HomeMy WebLinkAboutSWP272264(21) Phase 1 Design Report
Maplewood Creek Sedimentation Basin
Reconstruction and Improvement Project
November 1994
City of Renton, Washington
Prepared by
NORTHWEST, INC.
Phase 1 Design Report
Maplewood Creek Sedimentation Basin
Reconstruction and Improvement Project
November 1994
City of Renton, Washington
Prepared by
NORTHWEST, INC.
CERTIFICATE OF ENGINEER
Maplewood Creek Sedimentation Basin
Reconstruction and Improvement Project
Phase I Design Report
The technical material and data contained in this report were prepared by, or
under the supervision and direction of, the undersigned whose seal as professional
engineer is affixed below.
V:�RT LI
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-4 Albert Liou, .E.
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EXPIRES O -23-q5
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Phase I Design Report
TABLE OF CONTENTS
I. INTRODUCTION.......................................................................................... 1
A. Purpose of the Report.................................................................................................... 1
B. - Project Description........................................................................................................ 1
II. EXISTING CONDITIONS AND DESIGN CONSIDERATIONS............2
A. Site Description.............................................................................................................2
B. Geology......................................................................................................................... 3
C. Fish and Wildlife........................................................................................................... 3
D. Hydrology and Flood Flows .........................................................................................4
E. Sediment Load and Trap Efficiencies...........................................................................6
F. Future Fishway..............................................................................................................7
G. Evaluation of Alternatives ............................................................................................ 8
III. PROPOSED DESIGN....................................................................................9
A. Sedimentation Basin ..................................................................................................... 9
B. Main Spillway............................................................................................................. 11
C. Fishway Outlet and Maintenance Bypass................................................................... 11
D. Access Road................................................................................................................ 12
E. Upper Dam Removal .................................................................................................. 12
F. Channel and Bank Stabilization.................................................................................. 13
G. Erosion and Sediment Control Plan............................................................................ 13
H. Construction Cost Estimate and Schedule.................................................................. 14
I. Construction Permits................................................................................................... 15
IV. CONCLUSIONS AND RECOMMENDATIONS..................................... 16
A. Conclusions................................................................................................................. 16
B. Recommendations....................................................................................................... 17
EXHIBITS
APPENDIX A - Sediment Load and Geotechnical Evaluation Report
APPENDIX B - Aquatic and Terrestrial Resources Report
APPENDIX C - Preliminary Construction Plans
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Phase I Design Report
MAPLEWOOD CREEK
PHASE 1 DESIGN REPORT
I. INTRODUCTION
A. Purpose of the Report
The City of Renton is proposing to reconstruct and improve the existing sedimentation
basin located on Maplewood Creek above the Maplewood Golf Course in Renton, Washington
(Exhibit 1). The improvements will help protect public and private property downstream of the
basin from increased sediment deposition and potential flooding.
The City has applied to the Federal Emergency Management Agency (FEMA) for Hazard
Mitigation Grant Project funds for the project. Before FEMA can approve the grant request for
the construction phase of the project, it must address the potential impacts of the project in
compliance with the National Environmental Policy Act (NEPA). The information included in
this Phase 1 Design Report can be used by FEMA in preparation of its NEPA Environmental
Assessment (EA), and approval for funding the construction of the project. The Design Report
will also be used by the City to acquire all permits and approvals from various governmental
agencies necessary for construction of the project.
B. Project Description
The Maplewood Creek Sedimentation Basin Project involves reconstructing and
improving the existing sedimentation basin. The improvements include reconstructing the
existing sedimentation basin to develop a larger storage volume for sediment and debris,
removing the upper concrete dam and accumulated sediments, and stabilizing the upper creek
channel to reduce the severe channel and bank erosion. The existing access road running along
the west side of the basin and creek will be improved by placing a gravel road surface.
The new sedimentation basin is designed based on the expected sediment load from the
Maplewood Creek Basin and the minimum grain size desired for capture. The new
sedimentation basin will have a sediment storage volume twice as large as the existing basin,
with the expansion occurring downstream of the existing basin.
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The toe of the south bank at the upper concrete dam is not stable and will be reinforced
with riprap to prevent undermining after the dam is removed. A second section of the south
bank, located just below the upper dam, will also be reinforced with riprap.
A diversion structure will be installed in the sedimentation basin to direct water to a
future low flow fish passage channel that will be constructed across through the golf course. The
fish passage channel will be connected to a fish ladder and will allow migratory fish to travel up
Maplewood Creek into the canyon. The low flow fish passage channel will be a separate project
funded by the City.
II. EXISTING CONDITIONS AND DESIGN
CONSIDERATIONS
A. Site Description
Maplewood Creek drains land areas lying both within the City of Renton and
unincorporated King County. The creek drainage course travels from the plateau region north of
the golf course into a steep ravine, through the Maplewood Golf Course, and discharges to the
Cedar River on the south side of the Maple Valley Highway and the Milwaukee Railroad track.
The natural course of the creek has been channelized on the golf course, and the last 1100 feet of
the creek is confined in a culvert running under the highway and parallel to the railroad track
prior to discharging into the Cedar River. The culvert entrance is above the normal water level in
the river, and the culvert entrance and length act as a barrier to migratory fish passage.
There are two existing ponds on Maplewood Creek within the golf course property. The
lower pond located just north of the clubhouse parking lot was converted from an irrigation
diversion pond to the existing sedimentation basin. However, the sedimentation basin acts as a
barrier to fish passage and requires frequent sediment removal to maintain some efficiency.
The embankment containing the existing sedimentation basin consists of a rock and
earthen fill about 10 feet high and 50 feet long with a concrete weir located on the east side of the
embankment. An overflow floodway is located in native soil against the east bank beyond the
end of the constructed embankment. During a site visit in April 1994 the basin was filled with
gravelly sand and at least two thin, discontinuous layers of clayey silt in the upper few inches of
the deposit. Verbal communications with the golf course maintenance supervisor indicates that
approximately 400 cubic yards of sediment is removed from the pond annually.
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The upper pond is located approximately 500 feet north of the lower pond and was
originally constructed as an irrigation facility in the 1920's, but was abandoned in the 1980's or
earlier. The concrete dam which forms the upper pond was damaged by high storm flows which
have undercut the toe of the south bank slopes. This pond also acts as a barrier to fish passage,
and sediment has filled in behind it.
The lower portion of the Maplewood Creek Basin has been prone to flooding from the
runoff from the upper basin because of the unique geology and topography of the region. The
slopes connecting the upper basin plateau areas with the Cedar River valley are steep and highly
susceptible to erosion. Most soils are shallow with only thin layers of vegetation overlaying
deep deposits of glacial gravels and sands. As development has increased in the Maplewood
Creek Basin, erosion and flooding have increased in intensity and frequency. Water quality
problems have increased and fisheries and habitat areas in many parts of the creek have been
substantially altered, and many eliminated.
B. Geology
An evaluation report involving geologic conditions and field sampling in the project area
is included as Appendix A to this Phase 1 Design Report. The following is a summary from the
Appendix A report, pertaining to geology.
The geologic environment of the canyon formed by Maplewood Creek consists of sub-
horizontally bedded, glacial-derived sediments. Exposures within the canyon display sandy
gravel, sand and clay beds varying in thickness from about one foot to several feet. All slopes
observed in the canyon exhibit slope movement of varying degrees of severity. Near the creek,
bank undercutting occurs on nearly every outside bed. Several rotational slope failures were
identified.
A rotational slope failure is located on the east bank immediately upstream of the upper
concrete dam and a severely undercut slope is located about 100 feet downstream of the
structure. Stabilization of the slope failures near the upper dam may be facilitated by installing a
toe buttress for erosion protection and a toe surcharge to minimize slope movement by sliding.
C. Fish and Wildlife
An aquatic and terrestrial resource report was prepared and is included as Appendix B to
this Phase 1 Design Report. The following is a summary from the Appendix B report.
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While the Cedar River has a large natural run of sockeye salmon, steelhead and a
moderately-sized run of river smelt, these fish appear to seldom use Maplewood Creek for
spawning or rearing. The lower half-mile channel of Maplewood Creek through the golf course
and the culvert system under SR-169 is largely barren of habitat and functions primarily as a
drainage ditch. Erosion in the steep, lower reach of the east fork of Maplewood Creek has
washed fine sediments into potential spawning gravels and significantly impacted fish habitat. In
addition, the existing sedimentation basin and the upper abandoned concrete dam represent a fish
passage barrier to the upper canyon. Resident trout have been observed in the lower reaches of
Maplewood Creek, from the golf course area upstream into the steeper canyon reaches.
The upper end of the project area is in a forested ravine. The forest canopy is fairly open,
and a well-developed shrub and herbaceous layer is present. Vegetation immediately adjacent to
the upper concrete dam and siltation pond is herbaceous ground cover.
Trees and shrubs are dense to the edge of the exiting sedimentation basin. On the south
and west sides of the basin, vegetation is predominantly herbaceous and includes mixed grasses
and weedy forbs. The east bank of the creek at the lower end of the project area is forested
almost to the waterline. The west bank is bordered by dense thickets of blackberry measuring
approximately 10 feet in width and abutting the golf course parking lot.
Residential development on the uplands above the ravine, and recreational development
below the project area limits the diversity of wildlife occurring within the project area. Habitat
does not exist for large mammals requiring large territories, such as the black bear and mountain
lion. However, forest and riparian-dwelling wildlife species with moderate to small home range
requirements such as deer, birds, waterfowl, small mammals, reptiles and amphibians are likely
abundant along the main stem of Maplewood Creek.
No adverse effects to fish and wildlife are anticipated from project implementation,
except short-term disturbance during construction and revegetation planting. More discussion of
potential effects of the project and the revegetation plan , as well as monitoring and maintenance
of project elements, is provided in the Appendix B report. No wetlands other than the existing
basin and the upper dam siltation pond will be affected by the proposed project construction.
D. Hydrology and Flood Flows
Maplewood Creek has two major tributaries which begin by collecting storm water from
residential areas in the upper plateau regions of the basin. The west tributary discharges into the
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main channel in the middle of a steep ravine at the confluence with the east tributary. Below the
confluence the main channel of the creek continues for about 1500 feet down the steep ravine,
then passes through the upper concrete dam and into the existing sedimentation basin. From the
sedimentation basin it flows almost due south next to a maintenance road across the Maplewood
Golf Course. At the south side of the golf course the stream passes under the Maple Valley
Highway (SR 169) in a 42-inch culvert and is entirely contained in a 72-inch culvert which runs
to the west parallel to the railroad tracks prior to discharging to the Cedar River.
Maplewood Creek drains an area of approximately 1,099 acres (1.72 square miles). The
drainage area above the proposed sedimentation basin is slightly smaller, approximately 1,032
acres (1.61 square miles). Runoff contribution from the area downstream of the basin is
negligible. Average annual precipitation is approximately 43 inches as recorded in the City of
Renton. Mean annual flow is 3.20 cfs for current basin land-use conditions, and is projected to
be 3.72 cfs for future basin land-use conditions, based on King County's HSPF model
simulations. (Ref: King County Department of Public Works, Surface Water Management
Division. 1993. Cedar River Current and Future Conditions Report). A review of daily flow
data resulting from the simulations indicates that flows exceed 20 cfs approximately 5 to 7 days
annually on average, primarily during winter months.
Peak flows selected for design of the proposed sedimentation basin are provided below.
These flows were determined by simulating the rainfall and runoff process of Maplewood Creek
using the HEC-1 computer model developed by the U.S. Army Corps of Engineers. Details of
the peak flow simulations are described in the 1989 draft report entitled "City of Renton
Comprehensive Stormwater Plan: Maplewood Creek Basin Plan" prepared by Parametrix, Inc.
The peak flow for the 100-year, 24-hour storm corresponding to future land use conditions was
estimated to be 392 cfs, and was selected as the design flow for the sedimentation basin spillway
and dam.
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REC-1 Model Runoff Characteristics at Maplewood Golf Course
Existing Land Use Conditions Future Land Use Conditions
Storm Total Precipitation Peak Flow Runoff Volume Peak Flow Runoff Volume
Event (inches) (cfs) (acre-feet) (cfs) (acre-feet)
(24-
hour)
2-year 2.0 118 119 173 157
10-year 2.9 202 199 275 247
25-year 3.4 251 247 333 298
100-year 3.9 300 297 392 351
E. Sediment Load and Trap Efficiencies
An evaluation of sediment load and trap efficiencies is included in the Appendix A
report. The evaluation includes field sediment sampling and testing, estimates of sediment
supply distribution, and trap efficiencies for both existing and proposed sedimentation basins.
Tbe. following is a summary from the Appendix A report.
A total of 17 samples from the existing sedimentation basin, upstream side slopes, and
streambed were obtained for sieve analysis. The analysis results display an average distribution
of sand, gravel, and silt and clay, as shown below.
Sample Location Percent Gravel Percent Sand Percent silt/clay
Sedimentation Basin 41 55 3
Side Slopes 22 71 6
Streambed 28 64 6
The sieve results confirm that gravel to coarse sand is captured by the existing
sedimentation basin along with a small portion of the fine sand. Most of the fine sand and
practically all of the silt and clay are passed downstream. Actively sloughing slopes as observed
contribute large quantities of fine material.
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It is estimated that an average of 1,200 cubic yards of sediment is transported into or
through the existing sedimentation basin on an annual basis. An average of 250 to 300 cubic
yards of gravel and sand have been trapped in the basin each year under recent flow conditions.
The remaining 900 cubic yards of material consisting primarily of fine sand, silt and clay is
transported through the basin to further downstream. The estimated size distribution of the total
sediment load is provided below.
Grain Size Estimated Percent of Total Load Volume (cu yd)
Gravel 10 120
Coarse Sand 5 60
Medium Sand 25 300
Fine Sand 25 300
Silt and Clay 35 420
Total 100 1,200
The existing sedimentation basin has a surface area of approximately 4,000 square feet (at
pool El. 109) and a volume of 300-400 cubic yards when cleaned out. The current basin would
retain particles coarser than 0.2 mm (fine to medium sand) during a 2-year flood event under
ideal conditions. The trap efficiency, defined as the ratio of the quantity of deposited sediment to
the total sediment inflow, is estimated to be 25 percent (300 cubic yards annually) for the present
basin.
F. Future Fishway
The City of Renton is proposing to construct a fishway channel across the Maplewood
Golf Course under a separately funded project. The fishway channel project will provide
suitable stream habitat for salmon migration into the Maplewood Creek canyon. It will be
connected downstream to a fish ladder currently under construction by Washington State
Department of Transportation (WDOT) as a part of the WDOT project to widen SR 169. The
upstream end of the fishway channel will be connected to a fishway outlet structure to be
constructed as a part of the proposed sedimentation basin project. It is the City's current plan to
construct both the new sedimentation basin and the fishway channel in 1996.
The WDOT fish ladder has been designed for a hydraulic capacity of 40 cfs. However, a
review of the design drawings indicates that a maximum flow of approximately 50 cfs is possible
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for the fish ladder. The sedimentation basin fishway outlet structure should be designed for an
hydraulic capacity less than the fish ladder maximum flow, allowing additional flow contribution
from the golf course into the fishway channel.
Minimum flows should be maintained in the fishway channel at all times, even during
removal of the sediment captured in the new sedimentation basin. A bypass flow pipe will be
used to temporarily divert stream flow from above the sedimentation basin and discharge it to the
downstream fishway channel when sediment removal takes place. Sediment will usually be
removed once a year during the low-flow period in the summer.
G. Evaluation o f Alternatives
The following design alternatives for the sedimentation basin were evaluated:
Alternative A-1: The new dam was located approximately 100 feet downstream of the
existing dam. A bathtub overflow concrete spillway with a 6-foot diameter pipe
and outlet was incorporated into the design (See Exhibit 2).
Alternative A-2: New dam location was the same as that for Alternative A-1. An
overflow concrete spillway and stilling basin as a part of the dam section was
incorporated into the design. (See Exhibit 3)
Alternative B-1: The new dam location was located at the existing dam. A bathtub
overflow concrete spillway with a 6-foot-diameter pipe and outlet was incorporated
into the design. (See Exhibit 4).
Alternative B-2: New dam location was the same as that for Alternative B-1. An
overflow concrete spillway and stilling basin as a part of the dam section was
incorporated into the design. (See Exhibit 5)
Alternatives A-1 and A-2 represent a substantial expansion, approximately 3 times the
area and volume of the existing sedimentation basin. Alternatives B-1 and B-2 represent
reconstruction of the existing basin without any significant expansion in size. It was estimated
that the sediment trap efficiencies for Alternatives A-1 and A-2 will be approximately twice the
efficiencies for Alternatives 13-1 and B-2. Trap efficiencies between Alternatives A-1 and A-2,
or between Alternatives B-1 and B-2 were estimated to be approximately the same. All
alternatives include the same fishway outlet facility. Comparative construction cost estimates for
the alternatives are provided in Exhibits 6, 7, 8, and 9.
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The cost estimates indicate that the cost would increase by approximately $10,000 from
Alternative A-1 to Alternative A-2, or from Alternative B-1 to Alternative B-2. The cost
increase is primarily due to more spillway concrete required for Alternatives A-2 and B-2. It was
therefore determined that the bathtub spillway configuration used for Alternatives A-1 and 13-1 is
preferred over the spillway design configuration used for Alternatives A-2 and B-2.
The cost comparison also indicate that expansion of the sedimentation basin as shown in
Alternatives A-1 and A-2 would involve an additional cost of approximately $23,000, or 12
percent of the total construction cost, over the cost of rebuilding the existing basin as shown on
Alternatives 13-1 and B-2. Since the trap efficiency of the expanded sedimentation basin would
be double the efficiency of the rebuilt existing basin the 12 percent cost increase was considered
to be economically justified.
Alternative A-1 was reviewed by the City of Renton Surface Water Utility and Parks
Department, and the embankment location was moved 20 feet to the north to allow for planned
golf course redevelopment. The basin design then proceeded using the revised embankment
location.
III. PROPOSED DESIGN
A. Sedimentation Basin
The proposed sedimentation basin design is shown on drawing sheet 1 of Appendix C,
Preliminary Construction Plans. The new basin will have a normal pool level at El. 108.5. The
fishway outlet overflow weir crest is set at El. 107.5, and the spillway overflow weir crest at El.
109.0. The minimum pool during summer low flow months will approximately El. 108.0 and
maximum pool during the 100-year storm event will be at El. 110.5. The dam crest will be
constructed at El. 111.5 to provide a 1-foot freeboard during the 100-year storm event, and with a
minimum width of 12 feet for maintenance vehicle access.
The new basin will have a pool surface area of approximately 12,000 square feet and a
volume of 1,300 cubic yards at pool El. 109.0. The new basin is predicted to capture a larger
portion of the fine sand than the existing basin, with particles larger than 0.1 mm captured during
a 2-year storm event. It is estimated that the trap efficiency will increase from 25 percent for the
existing basin to 40 or 50 percent (500 to 600 cubic yards annually) for the new basin.
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Initially the basin bottom will be constructed at El. 105.0. This will provide a sediment
storage volume of approximately 600 cubic yards, assuming a minimum 2 feet of water depth for
sediment settling during high flow events when the water level reaches the spillway crest El.
109.0. The new basin will operate at an increased trap efficiency and will require cleaning an
average of once a year. If less frequent cleaning is desired, the bottom elevation could be
lowered by one or two feet to provide additional sediment storage volume. Depending upon the
storm frequency and intensity, the basin may need to be cleaned after a single large storm, or
may not require cleaning for several years if there are no high flow events.
A 75 foot long, 8-inch diameter underdrain pipe buried in a gravel-filled trench upstream
of the proposed spillway will be provided to facilitate draining ponded water prior to cleaning the
basin. A slide gate located on the discharging end of the pipe at the spillway structure will be
installed to control draining operation.
The new basin will be constructed as a compacted earthfill embankment. Offsite
materials from an established borrow source will be used for the compacted embankment core.
Local materials will be used at the outer edge of the embankment and for fill in other less critical
areas since they could contain organic debris that would make compaction more difficult. It is
recommended that bidding documents include specifications for borrow materials. Further
technical discussion of the embankment design and construction is provided in Section 11.0 of
the Appendix A report, Geotechnical Requirements for Proposed Embankment.
A private landowner, southeast of the existing golf course club house, has a property line
that appears to be described as the center of the creek. The land owner has expressed concern
with the idea of water being diverted from Maplewood Creek for the majority of the year. To
address those concerns a 8-inch bypass pipe and slide gate will be installed in the overflow
spillway. The gate will be adjusted to allow a small amount of flow (0.5 to 1 cfs) to be directed
down the main channel of Maplewood Creek at all times. The bypass pipe will also allow flow
to be directed to the main channel if the future fishway should become inoperable, or if the water
in the sedimentation basin needs to be lowered in an emergency.
The private landowner appears to have a water right which allows a diversion of 0.02 cfs,
or 1 acre-foot per year from Maplewood Creek. The landowner has a connection to an old
irrigation line that goes from the existing sedimentation basin to a pump station that was
previously used to irrigate the golf course. A new inlet will be constructed in the sedimentation
basin and connected to the existing irrigation line to provide the same access to water that now
exists for the private landowner.
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B. Main Spillway
A rectangular bathtub overflow spillway shown on drawing sheet 2 of Appendix C is
proposed for the new sedimentation basin. It will be a 24-foot-long by 12-foot-wide (excluding
concrete thickness) reinforced concrete structure, providing a total overflow crest length of 60
feet. The spillway crest will be at El. 109.0.
For the 100-year storm event the peak flow into the basin is 392 cfs and the pool
elevation will be El. 110.5. Approximately 347 cfs will flow over the main spillway and 45 cfs
will flow through the fishway outlet. It is estimated that the frequency of water flowing over the
main spillway will be approximately 7 days per year on average, primarily during the winter high
flow months.
The overflow spillway structure will be connected with a 30 foot long, 72-inch diameter
concrete outlet pipe buried under the dam embankment. A small concrete outlet structure will be
located at the downstream end of the pipe to discharge flow to Maplewood Creek. Excessive
hydraulic energy of the flows will be dissipated within the spillway, pipe and outlet structural
system.
C. Fishway Outlet and Maintenance Bypass
The proposed fishway outlet design is shown on drawing sheet 3 of Appendix C. The
outlet will be located on the west side of the sedimentation basin embankment, anticipating that
the future fishway through the golf course will be connected with the outlet at this point. The
fishway outlet will consist of two concrete weir structures connected by a 32 foot long, 42-inch
diameter concrete pipe buried under the dam embankment. The design of the weirs is exactly the
same as that used for the WDOT fish ladder weirs currently under construction. However, due to
additional backwater effect created by the connecting pipe, the maximum hydraulic capacity
through the fishway outlet will be approximately 45 cfs, slightly less than that of the WDOT fish
ladder. The slight reduction in hydraulic capacity will provide a safety margin, allowing some
flow contribution from the golf course area to the fishway during storm events.
The upstream weir crest of the fishway outlet is set at El. 107.5. The downstream weir
crest of the outlet will be 0.8 foot lower, at El. 106.7. Both weirs will be a trapezoidal shape with
a one-foot weir crest width at the bottom and an 8-foot width at the top. The fishway channel
bottom will be 3 feet below the weir opening. Flow discharge rating for the proposed fishway
outlet and main spillway is estimated as follows:
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Water Elevation In Fishway Outlet Main Spillway Total Flow
Sedimentation Basin Flow( cfs ) Flow (cfs ) ( cfs )
107.5 0 0 0
108.0 2 0 2.0
108.5 7.7 0 7.7
109.0 17 0 17
109.5 29 65 94
110.0 42 185 227
110.5 45 347 392
Fishway Outlet Weir at El. 107.5 Main Spillway Crest at El. 109.0
A 300 foot long, 12-inch diameter maintenance bypass pipe is proposed to be buried
along the west side of the sedimentation basin and access road. The bypass pipe system includes
a small inlet and gate structure located above the sedimentation basin, and a discharge point at
the fishway outlet weir. The bypass pipe system will have an hydraulic capacity of
approximately 5 cfs, which will be adequate to divert low flows during the summer for sediment
removal. The diversion will require temporary sand bagging of Maplewood Creek at the bypass
pipe inlet to stop flow from travelling into the basin.
D. Access Road
The existing access road along the west side of Maplewood Creek will be improved by
placing crushed rock surfacing a minimum of 4-inches deep and 12 feet wide. The west
embankment of the new sedimentation basin will be finished with the same crushed rock
surfacing to serve as part of the access road. A new ramp with a maximum 12.5 percent slope
will also be constructed at the south end of the basin.
E. Upper Dam Removal
The upper concrete dam located 500 feet upstream of the existing sedimentation basin
will be removed to facilitate fish passage into the upper creek area. Removal may be partial or
complete depending on the type and condition of the concrete and foundation. We recommend
the use of a track-hoe mounted pneumatic pavement breaker for removal of the dam.
At a minimum the concrete must be removed to a depth of one foot below stream grade
(approximately El. 122.5) measured on the downstream side of the wall. The opening should be
a minimum of 10 feet wide at the bottom and slope upward at 45 degrees to each bank. In the
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event that the dam does not have a foundation or that the opening extends the full height of the
wall, all of the concrete wall will be removed.
F. Channel and Bank Stabilization
Prior to the upper dam removal, the accumulated sediments in the 120 foot long section
of the creek upstream of the dam will be excavated and removed from the site. After the
sediments and upper dam are removed each bank will be armored using riprap (8-inch size rock)
for a distance of at least 60 feet upstream. This distance should coincide with the east bank slope
repair and existing armoring on the west bank.
Two east bank slopes near the upper dam are proposed for repair, involving installation of
a toe buttress for erosion protection and a toe surcharge to minimize slope movement by sliding.
Details of the proposed repairs are shown on drawing sheet 1 of Appendix C.
The Washington State Department of Fish and Wildlife suggests stream habitat
enhancement by placing 2- to 3-foot size boulders along the creek bottom at about 8 to 10 foot
spacing. The boulders will be placed from the upstream end of the new sedimentation basin to
100 feet upstream of the upper dam (for a total distance of approximately 400 feet).
G. Erosion and Sediment Control Plan
Project construction is planned to be started in July 1996 and completed in September.
Construction will require approximately eight weeks and will involve primarily earth-moving of
approximately 6,000 cubic yards of excavation and fill material. The control of erosion and
sediment at the construction work areas is addressed below and will be incorporated into the
construction contract to be issued for bid in the spring of 1996. In general, industrial standards
of soil erosion control, the erosion control requirements of the King County Surface Water
Design Manual, and Best Management Practices for erosion and sediment control will be used.
The proposed contractor staging area will be the existing parking lot immediately south
of the new sedimentation basin. Use of this area for staging will not require grading or removal
of any vegetation. Soil erosion or sedimentation will not result from the use of this site as a
staging area, so no special protection measures are proposed, other than routinely checking the
parking lot drainage and maintaining it in appropriate working condition during construction.
Access to the parking lot and sedimentation basin will be from the existing roads on the
golf course. A new access road and ramp will be constructed on the west side of the new
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 13
F:\7134GTH-I R[V_JII/21/9403'.25 P11
Phase 1 Design Report
sedimentation basin embankment to the upper dam. Several short ramps may be constructed
from the west side access road to the bottom of the creek to reach other work areas, such as the
upper dam and the slope stabilization areas.
Silt fences constructed from filter fabric will be used at the edge of all areas where soil is
disturbed to prevent sediment from reaching the creek. These areas include the slope
stabilization areas, the new access road, and construction of the new sedimentation basin After
construction is completed all accumulated sediment will be removed from the silt fences. The
existing sedimentation basin will be kept in working condition as long as possible to act as a
secondary sediment trap.
Prior to work in the creek the contractor will need to divert all stream flow. The
diversion method will probably involve sand-bagging the creek above the working area and
diverting the creek past the working area in a temporary 12- to 18-inch pipe. In some areas a
pump may be used during the workday instead of a pipe if equipment would need to cross the
diversion pipe location. All diversion methods used by the contractor will be subject to approval
by the City, and will be removed at the end of construction.
All of the excavated material, approximately 3,000 cubic yards of silt, sand, gravel and
top soil, will be backfilled or used in regrading ground contours in the finished work areas.
Excavated soil will be stockpiled in the work area in small quantities, and silt fences will be used
around the perimeter of the stockpile. Most of the 1,700 cubic yards of the embankment core fill
and all of the 300 cubic yards of rock and rip rap will be imported and delivered directly to the
work areas without stockpiling because of the small quantities involved. The 75 cubic yards of
concrete will also be delivered directly to the site for placement without any on-site process or
stockpiling.
Following construction, exposed soils will be revegetated to control erosion. A
discussion of the revegetation plan is provided in Appendix B. Detailed planting specifications,
including size of stock, spacing, care and handling of plant materials, will be prepared as part of
the construction plans and specifications.
H. Construction Cost Estimate and Schedule
The estimated construction cost for the proposed sedimentation basin reconstruction and
improvement project is $ 196,117 and is shown in Exhibit 10. The costs were developed from
the preliminary design details shown in Appendix C and are based on August 1994 prices.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pa(Ye 14
P M14GTH-I REV.J11/2I/94 i)3_'_5 PM
Phase 1 Design Report
Quantity estimates were made of work items and materials for the main components of the
proposed design, and approximate unit prices were applied to arrive at the base costs.
Allowances were made for taxes, engineering, permitting, and the City's administration.
It should be noted that the estimated costs are preliminary only, and contingent upon
approvals of the proposed design by FEMA and other agencies. The final project costs for the
proposed design would also depend on final design details, price escalation, and actual bidding
outcome. Because of these factors, the final project costs could vary from the estimates
presented herein.
The proposed schedule for design and construction of the proposed project is shown on
Exhibit 11. On-site construction is expected to be started in July 1996 and to be completed in
September 1996. The schedule is based on the Park Department's request that construction of the
new sedimentation basin not begin until after the new golf course club house is in operation. The
schedule also assumes that the Hydraulic Project Approval issued by the Washington
Department of Fish and Wildlife will only allow instream construction during the summer low-
flow months.
L Construction Permits
Permits and approvals which will be required for construction of this project include:
Section 404 Permit - Section 404 of the Federal Clean Water Act (P.L. 92-500) requires
that a U.S. Army Corps of Engineers permit (a Section 404 or Nationwide Permit) be applied for
if the project will dredge or fill materials into or out of the waters of the United States or on their
adjacent wetlands.
CZM Consistency and Water Quality Certifications - The Corps may take care of
obtaining the Water Quality Certification and approval from Washington Department of Ecology
(WDOE) that the project is consistent with the Coastal Zone Management Act as part of its
Section 404 Permit review. Many of the Corps' "nationwide" permits preclude the need for a
separate Water Quality Certification or CZM Consistency Certification.
Short-Term Water Quality Modification - This approval, obtained from the Department
of Ecology, defines which water quality parameters will be exceeded during instream
construction work. The City must define the parameters and the duration water quality may be
degraded below state standards.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 15
F'.\7134UPH-t REV.d-:11,21/94 03''_5 P.Ni
Phase 1 Design Report
Hydraulic Project Approval(HPA) - Pursuant to RCW 75.20.100, an HPA must be
obtained from Washington Department of Fish and Wildlife for any hydraulic project involving
waters of the State of Washington. The purpose of the approval is protection of fish resources,
and the permit will define instream work windows and may include construction-related
stipulations for the protection of aquatic life.
Archaeological Approval -Executive Order 11593 requires consultation with and
approval by the Washington State Office of Archaeology and Historic Preservation (OAHP) for
federally-approved projects. This involves sending a letter to OAHP describing the location of
the project, and requesting approval. If determined necessary by OAHP, an archaeological
reconnaissance survey could be required.
SEPA Compliance - Compliance with the State Environmental Policy Act of 1971
(SEPA) is required before state- and city-required permits and approvals can be issued. The City
of Renton will assume lead agency role and initiate the SEPA process by completing the
environmental checklist and making a threshold determination as to the need for an
Environmental Impact Statement. The checklist and the preliminary threshold determination will
be sent to all appropriate agencies for review.
Grading Permit- Access road excavation and grading will require approval from the City
of Renton.
Shoreline Subtantial Development Permit - Maplewood Creek has a mean annual flow
of less than 20 cfs, therefore a Shoreline Substantial Development Permit is not required.
IV. CONCLUSIONS AND RECOMMENDATIONS
A. Conclusions
Based on the results of the Phase 1 preliminary design and analysis performed for the
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project, it is concluded
that:
• The most cost-justifiable design for the new sedimentation basin is to provide an
expanded basin with a pool surface area of approximately 12,000 square feet and a
volume of 1,300 cubic yards, at pool El. 109.0. The proposed new basin size is
approximately triple the existing basin size.
ibtaplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 16
RM',4G�P1I-I REV.d-.11121194 03'.25 P%I
Phase 1 Design Report
• The new basin will provide a sediment storage volume of approximately 600 cubic
yards assuming a 2-foot water depth for settling during high flow events. This is
approximately twice the sediment storage volume of the existing basin.
• The new basin is predicted to capture a larger portion of the fine sand than the
existing basin, with particles larger than 0.1 mm captured during a 2-year flood
event. In comparison, the existing basin would only retain particles larger than 0.2
mm under ideal conditions. The trap efficiency is estimated to increase from 25
percent (300 to 400 cubic yard annually) for the existing basin to 40 or 50 percent
(600 cubic yards annually) for the new basin. To maintain the improved trap
efficiency, the new basin will need to be cleaned an average of once a year.
• The cost difference to construct the expanded basin is approximately $26,000 (15
percent) more than to rebuild the existing basin. In view of approximately doubling
the trap efficiency, the cost increase for the basin expansion is considered to be
economically justified.
• Construction of the proposed project will also provide opportunities for stream
bank slope stabilization and habitat improvements on Maplewood Creek. It will
also provide access to the upper section of Maplewood Creek for adult salmon
spawning by removing the upper concrete dam and providing a fishway passage at
the new basin.
B. Recommendations
It is recommended that the new expanded sedimentation basin and associated stream
bank and habitat improvements be constructed as proposed. The proposed basin reconstruction
and improvements are shown on the three preliminary design drawings in Appendix C, with all
configurations and major dimensions outlined. The estimated total construction cost for the
proposed works is $196,117 based on August 1994 price levels. It is recommended that the
schedule for the project design and construction as shown on Exhibit 11 be carried out for the
project to be completed in September 1996.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 17
F:M34GTH-I REV J-11/2 I;41:03:'_5 PM
EXHIBITS
EXHIBITS
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SOURCE: U.S.G.S. RENTON SHEET, 1:24,000
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City of Renton Maplewood Sedimentation Basin
Reconstruction and Improvement Project
LOCATION MAP
NORTHWEST, INC.
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Exhibit
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SCALE IN FEET
DATE: 5-25-94
ALTERNATIVE B- 1
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i �� ALTERNATIVE B-2
CONSTRUCTION COST ESTIMATE - ALTERNATIVE A-1
MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT
CITY OF RENTON, WASHINGTON
Item Quantity Unit Unit Price Amount
------------------------- -------- ---- ---------- --------
Clearing & Grubbing lump sum LS ----- $4, 000
Basin/Dam Embankment
excavation 1500 CY $6.00 $9, 000
core fill 1250 CY $12.00 $15, 000
shell fill 900 CY $6.00 $5,400
Overflow Spillway
excavation 120 CY $6.00 $720
reinforced concrete 50 CY $450.00 $22,500
6' -dia. concrete pipe lump sum LS ----- $1, 500
backfill 80 CY $6.00 $480
riprap 15 CY $30.00 $450
Fishway Outlet
excavation 60 CY $6.00 $360
reinforced concrete 10 CY $450.00 $4,500
4' -dia. concrete pipe lump sum LS ----- $800
backfill 40 CY $6. 00 $240
4'x4 ' slide gate lump sum LS ----- $1, 600
Upper Dam Removal
sediment removal 700 CY $6.00 $4,200
concrete removal lump sum LS ----- $1,500
Bank Slopes Repair
excavation 250 CY $6.00 $1,500
rockery rock 100 EA $56. 00 $5, 600
riprap 45 CY $30.00 $1,350
crushed rock 30 CY $12.00 $360
Access Road Upgrade lump sum LS ----- $3, 000
Stream Habitat Improvements lump sum LS ----- $3,500
Mobilization & Misc. lump sum LS ----- $33,273
Total Direct Construction Cost $120, 833
Sales Tax 8% $9, 667
Engineering/Permitting $52,200
Administration $10,440
TOTAL CONSTRUCTION COST $193,139
(June 1994 Dollars)
EXHIBIT 6
CONSTRUCTION COST ESTIMATE - ALTERNATIVE A-2
MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT
CITY OF RENTON, WASHINGTON
Item Quantity Unit Unit Price Amount
------------------------- ---- --- ---- ---------- --------
Clearing & Grubbing lump sum LS ----- $4,000
Basin/Dam Embankment
excavation 1500 CY $6. 00 $9, 000
core fill 900 CY $12.00 $10,800
shell fill 650 CY $6.00 $3,900
Overflow Spillway
excavation 150 CY $6.00 $900
reinforced concrete 75 CY $450. 00 $33,750
backfill 90 CY $6.00 $540
riprap 15 CY $30.00 $450
Fishway Outlet
excavation 60 CY $6. 00 $360
reinforced concrete 10 CY $450.00 $4,500
4' -dia. concrete pipe lump sum LS ----- $800
backfill 40 CY $6.00 $240
4'x4 ' slide gate lump sum LS ----- $1, 600
Upper Dam Removal
sediment removal 700 CY $6.00 $4,200
concrete removal lump sum LS ----- $1,500
Bank Slopes Repair
excavation 250 CY $6.00 $1, 500
rockery rock 100 EA $56.00 $5, 600
riprap 45 CY $30. 00 $1,350
crushed rock 30 CY $12.00 $360
Access Road Upgrade lump sum LS ----- $3, 000
Stream Habitat Improvements lump sum LS ----- $3,500
Mobilization & Misc. lump sum LS ----- $34,903
Total Direct Construction Cost $126,753
Sales Tax 8% $10,140
Engineering/Permitting $54,757
Administration $10, 951
TOTAL CONSTRUCTION COST $202,602
(June 1994 Dollars)
EXHIBIT 7
CONSTRUCTION COST ESTIMATE - ALTERNATIVE B-1
MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT
CITY OF RENTON, WASHINGTON
Item Quantity Unit Unit Price Amount
------------------------- -------- ---- ---------- --------
Clearing & Grubbing lump sum LS ----- $2,000
Basin/Dam Embankment
excavation 900 CY $6.00 $5,400
core fill 750 CY $12.00 $9,000
shell fill 600 CY $6.00 $3, 600
Overflow Spillway
excavation 120 CY $6.00 $720
reinforced concrete 50 CY $450.00 $22,500
6—dia. concrete pipe lump sum LS ----- $1,500
backfill 80 CY $6.00 $480
riprap 15 CY $30.00 $450
Fishway Outlet
excavation 60 CY $6.00 $360
reinforced concrete 10 CY $450.00 $4,500
4 ' -dia. concrete pipe lump sum LS ----- $800
backfill 40 CY $6.00 $240
4'x4 ' slide gate lump sum LS ----- $1,600
Upper Dam Removal
sediment removal 700 CY $6.00 $4,200
concrete removal lump sum LS ----- $1,500
Bank Slopes Repair
excavation 250 CY $6.00 $1, 500
rockery rock 100 EA $56.00 $5, 600
riprap 45 CY $30.00 $1,350
crushed rock 30 CY $12.00 $360
Access Road Upgrade lump sum LS ----- $3, 000
Stream Habitat Improvements lump sum LS ----- $3,500
Mobilization & Misc. lump sum LS ----- $28,181
Total Direct Construction Cost $102,341
Sales Tax 8% $8, 187
Engineering/Permitting $49,738
Administration $9,948
TOTAL CONSTRUCTION COST $170,213
(June 1994 Dollars)
EXHIBIT 8
CONSTRUCTION COST ESTIMATE - ALTERNATIVE B-2
MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT
CITY OF RENTON, WASHINGTON
Item Quantity Unit Unit Price Amount
------------------------- -------- ---- ---------- --------
Clearing & Grubbing lump sum LS ----- $2,000
Basin/Dam Embankment
excavation 900 CY $6.00 $5,400
core fill 400 CY $12.00 $4,800
shell fill 350 CY $6.00 $2,100
Overflow Spillway
excavation 150 CY $6. 00 $900
reinforced concrete 75 CY $450. 00 $33,750
backfill 90 CY $6.00 $540
riprap 15 CY $30.00 $450
Fishway Outlet
excavation 60 CY $6. 00 $360
reinforced concrete 10 CY $450. 00 $4,500
4' -dia. concrete pipe lump sum LS ----- $800
backfill 40 CY $6.00 $240
4'x4' slide gate lump sum LS ----- $1,600
Upper Dam Removal
sediment removal 700 CY $6. 00 $4,200
concrete removal lump sum LS ----- $1,500
Bank Slopes Repair
excavation 250 CY $6. 00 $1,500
rockery rock 100 EA $56. 00 $5,600
riprap 45 CY $30.00 $1,350
crushed rock 30 CY $12.00 $360
Access Road Upgrade lump sum LS ----- $3,000
Stream Habitat Improvements lump sum LS ----- $3,500
Mobilization & Misc. lump sum LS ----- $29,811
Total Direct Construction Cost $108,261
Sales Tax 8% $8,661
Engineering/Permitting $52,615
Administration $10,523
TOTAL CONSTRUCTION COST $180,060
(June 1994 Dollars)
EXHIBIT 9
CONSTRUCTION COST ESTIMATE - PROPOSED DESIGN
MAPLEWOOD CREEK SEDIMENTATION BASIN PROJECT
CITY OF RENTON, WASHINGTON
Item Quantity Unit Unit Price Amount
------------------------- -------- ---- ---------- --------
Clearing & Grubbing lump sum LS ----- $4,000
Basin & Dam Embankment
excavation 1800 CY $6.00 $10,800
core fill 1700 CY $10. 00 $17,000
shell fill 900 CY $6.00 $5,400
8"-dia drain system lump sum LS ----- $2,000
Overflow Spillway & Outlet
excavation 150 CY $6.00 $900
reinforced concrete 53 CY $400.00 $21,200
6' -dia. concrete pipe lump sum LS ----- $1,500
backfill 80 CY $6. 00 $480
riprap 15 CY $30.00 $450
Fishway Outlet & Flow Bypass
excavation 60 CY $6.00 $360
reinforced concrete 21 CY $400.00 $8,400
42"-dia. concrete pipe lump sum LS ----- $700
backfill 60 CY $6.00 $360
12"-dia. bypass system lump sum LS ----- $8,000
Upper Dam Removal
sediment removal 700 CY $6. 00 $4,200
concrete removal lump sum LS ----- $1,500
Bank Slopes Repair
excavation. 250 CY $6.00 $1,500
rockery rock 100 EA $56.00 $5,600
riprap 45 CY $30.00 $1,350
crushed rock 30 CY $12.00 $360
Access Road Upgrade lump sum LS ----- $3,000
Stream Habitat Improvements lump sum LS ----- $3,500
Mobilization & Misc. lump sum LS ----- $27,178
Total Direct Construction Cost $129,738
Sales Tax 8% $10,379
Engineering/Permitting $50,000
Administration $6,000
TOTAL CONSTRUCTION COST $196,117
(August 1994 Dollars)
EXHIBIT 10
Maplewood Creek Sedimentation Basin Project
Proposed Design and Construction Schedule
- -- - -- — - 1995 Dec —1996 —
Task Name Duration DecJanet�MarrApr a Jun_ Jul u e Oct o Jan a Ma A rMa Jun Jul u p
Start End
A. AGENCY CONSULTATION 16.00 m Dec/01/94 Apr/23/96:�!11111iji,:ui111111! iffll:�Hlffl1 Il lf1 11
1. FEMA Review/Approval 6.00 m Dec/01/94 Jun/08/95
2.Construction Permits 10.00 m Jun/09/95 Apr/23/96
B. CONTRACT DRAWINGS&SPECS 1.00 m Feb/26/96 Mar/26/96 UUM
2. Design Drawings 1.00 m Feb/26/96 Mar/26/96
3.Specifications _ 1.00 m Feb/26/96 Mar/26/96
C. CONTRACT BID/AWARD 3.00 m Mar/27/96 Jun/27/96
D.CONSTRUCTION 8.00 w Jul/15/96 Sep/N& Ir
1. Mobilization 1.00 w Jul/15/96 Jul/19/96
2. Basin&Dam Embankment 6.00 w Jul/22/96 rAug/30/96
3.Overflow Spillway-&Outlet 6.00-w Jul/22/96 Aug/30/96
4. Fishway&Flow Bypass 6.00 w Jul/22/96 Aug/30/96
5_Upper Dam Removal 1.00 w _Aug/19/96 Aug/23/96
_6. Bank Ss6es Repair 1.00 w Au /26/96 Au /30/96
7.Access Road Upgrade 1.00 w Au /12/96 Au /16/96
8.Stream Habitat Improvements 1.00 w Au /26/96 Au /30/96 1
9.Demobolization 1.00 w Sep/03/96 Se /09/96
Harza NW, Nov/21/94 Milestone A Summary
Fixed Delay - - -
APPENDIX A
Sediment Load and Geotechnical Evaluation Report
APPENDIX A
Sediment Load and Geotechnical Evaluation Report
Appendix A, Phase 1 Design Report
TABLE OF CONTENTS
1.0 Introduction.................................................................................................. 1
2.0 Geologic Conditions ..................................................................................... 1
3.0 Slope Stabilization........................................................................................2
4.0 Field Sampling and Testing.........................................................................4
5.0 Sediment Size Distribution..........................................................................4
6.0 Sediment Supply...........................................................................................6
7.0 Size of Sediment............................................................................................7
8.0 Sedimentation Basin Dynamics................................................................... 8
9.0 Sedimentation Basin Efficiency................................................................. 10
10.0 Removal of Deposited Sediments.............................................................. 10
11.0 Geotechnical Requirements for Proposed Embankment....................... 10
12.0 Concrete Dam Removal and Channel Modification............................... 12
References ............................................................................................................. 14
Figure
Figure 1 - Landslide and Sample Site Locations
Attachment A - Sieve Analyses Results
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i
F:\7134G\Geo-REV.doc:11/21/94:03:33 PM
Appendix A, Phase 1 Design Report
APPENDIX A
SEDIMENT LOAD AND GEOTECHNICAL EVALUATION
REPORT
1.0 Introduction
This Sediment Load and Geotechnical Evaluation Report was prepared for use in
analyzing options for reconstructing and improving the Maplewood Creek Sedimentation Basin.
A complete description of the project being proposed by the City of Renton is provided in the
"Phase 1 Design Report" to which this report is an appendix.
2.0 Geologic Conditions
Maplewood Creek watershed is 1,099 acres in area. The watershed area includes part of
the golf course, the wooded ravine that Maplewood Creek flows through and residential and
commercial areas on the plateau above the ravine. For determination of sediment yield an
acreage of 1,032 has been used which encompasses only the area upstream of the proposed
sedimentation basin. The deep part of the canyon containing the creek represents approximately
200 acres of this area. Slopes observed in the canyon are marginally stable to unstable. They are
heavily vegetated with numerous mature fir and alder trees. Approximately 10 significant
landslides were observed on the canyon slopes (some of which are located on the accompanying
Figure 1) during our field traverse on April 26, 1994. These unstable areas include raveling
slopes undercut by stream action, rotational failures, slope creep and debris flows.
The stream channel is remarkably free of debris derived from these slides. The channel
floor is covered by a thick blanket of sand and gravel possibly up to 10 feet thick. Organic
debris, such as logs, bridge the creek but intermittent stream flows must have been sufficiently
high to strip most fine organic debris from the channel. Two minor canyon debris jams were
found, but these do not impede the normal stream flow.
The geologic environment of the canyon formed by Maplewood Creek consists of
subhorizontally bedded, glacially-derived sediments. Exposures within the canyon display sandy
gravel, sand and clay beds varying in thickness from about one foot to several feet. Near the
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 1
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Appendix A, Phase I Design Report
mouth of the canyon the left (east) bank* consists of a massive clay bed apparently greater than
10 to 15 feet thick. Up slope on the right bank and vertically in the geologic section is a thick
layer of sandy gravel with a trace of silt and clay in the matrix. These layers alternate with clean
sand beds upward to the top of the canyon.
Most exposures of bedded sediments are covered by a steeply sloping mantle of gravelly
sandy clay that includes an abundance of organic material. All slopes observed in the canyon
exhibit slope movement of varying degrees of severity. Near the creek, bank undercutting occurs
on nearly every outside bend. Several rotational slope failures were identified. One was located
high on the left bank about two thousand feet upstream of the golf course and the second about
one thousand feet upstream on the right bank. Soil creep is visible under the vegetation cover on
nearly every slope. The mature trees in many cases reflect a long term exposure to soil creep.
The canyon is mapped as a large Holocene landslide in the Generalized Geologic Map of
Seattle and Suburban areas (Galster and Laprade, 1991). This slide mass is carved into the
recessional glacial deposits left by the retreat of glaciers about 10,000 years ago. The layering of
these clastic recessional deposits is conducive to the formation of complex slides. Descending
groundwater seeps laterally along the top of clay layers and discharges on the slope, undercutting
overlying bedding which fails by toppling or slumping. Clay layers may allow internal
hydrostatic pressures to increase where confinement is attained until rotational failure results.
The poorly consolidated sand beds are readily eroded by stream activity during floods and
sloughing of the creek banks occurs. The canyon bottom sloughing destabilizes the upper slopes
and keeps the whole complex slide system active.
3.0 Slope Stabilization
Evaluation of the canyon slopes identified two large landslides and about ten sloughing
slopes where creek undercutting was apparent. These two large slides appear to be in a thicker
till unit of the geologic section. The slides are marginally stable and do not appear to have
moved in recent years. Seepage was visible along the upper margin and sides of these slides.
Slope creep may be active on the upstream, east bank slide that is moving into the East Tributary
of Maplewood Creek.
The undercut stream banks could be repaired at significant cost and disturbance to the
stream. In most localities the stream is narrow and toe stabilization measures would take up a
* Nomenclature used in this report: Site is viewed looking down canyon,the left bank is the east side;right bank is
the west side.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 2
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Appendix A, Phase I Design Report
sizable portion of the stream bed. While the amount of sediment produced from the existing
failing slopes may be excessive, repairs are likely to only transfer the focus of erosion to adjacent
banks.
Stabilization of the canyon slopes would alter the natural character of the stream. The
stream channel is at a relatively uniform gradient from the upstream tributary confluence located
2,000 feet above the golf course. Dead falls, rock debris and gravel bars have effectively
stabilized the stream gradient and may tend to reduce flood velocities as water levels rise. There
are few large rock fragments in the stream channel. Most rock is gravel size and less than two
inches nominal diameter. There is no evidence that the large slope failures will develop at an
increasing rate since most of the present vegetation is mature and most failures, except the
undercut streambanks, appear to be quite old. It is our opinion that the sediments presently
found in the stream channel are representative of that which will be transported over the next
several years.
A rotational slope failure is located on the left bank immediately upstream of the upper
concrete dam, and a severely undercut slope is located about 100 feet downstream of the dam.
These two unstable areas are possibly the result of changes in stream energy resulting from the
construction of the upper concrete dam. A longitudinal profile along the creek (see Appendix C,
sheet 1, Section A) shows a significant scour zone below the dam.
Dam removal may reactivate slope erosion upstream of the structure. Protection placed at
the toe of the upper slipping slope will enhance the stability of the rotational failure area that has
developed (see Appendix C, sheet 1, Sections B and Q. Upon removal of the dam the
downstream scour zone is likely to fill, reducing the risk of slope failure on the left bank. Slope
protection is warranted until stability of the channel is attained.
We recommend no action be taken to stabilize the upper canyon slope failures and to
allow the stream and adjacent slopes to attain their own level of stability. Stabilization of the
slope failures near the upper dam may be facilitated by installing a toe buttress for erosion
protection and a toe surcharge to minimize slope movement by sliding (see Appendix C, sheet 1,
Sections B and Q. No additional repairs are recommended on other slopes in the canyon unless
additional significant movement is observed. At that time, selective remedial measures can be
employed.
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Appendix A, Phase I Design Report
4.0 Field Sampling and Testing
Five soil samples were collected and field classified using Unified Soil Classification
System descriptions (Table 1). Only descriptive parameters were obtained; Plasticity Index (PI)
or Liquid Limit (LL) were not measured. The soil samples were obtained from slope soils near
the site of the proposed sedimentation basin and from two sites upstream.
Table 1
Unified Soil Classification System Soil Descriptions (Field Classification Only)
Site A. Clay; CL-CH, dark brown, moist, organic rich, high plasticity,
medium to low dilatancy, high toughness, medium dry
strength, trace of silt.
Site B. Clay; CH-CL, dark brown, moist, organic rich, high plasticity,
medium to low dilatancy, high toughness, medium dry
strength, trace of silt.
Site C. Silty clay; NIL-CL, dark gray brown, moist, low to medium
plasticity, medium dilatancy, low toughness, medium dry
strength.
Site D. Silty clay; MI-CL, yellow brown, moist, medium to low
plasticity, no dilatancy, low toughness, high dry strength, till -
looks like claystone.
Site E. Clay; CL, dark brown, moist, low plasticity, medium
toughness, medium to low dry strength.
5.0 Sediment Size Distribution
A total of 17 soil samples were obtained from the sedimentation basin, stream bed,
canyon sidewalls and tributary streams in order to determine the bedload size distribution and the
potential volume of fines transported through the canyon. Sampling locations are shown on
Figure 1. The collected sediments were sieved on four screens which bracket the grain-size
range of interest. Results of the sieving are displayed in Attachment A at the end of this report,
and summarized in Table 2.
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Appendix A, Phase 1 Design Report
Table 2
Sediment Sampling Results
Sample Percent Percent Percent Silt
Number Gravel Sand and Clay Sample Location
Sedimentation Basin
1 52 46.5 1.0 In sedimentation basin,upstream right side.
2 52.5 45.7 1.6 In sedimentation basin, downstream right side.
3 4.3 86.5 9.1 In sedimentation basin, downstream left side.
4 56 43.0 0.9 In sedimentation basin,upstream left side.
Average 41 55 3
Side Slopes
5 22.5 68.1 9.3 75 feet upstream of dam, left slope, 30 feet from
pond.
6 6.6 82.2 11.2 East(left) of dam, left slope, 10 feet above top of
dam.
7 34.5 60.6 3.5 30 feet upstream of dam, 5 feet above road
elevation, right slope.
9 24.7 67.9 6.6 Sloughed area, left bank, 100 feet below concrete
dam.
10 4.6 90.9 4.4 Sloughed area, left bank stream terrace, 100 feet
below concrete dam.
13 15.7 78.2 5.1 Left streambank 200 yards upstream of concrete
dam.
14 48 49.0 1.2 100 feet upstream of access trail, right bank, 6
feet above streambed.
Average 22 71 6
Streambed
8 27 64.9 7.2 Stream deposits 250 feet upstream of
sedimentation pond.
11 27 66.8 3.1 Side stream from right bank below concrete dam.
12 49 48.6 0.6 Stream sample, 50 feet upstream of concrete
dam.
15 39 56.3 2.2 Left(East Tributary) streambed sample, at
confluence.
16 19.9 75.6 4.0 Right(West Tributary) streambed sample, at
confluence.
17 4.9 74.3 20.8 Streambed sample below large active slide.
Average 28 64 6
Sedimentation Basin: Three of the four samples (1, 2, 4) obtained in the basin contained
less than two percent silt and clay and had nearly equal amounts of gravel and sand. The fourth
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Appendix A, Phase I Design Report
sample (3) obtained from the left eddy zone upstream of the outlet channel contained 9 percent
silt and clay deposited in the last two highwater episodes and over 85 percent sand with half of
the sand component in the fine sand category.
Streambed Samples: The streambed sediments were sampled in the lower creek,
upstream of the sedimentation basin (samples 8, 11, and 12) and in the main channel and east and
west forks approximately 2,000 feet upstream of the basin (samples 17, 15 and 16). No apparent
coarsening upstream patterns were seen in the sampled sediments. Rather, sediments appeared to
reflect upstream source areas, particularly sample 17, which contains an abundance of silt and
clay (21 percent) and over 40 percent fine sand. The source of this high volume of fine material
is sloughing from the adjacent active slide. The streambed samples contain an average of 28
percent gravel, 64 percent sand, and 6 percent silt and clay.
Side Slope Samples: Samples of the canyon side slopes display an average of 6 percent
silt and clay, 71 percent sand, and 22 percent gravel.
These sieve results confirm that gravel to coarse sand is captured by the existing
sedimentation basin along with a small portion of the fine sand. Most of the fine sand and
practically all of the silt and clay are passed downstream. Actively sloughing slopes contribute
large quantities of fine material. Approximately ten actively eroding zones were observed on the
slopes between the sedimentation basin and the confluence of the East and West Tributaries.
6.0 Sediment Supply
The volume of sediment supplied to the existing and proposed sedimentation basins on
Maplewood Creek varies greatly from year to year. The amount of sediment transported into the
basin is a function of the amount eroded from mass movements, surface erosion, soil creep, and
bank erosion upstream of the basin, and the capacity of the stream to transport those sediments
downstream. Transport capacity is dependent upon the flow of water in the creek. The majority
of sediment is transported during high flows, with bedload transport generally being initiated
when flows exceed bankfull flow, roughly equivalent to the 1.5-year recurrence interval flood
flow.
Since there have been no direct measurements of sediment supply or transport in the
Maplewood Creek basin, several different methods were used to estimate the volume of sediment
supplied to the stream. Direct measurements of suspended sediment transport were made in the
nearby Snoqualmie River basin by Nelson (1971). He calculated average annual suspended
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Appendix A, Phase 1 Design Report
transport rates of 300 to 980 cubic yards/square mile in different subbasins. Assuming bedload -
transport rates of 10 percent of the suspended load, Nelson's rates for total transport would be
330 to 1080 cubic yards/square mile/year.
Estimates of sediment transport and deposition rates in the lower Cedar River and delta
area were made by Harza NW (1992). They estimated suspended sediment transport rates of 165
cubic yards/square mile/year and 50 cubic yards/square mile/year of bedload transport. These
rates correspond to sediment supply averaged over the entire lower Cedar River basin; sediment
supply from the actively eroding Maplewood Creek basin would be expected to be several times
higher.
The golf course maintenance supervisor reported that the existing sedimentation basin has
been cleaned out every year except 2 during the last 9 years. It also required cleaning following
the November 1990 flood event. Assuming 300 to 400 cubic yards of sediment (the total volume
of the basin) was removed from the basin 7 out of the last 9 years, an average of 230 to 300 cubic
yards is trapped by the basin each year. This is the equivalent of 145 to 185 cubic yards/square
mile. The material trapped in the sedimentation basin consists of gravel and sand. These
materials are carried as bedload in streams the size of Maplewood Creek. The estimates of
sediment supply rates from the sedimentation basin correspond to the bedload portion of the total
sediment supply in Maplewood Creek. Bedload is generally 5 to 20 percent of the total load of a
stream. Assuming 10 percent bedload, the total sediment supply rates based on these estimates
are 1,400 to 1,800 cubic yards/square mile.
Based on the above information and the actively eroding Maplewood Creek basin, it is
estimated that an average of 1,200 cubic yards of sediment is transported into the existing
sedimentation basin on an average annual basis. An average of 250 to 300 cubic yards of gravel
and sand have been trapped in the basin each year under recent flow conditions. The remaining
900 cubic yards of material consisting primarily of fine sand, silt, and clay is transported through
the basin and is deposited in the channel upstream of the highway culvert or is transported into
the Cedar River.
7.0 Size of Sediment
The grain size distribution of the total sediment load in Maplewood Creek is not known.
Sediment samples taken from the bed and sedimentation basin are representative of only the
coarsest fraction of the total load moving in the creek. Fine sand, silt, and clay particles that
make up the majority of the sediment load in most river systems are carried as suspended load
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Appendix A, Phase 1 Design Report
and are not retained in the streambed or in the existing sedimentation basin. The grains size
distribution of the total load can be estimated based on measured streambed size gradations and
measurements of suspended load from other systems.
Assuming the sedimentation basin traps all of the gravel and coarse sand transported into
it, a total of 120 cubic yards of gravel and 60 cubic yards of coarse sand is trapped on an annual
basis. These numbers correspond to 10 and 5 percent of the total load, respectively. Using these
numbers as end points and assuming the total sediment load curve follows a slope similar to the
grain size curves of measured samples from the creek and banks, an estimated grain size
distribution was constructed (Table 3).
Table 3
Estimated Size Distribution of Total Sediment Load
Grain Size Estimated Percent of Total Load Volume (cu yd)
Gravel 10 120
Coarse sand 5 60
Medium sand 25 300
Fine sand 25 300
Silt and clay 35 420
Total 100 1,200
This distribution shows that an average of 300 cubic yards each of medium and fine sand
are transported annually, along with 420 cubic yards of silt and clay. It should be noted that no
direct measurements of the silt and clay portion of the load have been made; accurate estimates
of suspended sediment transport rates and sizes require several years of sampling during varying
flow conditions.
8.0 Sedimentation Basin Dynamics
The basic principle governing the behavior of sedimentation basins is that by slowing the
velocity of sediment-laden water, the water will lose the energy necessary to transport the
particles in suspension or as bedload and the particles will settle out of the water column and be
deposited in the basin. In order for a particle to be trapped in the basin, the residence time of the
particle in the basin must be long enough to allow it to fall to the bottom before it is transported
out of the basin. Goldman et al. (1986) have derived the following formula for determining
sedimentation basin size:
As = 1.2QNS
where As = Surface area of sedimentation basin
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Appendix A, Phase I Design Report
Q = Discharge of water
Vs = Settling velocity of particle
The existing sedimentation basin has a surface area of 4,000 square feet assuming a pool
at El. 109 and a volume of 300-400 cubic yards when cleaned out. The proposed dimensions of
the new sedimentation basin would give it a surface area of 12,000 square feet and a volume of
1,300 cubic yards. Assuming each basin were in a cleaned out state, the size of particles trapped
in each under different flow conditions was calculated. The results are shown in Table 4.
Table 4
Size of Particles Retained in Existing and Proposed Settling Basins.
Existing Basin Proposed Basin
Settling Velocity of Particle Size Settling Velocity Particle Size
Flood Discharge Particles Retained Retained of Particles Retained
Frequency (cfs) (ft/s) (mm) 1 Retained(fds) (MM) 1
2 years 173 0.052 0.18 0.017 0.09
10 years 275 0.083 0.23 0.028 0.11
25 years 333 0.100 0.28 0.033 0.14
100 years 392 0.118 0.31 0.039 0.15
1 Grain size determined from empirical graph of settling velocities versus grain size(Goldman et al. 1986)at water temperature
of 10°C(50 T).
These calculations indicate that the current sedimentation basin would retain particles
coarser than 0.2 mm (fine to medium sand) under ideal conditions. Based on the size of particles
sampled from the main body of the basin (not the backwater area), 97 percent of the particles are
larger than 0.2 mm. Based on the grain size of sediments from streambed samples, with an
average of 15 to 20 percent finer than 0.2 mm, only a portion of this sized particle available for
transport in the creek is trapped in the basin. This indicates that the basin is not as efficient as
the calculations predict, likely due to turbulent eddies and resuspension of sediment as the basin
fills and water depths are reduced.
The proposed new pool is predicted to capture a larger portion of the fine sand than the
existing pool, with particles larger than about 0.1 mm captured during a 2-year flood event. As
with the existing pool, trap efficiencies will decrease as the pool fills with sediment. However,
the larger area and volume of the proposed pool will allow a greater volume of sediment to be
trapped before efficiencies are lowered, and will allow the water to slow and spread over a
greater area, reducing turbulence.
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Appendix A, Phase I Design Report
9.0 Sedimentation Basin Efficiency
Reservoir efficiency is defined as the ratio of the quantity of deposited sediment to the
total sediment inflow. This efficiency is dependent primarily on the sediment settling velocity
and the flow velocity through the reservoir. The present basin has an estimated trap efficiency of
25 percent (300 cubic yards). By increasing the size of the pool, the trap efficiency will increase.
Assuming the new basin will trap particles coarser than about 0.1 to 0.2 mm diameter, it is
estimated that trap efficiency will increase to 40 or 50 percent (500 to 600 cubic yards annually).
10.0 Removal of Deposited Sediments
Based on the proposed new-basin configuration, the trapped sediments should consist
primarily of gravel and sand which will be readily dewatered and small amounts of coarse silt
and clay representing less than 10 percent which should have no real effect on large-scale
dewatering but may result in extra weight hence higher hauling costs.
Removal of the debris should be initiated by the preliminary excavation of a bypass
channel through the basin to facilitate dewatering or utilization of the bypass pipe installed for
the pu Vose. A dewatering trench could be excavated a few days prior to clean out and may
significantly reduce the total tonnage of material removed.
In order to retain the optimum settling characteristics in the basin, at least 2 feet of water
depth should be provided for settling during high flow events when the basin pool level reaching
the proposed spillway crest at El. 109. This means that the basin floor should be deeper than 107
feet at all times. If the basin is designed with a bottom elevation of 105 feet, this will allow 600
cubic yards of the total 1,300 cubic yards to act as sediment storage volume and will require
cleaning on an average of once a year. If less frequent cleaning is desired, the bottom elevation
could be cleaned to 104 feet to provide a total of 900 cubic yards of storage. As with the present
basin, depending upon the storm frequency and intensity, the basin may need to be cleaned after
a single large storm, or may not require cleaning for several years if there are no high flow
events.
11.0 Geotechnical Requirements for Proposed Embankment
The proposed embankment is planned as a compacted earthfill embankment. The
embankment will be penetrated by a fishway and a spillway. Compacted fill will be required to
form the embankment and foundation for the fishway and the spillway. While the local materials
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Appendix A, Phase 1 Design Report
may be suitable, excessive organic debris may make use of this material an unattractive option
over importation of soils from an established borrow area.
No subsurface investigation of the site has been conducted. The local published geology
indicates that highly competent pre-Vashon glacial and nonglacial sediments may underlie the
embankment zone. These sediments, as well as the Vashon till and recessional sand and gravel,
can form a satisfactory foundation for the embankment. Minimal stripping may be necessary to
establish the base of the dam. Well logs obtained from the City indicate sand and gravel strata
approximately 10 feet below existing grade at the well sites about 500 feet south. We expect that
sand and gravel may be encountered at a similar depth along the embankment axis.
We recommend that bidding documents include specifications for borrow materials.
Prior to construction, samples will be collected and tested by Modified Proctor Tests to
determine optimum moisture content and maximum dry density. General specifications for the
compacted embankment will call for compaction to 98 percent of maximum dry density at no
more than 2 percent over optimum moisture content. No rock over six inches will be allowed in
the embankment. Additional soil parameters will be provided prior to construction. The fill
material should attain the following general specifications:
• Well graded sand and gravel,
• Less than 5 percent silt and clay,
• No rock 6 inches or greater, in size,
• Organic content less than 2 percent,
• Maximum dry density range of 120 - 130 pcf,
• Moisture content 8 to 12 percent optimum. ,
Prior to bidding for construction, a geotechnical investigation should be performed on the
site. We recommend that the embankment and structure foundations be stripped to sound
bearing soils and inspected by the geotechnical engineer prior to construction (see Appendix C,
sheet 1, Typical Dam Section). All soft spots in the foundation must be overexcavated and
backfilled with compacted fill. If locally derived soils are used in the embankment, we
recommend that they be used to fill out the outer slopes of the embankment. The core section of
the embankment should consist of imported fill conforming to the general specification. This
core with uniform slopes of 1:1 could be raised concurrently with the upstream and downstream
shell using locally derived organic-free sediments. All imported and local fill materials must
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Appendix A, Phase I Design Report
attain a compacted density of 98 percent of maximum dry density, and the moisture content must
lie within optimum moisture content or up to 2 percent above the optimum moisture content.
This latter requirement may be difficult to attain without substantial effort.
Because of the low height of the structures, field borings to verify subsurface conditions
may need to extend only a few feet below the ground surface. Borings within 500 feet indicate
sand and gravel approximately 10 feet below the surface. Overexcavation of soft materials and
replacement with imported compacted fill will provide a satisfactory embankment. Locally
derived fill material conforming to the general specifications identified above and compacted to
specification will readily hold at slopes of 2:1 (H:V) upslope and 2.5:1 downstream. The total
height of the embankment from top to downstream toe is about 8 feet. This height of
embankment, soil type, required compaction and low permeability should attain a satisfactory
factor of safety.
Seepage is not expected to be a problem if the embankment is constructed from well-
compacted glacial till. Normal pool water level is El. 108.5 feet and the base of the embankment
is about El. 103. This low head and wide embankment, as well as construction on a native soil of
glacial till, is expected to form a competent impermeable structure.
12.0 Concrete Dam Removal and Channel Modification
The upper concrete dam located 500 feet upstream of the existing sedimentation basin
will be removed to facilitate fish passage into the upper creek area. Removal may be partial or
complete depending on the type and condition of the concrete and foundation. We recommend
the use of a track-hoe mounted pneumatic pavement breaker for removal.
At a minimum the concrete must be removed to a depth of one foot below stream grade
(approximately El. 122.5) measured on the downstream side of the wall. The acquired opening
should be at minimum 10 feet in width at the bottom and slope outward at 45 degrees toward
each bank. In the event that the dam does not have a foundation or that the opening extends the
full height of the wall, all of the concrete wall shall be removed.
After removal of the dam and accumulated sediments each bank must be armored using
riprap (8-inch size rock for a distance of at least 60 feet upstream). This distance should be
coincide with the left bank slope repair and pre-existing armoring on the right bank.
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Appendix A, Phase I Design Report
Stream habitat enhancement calls for the placing of 2- to 3-foot size boulders along the
creek bottom with about 8 to 10 feet spacing. This method should extend from about 100 feet
upstream of the upper dam to the upstream end of the reconstructed sedimentation basin.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 13
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Appendix A, Phase I Design Report
References
Galster, R.W., Editor. 1989. Engineering Geology in Washington. Washington Division of
Geology and Earth Resources, Bulletin 78.
Goldman, S.J, K. Jackson, and T.A. Bursztnsky, 1986. Erosion and Sediment Control
Handbook. McGraw-Hill:New York.
Harza Northwest. 1992. Reconnaissance Sediment Transport Report for the Cedar River Delta
Project Renton, Washington. Unpublished report prepared for the City of Renton. March
1992.
Nelson, L.M.. 1971. Sediment Transport by Streams in the Snohomish River Basin,
Washington: October 1967 - June 1969. USGS Open-File Report 71-213.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Paue 14
F:A7134G\Geo-REV.doc:11/21/94:03:33 PM
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BULLETIN OF AEG, VOL 28, N0. 3
OBSERVED
850' \3 SLOPE FAILURES
City of Renton Maplewood Sedimentation Basin
k.lAdQ. 7
Reconstruction and Improvement Project
_4.A LANDSLIDE AND
NORTHWEST, INC. SAMPLE SITE LOCATIONS
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Figure 1
7134G AUG., 1994
Appendix A
ATTACHMENT A
SIEVE ANALYSES RESULTS
Description
Sieve analyses were performed on 17 samples obtained from the creek channel,
sedimentation pond and side slopes within the drainage area of Maplewood Creek. These
samples were obtained in order to characterize the type of materials transported through the
system.
Testing was done on the samples without regard to moisture loss or minor losses in
weighing. Errors by weight may be as much as 2-3 percent. The results of the sieve analyses are
shown on Figures Al through A 17 and Table A-1.
Table A-1
Results of Sieve Analyses
Retained on Sieve Size
Total Sample pan
Sample# Weight (gm) 16 mm 2 mm 0.5 mm 0.0625 mm Silt & Clay
1 968.9 236. 466.5 197.5 56.2 3.7
2 676.70 140.6 369.8 108.6 51.9 5.8
3 647.70 0 47.8 234.9 336.8 28.2
4 967.8 271.7 464.1 155.5 74.5 2.
5 469.8 50.3 95.9 77.7 222.5 23.4
6 401.6 0 45.4 58. 278.7 19.4
7 692.8 63.9 317.1 157.4 143.5 10.9
8 742.10 97.3 188.1 125.7 305.9 25.1
9 472.90 17.5 185. 175.8 75.5 23.9
10 638.4 0 50.2 360.4 219.7 8.1
11 695.3 120.7 151.3 212.7 208. 2.6
12 751.10 184.4 336.8 196.2 32.5 1.2
13 840.2 26. 196.2 267.4 338.5 12.1
14 766.6 203. 307.1 181.6 72.7 2.2
15 1 677.2 129.7 259.2 193.3 87.9 7.1
16 719.4 12.4 229.9 179.2 295.8 2.1
17 305.5 0 25.7 84.4 144.9 50.5
Maplewood Creek Project Pa-e A-1
F:\7131C\G--h.dac:l/_IrV.t_0 33 Phi
aLr-V z urr.1NI'Nu LN LNCHFS i U.S.SIEVE NUMBERS I HYDROMETER
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90
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GRAIN SIZE 124 MMLRAETERS
COBBLES GRAVEL SAND SILT OR CLAY
I
medium e coarse I fine arse
Specimen Identification Classification WC% %Gravel %Sand %Silt %Clay
• SAMPLE 1.0
Sampled upstream right bank-pond area
GRADATION CURVES, ASTM D-422
Maplewood Creek Sedimentation Study
NORTHWEST, INC. Renton, Washington
Consulting Engineers & Scientists PROJECT No. DATE FIcuRE
704G f Afay 6, 1994
U.S.SIEVE OPENING IN INCHES i U.S.SIEVE NUMBERS I HYDROMETER
4
100 3 2 1.5 1 3/4 1/2 3/8 3 4 6 310 1416 20 30 40 50 70 100140 200
90
80
P
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R 70
C
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20
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100 10 1 0.1 0.01 0.001
GRAIN SIZE IN MILLIMETERS
COBBLES GRAVEL SAND SILT OR CLAY
coarse I fine koarse I medium I fine
Specimen Identification Classification WC% %Gravel %Sand %Silt %Clay
• SAMPLE 2.0
r
Sampled downstream right side, pond area
LI GRADATION CURVES, ASTM D-422
Aj;;zW7rjk Maplewood Creek Sedimentation Study
NORTHWEST, INC. Renton, Washington
Consulting Engineers & Scientists PROJECT No. DATE FI NtJoRle/A 2
7134G May 6, 1"4 '-1
U.S. SIEVE OPENING IN INCHES U.S.SIEVE NUMBERS HYDROMETER
6 4 3 2 1.5 13/42/*2 /8 3 4 6 810 1416 20 30 40 50 70 100140 200
100
90
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1.50
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100 10 1 0.1 0.01 0.001
GRAIN SIZE IN MMI-2viETERS
COBBLES GRAVEL SAND SILT OR CLAY
I coarse I fine 6arse I medium I fine I
Specimen Identification Classification WC% %Gravel %Sand %Silt %Clay
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Sampled downstream left side, pond area
m7r GRADATION CURVES, ASTM D-422
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GRADATION CURVES, ASTM D-422
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NORTHWEST,, INC. Renton, Washington —
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GRADATION CURVES, ASTM D-422
Maplewood Creek Sedimentation Study
NORTHWEST, INC. Renton, Washington
Consulting Engineers & Sdentists i PROJECT No. DATE I FG:E,,4k 6
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LI GRADATION CURVES, ASTM D-422
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NORTHWEST, INC. Renton, Washington-Consulting Engineers & Scientists I PROJECT No. DATE f FIGURE 8
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Renton, Washington
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GRADATION CURVES, ASTM D-422
L4LA&Z7�r Maplewood Crftk Sedimentation Study
NORTHWEST, INC. Renton, Washington
Consulting Engineers & Scientists PROJECT No. DATE FIGURE
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Consulting Engineers & Scientists
A
APPENDIX B
Aquatic and Terrestrial Resources Report
APPENDIX B
Aquatic and Terrestrial Resources Report
Appendix B, Phase 1 Design Report
TABLE OF CONTENTS
1.0 Introduction.................................................................................................... 1
2.0 Existing Habitat Conditions.......................................................................... 1
2.1 Aquatic Habitat............................................................................................................. 1
2.2 Terrestrial Habitat.........................................................................................................2
2.2.1 Vegetation............................................................................................................2
2.2.2 Threatened, Endangered and Sensitive Plants ....................................................4
2.2.3 Wildlife................................................................................................................4
2.2.4 Threatened, Endangered and Sensitive Animals ................................................ 5
3.0 Potential Effects.............................................................................................. 5
4.0 Revegetation Plan........................................................................................... 6
5.0 Monitoring and Maintenance........................................................................7
6.0 References .......................................................................................................8
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page i
F_\7134G\Aqa-REV.J-11121194 C3:37 PN
Appendix B, Phase 1 Design Report
APPENDIX B
AQUATIC AND TERRESTRIAL RESOURCES REPORT
1.0 Introduction
This Aquatic and Terrestrial Resources Report was prepared for use in determining
impacts associated with the Maplewood Creek Sedimentation Basin Reconstruction and
Improvement Project. A complete description of the proposed project is provided in the "Phase 1
Design Report" to which this report is an appendix.
2.0 Existing Habitat Conditions
Harza biologists conducted a site visit on April 26, 1994, during which current terrestrial
habitat within the Project Area and vicinity were assessed. Potential project effects, mitigation
measures, and revegetation strategies were evaluated. Recently compiled aquatic habitat
literature and observations documented during the site visit were used for the aquatic habitat
section of this report. We also reviewed the 1989 Draft Maplewood Creek Basin Plan, the April
1993 Cedar River Current and Future Conditions Report and associated correspondence, and we
requested and received U.S. Fish and Wildlife Service (USFWS), Washington Department of
Fish and Wildlife (WDFW) and Washington Department of Natural Resources (DNR) database
searches.
2.1 Aquatic Habitat
While the Cedar River has a large natural run of sockeye salmon, steelhead and a
moderately-sized run of river smelt, these migratory fish appear to seldom use Maplewood Creek
for spawning or rearing. Resident trout have been observed in the lower reaches of Maplewood
Creek, from the golf course area upstream into the steeper canyon reaches. This section of
stream has been restocked by citizens a number of years ago with trout provided by the State
Department of Game (Draft Maplewood Creek Basin Plan 1989; Cedar River Current and Future
Conditions Report 1993).
Erosion in the steep, lower reach of the east fork of Maplewood Creek has washed fine
sediments into potential spawning gravels and significantly impacted fish habitat. In addition,
the two ponds originally constructed for golf course irrigation represent a passage barrier. The
upper concrete dam structure is severely damaged and has been undermined, severely eroding the
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 1
F:\71 JGWqu-Tan do l 1/:I/14.i)i.37 PM
Appendix B, Phase 1 Design Report
channel bottom. The lower dam has been maintained as a sediment/debris dam; however, it lacks
adequate fish passage.
As described in the Maplewood Creek Sediment Load and Geotechnical Evaluation
Report (Appendix A to Phase 1 Design Report), the stream channel is remarkably free of organic
debris despite approximately 10 significant landslides observed on the canyon slopes during the
site visit. Some logs bridge the creek but intermittent stream flows must be sufficiently high to
strip most fine organic fragments from the channel. Two minor canyon debris jams were found,
but these do not impede the normal stream flow. The channel floor is covered by a thick blanket
of sand and gravel possibly up to 10 feet thick.
The lower half-mile of Maplewood Creek is greatly affected by the Maplewood Golf
Course, the existing culvert systems under SR-169, and the railroad grade. The creek was placed
in a 72-inch diameter culvert for its lowermost 1,000 feet from the Cedar River, past the railroad
embankment, and under SR-169. This probably occurred during the construction of the railroad
or state highway. Through the golf course, the channel is largely barren of habitat and functions
primarily as a drainage ditch. Although coho salmon have been reported to migrate through the
culvert and into the golf course reach in recent years (Draft Maplewood Creek Basin Plan 1989),
the existing culvert system appears not ideal for adult fish migration. Therefore WDOT is
presently constructing a fish ladder immediately adjacent to the culvert outlet to the Cedar River
to be connected to a future fishway channel through the golf course to the reconstructed
sedimentation basin.
Little information is available on the quality of water in Maplewood Creek. The
continued presence of resident trout indicates that generally water quality within the creek is
adequate. During high stream flows, however, turbidity levels get very high from erosion in the
upper channel segments. These turbidity levels along with habitat changes may be limiting the
population of the resident trout fishery (Draft Maplewood Creek Basin Plan 1989).
2.2 Terrestrial Habitat
2.2.1 Vegetation
The upper end of the project area is in a forested ravine with moderate to steep slopes up
to the Renton Plateau. The topography flattens out at the golf course parking lot. Slopes on the
west side of the Maplewood Creek ravine are somewhat wetter than those on the east side, and
numerous groundwater seeps were observed during the site visit. The predominant plant
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pa-e 2
F\713(3\Aqu-Ten. I/^_1/91.11 37 P%1 "
Appendix B, Phase 1 Design Report
association is western hemlock (Tsuga menziesii)lswordfern (Polystichum munitum)-salal
(Gaultheria shallon). Western redcedar (Thuja plicata) is common on moister sites, and large
cedar stumps, indicating timber harvest several decades ago, are scattered throughout the stands.
Douglas fir (Pseudotsuga menziesii) is more common on the drier sites. The overstory also
contains a minor component of red alder (Alnus rubra), cottonwood (Populus trichocarpa) and
bigleaf maple (Acer macrophyllum) trees.
The forest canopy is fairly open, and a well-developed shrub and herbaceous layer is
present. Along the riparian zone, salmonberry (Rubus spectabilis) and Himalayan blackberry (R.
discolor) are dominant. Snowberry (Symphoricarpos alba), red elderberry (Sambucus
racemosa), vine maple (Acer circinatum), devil's club (Oplopanax horridum), and currant (Ribes
spp.) were also observed.
The banks around the upper concrete dam are steep and have been reinforced with rip-
rap. A gravellcobble bar is located upstream of the dam. Water depth averages approximately 1
foot. Vegetation immediately adjacent to the pond is herbaceous ground cover including
smartweed (Polygonum spp.), mixed grasses, Robert's geranium (Geranium robertianum), and
horsetail (Equisetum arvense, E. telmateia).
The lower sediment basin is located just above the golf course parking lot. The bottom of
the basin consists of a layer of fine sediments in its lower end and gravel substrate just below its
inlet. Water depths average 1-2 feet.
An old access road parallels the north shoreline of the creek. The south shoreline and
adjacent upland slope is steep. Trees and shrubs are dense to the edge of the pond. On the south
and west sides, vegetation is predominantly herbaceous, and includes mixed grasses and weedy
forbs such as dandelion (Taraxacum officinale), lance-leaved and common plantain (Plantago
lanceolata and P. major), hairy cat's ear (Hypochaeris radicata) and clovers (Trifolium repens,
T. pratense), with creeping buttercup (Ranunculus repens) and western bittercress (Cardamine
occidentalis) also common. Small amounts of reed canarygrass (Phalaris arundinacea), an
aggressive exotic species, are also present.
The creek reach at the southern end of the project area is confined to a narrow channel.
The east bank is forested almost to the waterline. The shrub layer is diverse and includes
snowberry, salmonberry, elderberry and vine maple. The west bank is bordered by dense
thickets of blackberry measuring approximately 10 feet in width. The golf course parking lot
and residential property abut the shoreline vegetation on the west.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pa-e 3
F\7134GUyv-Te Ji li"_I N94 13:37 P1,1
Appendix B, Phase I Design Report
2.2.2 Threatened, Endangered and Sensitive Plants
A search of the Washington Department of Natural resources (DNR) Natural Heritage
Information System (June 8, 1994) indicates that no records of rare plants, high quality native
wetlands, or high quality native plant communities exist for the project vicinity. Two threatened
plant species and 14 sensitive plant species are thought to occur in King County. Of these plants,
only the four noted below would be likely to occur in habitat types that will be affected by
construction of the new sedimentation basin, i.e., low elevation riparian and pond habitat.
Water lobelia(Lobelia dortmanna) is listed as threatened in Washington. Water lobelia
is an aquatic plant that grows in shallow water along lake or pond margins. No aquatic
vegetation was noted in either of the ponds on Maplewood Creek.
Bristly sedge (Carex comosa), on the state sensitive list, also grows along the shores of
lakes and ponds and other wet places. Bristly sedge is best identified from May through August
by its cylindrical, 2-7 cm, pedunculate spikes, similar to bottle-brushes. The only sedge noted on
the Project site during the survey was Dewey's sedge (Carex deweyana). Since Dewey's sedge is
a much smaller plant that produces sessile spikes only 7-20 mm in length, it is easily
distinguished from bristly sedge.
Bog clubmoss (Lycopodiella inundata) occurs most often in the cold, acidic soils of
sphagnum bogs, but may also be found in other wet habitats. No clubmosses were noted in areas
that would be affected by construction.
Lance-leaved grape-fern (Botrychium lanceolatum) has been documented to occur in
various habitat types, usually in forested situations. No grape-fern species were noted in the
project area.
2.2.3 Wildlife
Residential development on the uplands above the ravine and recreational development
below the project area limits the diversity of wildlife occurring within the project area. For
example, habitat does not exist for large mammals requiring large territories, such as the black
bear and mountain lion. However, forest and riparian-dwelling wildlife species with moderate to
small home range requirements such as deer, birds, waterfowl, small mammals, reptiles, and
amphibians are likely abundant along the mainstem of Maplewood Creek.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 4
F:\71?1G�Aqu-Ten.du 11/21/W 01:37 P%1
Appendix B, Phase 1 Design Report
During the site visit conducted on April 26, deer sign, a mallard pair, and rodent carcasses
were observed. In addition, many bird species were heard and observed. Cavities evident in the
scattered snags and large, live coniferous and deciduous trees indicate that habitat exists for
cavity-nesting birds and mammals. Species requiring cavities for nesting or foraging likely
present within the Project Area include the common flicker (Colaptes auratus), winter wren
(Troglodytes troglodytes), black-capped chickadee (Parus atricapillus), and the western gray
squirrel (Sciurus griseus). Gravel substrate and sandbars, observed within the shallow waters of
the lower sediment pond, likely provides foraging platforms suitable for great blue heron (Ardea
herodius). Although raccoon (Procyon lotor) sign was not observed, habitat is present, making it
probable that this species is also present within the project area.
Results from the WDFW Priority Habitat and Species database search, received on May
17, 1994, indicate that there are no records of species of concern occurring within the project
area.
2.2.4 Threatened, Endangered and Sensitive Animals
A search of the U.S. Fish and Wildlife Service database (June 17, 1994) for the
occurrence of threatened, endangered and sensitive species indicated that bald eagles could be
present in the project area during the winter. However, the WDFW's PHS data contained no
records of bald eagle nesting, roosting or concentrations in the vicinity. Construction is planned
for the low-flow period in late summer, and would therefore not disturb any eagles that might fly
near the area during the winter. No potential habitat will be removed. Enhancement of fish
passage in Maplewood Creek is intended to improve conditions for resident trout, which do not
represent an important forage resource for bald eagles. The project is not expected to have
adverse or beneficial effects on bald eagles.
3.0 Potential Effects
No adverse effects to fish and wildlife are anticipated from project implementation,
except short-term disturbance during construction and revegetation planting. Aquatic habitat is
currently low-quality due to high sediment loads and barriers to fish passage. Terrestrial habitat
that will be directly affected by construction includes riparian shrubs along approximately 80
feet of the creek and mixed grasses and weedy herbaceous species growing along the
sedimentation basin, dike and golf course parking lot. A 30" cottonwood and a few trees
measuring less than 10 inches in diameter at breast height (d.b.h.) will be removed from the east
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 5
F:\71?4G\,\q.-Tt d,,:1 /'_],94.01.}7 PM
Appendix B, Phase 1 Design Report
side of the sedimentation basin. The Revegetation Plan presented below is designed to minimize
construction-related impacts to terrestrial habitat.
Implementation of engineered elements of the Project are expected to provide benefits to
aquatic habitat. The expanded sedimentation basin will reduce flooding and control erosion.
Subsequently, sedimentation is reduced, improving downstream water quality. In addition, the
proposed bank stabilization work will help minimize erosion.
The removal of the upper concrete dam will restore access to the upper ravine and aquatic
habitat, and will help restore the channel to a more natural state. Stream habitat enhancement
calls for the placing of 2- to 3-foot size boulders along the creek bottom with about 8 to 10 feet
spacing. This method should extend from about 100 feet upstream of the upper dam to the
upstream end of the reconstructed sedimentation basin. Channel reconstruction and bank
stabilization will help to re-establish pools and riffles, provide areas for rearing and escapement,
and increase production of food organisms. The elimination of the pond behind the upper
concrete dam will be balance by the expansion of the sedimentation basin and restoration of the
channel. In addition, the fish passage structure proposed as part of the basin reconstruction and
improvement project, as well as the low flow fish passage channel proposed by the City in a
separate project, will improve access to the upper ravine by migratory fish species.
4.0 Revegetation Plan
Following construction, revegetation of exposed soils will be needed to control erosion.
Selection of native shrub and herbaceous species for revegetation will promote diversity in areas
that are currently dominated by grasses and weedy forbs. Plantings of shrubs along the new
pond margin will provide cover and increase forage opportunities for many species of reptiles,
amphibians, small mammals and birds. Planting of sedges, rushes and bulrushes in shallow
water areas of the pond will add another element of habitat diversity that is not currently present.
Plants for revegetation in areas affected by construction were selected based on their
capacity to 1) tolerate site conditions; 2) stabilize slopes and exposed soils; 3) provide shading
cover along streambanks and pond margins; 4) increase the structural complexity of the habitat,
providing additional forage and cover opportunities for wildlife; and 5) increase diversity in the
native plant community.
Tree species selected for planting include western redcedar, western hemlock and Oregon
ash (Fraxinus latifolia). Shrub species include willow (Salix species) and dogwood (Cornus
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Pa-e 6
F M34G Aq,-TJ� 11/2:,94 C3:37 Pit
Appendix B, Phase 1 Design Report
stolonifera) as cuttings, Pacific ninebark (Physocarpus capitatus), and Nootka rose (Rosa
nutkana).
Gradual contouring of the slopes around the new pond will allow for planting of
emergent species in shallow water and saturated soils. Small-fruited bulrush (Scirpus
microcarpus), broad-fruited burreed (Sparganium eurycarpum), beaked sedge (Carex rostrata),
Baltic rush (Juncus balticus) and dagger-leaf rush (J. ensifolius) will be considered for planting
at appropriate water depths.
A grass/forb seed mix will be applied to exposed soils to ensure erosion control during
the period of time when trees, shrubs and emergents are becoming established. The mix will
include colonial bentgrass (Agrostis tenuis), foxtail (Alopecurus pratense), red fescue (Festuca
rubra) and water smartweed (Polygonum hydropiperoides).
Strategically planting the trees and shrubs in suitable spots will enhance future growth.
Trees will be planted in small clumps for naturalizing purposes, while shrubs and emergents will
be placed to provide adequate soil coverage. Detailed planting specifications, including size of
stock, spacing, care and handling of plant materials, will be prepared as part of the construction
plans and specifications.
Seed mix can be applied and rooted stock can be planted immediately following
construction. Willow and dogwood cuttings are best planted during the period when they are
dormant (fall and winter).
5.0 Monitoring and Maintenance
Elements of the project that are designed to improve fish habitat and fish passage will be
maintained by the City. It is recommended that monitoring of the aquatic habitat, including
aquatic invertebrates and fish populations, be conducted within the Cedar River Management
Plan. The stream channel and bank stabilization work will be inspected by the City
approximately two times per year during the rainy season, particularly following heavy rainfall
events. Evidence of sloughing and/or erosion will be recorded, and appropriate mitigative
measures will be taken, if necessary.
Vegetation should be monitored at quarterly intervals during the first year after planting,
and then annually for the following two years, to ensure adequate survival and density of
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 7
FA71340Aqu-Tar d-:1 1/'_1/94-)3:37 P.\7
Appendix B, Phase 1 Design Report
plantings. Monitoring and maintenance could be performed by the City Stormwater Utility or by
golf course personnel.
6.0 References
Ingles, Lloyd G. 1965. Mammals of the Pacific States: California, Oregon, Washington.
Standford University Press, Stanford, California.
King County Department of Public Works, Surface Water Management Division. 1993. Cedar
River Current and Future Conditions Report.
Parametrix, Inc. 1989. City of Renton Comprehensive Stormwater Plan: Maplewood Creek
Basin Plan. Prepared for the City of Renton Public Works Department, Storm Water
Utility Division.
Robbins, Chandler S., B. Bruun, and H.S. Zim. 1983. Birds of North America: A Guide to Field
Identification. Golden Press, New York. Western Publishing Company, Inc. Racine,
Wisconsin.
USDA Forest Service. 1977. Cavity-Nesting Birds of North American Forests. Agriculture
Handbook No. 511. Washington, D.C.
Maplewood Creek Sedimentation Basin Reconstruction and Improvement Project Page 8
APPENDIX C
Preliminary Construction Plans
APPENDIX C
Preliminary Construction Plans
a
BYPASS PIPE INLET
/ SEE DWG. 2 CENTER NOTCH SECTION OF UPPER -- 120' LG SEDIMENTATION ZONE
e 12'MIN. DAM CREST / / CONCRETE DAM TO BE REMOVED AT REMOVE ACCUMULATED SEDIMENT ELEVATION
EL 111.5 "` 47 LEAST TO EL 122.5 OR ONE FOOT PRIOR TO DAM REMOVAL
BELOW DOWNSTREAM GRADE OF CREEK
SCOUR ZONE BOTTOM 130
DOWNSTREAM tF2.5 \ 2 2 UPSTREAM CL ACCESS ROAD AND 12.0 - / / / 1 --L -- - -
SIDE \ TO SIDE ADS N-12 BYPASS PIPE /
O ;1 O 1�\\ O (MIN. PIPE SLOPE 1%) / 113 / _ --
\ , \
\ \ i - 120
------------------/ /
ALL FILL COMPACTED TO 98% Y / /
MAXIMUM DRY DENSITY AND (E(= COMPACTED EXISTING ACCESS ROAD 1 / / / LONGITUDINAL PROFILE AT CONCRETE
DAM
FROM OPTIMUM MOISTURE BE IMPROVED SEE NOTE 1 / / CREEK ACROSS UPPER CONCRETE DAM
VARIES FILL OFFSITE /
CONTENT TO PLUS 2S. MATERIALS / / / /^o % SCALE: 1' = 20' H 110_
';F.= LOCALLY DERIVED 1' - 10 V
TYPICAL DAM SECTION FILL 'o /
SCALE: 1' = 10' (HORIZ. AND VERT.) A 4 MAN ROCK 24-30' DIA.
a" OCK // BB 2 MAN ROCK 12'-18'DIA. C 1• LENGTH OF REPAIR
/ T / /^ STREAM / 1 SECTION - 70 FEET
// �/ CHANNEL LENGTH OF REPAIR SECTION - 60 FEET / • TOE OF SLIDE WILL
/ RE _
60/ IV / // • TOE OF SLOUGH WALL REQUIRE 40 MAN ROCK. 30 4
B'0 X 75' LG ADS HEAVY N ti �, / BEDDING GRAVEL
DUTY PERFORATED DRAIN `„`� �� 40" MAPLE 2 MAN ROCK; 15 CUBIC YARDS OF
PIPE SEE DETAIL 2 DWG. 3 � � / CUBIC YARDS OF
B - B 2 MAN ROCK; 10 CUBIC YARDS OF / 2 MAN ROCK, 20
CRUSHED ROCK(2-INCH). / CUBIC YARDS OF
EXISTING 9'0 WOOD SCALE: 1' - 10' / CRUSHED ROCK
/ PIPE TO BE REMOVED • MINOR RESHAPING OF UPPER CHANNEL / • (2-INCH).
t4" HEMLOCK (2) p / p / SLOPE AND DISPOSAL CIF W�lF1
VEGETATION AND SURFACE �� RESHAPED SLOPE
SLOPE TO BE REVEGETATED ��ya 1/ / EXISTING 8'0 SOIL / a WILL REQUIRE
WITH A MIX OF EROSION e METAL PIPE TO - -- EXCAVATION AND
CONTROL GRASSES AND / 10 BE REMOVED DISPOSAL OF 25
NATIVE SHRUBS (TYP.) 14" HEMLO / 8, C — C CUBIC YARDS OF
/ / a END OF EXISTING ACCESS VEGETATION AND
EXISTING 4'0 PVC PIPE ROAD TO BE IMPROVED, SCALE: 1' = 10' SURFACE SOILS
TO BE REMOVED SEE NOTE 1 _ 4 MAN ROCK _ •
B - 2 MAN ROCK 2'18' DIA.
EL' 108 / SILT TO BE REMOVED BEFORE _
C- RESHAPE SLOPE
J / REMOVING CONCRETE DAM 1 O DD- REMOVE ACCUMULATED
30' COTTONWOOD SECTION / y SEDIMENTS
q FISHWAY OUTLET -- �, 1 / CENTER NOTCH SECTION OF �^�•
SEE DWG. 3 ,1p / o EXISTING CONCRETE DAM TO 6 J3YC.l�
20" HEMLOC �`1' / EL 105 / BE REMOVED. NOTCH SECTION
12'0 ADS N-12 - / MIN. 10' BOTTOM WIDTH AT nL QUANTITIES STATED ARE
BYPASS PIPE i ,�'�• / BO / ---REMOVE EXISTING 45'CUT BOTH SIDES V FOR ENGINEERING ESTIMATE
0' MAPLE IRRIGATION INLET I ONLY AND NOT TO.BE USED
NORM
EL 1 5 / AND PIPE UPSTREAM FOR BIDDING PURPOSES OF NEW INLET / CONTRACTORS MUST
I / PREPARE INDEPENDENT
18" MAPLE �0 \2/ / BOULDERS OF 2' TO 3' - / �j / QUANTITY ESTIMATES
SIZE TO BE PLACED ON 4" CEDAR
/ '^/7,F- ,b / i /
_ j1B / TO 10' SPACING (TYP.)
DAM CREST EL 111.5 - / CREEK BOTTOM AT 8' /
SEE TYPICAL DAM SECTION 7 I l /
08 �v FROM UPSTREAM END OF
3O" THE SEDIMENTATION BASIN / � HEMLOCK
GE E EXISTING L / TO 100' UPSTREAM OF THE
FUTURE FISHWAY i 1 30 PAVEMENT / / 2,1 o UPPER DAM /
CHANNEL SPILLWAY CREST M / SCOPE ^ N / 50" MAPLE
EL 109.0 cos /
^0 104 _ EL 19. / / ^EDGE OF EXISTING
ACCESS ROAD (TYP.) 'O p
11p 42" CEDAR
EXISTING CONCRE
\ 12" MAPLE
B TE
WEIR TO BE REMOVED
—EXISTING RIPRAP
TO BE REMOVED
--NEW INLET TO//
/ /CED REMOVE EXISTING PAVEMENT, J �Q EXISTING //
SEWER MH, PIPE AND TRENCH e � ow IRRIGATION
/ \ MATERIAL FROM BASIN AND / / o- PIPE / / 1. ACCESS ROAD SURFACE TO BE 4' DEEP
NDER DAM. CUT AND CAP PIPE 7/8' CRUSHED ROCK ROLLED ON A
MMIINIMUM ROAD 'MOTH
2'. FOR A
102
-EDGE OF EXISTING PA T(TYP. / �o / 0" AR
/ / ti j / D ,4 ^ 2. A& EXCAVATE TO RESHAPE
�\ /O? N / 4 ryo / / N � ry THE SLOPE.
SLOPE TO OVER EXCAVATED,
EMLOCK
Q. REPLACE WITH ROCKERY AND
H �F,
& GUY ANQHO / / RIPRAP WITH GRAVEL DRAIN.
co /
'o H SPILLWAY
DD OUTLET
/ CITY OF RENTON
SEE DWG. 2 / 0 10 20 40 /`p /` DEPARTMENT OF PUBLIC WORKS
y/ - -APPROXIMATE LOCATION NORTHWEST, INC. MAPLEWOOD CREEK SEDIMENTATION BASIN
OF EXISTING IRRIGATION S�
hj oo I PIPE �/1� SCALE IN2FEET eellewe,Wae inglon RECONSTRUCTION AND IMPROVEMENT PROJECT
` 0/ SITE PLAN AND SECTIONS
P/ 0 4" MAPLE\12" MAPLE DESIGNED:A.L.HNw
GJ/ O N DATE: 11-22-94 FILE NAME:
4 EDGE Of EXISTING BUILDING (TYP) �, / DRAWN: C.L.C.HNW
CHECKED:A.L.HNW SDALE: AS NOTED iIELD BOOK: PACE:
NO. REVISION DY APPR. DATE APPROVED: SHEEP: 1 OF:3
8' EMERGENCY
b� DRAIN GATE
Y I
' JOINT TO MATCH
r 72'0 PIPE END
(TYP•) F
b
D n D
--
0
I I i7
SPILLWAY _ _ I _ _ 72 9 OUTLET PIPE _ b
I i b
Tq
------- ------------------------
1'-0'SLOT I iq
b 8' SUBDRAIN IF -r-�
GATE PLAN
26'-0' 5'-0' 12'-0' 8'-0'
8' FLAT BACK LIGHT DUTY
SLUICE GATE PROVIDE TEE
HANDLE FOR GATE OPERATION
I
EL 111.5 100 YR. FLOOD MA E DAM CREST EL 111.5 DAM CREST EL 111.5
V POOL EL 110.5 25
1 SLR CUTTING
SPILLWAY CREST EL 109.0
2
1 EL 107.0 MATCH EXISTING EL 107.0_
INY. EL 1_06.0 ,. - 2 CREEK BED
BASIN BOTTOM EL 105.0
'
- --- --------------- EL 985 EL 104.0
1
\EL 104.0
� - INV. EL 102.0 � .� I t
72'0 X 30' LG CONCRETE PIPE ASTM-C-78 CL Y I I �� I
EL 98 5 b I — - ---- -
EL 97.5 °D o
I N,
L. I
EL 97.5
/-- 8'0 PERFORATED DRAIN
PIPE IN GRAVEL FILLED 1•-0' m
E - E TRENCH MIN. PIPE SLOPE TypI 12' - 18' DIA C r
1%SEE DETAIL 1 RIPRAP r r
5'-0'
FILTER FABRIC TO BE USED AS A
MARKER DURING POND CLEAN OUT AS
3�1--(0�1_(.,)M.I,Nj�) WELL AS A FILTER.
BASIN BOTTOM EL 105.0
b Y
c -- BACKRLL AROUND 8'0 PIPE USING
1 1/2 INCH NOMINAL DIAMETER WASHED
GRAVEL PERFORATIONS SHOULD BE ON
LOWER PART OF PIPE.
iD=
s CITY OF RENTON
4 g ^p ^ DEPARTMENT OF PUBLIC WORKS
NORTHWEST, INC. MAPLEWOOD CREEK SEDIMENTATION BASIN
SCALE
SEDIMENTATION POND SUBDRAIN LE IN FEET EN9m-. -d S-,tists RECONSTRUCTION AND IMPROVEMENT PROJECT
DETAIL 1 1' = 4 Bellevue, Washington SPILLWAY AND OUTLET PLAN, SECTIONS & DETAIL
DESIGNED:A.L.HNW DATE: 11-22-94 FILE NAME:
N.T.S.
DRAWN: C.L.C.HNW
CHECKED: A.L.HNW SCALE: AS NOTED riEiD eoox: vAc[.
REVISION BY APPR, DATE APPROVED 2 OF:3
CL 120 BYPASS .
PIPE
H
G — G
- -
----------- ---------
42�41-CONCRETE PIPE
£iFI�ITURE FlSHWAY ------
------------------------
CHANNEL
I I
o PLAN H o
FISHWAY OUTLET
STAFF GAUGE TO
DAM CREST BE INSTALLED
12*0 BYPASS W-O" 4'-0-
PIPE
42"0 PIPE
DAM CREST EL 111.5 EL 111.5
100 YR. FLOOD MAX
SEE DETAIL 3 P00L EL 110.5
EL 108.7 EL 109.5
INV. EL 107.0 '7 NORMAL POOL EL 108.5
2 EL 107.5
EL 108.7 - \ �1 - I
f42'1_ 32'_LG CONCRETE PIPE _ EL 104.5 SEE DETAIL 3 / 6• FILLET(TYP.)
BASIN BOTTOM EL 105.0 BASIN BOTTOM EL 105 0
MATCH BOTTOM OF EL 103.7 __\ EL 1D4.5
FUTURE FlSHWAY CHANNEL 1, ;
I
aD tl SECTION CUTTING PLANE
G - G
V-0" 1 0-
TYP. TYP.
H — H
J m J
ROADWAY 6" COVER MIN.
i_ BACKFILL AROUND 12"0 ADS N-12 PIPE •I 1"
M USING 1/4-INCH CRUSHED ROCK. 3- 2"
IN A MINIMUM OF 36-INCHES OF COVER 'a h
V-6" WITH LOCALLY DERIVED FILL. REQUIRED PLAATESTW/BES�STEEL
m p o w OVER PIPE WITHIN ROADWAY ALIGNMENT.
'd o I
a a WHERE COVER IS LESS THAN 36-INCHES,
BACKFILL WITH LEAN MIX-50 LB
PLAN Sri d� a CEMENT 350 LB FLYASH PER YARD 1
BYPASS PIPE INLET +o d (WITHIN ROADWAY ALIGNMENT ONLY).
o,
FINISHED GRADE TYPICAL FlSHWAY TYPICAL TOP OF
WEIR ELEVATION FlSHWAY WEIR
12"0 BYPASS PIAF
TEE HANDLE BYPASS PIPE 6" BED MIN. SCALE: 1" = 1'-0"
MIN. SLOPE 1% E OPERATION TYPICAL DETAIL 2
EL 116.5 N.T.S. DETAIL 3
EXISTING GRADE
12' FLAT BACKINV. EL 113.5
LIGHT DUTY 113 0SLUICE GATE -1 CITY OF RENTON
4 8 ' pDEPARTMENT OF PUBLIC WORKS
ZA
NORTHWEST, INC. MAPLEWOOD CREEK SEDIMENTATION BASIN
1._O. SCALE IN FEET Engineers and S,ientists RECONSTRUCTION AND IMPROVEMENT PROJECT
1" 4' hi W Bellows, Washington o ° F1SHWAY OUTLET PLANS, SECTIONS & DETAILS
N DESIGNED:A.L.HNW
DATE: 11-22-94 FILE NAME:
1-O" DRAWN: C.L.C.HNW
J — J CHECKED: A.L.HNW SCALE: AS NOTED n D&ON P GE
N0, REVISION BY APPR. DATE APPROVED: SHEET: 3 OF:3