY AND
FLOODWAY MAP
CITY OF
RENTON, WASHINGTON
KING COUNTY
PANEL 2 OF 5
(SEE MAP INDEX FOR PANELS NOT PRINTED)
COMMUNITY -PANEL NUMBER
530088 0002 B
EFFECTIVE DATE:
MAY 5, 1981
federal emergency management agency
federal insurance administration
JOINS PANEL 0002
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ELEVATION REFERENCE MARKS
REFERENCE ELEVATION
MARK (FT. NGVD)
DESCRIPTION OF LOCATION
RM9 17.82
Railroad spike 1.5 feet up south face of power telephone pole
number 1212; third pole west of Southwest 16th Street bridge
crossing of Springbrook Creek, on north side of road. Established
by City of Renton Public Works Department.
RM10 12.30
Railroad spike 3.3 feet up south face of power pole on north side
of Southwest 27th Street; first power pole east of Springbrook
Creek., Established by City of Renton Public Works Department.
RIM11 21.79
Chiseled square on top of concrete curb on east side of driveway
to house number 1516 on Southwest 43rd Street, 51.5 feet south
of north end of concrete curb and 29.5 feet south of south face of
house. Established by City of Renton Public Works Department.
I
I
O PRC ORATE LIMITS
KEY TO MAP
500-Year Flood Boundary IL
T9;
100-Year Flood Boundary
FLOODWAY FRINGE FLOODWAY
100-Year Flood Boundary
500-Year Flood Boundary
Approximate 100-Year
Flood Boundary
Cross Section Line
Elevation Reference Mark RM7X
River Mile • M1 .5
NOTES TO USER
Boundaries of the floodways were computed at cross sections and
interpolated between cross sections. The floodways were based on
hydraulic considerations with regard to requirements of the
Federal Insurance Administration.
This map was prepared to support minimum flood plain manage-
ment regulations; it may not show all areas subject to flooding
in the community or all planim etric features outside special
flood hazard areas.
For adjoining map panels, see separately printed Index To Map
Panels.
_Z&
APPROXIMATE SCALE
500 0 500 FEET
NATIONAL FL000 INSURANCE PROGRAM
FLOODWAY
FLOOD BOUNDARY AND
FLOODWAY MAP
CITY OF
RENTON, WASHINGTON
KING COUNTY
PANEL 4 OF 5
(SEE MAP INDEX FOR PANELS NOT PRINTED)
COMMUNITY -PANEL NUMBER
530088 0004 B
EFFECTIVE DATE:
MAY 5, 1981
federal emergency management agency
federal insurance administration
JOINS PANEL 0005