HomeMy WebLinkAboutAttach D - Alternative Assessment
Alternatives Assessment
Panther Creek at Talbot Road South Culvert
Replacement Project
Renton, Washington
for
City of Renton
March 12, 2025
1101 Fawcett Avenue, Suite 200
Tacoma, Washington 98402
253.386.4940
ATTACHMENT D
Alternatives Assessment
Panther Creek at Talbot Road South Culvert
Replacement Project
Renton, Washington
File No. 0693-093-00
March 12, 2025
Prepared for:
City of Renton
1055 South Grady Way
Renton, Washington 98057
Attention: Jared McDonald, PE
Prepared by:
GeoEngineers, Inc.
1101 South Fawcett Avenue, Suite 200
Tacoma, Washington 98402
253.383.4940
KPFF Consulting Engineers, Inc.
1601 Fifth Avenue, Suite 1600
Seattle, Washington 98101
206.622.5822
Ken Fellows, PE
Senior Civil Engineer
David Conlin, PWS
Associate Ecologist
Eric Mendel, PE
Associate Civil Engineer
Aaron Olson, PE
Principal Structural Engineer
KF:EM:DC:AO:leh:atk
Disclaimer: Any electronic form, facsimile, or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy
of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.
City of Renton | March 12, 2025 Page i
File No. 0693-093-00
Table of Contents
1.0 Introduction .................................................................................................................. 1
2.0 Description of Existing Conditions .................................................................................. 1
2.1 Stream ........................................................................................................................................... 1
2.1.1 Watershed Characteristics ................................................................................................ 1
2.1.2 Site Conditions................................................................................................................... 1
2.1.3 Hydrology ........................................................................................................................... 2
2.1.4 Federal Emergency Management Agency (FEMA) Floodplain Mapping ......................... 4
2.2 Road............................................................................................................................................... 4
2.3 Utilities ........................................................................................................................................... 4
2.4 Geotechnical Summary ................................................................................................................ 5
3.0 Concept Development and Evaluation ............................................................................ 5
3.1 Stream Design............................................................................................................................... 5
3.1.1 Crossing Type ..................................................................................................................... 5
3.1.2 Alignment ........................................................................................................................... 6
3.1.3 Profile ................................................................................................................................. 6
3.1.4 Hydraulic Opening ............................................................................................................. 7
3.1.5 Channel Section ................................................................................................................ 8
3.1.6 Large Woody Material (LWM) ............................................................................................ 8
3.1.7 Stream Alternative Summary ............................................................................................ 8
3.2 Geotechnical Considerations ....................................................................................................... 8
3.2.1 Construction Methods ....................................................................................................... 8
3.2.2 Structure Foundation ........................................................................................................ 9
3.3 Roads and Utilities ...................................................................................................................... 10
3.3.1 Design Speed ................................................................................................................... 10
3.3.2 Cross Slope ...................................................................................................................... 10
3.3.3 Proposed Roadway Design ............................................................................................. 10
3.3.4 Maintenance of Traffic .................................................................................................... 11
3.3.5 Utilities ............................................................................................................................. 11
3.3.6 Stormwater ...................................................................................................................... 12
3.4 Structural Design ........................................................................................................................ 12
3.4.1 Structural Constraints ..................................................................................................... 12
3.4.2 Precast Concrete Box Culvert ......................................................................................... 12
3.4.3 Steel Plate Arch Culvert................................................................................................... 13
3.4.4 Bridge Structure Alternative............................................................................................ 13
3.5 Summary of Potential Design Alternatives ................................................................................ 14
4.0 Cost Estimates and Recommended Conceptual Design ................................................ 15
4.1 Estimate of Construction Cost.................................................................................................... 15
4.2 Preferred Alternative ................................................................................................................... 16
5.0 Data Gaps ................................................................................................................... 17
6.0 References .................................................................................................................. 17
Page ii
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City of Renton | March 12, 2025
List of Figures
Figure 1. Vicinity Map
Figure 2. Plan View
Figure 3. Profiles and Sections
Figure 4. Road Closure and Detour Plan
Appendices
Appendix A. Hydraulic Design Field Report
Appendix B. FEMA Flood Panel
Appendix C. Design Concepts
Appendix D. Conceptual Design Opinion of Probable Construction Cost
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1.0 Introduction
This Alternative Assessment Report was prepared by GeoEngineers, Inc. (GeoEngineers) and KPFF
Consulting Engineers, Inc. (KPFF) on behalf of the City of Renton (City) in support of the Panther Creek at
Talbot Road South Culvert Replacement Project (project) in Renton, Washington. The City is proposing to
replace the existing culvert conveying Panther Creek from east to west under Talbot Road South to improve
fish passage and replace the existing crossing structure, which is in poor condition. The purpose of this
assessment is to identify and evaluate conceptual project alternatives for replacement of the existing
32-inch-diameter pipe culvert with a fish-passable design.
The project site is located at Talbot Road South, between South 38th Court and South 177th Street, in
Renton, Washington (Figure 1, Vicinity Map). The site is just northeast of the Valley Medical Center and the
intersections of State Route (SR) 167 and South 180th Street.
2.0 Description of Existing Conditions
2.1 STREAM
2.1.1 Watershed Characteristics
The Panther Creek watershed covers 1.79 square miles that includes a mix of natural forested and wetland
areas, as well as many residential developments. Panther Creek extends upstream of Talbot Road South
approximately 2.8 miles to the southeast. The first 0.7 miles of creek upstream of the crossing lies in a
confined ravine that has an increase in elevation from approximately 70 feet to approximately 400 feet,
resulting in an average slope of approximately 8 percent. Over the remaining 2.1 miles, the creek flows at
gentler slope of 1 to 2 percent over an upland plateau, where the watershed eventually reaches a high
point of approximately 475 feet elevation. Approximately 850 feet downstream of the project crossing, the
confined ravine topography transitions to a wider valley bottom as the creek approaches the greater Green
River Valley. In the vicinity of the project crossing, the average creek slope is approximately 4 percent (City
of Renton 2023).
2.1.2 Site Conditions
KPFF completed a topographic survey of the project site in July 2023 (see Figure 2, Plan View). The survey
extended approximately 300 feet upstream and 300 feet downstream of Talbot Road South. The vertical
datum for the survey was North American Vertical Datum of 1988 (NAVD88) (feet). Project specific
elevations noted in the remainder of this report are expressed in feet, NAVD88 vertical datum.
The ravine in the vicinity of the project crossing is mapped by Mullineaux (1965) as the Renton Formation
that is characterized by Arkosic sandstone, mudstone and shale. Areas surrounding the project crossing
are mapped as glacial till, consisting of compact, unsorted sand, silt, clay and gravel.
The existing culvert (Washington Department of Fish and Wildlife [WDFW] Site ID: 931933) is a 32-inch-
diameter corrugated steel pipe that appears to have been lined with fiberglass, approximately 140 feet
long, with a slope of approximately 4 percent (see Figure 2). The culvert is in poor condition. The bottom of
the culvert is completely scoured away in places. This creates a risk of rapid and total failure during a flood
event due to water leaking from the culvert, then flowing through pipe bedding and road embankment
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material. Replacement of the culvert is warranted due to its poor condition and also because the culvert
downstream end is elevated approximately 4 feet over the receiving pool, which creates a total barrier to
passage of salmonids.
The existing culvert is undersized, causing upstream backwatering during flood events. Backwatering of
flows appears to have resulted in deposits of sediment upstream of the culvert that are up to approximately
2 to 3 feet thick, causing the apparent stream bottom to widen as the ravine is filled over time.
Based on several Wolman pebble counts completed during GeoEngineers’ site visit (Appendix A, Hydraulic
Design Field Report), the existing streambed bed immediately adjacent to the culvert is a mix of sand,
gravel, cobbles and boulders, with a D50 of 1.5 to 3 inches and a D95 of 6 to 9 inches.
A reference reach is intended to be a section of creek that is relatively unaffected by artificial conditions or
infrastructure that can serve as a guide to design new or restored channels. For this project, a reference
reach approximately 100 feet long was identified approximately 450 feet upstream of the project crossing.
The reference reach has a single thread channel located within a meander bend with the apex oriented
along the right bank. The reach has an average slope of 4.4 percent and exhibits a step-pool bedform. An
approximately 35-foot-long portion of the reference reach appears more as a pool-riffle morphology with
steps upstream of pools. Water surface drops of several inches occur across these steps. Pools ranged
from approximately 2 to 5 feet long with a maximum depth measured of 5 inches. Streambed material in
the reference reach consists of small to medium-sized cobbles with coarse gravels and occasional small
boulders. Fine to coarse sands were observed along channel bank toes with a fine to coarse gravel armor,
or within undercut pools. A Wolman pebble count indicated a streambed sediment D50 of 2.3 inches and a
D95 of 8.5 inches. There appears to be a natural and on-going supply of appropriately sized sediment from
upstream areas to the project reach. No large wood was present in the reference reach.
The average design bankfull width (BFW) for sizing the proposed channel and structure opening is 9.5 feet.
The field report included in Appendix A includes a description of how this value was identified.
A small wetland is located on the right bank floodplain bench just downstream of the culvert, likely
supported by groundwater seepage (GeoEngineers 2023). No other wetlands were identified with the
project reach.
The Panther Creek Stream Assessment (see Appendix A) contains additional details about existing site
conditions based on GeoEngineers’ site visits completed in June and July 2023.
2.1.3 Hydrology
Hydrology within the Panther Creek watershed is understood to be highly influenced by urban development.
Basin hydrology was assessed using multiple simple methods to obtain a range of several peak flow
estimates for potential use in analysis and design. These simple methods included conducting a review of
nearby gages to complete a basin transfer analysis, calculating regional regression equation values,
completing a watershed scale rainfall-runoff continuous flow model analysis and reviewing existing
literature. Table 1 summarizes the results of these methods. Panther Creek does not have a stream gaging
station to provide a record of past flows.
GeoEngineers performed the basin transfer analysis using stream gage data from the King County gage
with site ID 31c located along Molasses Creek (King County 2023). The gage is located approximately
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2.9 miles northeast of the Panther Creek project crossing at Talbot Road South. The Molasses Creek
watershed has an area approximately 98 percent that of Panther Creek at the project location. Visual
inspection of aerial imagery within the Molasses Creek watershed suggests it is similar to that of Panther
Creek. The results of the basin transfer analysis were lower than expected for Panther Creek given the size
of the stream.
Regression equations are not valid for basins with more than 5 percent impervious area and the Panther
Creek watershed has an estimated impervious area of 30 percent. However, they are very easy to apply
and can provide a low-end estimate of peak flow hydrology for a developed watershed. The results of this
method were lower than those from the basin transfer method for both the 2- and 100-year events but
slightly larger for the 500-year event.
Rainfall-runoff modeling was carried out using MGSFlood, utilizing United Stated Geological Survey (USGS)
soil data and land use data from the cities of Renton and Kent as inputs. Peak flow estimates resulting
from the MGSFlood model were unrealistically high, with initial 2D model results indicating overtopping of
Talbot Road South during the 2-year peak flow event. This is likely due to the coarseness of the model
constructed, which represents the entire watershed as a single unit rather than dividing it into
sub-watersheds and directly modeling the existing stormwater infrastructure.
A study conducted by RW Beck (R.W. Beck 1997) includes descriptions of hydrology for the adjacent
Springbrook Creek basin, which Panther Creek is a tributary to. The study lists peak flow inputs to
Springbrook Creek from Panther Creek corresponding to the 2- and 100-year peak flow events on
Springbrook Creek. Neither the 2- and 100-year events on Panther Creek, nor the peaks, necessarily
coincide with those on Springbrook Creek. The flows for Panther Creek correspond to a location just
upstream of a point along SR 167 approximately 1.5 miles downstream of the project crossing on Panther
Creek. Most of this downstream reach of Panther Creek flows within a wetland running parallel to SR 167
along its east side, and there are several piped locations conveying flow from the wetland to the west below
SR 167. The effects of these piped connections to the wetland are not well understood. Despite these facts,
the flows reported seem reasonable for the Panther Creek crossing location at Talbot Road South and they
were identified in the study using detailed hydrologic modeling and therefore in our judgement represent
the best available hydrologic data and serve as the basis for our analyses for this project.
TABLE 1: PEAK FLOW HYDROLOGY SUMMARY
AVERAGE RECURRENCE
INTERVAL PEAK FLOW EVENT
(YEAR)
BASIN TRANSFER FROM
MOLASSES CREEK
(CFSA)
USGS
REGRESSION
(CFS)
MGS FLOOD, 15-MIN
TIMESTEP (CFS)
SPRINGBROOK BASIN
STUDY (CFS)B
2 37 28 179 67
100 90 57 500 197
500 111 127 638 251c
Projected 2080 100d 107 68 597 235
Notes:
1. Bolded flows denote those used for analysis and design
2. Extrapolated from data using a logarithmic curve fit.
3. Estimated using WDFW climate change tool.
cfs = cubic feet per second
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2.1.4 Federal Emergency Management Agency (FEMA) Floodplain Mapping
Panther Creek at Talbot Road South is within a FEMA Zone X, indicating that it is unmapped by either
detailed or approximate methods and considered to be within an area of minimal flood hazard risk, as
shown in the FIRMette panel (FEMA 2023) included in Appendix B, FEMA Flood Panel.
2.2 ROAD
Panther Creek crosses from east to west under Talbot Road South, which is a two-lane road aligned north
and south. At the roadway centerline, the depth of fill over the top of the culvert is approximately 26 feet.
The paved width of the road is approximately 40 feet with 11-foot lanes and 4-foot shoulders. There is an
existing 5-foot sidewalk on the west side of the roadway. The east side of the roadway has a guardrail with
no curb and gutter or sidewalk. At the south end of the culvert crossing, the roadway is transitioning from
2 lanes to 3 lanes. The roadway is crowned with a cross slope of approximately 4 percent. There is minimal
illumination in the project area. Fill slopes on the east and west of the roadway are slightly steeper than
2H:1V (horizontal:vertical). The existing Talbot Road South surface is hot-mix asphalt (HMA).
2.3 UTILITIES
Two storm drains discharge to the area upstream of and near to the project crossing. The nearest storm
drainpipe conveys road runoff from Talbot Road South to Panther Creek on the left bank (south side)
immediately upstream of the project culvert inlet near the toe of the roadway embankment. A second storm
drainpipe outfalls to Panther Creek from the right bank (north side) approximately 95 feet upstream of the
project culvert inlet. This latter storm drainpipe had variable flow over the duration of the site visit,
increasing noticeably over just several hours while the flow in the channel remained essentially constant.
This variability could be due to pumping. In addition to stormwater infrastructure in the vicinity of the
crossing, both drinking and wastewater sanitary sewer main lines run underground north to south over the
crossing parallel to Talbot Road South.
The water main is a 12-inch steel pipe. According to as-built drawings provided by the City, there is also an
abandoned 20-inch steel water main pipe adjacent to the active main.
The sanitary sewer main is an 21-inch concrete pipe that runs north to south near the roadway centerline.
The sanitary sewer line (top of pipe) is approximately 12 feet below existing grade in the vicinity of the
existing culvert.
Two-inch and 16-inch gas lines have been identified along the project limits. Both lines run north to south
through the project on the west side of the roadway. Gas lines were assumed to have a minimum cover of
2 feet. Potholing will be performed later in design to confirm depths and locations.
Multiple overhead power and communication lines have been located along Talbot Road South at the
project location. Overhead power lines and poles are located on both the west and east side of the roadway.
Franchise utility companies will need to be contacted to verify locations of existing facilities, including depth,
of underground utilities, within the project limits.
Potential relocation requirements, schedule, cost and design recommendations will be coordinated with
utility owners during the design process.
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2.4 GEOTECHNICAL SUMMARY
GeoEngineers completed a geotechnical investigation of the site, which is documented in a Preliminary
Geotechnical Design Report for 10% Design (GeoEngineers 2025). The geotechnical study included
installing three borings along the eastern edge of Talbot Road South. Boring B-1 was installed
approximately 75 feet north of the existing culvert to a depth of approximately 30 feet below the ground
surface. Boring B-2 was installed approximately 10 feet north of the existing culvert to a depth of
approximately 25 feet below the ground surface where it met refusal. Boring B-3 was installed
approximately 65 feet south of the existing culvert to a depth of approximately 35 feet below the ground
surface. For reference, the road surface elevation varies from approximately 96 feet at the north boring to
approximately 98 feet at the south boring and the culvert invert elevation at the road centerline is
approximately 67 feet.
Figure 3 in the Preliminary Geotechnical Design Report for 10% Design (GeoEngineers 2025) is a cross
section along Talbot Road South depicting the materials encountered in the borings. Subsurface soils were
identified as up to approximately 20 to 25 feet of various types of poor-quality fill (loose clayey silty sands)
over a layer of dense glacial till approximately 10 to 15 feet thick, over Renton formation bedrock
(siltstone/sandstone). The fill layer extends the deepest at Boring B-2, which met refusal at approximately
Elevation 70 feet, possibly hitting a concrete object, possibly the foundation of a wood trestle bridge that
previously existed at the site based on old King County plans recovered by the City (King County 1943). The
fill layer likely extends to the north and south to the history valley walls.
Boring B-2 did not reach the bottom of the fill layer; no glacial till or bedrock was encountered. Therefore,
it is uncertain whether glacial till and/or bedrock are present in the immediate vicinity of the existing culvert.
3.0 Concept Development and Evaluation
Several factors were considered in developing a suite of potential conceptual designs that the project team
reduced in number using professional experience and judgement. These project alternatives were then
evaluated and compared with the goal of selecting a preferred alternative to carry forward to preliminary
design. The following sections summarize the various factors that were considered and discuss the benefits
and constraints of each option.
3.1 STREAM DESIGN
The primary stream factors that could be varied to develop conceptual alternatives include alignment,
profile and hydraulic opening width.
3.1.1 Crossing Type
The crossing under Talbot Road South should be formed of alluvial material to meet requirements of the
Water Crossing Design Guidelines (WCDG) (Barnard et al. 2013). General conformance to the Washington
State Department of Transportation (WSDOT) Hydraulics Manual (WSDOT 2023), while not mandatory, is
recommended. Acceptable crossing structure types per these guidelines would be a bottomless three-sided
concrete box culvert, a bottomless arch culvert, or a bridge. We expect the crossing will follow confined
bridge methodology due to an estimated floodplain utilization ratio (FUR) less than 3.0 within the reference
reach upstream of the crossing and of the channel downstream of the crossing. The floodplain utilization
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ratio is defined as the flood prone width (FPW), often taken to be the calculated 100-year water surface
width, divided by the BFW at a given location within the channel.
3.1.2 Alignment
Figure 2 shows the two proposed creek alignment alternatives. Alignment A closely follows the existing
creek alignment. In the area just upstream of the existing culvert, the existing channel (Alternative A)
alignment appears to be undergoing slow, but progressive migration to the north, eroding the base of the
steep slopes on private property. Alternative A provides little space to install bank protection measures.
Alignment B realigns the creek to be perpendicular to Talbot Road South. Upstream of the culvert,
Alignment B shifts the creek to the south to remove the slight overshoot in the existing alignment and
provide space for installation of bank protection measures. The overshoot is undesirable as it prevents flow
from smoothly entering the culvert and could contribute to further bank erosion and channel migration to
the north, making the overshoot worse with time. Downstream of the crossing, Alignment B moves the creek
slightly north to reduce the potential for further erosion of the severely undercut left bank but shifts the
creek into the wetland area on the right bank. The impact to the wetland appears to be under 1,000 square
feet (a specific impact area will be identified during project preliminary design phase) and it is anticipated
to be feasible to mitigate wetland impacts on-site resulting in no net loss.
Due to the additional space available with Alternative B to install bank protection measures, the measures
are expected to be more effective than for Alternative A. Additionally, the consequences of mild to moderate
channel migration by Alternative B are less in comparison to similar migration associated with Alternative A.
In the event that future maintenance is required, the maintenance needed for Alternative B is anticipated
to be less costly and easier to implement as compared to Alternative A.
3.1.3 Profile
The existing reach average slope in the vicinity of the crossing is 3.9 percent as identified from the channel
survey limits. The WDCG (Barnard, et al. 2013) allow the restored profile to have a slope up to 1.25 times
the existing reach average slope, equal to 4.9 percent. Profiles A and B follow Alignments A and B,
respectively (see Figure 2). Alignment A and B start at the same physical points on the existing creek
alignment downstream of the existing crossing, but upstream of the crossing Alignment A ties into the
existing channel approximately 24 feet downstream of the stormwater outfall discharging from the right
bank and Alignment B ties in approximately 33 feet upstream of it. Alignment B is therefore approximately
57 feet longer than Alignment A and ties into a higher elevation upstream than Alignment A. This results in
both Profile A and Profile B having equal slopes of 4.8 percent when rounded to the nearest 10th of
1 percent. Both alternative creek profiles fill in the scour pool downstream of the existing culvert.
To assess the effect of the increased creek slope on stream velocities, idealized stream sections were
analyzed to estimate average flow velocities for the full cross sections at the estimated 2-year and 100-year
flood flows. Table 2 summarizes the results of the analyses. Based on the similarity between these results,
we are not recommending developing alternative design concepts that consider alternative creek slopes.
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TABLE 2: SUMMARY OF CALCULATED AVERAGE FLOW VELOCITIES OUTSIDE OF THE CROSSING STRUCTURE
SCENARIO
SLOPE
(%)
APPROXIMATE
LENGTH OF
STREAM RE-
GRADE (FEET)
2-YEAR FLOOD
FLOW VELOCITY
(FEET PER
SECOND)
2-YEAR
FLOOD FLOW
TOP WIDTH
(FEET)
100-YEAR FLOOD
FLOW VELOCITY
(FEET PER
SECOND)
100-YEAR
FLOOD FLOW
TOP WIDTH
(FEET)
Slope equal to
existing reach
average
3.9 618 3.8 20.8 4.9 24.7
Alternative A 4.8 365 4.1 20.5 5.3 24.2
Alternative B 4.8 392 4.1 20.5 5.3 24.2
Maximum slope
per WCDG
4.9 383 4.2 20.5 5.4 24.2
3.1.4 Hydraulic Opening
The conceptual alternatives considered in this alternatives analysis assume a minimum hydraulic opening
(MHO) of 18 feet, with the final MHO to be determined during a future design phase. Based on various
design methodologies, the estimates of the MHO ranges from 14 to 21 feet. The value of 14 feet is based
on our measurements of the channel average BFW of 9.5 feet, and the stream simulation design method
per the WCDG (Barnard, et al. 2013). The value of 18 feet considers additional hydraulic factors that will
be further evaluated through hydraulic modeling to be completed at the preliminary design stage. The value
of 21 feet is based on the design channel width outside the existing culvert. The City has identified
advantages of structure width greater than 20 feet as compared to a narrower structure, including inclusion
in the City’s bridge inspection program and potential availability of repair funds in the event of flood damage
Increasing the proposed structure width would increase flood conveyance capacity, reduce velocities and
is expected to have reduced scour as compared to the minimum width. Additionally, a wider hydraulic
opening would provide additional areas of streambank floodplain benches that would provide more
floodplain continuity with areas upstream and downstream of the crossing and allow for more complex
channel morphology through the crossing that forms higher quality aquatic habitat for salmonids. Wider
widths are also typically supported by co-managers, including WDFW and the Muckleshoot Indian Tribe;
therefore, facilitating co-manager support of the project and streamlining permitting.
The structure freeboard must provide a minimum of 2 feet vertical clearance above the proposed 100-year
flood elevation. Detailed hydraulic modeling of the creek will be completed as part of preliminary design.
Based on preliminary, simplified analyses completed for this alternatives assessment, the estimated
100-year water surface elevation at the road centerline is approximately 69 feet, based on a thalweg
elevation of 67 feet, and a 100-year flood flow depth of 2 feet. Therefore, the elevation of crown of the
culvert or bottom of the bridge structure at the roadway centerline must be at least 71.9 feet; however, as
noted below, we recommend providing additional vertical clearance. The projected 2080 100-year flow
would increase these values by 0.1 feet. For a culvert option, a higher culvert top elevation will also result
in a shorter culvert length but increase the size of the culvert wing walls. For a bridge option, vertical
clearance would be easily achieved due to the height of the existing road embankment.
The conceptual alternatives considered in this alternatives analysis assume providing a minimum of
6.0 feet of maintenance clearance (above the floodplain bench). A maintenance clearance up to 8.0 feet
is workable for a culvert option considering other project constraints and would have a negligible cost
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increase compared to the lower maintenance height. The final value will be determined during a future
design phase. The purpose of the maintenance clearance is to accommodate channel inspections, and
future adjustment of stream channel complexity and habitat features within the structure if necessary
throughout the life of the project. A 6.0 foot maintenance clearance is consistent with guidance contained
in the WSDOT Hydraulics Manual (WSDOT 2023). Greater clearance provides the City with additional
flexibility during design, construction and the post-construction design life of the project. Greater clearance
could also facilitate wildlife passage.
3.1.5 Channel Section
Figure 3, Profiles and Sections illustrates the proposed typical channel section both upstream/downstream
of the crossing and through the crossing. The proposed channel section outside of the crossing has a width
of 20.5 feet at approximately the 2-year flood flow level, cresting above the proposed banks and inundating
the adjacent floodplain benches.
3.1.6 Large Woody Material (LWM)
LWM is expected to be incorporated into the proposed channel design outside of the crossing structure. It
will be designed to promote the target channel morphology and follow standard engineering practices for
the placement of LWM within streams in western Washington.
3.1.7 Stream Alternative Summary
The conceptual alternatives considered in this alternatives analysis assume stream alignment
Alternative B, an MHO of 18 feet, and minimum maintenance clearance of 6.0 feet.
3.2 GEOTECHNICAL CONSIDERATIONS
3.2.1 Construction Methods
Open-cut excavation of the site appears feasible, subject to temporary road closure and temporary
relocating utilities as described in Section 3.3 Roads and Utilities, below. The elevation of deepest
excavation will be driven by depths needed for streambed substrate through the crossing as described in
Section 3.2.2 Structure Foundation, below, which would be used to determine footing depths for a culvert
option.
Loose road embankment fill excavated to construct a culvert crossing is recommended to be disposed of
offsite rather than re-used. For a culvert option, the excavation would be backfilled with granular structural
fill. For a bridge option, less back fill would be necessary. A key geotechnical parameter to be developed in
the preliminary design phase is the estimated practical temporary construction slope, which will determine
the horizontal extents of the excavation and impacts to Talbot Road South and associated utilities.
Potential trenchless construction methods include ramming, jacking and tunnelling; however, the identified
subsurface conditions consisting of loose fill, dense glacial till and bedrock are not suitable for these
construction methods, which are therefore not considered further.
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3.2.2 Structure Foundation
3.2.2.1 CULVERT OPTIONS
Simple spread footings appear feasible to support a culvert, assuming dense material is present at a
reasonable depth at the location of the proposed culvert. The presence of dense material was not
confirmed because Boring B-2 encountered refusal at 25 feet below the ground surface, slightly above the
elevation where adjacent borings suggest that till or bedrock might be present. The reason Boring B-2 met
refusal is not known, as the till and bedrock encountered in the adjacent borings was drillable.
The following sections describe the process to develop a preliminary estimate for the culvert footing depth,
which will be refined during the project preliminary design phase. The footing depth will be based on the
depth of alluvial streambed substrate needed in the culvert below the thalweg elevation, plus the footing
thickness.
3.2.2.1.1 Streambed Substrate Depth
From a permitting and fisheries perspective, the channel through the crossing may need to be comprised
of alluvial streambed material to meet fish passage design requirements. Alluvial material is potentially
unstable over a hard smooth surface such as concrete or bedrock. Therefore, our preliminary assumption
is that till/bedrock would need to be removed (if present) to a depth that leaves at least 3 feet of material
over any hard surface, after considering potential scour. This would promote fish passage conditions, which
may otherwise be compromised if bedrock were exposed through the crossing. Exposure of bedrock through
the crossing could possibly result in inadequate water depth during times of low flow and/or a vertical drop
as a result of scour where bedrock transitions to gravel substrate. Although bedrock may have been the
natural pre-disturbance condition in some portions of the stream bed, we anticipate that current regulatory
requirements for crossing replacement will require fish passage parameters to be achieved, precluding the
option of leaving a bedrock stream bed.
Scour depth and long-term regrade will be evaluated after completion of hydraulic modeling during the
preliminary design phase. As a preliminary estimate, the depth of streambed material through the crossing
is recommended to be 5 feet, assuming a minimum scour depth of 3 feet per WSDOT design guidance plus
2 feet below the total scour depth. Assuming a thalweg elevation for the proposed creek of 67 feet at the
Talbot Road South centerline, the estimated base of the streambed substrate would be at Elevation 62 feet.
3.2.2.1.2 Foundation Elevation
The top of the footing is estimated to be at or below the base of the streambed substrate (estimated above
at 62 feet). The bottom elevation of the footing is estimated at approximately 60 feet, assuming a footing
thickness of 2 feet (to be refined during the project preliminary design phase).
3.2.2.1.3 Potential Removal of Till/Bedrock
If dense glacial till and/or bedrock as encountered in Borings B-1 and B-3 is present at the location of the
new culvert, it may need to be removed to elevation approximately 60 feet to construct the culvert footings.
3.2.2.2 BRIDGE OPTIONS
For a bridge alternative, deep foundations are anticipated, assumed to be drilled shafts. The design flood
and check flood scours are assumed to be 3 feet. The scour angle of repose is 26 degrees per Geotechnical
City of Renton | March 12, 2025 Page 10
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recommendations. The scour catch point begins at the edge of the stream section. Lateral migration is a
potential concern for this stream crossing and will need to be assessed in future design advancement.
The top of shaft caps would be placed below the scour line in accordance with WSDOT BDM 7.1.7 and the
bottom of wing walls, if necessary, would be placed 2 feet below the scour line or finished grade in
accordance with WSDOT BDM 8.1.10. Foundations for the bridge option are advantageous over the culvert
option described in the preceding section due to the likely presence of bedrock near the streambed
elevation that may complicate design and construction of culvert foundations, particularly if additional
geotechnical data is not obtained.
3.3 ROADS AND UTILITIES
3.3.1 Design Speed
The existing roadway has a posted speed limit of 35 miles per hour (mph). The roadway will be designed in
accordance with American Association of State Highway and Transportation Officials (AASHTO) Geometric
Design of Highways and Streets (AASHTO 2018), using a design speed of 35 miles per hour.
3.3.2 Cross Slope
The existing roadway has a 4 percent cross slope. The City standard is to provide a maximum of 2 percent
cross slope. The proposed project will maintain the existing 4 percent cross slope to minimize the project
impacts that would be required to provide 2 percent slopes and transition back into the existing 4 percent
cross slopes.
3.3.3 Proposed Roadway Design
The proposed roadway design will be similar to the existing horizontal and vertical alignment for Talbot
Road South, which meets current sight distance requirements. Several alternative lane configurations were
considered, as illustrated in Appendix C, Sheet C-7, including:
1. Two 11-foot vehicular lanes, two 4-foot shoulders, two 5.5-foot sidewalks with curbs, and 2-foot
clearance between the back of sidewalk and slope on both sides (total road section is 45 feet).
2. Three 11-foot vehicular lanes, one 4-foot shoulder (one side) and one 5-foot bike lane (other side), two
5.5-foot sidewalks with curbs, and 2-foot clearance between the back of sidewalk and slope on both
sides (total road section is 57 feet).
Guardrail will not be required on this project, as the proposed roadway section satisfies clear zone
requirements on both sides of the road. Traffic barrier and fall protection would be included for a bridge
option and extended north and south of the bridge as needed to meet vertical grade difference
requirements. Table 3 summarizes the roadway classifications and standards used for design criteria.
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TABLE 3: SUMMARY OF ROADWAY DESIGN PARAMETERS
TALBOT ROAD SOUTH
Roadway Functional Classification Major Collector
Posted Speed 35 mph
Design Speed 35 mph
Minimum Right-of-Way (ROW) Width 60 feet
Travel Lane Width 11 feet
Shoulder Width 4 feet
Shoulder Slopes 0.02 ft/ft
Embankment Slopes 2H:1V
Notes:
ft/ft = feet per foot
3.3.4 Maintenance of Traffic
Maintaining traffic through the work zone would be logistically challenging based on the topography of the
ravine. Constructing the crossing while maintaining traffic would require a temporary bypass roadway
adjacent to existing roadway or building the new structure in phases. A temporary bypass roadway (i.e.,
shoofly) would require a temporary bridge and approach roadway fills. Phasing construction would require
significant shoring to support the existing prism. Either of these alternatives would add significant
construction duration and costs when compared to a full roadway closure during construction.
North of the project site is residential. A key criterion of the analysis was to ensure access to the hospital
would be maintained during the construction period. In August 2023, the City met with representatives of
the Valley Medical Center Hospital (a large regional hospital located just south of the project site) to discuss
access needs during construction of the project. The hospital stated a full road closure, for approximately
3 to 4 months, would be acceptable with the proposed detours allowing access from the north. The south
access to the hospital will remain unaffected by this project.
The alternative to the full road closure would be to construct the crossing structure in phases with
temporary shoring to allow one lane access through the project site on fill or using a temporary bridge
structure on either side of the project site. This option adds significant costs for shoring or constructing a
temporary bridge structure. This option would also increase the construction duration, associated traffic
impacts and environmental impacts. This option was not analyzed further upon acceptance of full road
closure by the hospital and the acceptable detour route available.
Detour options are shown on Figure 4, Road Closure and Detour Plan. Detour planning and potential
impacts to the residential areas to the north of the project site and the Valley Medical Center Hospital and
other businesses to the south of the project site will be further considered during the project preliminary
design phase.
3.3.5 Utilities
The project site has significant utilities that cross over the existing culvert. A solution to attach the utilities
to a bridge at the stream crossing is a major challenge of the bridge option considered. Attaching the utilities
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to a bridge would require them to be much higher in elevation than the existing utility locations or to be
suspended well below the superstructure span. One of the existing utilities is a large diameter gravity
sanitary sewer main. Raising this pipe up to attach it to a bridge would require expanding the work area
laterally along Talbot Road South in both directions to vertically realign the sewer, which would result in
unacceptable impacts to the hospital, potentially require addition of a pump station, and add significant
cost to the project; this was therefore not considered a viable option. Suspending the sewer line below the
bridge at its current elevation limits the structure types feasible for a bridge option or would require a
separate utility bridge.
The box culvert and arch culvert options allow the project to replace the existing utilities at the current
elevations and support them in place or temporarily relocate utilities during the construction process. These
relocations will be analyzed further during subsequent design phases. The length of the temporary utility
relocation is anticipated to be from valley wall to valley wall, as noted in Section 3.2.2 due to the need to
remove the full extent of loose embankment fill.
3.3.6 Stormwater
The site has several existing stormwater catch basins and two storm drainage outfalls within the stream
ravine on the east side of the road. The existing outfall on the southeast side of the stream crossing will
need to be relocated and replaced.
The proposed project is anticipated to create approximately 1,000 to 2,000 square feet of new impervious
surfaces, depending on which road section is selected, as well as replace approximately 10,000 square
feet of existing impervious surfaces. This project is exempt from flow control and water quality treatment
requirements per the City of Renton Surface Water Design Manual (2022). Existing roadway drainage
patterns will be largely maintained.
3.4 STRUCTURAL DESIGN
3.4.1 Structural Constraints
The primary constraints that impact the structural alternatives analysis include estimated MHO, depth of
roadway fill above the thalweg of the creek, maintenance of traffic (MOT), and buried utilities. The following
section describes how these constraints impact the selection of the preferred structural alternative.
The recommended MHO is 18 feet. If the face of the proposed structure were placed at the outside edge
of the MHO, then the structure would not be classified as a bridge as defined by the Federal Highway
Administration (FHWA), which regulates structures over 20 feet in length. Structural options for the shorter
span length proposed include precast concrete culverts (three-sided or four-sided) and steel plate arch
structures.
3.4.2 Precast Concrete Box Culvert
This design alternative is illustrated in Appendix C, Sheets C-1, C-4 and C-8. A precast concrete box culvert
would be placed at the bottom of the roadway prism and fill would be used to carry the road across the
ravine. This structure type can be prefabricated offsite and then delivered and constructed relatively rapidly
once embankment excavation is complete and utilities temporarily relocated. Installation would require
removal of a significant amount of the existing roadway fill and then backfill with suitable roadway fill to
restore the roadway after the structure has been placed. The existing fill soils contain a high percentage of
fines with some organic material and are also more than double the moisture content required for adequate
compaction. As such, on-site soils are not suitable for reuse as fill on the project.
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Precast concrete box culverts typically come in two varieties: three-sided and four-sided structures. A
three-sided structure consists of an inverted u-shaped precast culvert section that is supported on a cast-
in-place (CIP) concrete stem wall and footing. A four-sided structure consists of two C-shaped precast
concrete units that are placed to form an enclosed box. The bottom section of the box serves as the
foundation support for the culvert. In general, a three-sided box will have a longer construction duration
associated with forming and pouring the CIP concrete stem wall and footing. However, it is our
understanding based on early coordination with permitting and tribal stakeholders that a three-sided
structure is generally preferred over a four-sided structure. Based on this feedback, only the three-sided
box was advanced for further consideration. Construction of culvert footings may be complicated by the
potential presence of bedrock at the stream elevation.
3.4.3 Steel Plate Arch Culvert
This design alternative is illustrated in Appendix C, Sheets C-2, C-5 and C-9. Like a precast concrete box
culvert, a steel plate arch culvert would also be placed at the bottom of the roadway prism and fill would
be used to carry the road across the ravine. Like the precast concrete box culvert option, this structure type
can be prefabricated offsite and then delivered and constructed relatively rapidly. Also, like the concrete
box culvert option, installation would require removal of a significant amount of the existing roadway fill
and then backfill with suitable roadway fill to restore the roadway after the structure has been placed. For
a given MHO, the excavation necessary to install an arch culvert would be greater when compared to a box
culvert. This is driven primarily by the geometric properties of the arch whereby the base of the arch must
be much wider to fit a given MHO.
Like three-sided box culverts, steel plate arch culverts require CIP concrete stem walls and footings.
However, due to the thrust loads at the base of the arch, these foundations would likely need to be larger
than a similarly sized three-sided box culvert foundation. For the proposed MHO, a steel plate arch culvert
does not have any significant advantages when compared to a precast box culvert and will likely result in
greater construction costs due to greater impacts to utilities and potentially needing to remove more
bedrock as compared to a box culvert.
3.4.4 Bridge Structure Alternative
This design alternative is illustrated in Appendix C, Sheets C-3, C-6 and C-10. As mentioned previously,
Panther Creek is located in a steep ravine where the depth of roadway fill measured from the top of roadway
to the thalweg of the creek is approximately 30 feet. Spanning the ravine from top of slope to top of slope
would require a bridge structure with a minimum span of approximately 75 feet based on the MHO and
anticipated side slopes, and up to approximately 150 feet if the entirety of the valley fill material is removed.
Alternatively, if the abutment walls were placed at the edge of the MHO, they would be approximately
30 feet tall.
The primary challenge with a bridge structure is that the buried roadway utilities would need to be
permanently relocated around the site or attached to the structure itself. This is particularly challenging for
the 21-inch sanitary sewer that is approximately 12 feet below the roadway surface and is gravity fed. This
utility would either need to be raised to the girder level, suspended below the structure at its current
elevation, or placed on a separate utility bridge structure. As noted above (Section 3.3.5 Utilities), raising
the sewer line is not considered to be feasible for this project given its current configuration requiring
significant, costly rework and additional impacts to hospital access. Suspending the sanitary sewer below
the bridge or placing it on a separate utility bridge are more feasible options.
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3.5 SUMMARY OF POTENTIAL DESIGN ALTERNATIVES
Table 4 summarizes the design alternatives that we evaluated, as discussed in the preceding sections.
TABLE 4. SUMMARY OF POTENTIAL DESIGN ALTERNATIVES
DESIGN FACTORS ALTERNATIVES EVALUATED DESCRIPTIONS AND VARIATIONS
Stream alignment and
profile
Alignment A Existing stream alignment, 4.8 percent slope
Alignment B Optimized stream alignment, 4.8 percent slope
Hydraulic Opening
Minimum width 14.0 feet
Recommended width 18.0 feet
Minimum height
10.2 feet (2.2 feet 100-year flood WSE plus
3 feet freeboard plus 3 feet scour depth plus 2
feet foundation burial below scour depth)
Recommended height
13.0 feet (providing 6 feet of maintenance
clearance in addition to minimum parameters
above)
Roadway
Alternative 1
Two 11-foot vehicular lanes, two 4-foot shoulders,
two 5.5-foot sidewalks with curbs, and 2-foot
clearance between the back of sidewalk and
slope on both sides (45-foot total road section)
Alternative 2
Three 11-foot vehicular lanes, one 4-foot shoulder
(one side) and one 5-foot bike lane (other side),
two 5.5-foot sidewalks with curbs, and 2-foot
clearance between the back of sidewalk and
slope on both sides (57-foot total road section)
Construction Methods and
Maintenance of Traffic
Cut and cover; remove existing
fill; full road closure Shortest construction duration and lowest cost
One-lane bypass or single-lane
closure with phased
construction
Additional shoring or shoofly would be required,
adding substantial cost, additional impacts, and
extending construction duration.
Utilities
Replace in existing location
Will need to be relocated and maintained during
construction. For culvert options, utilities would
be buried in fill prism over structure. For bridge
option, sanitary sewer would be suspended below
structure.
Raise sanitary sewer to attach
to bridge
Would require extending utility work well beyond
project footprint, impacting hospital access, and
potentially requiring a lift station.
Construct separate utility bridge More costly than suspending below bridge
structure.
Structure Type
Alternative a: Precast Concrete
Box Culvert
Three-sided box on shallow foundation
Four-sided box
Alternative b: Steel Plate Arch
Culvert Steel plate arch on shallow foundation
Alternative c: Bridge Precast concrete girders on deep foundations
Notes:
WSE = water surface elevation
City of Renton | March 12, 2025 Page 15
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4.0 Cost Estimates and Recommended Conceptual Design
Based on the potential design alternatives summarized in Table 4, above, and the discussion of these
various factors in Section 3.0 of this report, we identified eight feasible conceptual design alternatives and
developed rough-order-of magnitude cost estimates for each. Conceptual design drawings are included in
Appendix C, Design Concepts. For the bridge alternatives, sub-alternatives included supporting the utilities
on the proposed bridge or constructing a separate utility bridge. These alternatives are summarized in
Table 5, below.
TABLE 5. CONCEPTUAL DESIGN ALTERNATIVES
ALTERNATIVE ROAD
SECTION STRUCTURE TYPE
1a 1 (45 feet) Three-sided pre-cast concrete box culvert on shallow slab
1b 1 (45 feet) Steel plate arch culvert on shallow slab
1c.1 1 (45 feet) Bridge, prestressed concrete girders, CIP concrete deck on drilled shafts with
separate utility bridge
1c.2 1 (45 feet) Bridge, prestressed concrete girders, CIP concrete deck on drilled shafts with utilities
hung on bridge
2a 2 (57 feet) Three-sided pre-cast concrete box culvert on shallow slab
2b 2 (57 feet) Steel plate arch culvert on shallow slab
2c.1 2 (57 feet) Bridge, prestressed concrete girders, CIP concrete deck on drilled shafts with
separate utility bridge
2c.2 2 (57 feet) Bridge, prestressed concrete girders, CIP concrete deck on drilled shafts with utilities
hung on bridge
4.1 ESTIMATE OF CONSTRUCTION COST
The conceptual-level engineer’s estimate of probable costs for the eight alternatives identified above are
provided in Appendix D, Conceptual Design Opinion of Probable Construction Cost.
Key assumptions and data gaps related to the cost estimates are noted below:
■ For all alternatives, construction will require easements with owners of three to four private properties
upstream, and four properties adjacent to the project.
■ Temporary stream bypass can be implemented using a gravity system without pumping.
■ Closure of Talbot Road South will be required with associated detour of traffic. As a preliminary
estimate, road closure and detour are anticipated to take 12 to 20 weeks. Construction of the new
crossing structure in upstream/downstream phases that would allow for keeping Talbot Road South
open to alternating traffic is not considered feasible due to the extensive costs associated with
temporary bridge structures and shoring associated with building in phases to maintain access.
■ Excavation extents north and south along Talbot Road South and associated utility impact zones remain
to be identified. The current recommendation is to remove all of the loose embankment fill between
the historic valley walls.
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■ Costs for utility bypass are preliminary estimates that will be refined during preliminary design through
coordination with utility owners.
■ Streambed substrate is anticipated to be a mix of boulders, cobbles, gravel and sand. A specific
gradation will be developed during project final design.
■ Substantial quantities of large wood will be incorporated into the stream banks as required to meet
applicable guidelines.
■ Minor impacts to the wetland downstream of the crossing are anticipated to be accommodated within
the permitting process anticipated for the project, without additional mitigation.
■ Cost estimates include a 40 percent contingency.
Costs for the alternatives ranged from $8.0 million for Alternative 1a to $10.3 million for Alternative 2c.1.
The bridge alternatives are estimated to have higher costs as compared to the culvert alternatives. The
difference in costs between the least expensive alternative (1a) and the most expensive alternative (2c.1)
is approximately $2.3 million, which may be within the range of error given the conceptual level of design
and contingency factor applied across all alternatives. All alternatives using the smaller road section are
slightly less costly than the equivalent structure type for the larger road section. Bridge Alternative 2c.1 that
included constructing a separate utility bridge was approximately 10 percent more expensive than
alternative 2c.2 that supported utilities on the primary bridge structure.
4.2 PREFERRED ALTERNATIVE
Selection of a preferred alternative was completed in collaboration with the City of Renton Surface Water
Utility and Transportation Departments and was not based on cost alone. As noted above, the bridge
alternatives were more costly than buried culvert alternatives; however, the difference in costs may be
within the margin of error at the current level of design analysis. Furthermore, bridge alternatives offer the
following advantages:
■ Bridge alternatives keep all permanent infrastructure within existing City-owned right-of-way. All culvert
alternatives would require permanent easements or right-of-way acquisition on adjacent properties.
■ Bridge alternatives are more likely to gain acceptance by regulatory agencies, particularly in light of the
potential bedrock present below the existing culvert. If a bridge crossing is selected and the stream
channel erodes, exposing bedrock and resulting in formation of a fish passage barrier after crossing
replacement, the barrier may be considered natural by regulatory agencies and not require corrective
actions. For a culvert structure, fish passage parameters may be required to be maintained by the City.
■ There may be opportunity to complete some advanced work before shutting down the road completely
during construction. For example, alternating lane closures may be feasible while installing drilled shaft
bridge foundations. For culvert alternatives, embankment excavation would require road closure at the
construction outset.
■ There are less design parameter data gaps for bridge foundations whereas the culvert footing design
is subject to revision or possible adjustment during construction depending on where bedrock is
encountered during excavation.
■ There is no need to backfill the valley excavation with a large amount of imported structural fill material
with the bridge alternatives.
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■ There may be more potential construction or maintenance funding opportunities associated with bridge
infrastructure funding.
■ Bridge inspections and maintenance may be easier than descending into the ravine to conduct culvert
inspections with limited headroom.
For these reasons, the City prefers the bridge alternatives to the culvert alternatives examined in this
analysis. The City has also selected to proceed with the larger of the two road section widths (Alternative 2),
with some minor modifications: the two-way left turn lane width is increased to 12 feet and bike lanes are
proposed on both sides of the roadway. The larger road section width provides for greater public safety and
transportation connectivity by providing bike lanes as well as continuing the existing central two-way left
turn lane present to the south onto the bridge, which provides vehicles more time to merge into traffic.
Suspending the utilities from the bridge structure is estimated to be less costly than constructing a separate
utility bridge, which provides no other advantages.
Therefore, the preferred alternative has the following parameters:
■ Structure: bridge, prestressed concrete girders, CIP concrete deck on drilled shafts.
■ Stream Alignment and Channel Section: Alternative B, slope of 4.8 percent, 18-foot channel section
width.
■ Road Section: Two 11-foot vehicular lanes, one 12-foot two-way left turn lane, two 5-foot bike lanes,
two 5.5-foot sidewalks with curbs, and 2-foot clearance between the back of sidewalk and slope on
both sides (total road section is 59 feet).
■ Maintenance of Traffic: full road closure during construction with detour route.
■ Utilities: replaced in existing location and suspended from bridge structure.
5.0 Data Gaps
The following data gaps have been identified and are recommended to be addressed as part of 30 percent
design advancement:
■ Identify appropriate excavation slopes to develop extents of excavation.
■ Coordinate with utility providers regarding allowable outages and other temporary relocation
requirements during construction activities, and associated costs.
■ Verify utility depth and location with potholing to advance design and reduce project risk.
■ Additional geotechnical borings may be needed at each proposed bridge abutment.
6.0 References
American Association of State Highway and Transportation Officials (AASHTO). 2018. A Policy on Geometric
Design of Highways and Streets, 7th Edition. ISBN No. 978-1-56051-676-7.
City of Renton | March 12, 2025 Page 18
File No. 0693-093-00
Barnard, R., Johnson, J., Brooks, P., Bates, K., Heiner, B., Klavas, J., Powers, P. .2013) Water Crossing
Design Guidelines. Washington Department of Fish and Wildlife. Olympia, WA.
City of Renton. 2023. City of Renton COR MAPS System, 2021 Digital Elevation Model Layer, Accessed
November 8, 2023)
Federal Emergency Management Agency (FEMA). 2023. National Flood Hazard Layer FIRMette, Panel
53033C0979G, effective 8/19/2020. Exported on November 7, 2023.
GeoEngineers, Inc. (GeoEngineers). 2023. Critical Areas Assessment, Panther Creek at Talbot Rd S Culvert
Replacement Project. Prepared for City of Renton, October 23, 2023. GEI File No. 0693-093-00.
GeoEngineers, Inc. (Geoengineers). 2025. Preliminary Geotechnical Design Report for 10% Design, Panther
Creek Culvert Replacement Project, Renton, Washington. Prepared for City of Renton, February 12,
2025. GEI File No. 0693-093-00.
King County. 2023. Hydrologic Information Center. Retrieved from Kingcounty.gov:
https://green2.kingcounty.gov/hydrology/DataDownload.aspx?G_ID=97&Parameter=Stream%20
Flow
King County. 1943. John Langston Rd Revn for Fill Bridge No. 80c. King County Sec. Road Proj. No. 49,
Comissioner's District 2, Approved Feb 19, 1934.
Mullineaux, D. 1965. Geologic map of the Auburn quadrangle, King and Pierce Counties, WA. U.S. Geologic
Survey, Geologic Quadrangle Map GQ-406.
R.W. Beck. 1997. East Side Green River Watershed Project, Environmental. Prepared for City of Renton,
September 1997.
Washington State Department of Transportation (WSDOT). 2023. Hydraulics Manual. Design Office,
Engineering and Regional Operations Division, Publication Number M23-03.
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Disclaimer: This figure was created for a specific purpose and project. Any use of this figure
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The locations of features shown may be approximate. GeoEngineers makes no warranty or
representation as to the accuracy, completeness, or suitability of the figure, or data contained
therein. The file containing this figure is a copy of a master document, the original of which is
retained by GeoEngineers and is the official document of record.
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PUBLIC HOSPITAL DISTRICT #1
3401 TALBOT RDS.
TPN 3023059034
PUBLIC HOSPITAL DISTRICT #1
3901 TALBOT RDS.
TPN 3123059065
•Survey from KPFF, dated 7/14/2023.
Coordinate System: Washington State Plane, North Zone, NAD83, US Foot.
Disclaimer: This figure was created for a specific purpose and project. Any use of this figure for any other project or purpose shall be at the user's sole risk and without liability to GeoEngineers. The locations of features shown may be approximate. Geo Engineers makes no warranty or representation as to the accuracy, completeness, or suitability of the figure, or data contained therein. The file containing this figure is a copy of a master document, the original of which is retained by GeoEngineers and is the official document of record.
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Legend (Exi�ting) f Parcel Property Line Culvert Ordinary High Water Line Wetland Line Panther Creek Thalweg Alignment Existing Major (5-ft) Contour Line Existing Minor (1-ft) Contour Line Underground Power Overhead Utilities Underground Telecommunications Water Line Gas Line
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Plan View
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Panther Creek at Talbot Road S .
Culvert Replacement Project
Renton, Washington
Figure 2 a:---------------------------------------------------------------------------------------------------------------------------------------------------·
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Existing Ground Surface
4.8%
4.6%
367.9'
424.6'
Proposed Thalweg
(See Note 1)
Match to
Existing
Grade
Match to Existing Grade
Existing Ground Surface
Proposed
Thalweg
(See Note 1)
Match to
Existing
Grade
Match to Existing Grade
Existing Panther
Creek Thalweg
Talbot Road S. CLExisting 36" CMP Culvert
Talbot Road S. CL
Existing 36" CMP Culvert
Existing Panther
Creek Thalweg
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0 5 10 15 200-5-10-15-20
Streambed
Material
Existing Ground Surface
Proposed Grade
Match to Existing Grade
Match to Existing Grade
10:1 2:1 2:110:1 10:1
10:1 2:1
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0 5 10 15 200-5-10-15-20
2:1
Topsoil and Native Planting on
Floodplain Benches and Slopes
Preliminary Minimum
Hydraulic Opening =
14 - 18 Ft (18 Ft
Recommended, to be
Refined During
Preliminary Design)
Existing Ground Surface
Existing Culvert
(Approximate)
Talbot Road S. CL
Preliminary
Culvert Height
Above Thalweg
(5.3 Ft)
Culvert Type and Size
to Determined. Section
Shows Preliminary
Concept for 18 Ft. Wide
3-Sided Concrete Box
Culvert.
Fill: Typically
Clayey to Silty Fine
Sand with Gravel
(Variable, Loose)
Possible Zone of Renton Formation
Bedrock (Inferred from Geotechnical
Borings). See Note 3.
Possible Zone of
Very Dense Glacial
Till (Inferred from
Geotechnical
Borings). See Note 3.
Thalweg at
Talbot Rd. S. CL
(See Profile):
Alt A IE: 66.70 Ft
Alt B IE: 66.72 Ft
Streambed
Material
10.0'
1.0'
Preliminary Estimate of Footing Depth
Below Thalweg (5 Ft). Remove Bedrock to
this Depth. Additional Bedrock Removal
May be Needed for Footing Thickness.
Figure 3
Profiles and Sections
Datum: NAVD88
Disclaimer: This figure was created for a specific purpose and project. Any use of this figure for any other
project or purpose shall be at the user's sole risk and without liability to GeoEngineers. The locations of
features shown may be approximate. GeoEngineers makes no warranty or representation as to the accuracy,
completeness, or suitability of the figure, or data contained therein. The file containing this figure is a copy of
a master document, the original of which is retained by GeoEngineers and is the official document of record.
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Horizontal Feet
0 100
100
Vertical Feet
0
Vertical Exaggeration = X1
Panther Creek at Talbot Road S.
Culvert Replacement Project
Renton, Washington
Alternative A Profile
Alternative B Profile
Horizontal Feet
0 10
10
Vertical Feet
0
Vertical Exaggeration = X1
Typical Creek Section
Typical Creek Section in Culvert
Notes:
1. Creek thalweg will have vertical undulations to create
pool/riffle habitat zones.
2. Proposed streambed substrate will be mix of fines, sand,
gravel, and cobbles similar to existing reference reach.
3. The subsurface conditions shown are based on
interpolation between widely spaced explorations and
should be considered approximate; actual subsurface
conditions may vary from those shown.
4. Existing utilities not shown (See Figure X).
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
Feet
0 500 1000
PANTHER CREEK CULVERT REPLACEMENT
ROAD CLOSURE AND DETOUR PLAN Figure
4
Appendices
Appendix A
Hydraulic Design Field Report
☐ THIS FIELD REPORT IS PRELIMINARY
A preliminary report is provided solely as evidence that field observation was performed. Observations
and/or conclusions and/or recommendations conveyed in the final report may vary from and shall take
precedence over those indicated in a preliminary report.
FIELD REPRESENTATIVE DATE
Chelsey Gohr, LG 8/2/23
Evan Deal, PE 8/2/23
David Conlin, PWS 7/20/23
☒ THIS FIELD REPORT IS FINAL
A final report is an instrument of professional service. Any conclusions drawn from this report should be
discussed with and evaluated by the professional involved.
REVIEWED BY DATE
Ken Fellows, PE 8/7/23
Dan Eggers, PE 8/13/23
This report presents opinions formed as a result of our observation of activities relating to our services only. We rely on the contractor to comply with the plans and specification throughout the duration of the project irrespective of
the presence of our representative. Our work does not include supervision or direction of the work of others. Our firm will not be responsible for job or site safety of others on this project. DISCLAIMER: Any electronic form, facsimile
or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official
document of record.
Attachments: Figures 1 through 15
Distribution:
Field Report File Number:
0693-093-00
1101 Fawcett Ave, Suite 200
Tacoma, WA 98402
253.383.4940
Project:
City of Renton, Panther Creek Culvert Replacement
Date(s):
June 28, 2023,
July 31, 2023
Owner:
City of Renton
Time of Arrival:
9:00 AM
Report Number:
FR-01
Prepared by:
Chelsey Gohr, LG, Peter Savchik,
Bea Renaud, David Conlin, PWS,
and Evan Deal, PE
Location:
Panther Creek at Talbot Road South
Renton, Washington
Time of Departure:
varies
Page:
1 of 16
Purpose of visit:
Stream Reconnaissance
Weather:
Sunny, dry
Travel Time:
varies
Permit Number:
n/a
Upon arrival to the site, I assessed personal safety hazards: Yes or Referred to Site Safety Plan and Safety Tailgate if applicable
Safety Hazards Were Addressed by : Staying Alert to Traffic Slip, Trip and Falls
0BINTRODUCTION
Washington Department of Fish and Wildlife (WDFW) has identified the crossing of Panther Creek under Talbot
Road South (WDFW Site ID: 931933) as a total fish passage barrier due to water surface drop (WDFW 2022)
(Figure 1 and Figure 2). The City of Renton has also identified the existing crossing structure at this location as
failing, presenting a risk to traveling public. GeoEngineers, Inc. (GeoEngineers) is working under contract to the City
of Renton to complete a hydraulic design for replacement of the deteriorated crossing structure at this location that
meets fish passage criteria and reduces risk to the public. This field report documents our observations of the
existing geomorphic, biological, and hydraulic conditions of Panther Creek in the vicinity of the existing crossing.
Fieldwork was completed on June 28 and July 31, 2023, including general site observations, assessment of stream
conditions, identification of a reference reach, and collecting bankfull width measurements and Wolman pebble
count data. The GeoEngineers’ field team (Table 1) assessed the crossing structure inlet and outlet, the upstream
channel within approximately 230 feet upstream and from approximately 350 to 450 feet upstream of the culvert
inlet, and the downstream reach within approximately 200 feet downstream from the culvert outlet.
File No. 0693-093-00
August 14, 2023
Page 2
TABLE 1. FIELD TEAM
Name Role
Evan Deal, PE River Engineer
Peter Savchik Staff River Engineer
Chelsey Gohr, LG Staff Fluvial Geomorphologist
David Conlin, PWS Senior Ecologist
Bea Renaud Staff Biologist
1BGENERAL SITE DESCRIPTION
The project site is located in the City of Renton, Washington, in King County. The subject crossing is located where
Panther Creek crosses Talbot Road South, just north of Valley Medical Center. The City of Renton plans to replace
the culvert passing underneath Talbot Road South, as it is deteriorated and therefore at risk of failure, as well as
being a barrier to fish passage. Talbot Road South, at this location, provides hospital access from the north.
The project crossing of Panther Creek is located along the gradual transition from steeper sloped terrain near the
stream headwaters on Benson Hill to shallower sloped terrain in the valley bottom associated with the Green River
floodplain and several tributaries to the Green River. Panther Creek originates at Panther Lake approximately
1.75 miles to the southeast and flows generally northwest or west through a confined ravine and through the project
crossing. Approximately 850 feet downstream of the project crossing, the confined ravine topography transitions to
a wider valley bottom in the greater Green River Valley. Through the Green River Valley, Panther Creek flows north
for approximately one-half mile through several low-gradient wetland complexes before turning west under SR 167.
The remainder of Panther Creek is generally ditched through an industrial and commercial area, where it flows into
Springbrook Creek approximately 0.85 miles downstream of the SR 167 crossing, and then into the Black River
and Green/Duwamish River, eventually flowing into the Puget Sound at the Duwamish waterway in Seattle.
Downstream of the project crossing, there are no other structures currently considered by WDFW to be barriers to
fish passage (WDFW 2023).
The ravine in which the project site is located is mapped by Mullineaux (1965) as the Renton Formation and is
characterized by Arkosic sandstone, mudstone, and shale. All other areas surrounding the project reach, including
the reference reach, are mapped as glacial till, consisting of compact, unsorted sand, silt, clay, and gravel.
2BREFERENCE REACH
A reference reach was established during the July 31st site visit starting approximately 350 feet upstream of the
project crossing where longitudinal channel slopes are similar to design slope targets. The field team then
progressed upstream to an area assumed to be out of the area of influence of the confluence of unnamed tributary
(UNT) to Panther Creek and Panther Creek (located at approximately 500 feet upstream of the crossing inlet) to
mark the upstream most end of the reference reach approximately 450 feet upstream of the project crossing. See
Figure 3 and Figure 4 for upstream and downstream reference conditions.
The approximately 100-foot-long reference reach is a single thread channel located within a meander bend with
the apex oriented along the right bank. The reach has an average slope of 4.4 percent (Washington State
Department of Natural Resources, 2021) and exhibits a step-pool bedform. An approximate 35-foot-long portion of
the reference reach appears more as a step-riffle morphology as pools are very shallow. Water surface drops off
several inches occur across these steps (Figure 5). Pools ranged from approximately 2 to 5 feet long with a
File No. 0693-093-00
August 14, 2023
Page 3
maximum depth measured of 5-inches deep. Streambed material in the reference reach consists of small to
medium-sized cobbles with coarse gravels and occasional small boulders. Fine to coarse sands were observed
along channel bank toes with a fine to coarse gravel armor, or within undercut pools.
On the inside (left bank) of the meander bend, the banks were up to 6 feet high. Undercut banks were common
and multiple areas of bank failure were observed as bare (lack of vegetation), vertical banks. On the right bank, or
outside of the meander bend, channel banks ranged from a few inches to up to 1.5 feet high. Floodplains and
discontinuous benches were observed along the right bank throughout the reference reach with the exception of
the downstream end of the reference reach where the right bank rises up to 4 feet above the channel and the left
bank becomes accessible to higher flows (Figure 6).
3BSEDIMENT SAMPLING
GeoEngineers completed four Wolman pebble counts (PCs): three upstream and one downstream of the project
crossing (Table 3). One pebble count (PC1) is located within the reference reach. The field team collected each
pebble count across 10 separate linear transects perpendicular to flow through a riffle and within the bankfull
width. The largest naturally occurring clasts in the system were small to medium boulder sized.
TABLE 2: WOLMAN PEBBLE COUNT DATA
Pebble Count PC1 Upstream
(Reference Reach)
(in)
PC2 Upstream
(in)
PC3 Upstream*
(in)
PC4 Downstream
(in)
Diameter
Percentile
D16 0.6 0.4 1.1 0.5
D50 2.3 1.5 2.9 1.6
D84 5.8 4.2 4.9 4.3
D95 8.5 9.6 6.8 6.0
*Note – Pebble count data collected in a location with a bankfull width measurement excluded from the design average BFW calculation
4BBANKFULL WIDTH
The field team recorded nine bankfull width measurements (BFWs; Table 3); six upstream of the crossing and three
downstream. Three of the upstream measurements were taken within the reference reach. Four of the bankfull
measurements coincide with the locations of pebble counts collected at the site. Table 3 presents the bankfull
width measurements and locations. The two bankfull width measurements upstream of and nearest to the crossing
inlet were not included in the design bankfull width calculation. These measurements were not considered to be
representative of the natural stream condition because they are likely within a depositional reach caused by the
backwater influence of the existing, undersized crossing structure expected to occur during flood flows.
File No. 0693-093-00
August 14, 2023
Page 4
TABLE 3: GEOENGINEERS BANKFULL WIDTH MEASUREMENTS
Approximate Distance (feet) Upstream or
Downstream from Crossing Inlet or Outlet
Respectively
Bankfull Width (feet) Used in Design BFW Average?
40 (Upstream) 17.5 No
70 (Upstream, at PC3) 14 No
215 (Upstream, at PC2) 8.8 Yes
350 (Upstream within reference reach; at PC1) 9 Yes
405 (Upstream within reference reach 9.8 Yes
450 (Upstream within reference reach) 8.7 Yes
75 (Downstream, downstream of pool) 14.3 Yes
172 (Downstream) 8.6 Yes
182 (Downstream, at PC4) 7 Yes
Design Average 9.5 -
5BOBSERVATIONS
8BProject Crossing
The project crossing is comprised of a 32-inch diameter fiberglass reinforced corrugated steel pipe with a slope of
4.11 percent (WDFW, 2022). There is a significant amount of road fill above the culvert; about 34 feet at the
downstream end and 20 feet at the upstream end. The upstream end of the culvert is framed by a concrete headwall
and wingwall, and considerable structural damage to the pipe due to gravel wear along its invert was observed
within the first several feet of pipe length at the inlet (Figure 1). This damage is likely the result of wear from
sediment transported through the pipe. A channel-spanning log was observed within the channel at the inlet,
creating an approximately 1.5-foot drop into the inlet and accumulating streambed sediment upstream.
Downstream, the elevated crossing outlet has produced a 3.9-foot drop, as measured at the time of the field
reconnaissance, from the culvert exit into a large scour pool below (Figure 2). The outlet scour pool had a maximum
water depth of approximately 4 feet, as measured at the time of the field reconnaissance.
In addition to the project culvert, two additional flow inputs were observed upstream of the crossing: stormwater
road runoff from Talbot Road South was observed entering Panther Creek at the left bank immediately upstream
of the project culvert inlet, and a municipal stormwater pipe was observed discharging to Panther Creek from the
right bank approximately 95 feet upstream of the crossing inlet.
9BLarge Woody Material
In the approximately 230-foot reach observed upstream of the project crossing, large woody material (LWM) is
typically lacking, with several notable exceptions. At the upstream end of the observed reach (230 feet upstream
of the inlet), woody material pieces consisting of fallen branches and small mobile woody material were present
and contributed to the development of diverse micro habitats and in-channel complexity. Approximately 180 feet
upstream of the crossing, a roughly 2-foot diameter channel spanning log covered by a thick layer of vines (English
ivy, Hedera helix) was observed. The log rests approximately 3 feet above the channel on both the right and left
banks and provides cover and shade over the channel. Just before the crossing, there is a large channel spanning
log embedded into the channel bottom and wedged between the concrete wingwalls and/or riprap armor material,
creating an approximately 1.5-foot drop into the culvert inlet (Figure 7). Several pieces of large, milled lumber line
File No. 0693-093-00
August 14, 2023
Page 5
the right bank just upstream of the inlet and appear to be placed material, forming a bank armoring structure.
These pieces appear to have little interaction with the channel except for at higher flows. Approximately 35 feet
upstream of the crossing there is a collection of woody material concentrated on the right of the channel, followed
by a scour pool (Figure 8).
Downstream of the culvert, there are a number of pieces of LWM interacting with flow. Directly below the culvert
outlet several LWM pieces were observed within the scour pool. Downstream from the scour pool, several single
logs were observed interacting with flow, either entering obliquely from the bank or spanning the channel, creating
steps and pools (Figure 9).
No LWM was observed within the reference reach. Portions of the reference reach included branches up to
approximately 0.5 inches in diameter hanging into the channel (Figure 3). Near the upstream end of the reference
reach there were fallen branches of approximately 1.0 to 2.0 inches in diameter racked up near an approximately
36-inch diameter boulder. Combined, these branches spanned the channel reinforcing the step adjacent to the
boulder.
10BGeomorphology
Panther Creek flows as a sinuous, single-thread channel with varying slopes, bedforms and cross-sectional
characteristics. Average reach slopes range from about 1.9 to 4.4 percent. A reach-based longitudinal profile is
presented in Figure 11.
Upstream of Project Crossing
Panther Creek flows slightly sinuous to sinuous and is confined within a ravine. Between the crossing inlet and the
confluence with the municipal stormwater pipe (approximately the first 100 feet upstream of the inlet), the channel
widens to nearly double the size of the uppermost observed reaches. Bed material is predominantly cobbles, small
boulders, and gravel and form steps within the channel down to the inlet. Just upstream of the confluence with the
municipal stormwater pipe (approximately 95 feet upstream of inlet) channel banks are nearly vertical and range
from 1.0 to 2.5 feet high and channel widths were observed to be approximately 7 to 9 feet. Minor toe erosion was
observed throughout, and banks were heavily vegetated to the channel bank toe. Channel morphology is pool-riffle.
Both riffles and pools were generally long running with pool depths no more than a few inches deep. Narrow, lateral
gravel and sand bars were also observed. Throughout the entire upstream reach observed, floodplains are generally
more accessible along the left bank.
Sediment is predominantly very coarse gravel with cobbles and occasional boulders and a few angular concrete
pieces of riprap were observed. Most of the boulder-sized material is covered with moss and not likely mobile except
at very high flows. Few pieces of large wood interact with flow as are observed hanging over the channel with
branches in the flow racking minor small mobile woody material.
See Reference Reach section above for detailed geomorphic assessment of the reference reach.
Downstream of Project Crossing
At the downstream outlet, there is a large scour pool that reaches depths of approximately 4 feet. Immediately
downstream of the pool, there is an accumulation of small cobbles and gravel with sand (Figure 12). The left bank
coincides with the left valley wall, and exposed sandstone and mudstone is observed (Figure 14). The right bank
offers backwater habitat at high flows that is most accessible approximately 27 feet downstream of the pool. The
200 feet of observed reach downstream of the culvert is pool-riffle morphology, with riffles on average measuring
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August 14, 2023
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twice as long as pools (Figure 13). Bedform is mainly riffle, with some sections that are glide. Pool depths ranged
from just a few inches to up to 1.1 feet deep. The deeper pools were observed just downstream of log pieces.
For almost the entire reach that was observed, the left valley wall is confined with no accessible floodplain;
discontinuous benches are approximately 2 feet above channel bed, but as high as 4 feet with vertical banks. In
general, the right banks are sloped back and are no higher than 1.5 feet. Minor undercutting and toe erosion were
observed. Lateral spanning channel bars consisted of coarse gravels and cobbles and a few sand deposits were
observed. As the slope declines (1.9 percent slope) moving downstream, the left bank floodplain becomes
accessible.
11BAquatic Habitat
Panther Creek appears to provide decent habitat for fish, particularly upstream of the project crossing, which has
more intact riparian forest vegetation (e.g., Figure 4). Flow is perennial and sufficient to support all life stages of
salmon or trout year-round. The primary physical limiting factors for fish utilization in the project vicinity are
anticipated to be: (a) limited riparian cover and closure in the reach immediately downstream (Figure 15), and
(b) the total fish barrier presented by the subject culvert. Water quality may also be an issue, particularly in light of
the stormwater discharge to the creek as well as the large outfall from a stormwater detention pond. Panther Creek
is 303(d) listed for Benthic Index of Biotic Integrity, indicating degraded water quality. Panther Creek is also listed
as Category 4A for temperature and there is a total maximum daily load (TMDL) in place for the Green River
Watershed. Stormwater management from urban runoff as well as lack of riparian shade may contribute to elevated
temperatures in Panther Creek.
There are no fish barriers present within the system downstream of the project crossing. Anadromous fish may
access Panther Creek up to the project crossing, but the subject culvert is believed to be a total fish barrier (WDFW
2022). Resident fish populations may occur both upstream and downstream of the crossing, and would also benefit
from crossing replacement. The stream gradient is typically within the range for fish utilization.
Substrate conditions throughout the reaches observed appeared generally appropriate for use by salmonids.
Embeddedness is low and the distribution of sediment sizes, including boulders, cobbles, gravel, and sand appears
to be appropriate for salmonid use (e.g., Figure 4 and Figure 13). However, some materials of artificial origin (e.g.,
broken concrete, angular rock) were also observed in the channel, and bank armoring (e.g., angular rock, milled
lumber) is present, particularly upstream of the crossing.
Pools are present throughout the observed reach, typically associated with LWM and/or naturally occurring boulder
clusters forcing small steps followed by small pools (e.g., Figures 3, 4, 5, 6 and 9). LWM is generally limited, except
in a few select locations described above (Figures 8 and 9). Several key pieces of LWM are present in the short
reach immediately upstream and immediately downstream of the crossing, but overall the quantities currently
occurring are insufficient to provide optimal fish habitat conditions.
12BRiparian Areas
Panther Creek flows through a forested ravine, with urban residential, commercial, and institutional development
beyond the immediate riparian area at the top of the valley walls. The vegetated ravine is typically approximately
130 to 200 feet wide in the vicinity of the project crossing both upstream and downstream, interrupted only by
Talbot Road South, which crosses perpendicular to the stream.
The Panther Creek ravine immediately upstream of the crossing is forested, creating dense shade even on the hot
summer day that characterized site reconnaissance. Typical forest canopy species include bigleaf maple (Acer
macrophyllum), red alder (Alnus rubra), and Western redcedar (Thuja plicata). Understory vegetation is severely
File No. 0693-093-00
August 14, 2023
Page 7
compromised in this reach by invasive species, including English ivy (Hedera helix) and Himalayan blackberry
(Rubus armeniacus). Native understory vegetation includes salmonberry (Rubus spectabilis), vine maple (Acer
circinatum), sword fern (Polystichum munitium) and field horsetail (Equisetum arvense).
Downstream of the project crossing, the forest canopy is more open immediately adjacent to the stream. The open
area is dominated by invasive species, typically Himalayan blackberry and reed canarygrass (Phalaris arundinacea),
as well as native salmonberry and beaked hazelnut (Corylus cornuta). Forested canopy set back from the stream
bank includes bigleaf maple (Acer macrophyllum), Western redcedar (Thuja plicata) and some Western hemlock
(Tsuga heterophylla). Forested areas and slopes in this area are also affected by proliferate English ivy (Hedera
helix).
6BREFERENCES
Mullineaux, D.R. 1965. Geologic map of the Renton quadrangle, King County, Washington, Washington: U.S.
Geological Survey Numbered Series Map 405, scale 1:24,000,
https://ngmdb.usgs.gov/Prodesc/proddesc_872.htm.
Washington Department of Fish and Wildlife. 2022. Fish Passage & Diversion Screening Inventory Database Site
Description Report: Site ID 931933. February 28, 2022.
Washington Department of Fish and Wildlife. 2023. Washington State Fish Passage Online Database. Accessed
July 2023. Available at: https://geodataservices.wdfw.wa.gov/hp/fishpassage/
index.html.
Washington State Department of Natural Resources. (2021). King County (WA) West 2021. Retrieved from WA
LiDAR Portal : https://lidarportal.dnr.wa.gov/
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August 14, 2023
Page 8
7BPHOTOS
Figure 1. Project crossing inlet, looking downstream.
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Figure 2. Project crossing outlet, looking upstream
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Figure 4. At bottom of reference reach, looking downstream
Figure 3. Upstream end of reference reach, looking upstream
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Figure 5. Cobble and boulder steps within the reference reach, looking upstream
Figure 6. Example of confined left bank and accessible right bank floodplain within reference reach, looking upstream
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Figure 8. Large wood jam and scour pool approximately 35 feet upstream of crossing inlet, looking downstream
Figure 7. Channel spanning log creating a 1.5-foot drop into inlet
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Figure 10: Small branches racked up on and beside an approximately 36-inch diameter boulder within the reference reach, looking upstream
Figure 9. LWM within channel approximately 85 feet downstream of the outlet, looking upstream
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Figure 11. Reach-based longitudinal profile of the project crossing
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Figure 13. Pool-riffle channel morphology downstream of the outlet, looking upstream
Figure 12. Channel spanning cobble and gravel bar at downstream end of outlet scour pool, looking downstream
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Figure 14. Siltstone and mudstone exposed along the left bank near the outlet
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Figure 15. Typical open riparian canopy downstream, dominated by invasive species with few trees
set further back from the stream channel.
Appendix B
FEMA Flood Panel
National Flood Hazard Layer FIRMette
0 500 1,000 1,500 2,000250
Feet
Ü
SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT
SPECIAL FLOOD
HAZARD AREAS
Without Base Flood Elevation (BFE)
Zone A, V, A99
With BFE or DepthZone AE, AO, AH, VE, AR
Regulatory Floodway
0.2% Annual Chance Flood Hazard, Areas
of 1% annual chance flood with average
depth less than one foot or with drainage
areas of less than one square mileZone X
Future Conditions 1% Annual
Chance Flood HazardZone X
Area with Reduced Flood Risk due to
Levee. See Notes.Zone X
Area with Flood Risk due to LeveeZone D
NO SCREEN Area of Minimal Flood Hazard Zone X
Area of Undetermined Flood HazardZone D
Channel, Culvert, or Storm Sewer
Levee, Dike, or Floodwall
Cross Sections with 1% Annual Chance
17.5 Water Surface Elevation
Coastal Transect
Coastal Transect Baseline
Profile Baseline
Hydrographic Feature
Base Flood Elevation Line (BFE)
Effective LOMRs
Limit of Study
Jurisdiction Boundary
Digital Data Available
No Digital Data Available
Unmapped
This map complies with FEMA's standards for the use of
digital flood maps if it is not void as described below.
The basemap shown complies with FEMA's basemap
accuracy standards
The flood hazard information is derived directly from the
authoritative NFHL web services provided by FEMA. This map
was exported on 11/7/2023 at 1:38 AM and does not
reflect changes or amendments subsequent to this date and
time. The NFHL and effective information may change or
become superseded by new data over time.
This map image is void if the one or more of the following map
elements do not appear: basemap imagery, flood zone labels,
legend, scale bar, map creation date, community identifiers,
FIRM panel number, and FIRM effective date. Map images for
unmapped and unmodernized areas cannot be used for
regulatory purposes.
Legend
OTHER AREAS OF
FLOOD HAZARD
OTHER AREAS
GENERAL
STRUCTURES
OTHER
FEATURES
MAP PANELS
8
B 20.2
The pin displayed on the map is an approximate
point selected by the user and does not represent
an authoritative property location.
1:6,000
122°13'W 47°26'54"N
122°12'22"W 47°26'30"N
Basemap Imagery Source: USGS National Map 2023
Appendix C
Design Concepts
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 1a - PLAN
0 15'30'
C-1
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
0 15'30'
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 1b - PLAN
0 15'30'
C-2
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
0 15'30'
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 1c - PLAN
0 15'30'
C-3
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
0 15'
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 2a - PLAN
0 15'30'
C-4
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
0 15'30'
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 2b - PLAN
0 15'30'
C-5
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
0 15'30'
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 2c - PLAN
0 15'30'
C-6
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com C-7
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 1 - PROFILE AND CULVERT SECTION Figure
6
DR
A
F
T
C-83-SIDED BOX CULVERT PROFILE AND SECTION
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com
PANTHER CREEK CULVERT REPLACEMENT
ALTERNATIVE 2 - PROFILE AND CULVERT SECTION
Figure
9
DR
A
F
T
C-9STEEL PLATE ARCH CULVERT PROFILE AND SECTION
PANTHER CREEK CULVERT REPLACEMENT
CITY OF RENTON
1601 5th Avenue, Suite 1600
Seattle, WA 98101
206.622.5822
www.kpff.com 10
%
D
E
S
I
G
N
-
N
O
T
F
O
R
C
O
N
S
T
R
U
C
T
I
O
N
City of Renton
1055 S. Grady Way
Renton, WA 98057
(425) 430-6400
Know what's below
before you digCall
R
PANTHER CREEK CULVERT REPLACEMENT
ROADWAY PLAN AND PROFILE RD01C-10BRIDGE PLAN AND PROFILE
Appendix D
Conceptual Design Opinion of Probable Construction Cost
Estimate of Probable Cost
Panther Creek at Talbot Rd S Culvert Replacement Project
Renton, WA
Unit Price Unit QTY Total Cost QTY Total Cost QTY Total Cost QTY Total Cost QTY Total Cost QTY Total Cost QTY Total Cost QTY Total Cost
PREPARATION, GENERAL
1 Mobilization (10% of total)LS 1 439,050$ 1 468,254$ 1 560,166$ 1 505,166$ 1 443,468$ 1 479,831$ 1 566,063$ 1 511,063$
2 Clearing, Grubbing, and Roadside Cleanup 50,000$ AC 0.45 22,500$ 0.38 19,000$ 0.38 19,000$ 0.38 19,000$ 0.45 22,500$ 0.38 19,000$ 0.38 19,000$ 0.38 19,000$
3 Removal of Structures and Obstructions 10,000$ LS 1 10,000$ 1 10,000$ 1 10,000$ 1 10,000$ 1 10,000$ 1 10,000$ 1 10,000$ 1 10,000$
4 Sawcut Asphalt Conc. Pavement 45$ LF 101 4,545$ 101 4,545$ 101 4,545$ 101 4,545$ 101 4,545$ 101 4,545$ 101 4,545$ 101 4,545$
5 Planing Butiminous Pavement 55$ SY 184 10,120$ 184 10,120$ 184 10,120$ 184 10,120$ 184 10,120$ 184 10,120$ 184 10,120$ 184 10,120$
6 Structure Surveying 5,000$ LS 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$
7 Roadway Surveying 5,000$ LS 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$
8 As-bult Survey and Record Drawings 5,000$ LS 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$ 1 5,000$
9 Work Access (stream)50,000$ LS 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$
10 TESC Measures (5% of total)LS 1 219,525$ 1 234,127$ 1 280,083$ 1 252,583$ 1 221,734$ 1 239,916$ 1 283,031$ 1 255,531$
SUB-TOTAL 770,740$ 811,046$ 948,914$ 866,414$ 777,367$ 828,412$ 957,759$ 875,259$
EARTHWORK AND SURFACING
11 Roadway Excavation, incl. Haul 55$ CY 359 19,745$ 359 19,745$ 359 19,745$ 359 19,745$ 385 21,175$ 385 21,175$ 385 21,175$ 385 21,175$
12 Rock Excavation 1,000$ CY 485 485,000$ 649 649,000$ 485 485,000$ 485 485,000$ 485 485,000$ 649 649,000$ 485 485,000$ 485 485,000$
13 Structure Excavation Class A incl. Haul 60$ CY 15,371 922,260$ 15,105 906,300$ 8,362 501,720$ 8,362 501,720$ 15,382 922,920$ 15,311 918,660$ 8,440 506,400$ 8,440 506,400$
14 Channel Excavation Incl. Haul 100$ CY 600 60,000$ 600 60,000$ 600 60,000$ 600 60,000$ 600 60,000$ 600 60,000$ 600 60,000$ 600 60,000$
15 Dewatering 20,000$ LS 1 20,000$ 1 20,000$ 1 20,000$ 1 20,000$ 1 20,000$ 1 20,000$ 1 20,000$ 1 20,000$
16 Streambed Sediment 100$ Ton 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$
17 Streambed Sand 200$ Ton 80 16,000$ 80 16,000$ 80 16,000$ 80 16,000$ 80 16,000$ 80 16,000$ 80 16,000$ 80 16,000$
18 Streambed Cobbles 100$ Ton 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$ 720 72,000$
19 Streambed Boulder Type 1 150$ EA 300 45,000$ 300 45,000$ 300 45,000$ 300 45,000$ 300 45,000$ 300 45,000$ 300 45,000$ 300 45,000$
20 Compost 50$ CY 100 5,000$ 100 5,000$ 100 5,000$ 100 5,000$ 100 5,000$ 100 5,000$ 100 5,000$ 100 5,000$
21 Crushed Surfacing Base Course 60$ Ton 501 30,060$ 501 30,060$ 146 8,760$ 146 8,760$ 534 32,040$ 534 32,040$ 154 9,240$ 154 9,240$
22 Gravel Borrow 30$ Ton 27,100 813,000$ 25,200 756,000$ 1,400 42,000$ 1,400 42,000$ 27,800 834,000$ 26,600 798,000$ 1,700 51,000$ 1,700 51,000$
23 HMA CL. 1/2 IN. PG 58H-22 200$ TN 215 43,000$ 215 43,000$ 63 12,600$ 63 12,600$ 232 46,400$ 232 46,400$ 67 13,400$ 67 13,400$
24 Cement Conc. Sidewalk 150$ SY 288 43,200$ 288 43,200$ 58 8,700$ 58 8,700$ 292 43,800$ 292 43,800$ 65 9,750$ 65 9,750$
SUB-TOTAL 2,646,265$ 2,737,305$ 1,368,525$ 1,368,525$ 2,675,335$ 2,799,075$ 1,385,965$ 1,385,965$
STRUCTURE
25
3-Sided Conc. Box Culvert incl. footings,
stemwalls, headwalls and wingwalls 1,102,500$ LS 1 1,102,500$ - -$ - -$ - -$ 1 1,117,605$ - -$ - -$ - -$
26
Steel Plate Arch Culvert incl. footings and
wingwalls 1,307,000$ LS - -$ 1 1,307,000$ - -$ - -$ - -$ 1 1,361,000$ - -$ - -$
27 Bridge w/ SS on own bridge 3,594,899$ LS - -$ - -$ 1 3,594,899$ - -$ - -$ - -$ 1 3,636,426$ - -$
28 Bridge w/ SS on structure 3,044,899$ LS - -$ - -$ - -$ 1 3,044,899$ - -$ - -$ - -$ 1 3,086,426$
SUB-TOTAL 1,102,500$ 1,307,000$ 3,594,899$ 3,044,899$ 1,117,605$ 1,361,000$ 3,636,426$ 3,086,426$
UTILITIES
26 Adjust Catch Basin 800$ Each 1 800$ 1 800$ 1 800$ 1 800$ 1 800$ 1 800$ 1 800$ 1 800$
27 Drain Pipe, 12" Diam.30$ LF 69 2,070$ 69 2,070$ 69 2,070$ 69 2,070$ 69 2,070$ 69 2,070$ 69 2,070$ 69 2,070$
28 Temporary Utility Relocations 100,000$ LS 1 100,000$ 1 100,000$ 1 100,000$ 1 100,000$ 1 100,000$ 1 100,000$ 1 100,000$ 1 100,000$
SUB-TOTAL 102,870$ 102,870$ 102,870$ 102,870$ 102,870$ 102,870$ 102,870$ 102,870$
TRAFFIC
29 Temporary Traffic Control (3% of total)LS 1 131,715$ 1 140,476$ 1 168,050$ 1 151,550$ 1 133,040$ 1 143,949$ 1 169,819$ 1 153,319$
30 Paint Line 3$ LF 401 1,203$ 401 1,203$ 401 1,203$ 401 1,203$ 401 1,203$ 401 1,203$ 401 1,203$ 401 1,203$
31 Permanent Signing 1,500$ LS 1 1,500$ 1 1,500$ 1 1,500$ 1 1,500$ 1 1,500$ 1 1,500$ 1 1,500$ 1 1,500$
SUB-TOTAL 134,418$ 143,179$ 170,753$ 154,253$ 135,743$ 146,652$ 172,522$ 156,022$
HABITAT AND LANDSCAPE
32 Riparian Restoration 200,000$ AC 1 200,000$ 1 200,000$ 1 200,000$ 1 200,000$ 1 200,000$ 1 200,000$ 1 200,000$ 1 200,000$
33 Temporary Stream Diversion 50,000$ LS 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$ 1 50,000$
34 Log Structure 6,000$ EA 29 174,000$ 29 174,000$ 29 174,000$ 29 174,000$ 29 174,000$ 29 174,000$ 29 174,000$ 29 174,000$
SUB-TOTAL 424,000$ 424,000$ 424,000$ 424,000$ 424,000$ 424,000$ 424,000$ 424,000$
CONSTRUCTION COST SUBTOTAL 5,180,794$ 5,525,401$ 6,609,961$ 5,960,961$ 5,232,920$ 5,662,009$ 6,679,542$ 6,030,542$
CONTINGENCY 40.0% 2,072,317$ 40.0% 2,210,160$ 40.0% 2,643,984$ 40.0% 2,384,384$ 40.0% 2,093,168$ 40.0% 2,264,804$ 40.0% 2,671,817$ 40.0% 2,412,217$
SALES TAX 10.1%732,564$ 10.1%781,292$ 10.1%934,649$ 10.1%842,880$ 10.1%739,935$ 10.1%800,608$ 10.1%944,487$ 10.1%852,719$
ESTIMATED TOTAL CONSTRUCTION COST W/CONTINGENCY & SALES TAX 7,985,675$ 8,516,853$ 10,188,594$ 9,188,226$ 8,066,023$ 8,727,421$ 10,295,846$ 9,295,478$
Alternative 1a
Pre-Cast Concrete Box
Item#Item Description
Alternative 1c.1
Bridge w/ SS on own Bridge
Alternative 2c.1
Bridge w/ SS on own Bridge
Alternative 2c.2
Bridge w/ SS on Structure
Alternative 2a
Pre-Cast Concrete Box
Alternative 1b
Steel Plate Arch
Alternative 2b
Steel Plate Arch
Alternative 1c.2
Bridge w/ SS on Structure
GeoEngineers KPFF Conceptual Design Alternatives Page 1