HomeMy WebLinkAboutChimacum Creek No Rise AssessmentOsborn Consulting, Inc.
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BELLEVUE • SEATTLE • SPOKANE • BELLINGHAM
T ECH NI CA L ME MO R AND UM
Date: November 13, 2023
Project: WSDOT US101/SR116 North Olympic Peninsula - Remove Fish Barriers
To: Patrick Allen, PE, Design Manager | Kiewit
From: Matt Gray, PE, SDE | Osborn Consulting, Inc.
Jason Neibergs, PE, Civil Engineer | Osborn Consulting, Inc.
Mike Zarecor, PE, Civil Engineer | Osborn Consulting, Inc.
cc: Katie Mozes, PE, Hydraulics Engineer | Northwest Hydraulic Consultants
Subject: SR 116 MP 0.22 Chimacum Creek No-Rise Assessment
TABLE OF CONTENTS
1. Introduction ............................................................................................................................................ 2
2. No-Rise Assessment ............................................................................................................................. 4
2.1. Data Compilation (Compiled by NHC) .......................................................................................... 4
2.1.1. HEC-2 Model ......................................................................................................................... 4
2.1.2. Terrain Data .......................................................................................................................... 4
2.1.3. Hydrologic Data ..................................................................................................................... 4
2.2. Duplicate Effective Floodplain and Floodway Models (Developed by NHC) ................................ 5
2.3. Corrected Effective Floodplain and Floodway Models .................................................................. 5
2.4. Existing Conditions Floodplain and Floodway Models .................................................................. 6
2.5. Proposed (Post-Project) Floodplain and Floodway Models .......................................................... 6
2.6. Comparison of Existing and Proposed 100-Year Water Surface Elevations ................................ 6
3. Summary of No-Rise Assessment ....................................................................................................... 11
4. References ........................................................................................................................................... 12
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1. INTRODUCTION
The Washington State Department of Transportation (WSDOT) is proposing a replacement structure for
the State Route (SR) 116 crossing of Chimacum Creek at Mile Post (MP) 0.22, which is located south of
Irondale in Jefferson County, Washington (Figure 1). The existing 8-foot span and 9-foot rise Corrugated
Metal Pipe Arch (CMPA) on SR 116 was identified as a fish barrier by the Washington Department of Fish
and Wildlife (WDFW) and the WSDOT Environmental Services Office (ESO) (Site ID 990077) due to its
excessive slope, which is above the limits required for fish passage (WDFW, 2019). The proposed project
will replace this existing CMPA with a 70.5-foot span structure, associated channel grading, and Large
Woody Material (LWM) elements (see Appendix A), designed to meet the 2013 WDFW Water Crossing
Design Guidelines (WCDG) and WSDOT Hydraulics Manual (Barnard et al., 2013) (WSDOT, 2023).
The project is located within a Federal Emergency Management Agency (FEMA) Zone AE Special Flood
Hazard Area (SFHA) with a regulatory floodway, as indicated in the effective FEMA Flood Insurance Rate
Map (FIRM) Panels No. 53031C0142C and 53031C0145C, published by FEMA in June 2019 (FEMA,
2019a). The extents of the mapped floodplain are shown in Figure 1 and the Effective FEMA Firm panels
are available in Appendix B. In order to replace existing infrastructure at the SR 116 crossing of
Chimacum Creek, WSDOT will need to comply with the “No-Rise” development regulations set forth in 44
Code of Federal Regulations (CFR) §60.3 entitled “Flood Plain Management Criteria for Flood-Prone
Areas”.
Northwest Hydrology Consultants (NHC) complied the existing data and prepared duplicate effective
models of the floodplain and floodway in 2020. Osborn Consulting has verified the duplicate effective
models and modeled the pre- and post-project conditions. These models were used to determine how the
project will affect floodplain and regulatory floodway water surface elevations (WSEs) compared to
existing conditions, and document a No-Rise Assessment following FEMA Region X guidelines.
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Figure 1. Study Location of the SR-116 Chimacum Creek Culvert Replacement Project with FEMA Floodplain
Data and Hydraulic Model Cross-Section Locations.
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2. NO-RISE ASSESSMENT
In accordance with the FEMA Region X guidance for conducting No-Rise Assessments, Osborn
completed the following technical tasks for the proposed SR 116 Chimacum Creek crossing:
1. Reviewed existing data including the FEMA 1D model used for delineating the floodplain and
floodway of the effective FIRM, as well as terrain and hydrologic data (compiled by NHC);
2. Reviewed duplicate effective floodplain and floodway models (developed by NHC);
3. Developed corrected effective floodplain and floodway models;
4. Developed existing (i.e., pre-project) conditions floodplain and floodway models;
5. Developed proposed (i.e. post-project) conditions floodplain and floodway models; and
6. Compared the proposed to existing condition water surface elevations (WSEs) for the FEMA
effective 100-year peak flow.
The purpose of the No-Rise Assessment is to show that the proposed project does not cause a rise in
WSE between the existing and proposed floodplain and floodway simulations. These tasks are discussed
in detail in the following sections, 2.1 through 2.6. All elevations specified in this memo are referenced to
the NAVD88 vertical datum.
2.1. Data Compilation (Compiled by NHC)
2.1.1. HEC-2 Model
WSDOT obtained, and provided to NHC, the effective one-dimensional (1D) hydraulic model used in
developing the FEMA floodplain maps. The original study is over 40 years old. The 1D model used the
Hydrologic Engineering Center 2 (HEC-2) software (USACE, 1991), was developed in 1978, and became
effective in July 1982 based on data provided by FEMA (Appendix C).
2.1.2. Terrain Data
Terrain data used in the analysis originated from two sources, namely:
1. The original geometric data used for the development of the FEMA HEC-2 model. The HEC-2
model included station-elevation data (referenced to the NGVD29 vertical datum) for lettered
cross-sections A through W along Chimacum Creek (Appendix C). No information on the exact
acquisition date for this geometric data was available; however, it is prior to the August 1978,
when the HEC-2 model simulations were performed.
2. A terrain surface created from two topobathymetric surveys, conducted by the WSDOT Olympic
and South-Central Region Survey Teams in June and December 2019, respectively (WSDOT,
2020). The WSDOT South Central Region Survey Team combined these surveys with the most
recent available LiDAR data (USGS, 2019) and provided this surface to Osborn during the RFP
phase. This terrain surface extends about 700 feet downstream of SR 116 to the Hunt Road
crossing, and about 1,000 feet upstream to the FEMA lettered cross-section P.
2.1.3. Hydrologic Data
All hydraulic analyses conducted for this study utilized the FEMA 100-year peak flow (FEMA, 2019b) of
1,020 cubic feet per second (cfs), published in the FEMA effective Flood Insurance Study (FIS) as the
Chimacum Creek flow upstream of Puget Sound and downstream of the confluence with East Chimacum
Creek. This is the same flow utilized for the HEC-2 model analysis from the FEMA effective study and
was determined from the analysis of USGS Streamgage No. 12051500 located near Chimacum, WA. The
gage record spans from 1953 to 1957, though no details on the data analysis are provided in the FIS
Report. As the gage data included so few values, and because no additional gages were available near
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the project site for comparison, the FEMA published flows were compared to the 100-year peak flow
estimate from the United States Geological Survey (USGS) Region 3 Regression Equation. The FEMA
published flows was found to overpredict the 100-year peak flow in comparison to the Region 3 USGS
Regression Equation.
2.2. Duplicate Effective Floodplain and Floodway Models (Developed by NHC)
Following the FEMA Region X guidelines, the duplicate effective floodplain and floodway models were
developed by NHC utilizing the Hydrologic Engineering Center River Analysis System (HEC-RAS v6.4.1)
(USACE, 2019). The duplicate effective model utilized the same hydrologic data, Manning’s roughness
coefficients for the channel and overbank areas, and bank stations as in the HEC-2 model. The models
also utilized the HEC-2 geometric data, which was translated from the NGVD29 to the NAVD88 vertical
datum to match the effective FEMA FIRM (Appendix B) and FIS (FEMA, 2019a). For consistency, the
WSE specified as the boundary condition at the downstream end of the duplicate effective models was
also translated to the NAVD88 datum. The translated elevations in NAVD88 were calculated by adding
3.5 feet to the corresponding elevations referenced in NGVD29 (Appendix D; FEMA, 2019b).
Additionally, the duplicate effective floodway model replicated the floodway widths estimated by the HEC-
2 model and published in the FIRM and the FIS. Selected results from the duplicate effective floodplain
and floodway models are provided in Appendix E.
2.3. Corrected Effective Floodplain and Floodway Models
The corrected effective floodplain and floodway models were developed by updating the topobathymetry
and the 1D modeling procedures used in the corresponding duplicate effective models between cross-
sections M and R. Cross-sections N, O and P were updated with elevation data extracted from the 2019
WSDOT survey. This update was deemed necessary due to the poor quality (drastic elevation differences
compared to the WSDOT survey data) and low resolution (i.e., 1,500- to 2,000-foot-wide floodplains
defined with only typically 10 to 15 points and the main channel with only 4 to 6 points) of the HEC-2
cross-sectional geometry data.
The 100-year WSE simulated by the duplicate effective floodplain and floodway models at cross-sections
P, Q, and R defaulted to critical depth, as was depicted in the HEC-2 model results. Two additional cross-
sections were extracted from the 2019 WSDOT survey at Stations 13668 and 13898 located between
cross-sections O and P, in order to prevent the model from defaulting to critical depth at cross-section P.
For the same reason, additional cross-sections were interpolated between cross-sections P and Q, and Q
and R using the built-in HEC-RAS cross-section interpolation routine.
The Manning’s roughness coefficient values for the main channel and overbank areas at all added cross-
sections were set to 0.05 and 0.1, to match the duplicate effective model. The bank stations were
determined based on an assessment of the additional cross-section geometry, or through linear
interpolation for the interpolated cross-sections.
Additionally, the corrected effective floodplain and floodway models include the existing 8-foot tall, 9-foot
span CMPA (as documented in the 2019 WSDOT survey), to correct the 6.3-foot wide by 8-foot tall
rectangular slot that was documented in the respective HEC-2 FEMA models and the duplicate effective
models. The existing culvert was modeled utilizing culvert analysis routine built into HEC-RAS. Two
cross-sections were extracted at Stations 13110 and 13200 upstream and downstream of the existing
culvert from the 2019 WSDOT survey. Since these cross sections are present in the HEC-2 FEMA
models, but are not shown in the effective FIRM, their locations were identified using the distances
between sections listed in the HEC-2 data.
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Ineffective flow areas were added to cross-sections N and O, as well as the cross sections at stations
13110 and 13200. The ineffective area stations at these cross-sections were determined based on the
length of flow overtopping SR 116, calculated with HEC-RAS.
Finally, the floodway widths at Stations 13110 and 13200 immediately downstream and upstream of the
SR 116 crossing were updated to match the 128.1- and 126.2-foot floodway widths, respectively as
measured using the published FIRM (Appendix B). The mapped floodway widths at these cross-sections
differ significantly from the HEC-2 and duplicate effective floodway model estimates, which were 16.4 and
366.6 feet, respectively.
After all corrections, the FEMA surcharge in 100-year WSE from the floodplain to the floodway model was
less than the allowable 1.0 foot at all cross-sections.
2.4. Existing Conditions Floodplain and Floodway Models
The existing condition model is the same as the corrected effective model since there is no information to
indicate that significant changes have occurred to the terrain or the bridge structure between the time
when the effective study was conducted and existing conditions.
2.5. Proposed (Post-Project) Floodplain and Floodway Models
The existing condition model was modified to create the proposed condition model. Model modifications
included the proposed project elements including replacing the existing culvert with a 70.5-foot hydraulic
opening structure, channel grading, and LWM elements of the proposed design (see Appendix A).
Cross-sections downstream and upstream of the proposed structure (Stations 13110 and 13200) were
extracted from the proposed (post-project) conditions terrain surface developed by Osborn and Kiewit.
Ineffective flow areas were updated for cross-sections N and O, as well as the cross sections at stations
13110 and 13200 to reflect the overbank flow conditions resulting from the proposed structure. Two-
dimensional model results were used to verify the locations of the ineffective areas.
LWM elements on the right bank of cross-section 13100 were simulated by increasing the Manning’s
roughness coefficient to 0.15 from 0.1 based on the recommendations of Yochum (2017).
2.6. Comparison of Existing and Proposed 100-Year Water Surface Elevations
Table 1 and Table 2 compare the 100-year WSEs from the existing and proposed conditions floodplain
and floodway models, respectively. The existing and proposed conditions 100-year WSE profiles through
the project reach, calculated from the floodplain and floodway models are provided in Figure 2 and
Figure 3, respectively. As shown in the figures, the 100-year WSE does not default to critical at any
location of any of the models. The results indicate the proposed project does not create a rise in the 100-
year floodplain or floodway WSEs and thus meets the FEMA Region X No-Rise criteria.
The results indicate significant decreases in WSE upstream of the crossing due to the elimination of
backwater resulting from the undersized existing culvert. The WSE downstream of the culvert shows a
minimal decrease in WSE, which likely occurs due to flow overtopping the roadway in the existing
condition.
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Table 1. Comparison of the 100-Year Water Surface Elevations for the Existing and Proposed Conditions
Floodplain Models.
Cross-Section
Station
Cross-Section
Letter
Designation
Existing Water
Surface Elevation
(Feet, NAVD88)
Proposed Water
Surface
Elevation
(Feet, NAVD88)
Difference
(Feet)
12470 M 80.24 80.24 0.00
13060 N 81.05 81.03 -0.02
13110 - 81.15 81.1 -0.05
13199 SR 116 N/A N/A N/A
13200 - 86.28 81.66 -4.62
13310 O 86.69 81.93 -4.76
13668 - 86.69 82.91 -3.78
13898 - 86.67 83.83 -2.84
14160 P 87.01 85.75 -1.26
14422.0* Interpolated 87.51 86.75 -0.76
14684.0* Interpolated 87.58 86.87 -0.71
14946.0* Interpolated 87.63 86.96 -0.67
15208.0* Interpolated 87.68 87.07 -0.61
15470 Q 87.75 87.24 -0.51
15615.0* Interpolated 87.82 87.41 -0.41
15760.0* Interpolated 88.01 87.81 -0.20
15905.0* Interpolated 88.41 88.38 -0.03
16050.0* Interpolated 88.97 88.97 0.00
16195.0* Interpolated 89.55 89.55 0.00
16340.0* Interpolated 90.13 90.13 0.00
16485.0* Interpolated 90.7 90.7 0.00
16630.0* Interpolated 91.27 91.27 0.00
16775.0* Interpolated 91.83 91.83 0.00
16920 R 92.4 92.4 0.00
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Table 2. Comparison of the 100-Year Water Surface Elevations for the Existing and Proposed Conditions
Floodway Models.
Cross-Section
Station
Cross-Section
Letter
Designation
Existing Water
Surface
Elevation
(Feet, NAVD88)
Proposed Water
Surface
Elevation
(Feet, NAVD88)
Difference
(Feet)
12470 M 80.86 80.86 0.00
13060 N 81.75 81.75 0.00
13110 - 81.82 81.82 0.00
13199 SR 116 N/A N/A N/A
13200 - 86.73 82.2 -4.53
13310 O 87.14 82.4 -4.74
13668 - 87.1 82.9 -4.20
13898 - 87.31 84.79 -2.52
14160 P 87.52 86.06 -1.46
14422.0* Interpolated 88.31 87.29 -1.02
14684.0* Interpolated 88.4 87.43 -0.97
14946.0* Interpolated 88.46 87.54 -0.92
15208.0* Interpolated 88.52 87.67 -0.85
15470 Q 88.63 87.9 -0.73
15615.0* Interpolated 88.73 88.14 -0.59
15760.0* Interpolated 88.92 88.56 -0.36
15905.0* Interpolated 89.27 89.11 -0.16
16050.0* Interpolated 89.77 89.72 -0.05
16195.0* Interpolated 90.35 90.33 -0.02
16340.0* Interpolated 90.95 90.94 -0.01
16485.0* Interpolated 91.56 91.55 -0.01
16630.0* Interpolated 92.16 92.16 0.00
16775.0* Interpolated 92.78 92.78 0.00
16920 R 93.4 93.4 0.00
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Figure 2. Comparison of the 100-year Water Surface Elevation Predicted by the Existing and Proposed
Conditions Floodplain Models Near the Project Site.
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Figure 3. Comparison of the 100-year Water Surface Elevation Predicted by the Existing and Proposed
Conditions Floodway Models Near the Project Site.
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3. SUMMARY OF NO-RISE ASSESSMENT
The simulated WSDOT proposed SR-116 replacement structure, with associated channel grading and
LWM elements, does not cause a rise in the 100-year WSE calculated by both the floodplain and
floodway models (Section 2.6). The project therefore meets the No-Rise criteria following 44 CFR §60.3
entitled “Flood Plain Management Criteria for Flood-Prone Areas”. The signed No-Rise Certification Form
is available in Appendix F.
Prepared under the direct supervision of:
Matthew Gray, SDE
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4. REFERENCES
Barnard, R.J., J. Johnson, P. Brooks, K.M. Bates, B. Heiner, J.P. Klavas, D.C. Ponder, P.D. Smith, and
P.D. Powers (2013). Water Crossing Design Guidelines. Washington State Department of Fish and
Wildlife. Olympia, WA.
Federal Emergency Management Agency (2019a). National Flood Insurance Program, Flood Insurance
Rate Map for Jefferson County, Washington and Incorporated Areas. Map numbers 53031C0142C and
53031C0145C. Available at:
https://msc.fema.gov/portal/availabilitySearch?addcommunity=530069&communityName=JEFFERSON%
20COUNTY%20UNINCORPORATED%20AREAS#searchresultsanchor
Federal Emergency Management Agency (2019b). Flood Insurance Study for Jefferson County,
Washington and Incorporated Areas. Flood Insurance Study Number 53031CV00A, Version No. 2.3.2.2.
Available at:
https://msc.fema.gov/portal/availabilitySearch?addcommunity=530069&communityName=JEFFERSON%
20COUNTY%20UNINCORPORATED%20AREAS#searchresultsanchor
United States Army Corps of Engineers (2019). HEC-RAS River Analysis System V.6.4.1. Available at:
https://www.hec.usace.army.mil/software/hec-ras/download.aspx
United States Army Corps of Engineers (1991). HEC-2 Water Surface Profiles.
United States Geological Survey (2019). Olympic Peninsula, Washington 3DEP LiDAR - Area 1 Technical
Data Report. Contract No. G16PC00016, Task Order No. G17PD00827.
Washington Department of Fish and Wildlife (2019) Habitat Assessment Data for the Chimacum Creek
(Site ID 990077) at SR 116. Conducted on October 28, 2015. Available at:
http://apps.wdfw.wa.gov/fishpassagephotos/Reports/990077_Report.pdf
Washington State Department of Transportation (2020). SR 116 MP 0.22 Chimacum Creek: Preliminary
Hydraulic Design Report. Olympia, WA.
Washington State Department of Transportation (2023). Hydraulics Manual, Olympia, WA
Yochum, S.E. (2017). Flow Resistance Coefficient Selection in Natural Channels: A Spreadsheet Tool.
Technical Summary TS 103.2, National Stream and Aquatic Ecology Center, United States Department of
Agriculture. Available at: https://www.fs.fed.us/biology/nsaec/products-tools.html