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ENGINEERING*NO-RISE" CERTIFICATION
This is to certifu that I am a duly qualified Engineer licensed to practice in the State of Washington.
It is to further certifr that the attached 2020 flood effect on the previous "No-Rise" study is still valid"
The 2020 flood event altered the river channel and bank around the Broodstock Collection Facility in the
Cedar River, just upstream of I-405 in Renton Washington. The proposed permanent weir for the
Broodstock Collection Facility will not impact the base flood elevations or the l-percent annual chance
flood (100-year) for weir elevations at or below elevation 29.6 feet. The floodway widths are not affected
as per the previous "No-Rise" analysis. The no-rise effect due to the proposed permanent weir for the
Broodstock Collection Facility is still valid.
The attaehed Technical Memorandum 007 on the "2020 Flood Effect on the No Rise Study * Cedar River
Broodstock Collection Facility", documents and supports the no impact findings.
17 November 2A2A
Nathan C. Cox
Hydraulic Engineer
I4Tl Sharlins Driv*, Suite 1S$
Boise, Idaho 8370?
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Rev. No. 0 / November 2020 1 McMillen Jacobs Associates
Technical Memorandum
Technical Memorandum 007
To: Fernando Platin, PE
Seattle Public Utilities
Project: Cedar River Broodstock Collection Facility
(BCF)
From: Derek Nelson, PE
McMillen Jacobs Associates
cc: File
Prepared
by:
Nathan Cox, P.E.
Marcia Rojas
McMillen Jacobs Associates
Job No.: 18-101
Date: November 17, 2020
Subject: 2020 Flood Effect on No-Rise Study – Cedar River Broodstock Collection Facility
1.0 Introduction
This section contains the purpose of this memorandum, and a project description for the Cedar River
Broodstock Collection Facility (BCF) for Seattle Public Utilities (SPU).
1.1 Purpose
This Technical Memorandum (TM) documents the work completed to determine if the event in February
of 2020, that resulted in alterations to the channel, has adversely affected the previously completed no-rise
condition (McMillen Jacobs, 2019), see Appendix B, for the proposed replacement of the BCF as part of
the SPU BCF (Project).
1.2 Project Description
The BCF is located on River Mile (RM) 1.7 of the Cedar River (Renton, WA) immediately upstream of the
Interstate 405 Bridge, see Figure 1. Originally constructed by SPU in 2008 as part of the Landsburg
Mitigation Agreement (LMA), the current adult collection facility is operated seasonally (~ Sept. - Nov.
annually) by the Washington Department of Fish and Wildlife (WDFW). The current design is composed
of a permanent substrate rail, perpendicular to the flow, to which temporary resistance-board panels attach
during operation. Since this facility was installed, WDFW and SPU have made several modifications to
the weir to improve collection efficiency. These modifications have improved some components and
collection methods; however, the BCF is still not meeting the project goals.
The proposed replacement option provides a permanent concrete sill with an electric actuated picket lifting
system. The pickets would be removable, similar to the existing conditions. The trap and picket
modifications would improve access and attraction flow.
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Figure 1. Project Location
2.0 Survey
The survey data includes points between the Renton library and cross-section 192.3. Additional pictures
of the site survey can be seen in Appendix A. The points can be seen in Figure 2. The pertinent survey
points comprise of two clusters. The first cluster influences cross-sections 165, 165.5, and 169.3, while the
second influences the sandbank at cross-section 179.5.
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Figure 2. Focused View of Model Cross Sections, New Survey Cross Sections, and DEM
2.1 Affected HEC-RAS Cross-Sections
Cross-sections 165, 165.6, 169.3, and 179.5 were altered using the DEM derived from the two survey point
clusters. Other points such as those near the library, were not included because these would sway the DEM
approximation due to the low point density. The four cross-sections were only altered where the DEM of
new bathymetry data intersects the original cross-section, see Figure 3 for changes. Overall, the cross-
sections experienced erosion on the river-left bank as well as at the deepest center section.
The center of cross-section 165 eroded, somewhat shifting the thalweg to the right, while deposition
occurred on the slope of the left side. Cross-section 165.6 experienced erosion on the center riverbed and
river-left bank that decreased the slope to the bed of the river. Similarly left bank on 169.3 eroded, however
at the left shelf there seems to be a new raised deposition. The center seems to have equally had deposition
and erosion, left-center and right-center respectively. Cross-section 179.5 eroded at the left bank. Additional
detail on how the cross-sections were modified can be found in Appendix A.
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Figure 3. Comparison of Survey Data and Pre-Event Cross Sections,
Resulting in Updated Cross Sections
3.0 HEC-RAS Model
The Proposed Conditions Model was updated to reflect the new geometry from the post-event survey data.
The updated model maintains the same model parameters as before, including the weir coefficient and
floodway representation, as well as the cross-section and in-line structure (BCF-weir) locations. The only
change was to the elevation details of the cross-sections shown above. The updated model with BCF-weir
does not show an increase in the Base Flood Elevations (BFE) and instead shows a decrease in Water
Surface Elevation (WSE).
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Figure 4. Profile of HEC-RAS Results for Eroded Cross Sections
Figure 5. Cross Section View of HEC-RAS Results for Eroded Cross Sections
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Figure 5 cont. Cross Section View of HEC-RAS Results for Eroded Cross Sections
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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4.0 Results
The event in February of 2020 that resulted in alterations to the channel was evaluated in to ways; first, a
comparison to understand if the changes would affect the hydraulics of the existing conditions (no-weir),
and second to understand if the addition of the BCF-weir under the new channel geometry would modify
results from the previous No-Rise analysis.
These two comparisons were determined numerically, a visualization of which can be seen in Figures 6a-
b. The 2020 event did alter the stream cross sections sufficiently to change the water surface elevation at
all cross-sections (Figure 6a). Most changes were a decrease in WSE except for cross-section 179.5.
The second comparison was of the Existing conditions after the 2020 event (the new corrected effective
model), with and without the BCF-weir were. The results show that placing the weir in the new corrected
effective model will result in lowering or maintaining the same WSE (Figure 6b, Table 1). The 0.1ft increase
in WSE in cross-section 179.5 (Figure 6a) between the pre- and post-2020 event models is neutralized with
the addition of the weir, which had a -0.1ft change at that cross-section. Therefore, the WSE of 179.5 with
the weir in the new corrected effective model is the same as pre-2020 event model version without the weir.
b
a
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Figure 6a-b. Comparison of Water Surface Elevations
Table 1. Water Surface Elevation Comparison.
Cross
Section
HEC-RAS
River
Station
(-)
Distance
(ft)
FIS
100Yr
Regulatory
WS Elevation
(ft)(1)
2020 Existing
Conditions
Model
WS Elevation
(ft)(2)
2020 Proposed
Conditions
Model
WS Elevation
(ft)(3)
No-Rise
WS
Elevation
(ft)
AF 275 14,481 54.2 54.16 54.16 0
- 274.85 Riverview Park Bridge
AE 274.7 14,467 54.1 54.09 54.09 0
AD 260.7 13,726 51.3 51.28 51.28 0
AC 250.6 13,187 50.8 50.76 50.76 0
AB 242.2 12,741 48.7 48.72 48.72 0
AA 231.4 12,173 48.3 48.24 48.24 0
- 220.7 11,600 - 46.6 46.59 -0.01
- 211.2 11,096 - 45.05 45.03 -0.02
Z 204.7 10,776 44.1 44.07 44.03 -0.04
- 192.3 10,103 - 43.28 43.2 -0.08
- 184.6 9,803 - 43.01 42.91 -0.10
- 179.5 9,426 - 42.65 42.55 -0.10
Y 169.3 8,891 42.0 41.97 41.82 -0.15
168 Broodstock Collection Facility Weir
X 165.6 8,694 42.3 42.29 42.29 0
- 165.3 Pedestrian Bridge, Under I-405
- 165 8,664 - 42.17 42.17 0
W 160.8 8,443 41.6 41.6 41.6 0
- 160.3 Houser Way Bridge
V 159.7 8,383 40.2 40.17 40.17 0
U 153.1 8,011 39.8 39.8 39.8 0
- 151.3 Renton Library Bridge
WS Elevation = Water Surface Elevation, ft = feet, = Comparison of the Water Surface Elevations.
(1) 1-Percent Annual Chance Flood Regulatory Water Surface Elevation, Table 6 – Floodway Data (FEMA, 2017).
(2) HEC-RAS, Plan: 2020event_Cedar-2003-FIS(FW-Final), Geometry: 2020event_Cedar-2003-FIS(100-Final), Flow: Cedar-2003-
FIS(FW).
(3) HEC-RAS, Plan: BCF_2020event_Cedar-2003-FIS(FW-Final), Geometry: BCF_2020event_Cedar-2003-FIS(100-Final), Flow:
Cedar-2003-FIS(FW).
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5.0 Conclusion
Assessing channel models without the BCF weir, the natural channel alteration from February 2020 event
for the most part lowered the WSE, except for one cross-section. The addition of the weir in the new
corrected effective model lowers this WSE at all cross-sections. Including the Broodstock Collection
Facility (BCF) in the channel at the proposed location will have a no-rise effect on the 1% annual chance
flood or base flood elevation (BFE), if the weir is at or below 29.6 feet.
6.0 References
City of Seattle, et al.; “Landsburg Mitigation Agreement”, April 21, 2000.
FEMA. 2017. Flood Insurance Study, King County, Washington, and Incorporated Areas. Flood
Insurance Study Number 53033CV001B. Preliminary September 15, 2017.
McMillen Jacobs Associates (McMillen Jacobs). 2019. No-Rise Study – Cedar River Broodstock
Collection Facility. Technical Memorandum 002, To Kay Yesuwan of Seattle Public Utilities.
November 18, 2019.
Seattle Public Utilities – Broodstock Collection Facility 2020 Flood Event Effect on No-Rise Study
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Appendix A
Post-February 2020 Event Site Visit and HEC-RAS Updates
Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Post-February 2020 Event Site Visit
Viewpoint: Rocky bank Viewpoint: Retention side, upstream Viewpoint: Retention side, at BCF
Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Viewpoint: Road Access ramp Viewpoint: Road Access
Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Viewpoint: Upstream Road Access
Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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HEC-RAS Updates
Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Seattle Public Utilities – Broodstock Collection Facility Appendix A – Site Visit HEC-RAS Changes
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Appendix B
No-Rise Analysis Completed on November 18, 2019
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Technical Memorandum
Technical Memorandum 002
To: Kay Yesuwan, PE
Seattle Public Utilities
Project: Cedar River Broodstock Collection Facility
(BCF)
From: Derek Nelson, PE
McMillen Jacobs Associates
cc: File
Prepared
by:
Nathan Cox, P.E.
McMillen Jacobs Associates
Job No.: 18-101
Date: November 18, 2019
Subject: No-Rise Study – Cedar River Broodstock Collection Facility
1.0 Introduction
This section contains the purpose of this memorandum, and a project description for the Cedar River
Broodstock Collection Facility (BCF) for Seattle Public Utilities (SPU).
1.1 Purpose
This Technical Memorandum (TM) documents the work completed to determine a no-rise condition for
the proposed replacement of the BCF as part of the SPU BCF (Project). The no-rise condition analysis
was conducted following the 2013 Federal Emergency Management Agency (FEMA) guidance document
to ensure that placement of the BCF weir would not cause any increase in flood levels within the Cedar
River floodplain during the occurrence of the base (100-year) flood discharge.
1.2 Definitions
The following are definitions of terms used through this TM.
Base Flood Elevation (BFE): The computed elevation to which floodwater is anticipated to rise
during the base flood. The BFE is also referred to as the 1-percent annual chance flood or the
100-year flood.
Conditional Letter of Map Revision (CLOMR): FEMA's comment on a proposed project that would,
upon construction, affect the hydrologic or hydraulic characteristics of a flooding source and thus
result in the modification of the existing regulatory floodway, the effective Base Flood Elevations
(BFEs), or the Special Flood Hazard Area (SFHA). The letter does not revise an effective NFIP
map, it indicates whether the project, if built as proposed, would be recognized by FEMA.
Flood Insurance Rate Map (FIRM): Official map of a community on which FEMA has delineated the
Special Flood Hazard Areas (SFHAs), the Base Flood Elevations (BFEs) and the risk premium
zones applicable to the community.
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Flood Insurance Study (FIS): a compilation and presentation of flood risk data for specific
watercourses, lakes, and coastal flood hazard areas within a community.
Floodplain: Any land area susceptible to being inundated by floodwaters from any source.
Floodway: The channel of a river or other watercourse and the adjacent land areas that must be
reserved in order to discharge the base flood without cumulatively increasing the water surface
elevation more than a designated height.
Letter of Map Revision (LOMR): FEMA's modification to an effective Flood Insurance Rate Map
(FIRM. LOMRs are generally based on the implementation of physical measures that affect the
hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of
the existing regulatory floodway, the effective Base Flood Elevations (BFEs), or the Special
Flood Hazard Area (SFHA). The LOMR officially revises the Flood Insurance Rate Map
(FIRM), and sometimes the Flood Insurance Study (FIS) report, and when appropriate, includes a
description of the modifications. The LOMR is generally accompanied by an annotated copy of
the affected portions of the FIRM, FBFM, or FIS report.
National Flood Insurance Program (NFIP): The program of flood insurance coverage and floodplain
management administered under the Act and applicable federal regulations promulgated in Title
44 of the Code of Federal Regulations, Subchapter B.
1.3 Project Description
The BCF is located on River Mile (RM) 1.7 of the Cedar River (Renton, WA) immediately upstream of
the Interstate 405 Bridge, see Figure 1. Originally constructed by SPU in 2008 as part of the Landsburg
Mitigation Agreement (LMA), the current adult collection facility is operated seasonally (~ Sept. - Nov.
annually) by the Washington Department of Fish and Wildlife (WDFW). The current design is composed
of resistance-board panels, with the only permanent component of the facility is a substrate rail,
perpendicular to the flow, where the panels attach. Since this facility was installed, WDFW and SPU
have made several modifications to the weir to improve collection efficiency. These modifications have
improved some components and collection methods; however, the BCF is still not meeting the project
goals.
The proposed replacement option provides a permanent concrete sill with an electric actuated picket
lifting system. The pickets would be removable, similar to the existing conditions. The trap and picket
modifications would improve access, and improve attraction flow. The purpose of the no-rise analysis is
to determine the allowable permanent concrete weir elevation to not affect the 1% annual chance flood.
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Figure 1. Project Location.
2.0 FEMA Flood Map Service Center
The FEMA Flood Map Service Center (MSC) is a public source for flood hazard information in support
of the National Flood Insurance Program (NFIP). The MSC is used to find flood maps, and other flood
hazard product to communicate flood risk. The following is a discussion of the Effective Products and
Preliminary Products contained on the MSC that effect the no-rise study.
2.1 Effective Products
At the project location, the documents identified in Table 1 are listed as the effective products.
Table 1. FEMA Effective Products for Project Location.
Description
Map / FIS
Number
Effective
Date
Flood Insurance Rate Map (FIRM) 53033C0977F May 16, 1995
Flood Insurance Study (FIS) 53033CV001A April 19, 2005
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2.2 Preliminary Products
The King County and the City of Renton are in the process of updating the existing FEMA FIS to reflect
current hydraulic conditions along the Cedar River. The update is based on the following: the peak flood
discharges for Cedar River were too low, a landslide (at river mile 5.1) blocked the main channel
redirecting the river, the channel was regraded (upstream of Highway 169), better in-channel survey was
collected (downstream river mile 3.0), and a USACE flood control project to mitigate recurring flooding
problems. At the project location, the documents identified in Table 2 are listed as the preliminary
products. It is anticipated that these preliminary products will become effective in February 2020.
Table 2. FEMA Preliminary Products for Project Location.
Description
Map / FIS
Number
Preliminary
Date
Flood Insurance Rate Map (FIRM) 53033C0977G September 9, 2017
Flood Insurance Study (FIS) 53033CV001B September 15, 2017
3.0 HEC-RAS Model
The following is a discussion of the current effective model, duplicate effective model, corrected effective
model, and existing conditions model.
3.1 Current Effective Model
The current effective model is the model used to develop the effective FIRM produced in 1995. Figure 2
shows the project location on the effective FIRM. This model will be superseded before the Project is
constructed.
3.2 Duplicate Effective Model
The current effective model was not duplicated utilizing the most current version of the Hydrologic
Engineering Center River Analysis System (HEC-RAS) because the effective model will be superseded
before the project is constructed.
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Figure 2. Current Effective Model from Effective FIRM 53033C0977F.
3.3 Corrected Effective Model
The corrected effective model is a geo-referenced HEC-RAS model was provided to McMillen Jacobs
Associates (McMillen Jacobs) by the City of Renton. The corrected effective model incorporates changes
made to Cedar River. The model was prepared by Northwest Hydraulic Consultants for the City of
Renton. Model assumptions and documentation can be found in the Flood Insurance Mapping Study for
the Cedar River (nhc, 2006). Figure 3 shows the project location on the preliminary FIRM.
Data reported in the Preliminary Flood Insurance Study (FIS) (FEMA 2017) was compared with the
corrected effective model. Plate 1 shows the model comparison, for the Cedar-Lower Reach, with data
presented in Table 6 – Floodway Data in the FIS study (FEMA, 2017). The following is a brief
description of how the data compared:
• All water surface elevations for the regulatory and floodway for the 1% annual chance flood
matched within ± 0.1, which can be attributed to rounding.
• The floodway widths and mean velocities also matched well, with the exception of a few cross
sections. The average percent change for the floodway widths and mean velocities are 1% and
18% respectively.
• The section area for the floodway were different when compared to the HEC-RAS model, with an
average and maximum percent change of 18% and 81% respectively. It is uncertain why only the
sectional area data does not match for any reported cross section.
With the water surface elevations for the regulatory and with floodway, and the floodway widths
matching for the majority of the cross sections, the model is considered to be reproducing the preliminary
FIS study data effectively to complete a no-rise comparison for the Project.
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Figure 3. Corrected Effective Model from Preliminary FIRM 53033C0977G.
3.4 Existing Conditions Model
There are two documented changes to the FIRM. The documented amendments to the FIRM are shown
in Table 3. Case number 16-10-0468A-530088 is away from the main channel, located outside the 0.2%
annual chance flood, which will not affect the proposed Project, therefore this amendment has not been
added to the model. Case number 13-10-0684A-530088 is not located within the floodway, and is in the
0.2% annual chance flood area, therefore this amendment has not been added to the model because it is
beyond the 1% annual chance flood. The existing conditions model is the current effective model. Figure
4 shows the existing conditions model cross section around the project location.
Table 3. FEMA Documented Amendments to FIRM.
Address Case Number Date
55 W illiams Avenue South 13-10-0684A-530088 March 07, 2013
1 South Grady Way 16-10-0468A-530088 January 18, 2016
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Figure 4. Existing Conditions Model at Project Location.
4.0 Proposed Conditions Model
Utilizing a limited survey completed around the Project, a comparison was made with the HEC-RAS
model cross sections and the survey data. The survey cross sections match very closely with the HEC-
RAS model cross sections. Cedar River is constrained at the Project location by the right retaining wall.
The HEC-RAS model incorporates a sediment fill that accounts for the maximum allowable
sedimentation accumulation before the river is dredged downstream from the Project. The model
accounts for the maximum allowable sedimentation infill, before dredging operations, to establish the
worst case base flood elevations (BFE) or 1% annual chance flood elevations. Given that the survey
matches the HEC-RAS model cross sections, the proposed BCF permanent weir will be modeled utilizing
an inline structure within HEC-RAS.
The Existing Conditions Model was modified to incorporate the permanent weir for the BCF. The BCF
weir was modeled utilizing an Inline Structure, within HEC-RAS, 32-feet downstream of cross section Y
at elevation 29.6 feet. Figure 5 shows the cross section with the BCF weir included in the model. A weir
coefficient of 2.85 was used to represent the BCF weir. The weir elevation was varied until a no-rise
condition was achieved. The BCF weir does not increase the BFE, but slightly decreases the elevations
due the presence of the weir. The presence of the weir increases the velocity which in turn increases the
Froude Number, resulting in a decrease in the water surface elevation. The effect is minimal and does not
increase the BFE. The BCF will not have a negative impact on the 1% annual chance flood elevations.
Figure 6 shows the water surface profile for both the existing conditions and proposed conditions model.
Table 4 shows the water surface elevations reported in the FIS report and a comparison between the
existing conditions and the proposed conditions model with the BCF weir at elevation 29.6 feet.
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Figure 5. HEC-RAS Cross Section of BCF Weir.
Figure 6. HEC-RAS Profile at BCF Weir Location.
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Table 4. BFE Water Surface Elevation Comparison.
Cross
Section
HEC-RAS
River
Station
(-)
Distance
(ft)
FIS
100Yr
Regulatory
WS Elevation
(ft)(1)
Existing
Conditions
Model
WS Elevation
(ft)(2)
Proposed
Conditions
Model
WS Elevation
(ft)(3)
No-Rise
WS Elevation
(ft)
AF 275 14,481 54.2 54.16 54.16 0.00
- 274.85 Riverview Park Bridge
AE 274.7 14,467 54.1 54.09 54.09 0.00
AD 260.7 13,726 51.3 51.28 51.28 0.00
AC 250.6 13,187 50.8 50.77 50.76 -0.01
AB 242.2 12,741 48.7 48.73 48.72 -0.01
AA 231.4 12,173 48.3 48.25 48.24 -0.01
- 220.7 11,600 - 46.61 46.60 -0.01
- 211.2 11,096 - 45.07 45.05 -0.02
Z 204.7 10,776 44.1 44.10 44.06 -0.04
- 192.3 10,103 - 43.34 43.27 -0.07
- 184.6 9,803 - 43.08 42.99 -0.09
- 179.5 9,426 - 42.55 42.46 -0.09
Y 169.3 8,891 42.0 41.99 41.87 -0.12
168 Broodstock Collection Facility Weir
X 165.6 8,694 42.3 42.30 42.30 0.00
- 165.3 Pedestrian Bridge, Under I-405
- 165 8,664 - 42.21 42.21 0.00
W 160.8 8,443 41.6 41.60 41.60 0.00
- 160.3 Houser Way Bridge
V 159.7 8,383 40.2 40.17 40.17 0.00
U 153.1 8,011 39.8 39.80 39.80 0.00
- 151.3 Renton Library Bridge
WS Elevation = Water Surface Elevation, ft = feet, = Comparison of the Water Surface Elevations.
(1) 1-Percent Annual Chance Flood Regulatory Water Surface Elevation, Table 6 – Floodway Data (FEMA, 2017).
(2) HEC-RAS, Plan: Cedar-2003-FIS(FW-Final), Geometry: Cedar-2003-FIS(100-Final), Flow: Cedar-2003-FIS(FW).
(3) HEC-RAS, Plan: BCF_Cedar-2003-FIS(FW-Final), Geometry: BCF_Cedar-2003-FIS(100-Final), Flow: Cedar-2003-FIS(FW).
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5.0 Floodway
The floodway describes the river channel and the adjacent land areas that must be reserved to pass the 1%
Annual Chance Flood (100-year) without increasing the water surface elevation more than 1 foot. The
floodway width is a theoretical representation to ensure that there are no encroachments into the river that
could increase upstream flood elevations. The floodway represents where the majority of the flow
conveyance occurs within the river channel. A comparison of the floodway widths and the with floodway
water surface elevations for the existing conditions model and proposed conditions model, show that there
is no change to the floodway widths or with floodway 1% annual chance water surface elevations for the
proposed permanent BCF weir. Figure 7 shows that the BCF weir floodway width are unchanged. Table
5 shows the comparison between the floodway widths and the with floodway 1% annual chance water
surface increase for the FIS study, existing conditions model, and proposed conditions model.
Figure 7. Floodway at Project Location, BCF Weir.
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Table 5. Floodway Data for 1-Percent Annual Chance Flood Water Surface Elevation Comparison .
Cross
Section
HEC-
RAS
River
Station
(-)
Distance
(ft)
FIS Study(1)
Existing
Conditions Model(2)
Proposed
Conditions Model(3)
Floodway
Width
(ft)
With
Floodway
WSEL
(ft)
Floodway
Width
(ft)
With
Floodway
WSEL
(ft)
Floodway
Width
(ft)
With
Floodway
WSEL
(ft)
AF 275 14,481 113 54.5 113 54.5 113 54.5
- 274.85 Riverview Park Bridge
AE 274.7 14,467 113 54.5 113 54.5 113 54.5
AD 260.7 13,726 92 51.8 92 51.8 92 51.8
AC 250.6 13,187 125 51.3 125 51.3 125 51.3
AB 242.2 12,741 95 49.5 95 49.5 95 49.5
AA 231.4 12,173 120 49.0 120 49.0 120 49.0
- 220.7 11,600 - - 90 47.3 90 47.3
- 211.2 11,096 - - 84 45.9 84 46.0
Z 204.7 10,776 87 45.0 87 45.0 87 45.0
- 192.3 10,103 - - 117 44.3 117 44.3
- 184.6 9,803 - - 111 43.9 111 43.9
- 179.5 9,426 - - 115 43.5 115 43.5
Y 169.3 8,891 166 43.0 166 43.0 166 43.0
168 Broodstock Collection Facility Weir
X 165.6 8,694 171 43.3 171 43.3 171 43.3
- 165.3 Pedestrian Bridge, Under I-405
- 165 8,664 - - 171 42.7 171 42.7
W 160.8 8,443 114 42.1 114 42.1 114 42.1
- 160.3 Houser Way Bridge
V 159.7 8,383 114 40.6 114 40.6 114 40.6
U 153.1 8,011 130 40.3 130 40.3 130 40.3
- 151.3 Renton Library Bridge
WSEL = Water Surface Elevation, ft = feet.
(1) 1-Percent Annual Chance Flood with Floodway Water Surface Elevation, Table 6 – Floodway Data (FEMA, 2017).
(2) HEC-RAS, Plan: Cedar-2003-FIS(FW-Final), Geometry: Cedar-2003-FIS(100-Final), Flow: Cedar-2003-FIS(FW).
(3) HEC-RAS, Plan: BCF_Cedar-2003-FIS(FW-Final), Geometry: BCF_Cedar-2003-FIS(100-Final), Flow: Cedar-2003-FIS(FW).
B12
Seattle Public Utilities – Broodstock Collection Facility No-Rise Study
Rev. No. 3 / November 2019 12 McMillen Jacobs Associates
6.0 No Net Rise Study Conclusion
Using the methods provided in the 2013 FEMA guidance document, the addition of the permanent weir
for the Broodstock Collection Facility (BCF) will have a no-rise effect on the 1% annual chance flood or
base flood elevation (BFE), if the weir elevation is at or below elevation 29.6 feet. The floodway widths
are not affected for the with floodway 1% annual chance flood water surface elevations. Therefore, there
is a no-rise effect due to the proposed permanent weir for the Broodstock Collection Facility.
7.0 References
City of Seattle, et al.; “Landsburg Mitigation Agreement”, April 21, 2000.
FEMA (Federal Emergency Management Agency). 2005. Flood Insurance Study, King County,
Washington and Incorporated Areas. Flood Insurance Study Number 53033CV001A. Revised April
19, 2005.
FEMA. 2013. Procedures for “No-Rise” Certification for Proposed Developments in the Regulatory
Floodway. Available at: https://www.fema.gov/no-rise-certification-floodways. Accessed January
2019.
FEMA. 2017. Flood Insurance Study, King County, Washington and Incorporated Areas. Flood
Insurance Study Number 53033CV001B. Preliminary September 15, 2017.
Northwest Hydraulic Consultants (nhc). 2006. Flood Insurance Mapping Study for the Cedar River. Lake
Washington to Renton City Limits. Renton, Washington. Prepared for City of Renton. April 2006.
B13
Seattle Public Utilities – Broodstock Collection Facility No-Rise Study
Rev. No. 3 / November 2019 13 McMillen Jacobs Associates
PLATE
B14
FLOOD INSURANCE STUDY HEC-RAS 5.0.6 - Cedar River - 2003 FIS
King County, Washington and Incorporated Areas Plan:Cedar-2003-FIS(FW-Final)
Flood Insurance Study Number 53033CV001B Geometry:Cedar-2003-FIS(100-Final)
Revised: April 19, 2005 Flow:Cedar-2003-FIS(FW)Average =0%1%18%4%0%
Reach:Cedar-Lower Minimum =0%-6%-35%-1%0%
Maximum =0%21%81%22%0%
100Yr
Regulatory
100Yr
Regulatory
CROSS SECTION DISTANCE
(FEET)
WIDTH
(FEET)
SECTION
AREA
(SQ. FEET)
MEAN
VELOCITY
(FEET/SEC.)
REGULATORY
(FEET NAVD)
WITHOUT
FLOODWAY
(FEET NAVD)
WITH
FLOODWAY
(FEET NAVD)
INCREASE
(FEET)
Cross
Section
HEC-RAS
Channel Length
HEC-RAS
River Sta Structure WSEL Width
Section
Area
Mean
Velocity WSEL
WSEL
Comparison
Width
Comparison
Section Area
Comparison
Mean
Velocity
Compariosn
WSEL
Comparison
CEDAR RIVER (ft)(-)(ft)(4)(ft)(1)(sq ft)(2)(ft/s)(3)(ft)(5)(%)(%)(%)(%)(%)
A 119 221 1,216 7.2 24.2 24.2 24.2 0.0 AF 14,481 275 0.0 0.3 -91.7 0.0 0.0 0%0%-6%0%0%
B 975 153 1,218 8.4 24.8 24.8 24.8 0.0 --274.85 Riverview Park Bridge ----------
C 1,640 155 1,226 9.1 25.4 25.4 25.4 0.0 AE 14,467 274.7 0.0 0.3 -94.8 0.0 0.0 0%0%-7%0%0%
D 2,438 140 1,169 9.7 26.4 26.4 26.7 0.3 AD 13,726 260.7 0.0 0.4 -524.5 0.0 0.0 0%0%-35%0%0%
E 3,364 145 1,228 8.9 28.1 28.1 28.8 0.7 AC 13,187 250.6 0.0 0.3 24.4 -0.1 0.0 0%0%2%-1%0%
F 3,962 160 1,164 8.0 29.6 29.6 30.0 0.4 AB 12,741 242.2 0.0 -0.3 -153.7 0.0 0.0 0%0%-13%0%0%
G 4,063 145 1,142 9.0 29.6 29.6 30.0 0.4 AA 12,173 231.4 0.0 -0.4 125.7 0.0 0.0 0%0%10%0%0%
H 4,344 128 1,134 10.0 30.0 30.0 30.4 0.4 -11,600 220.7 ----------
I 5,255 138 1,173 9.4 32.1 32.1 32.5 0.4 -11,096 211.2 ----------
J 5,565 164 1,156 7.4 33.2 33.2 33.6 0.4 Z 10,776 204.7 0.0 -0.1 -59.1 0.0 0.0 0%0%-5%0%0%
K 5,636 180 1,181 6.4 33.6 33.6 33.9 0.3 -10,103 192.3 ----------
L 5,746 149 1,173 6.7 33.8 33.8 34.3 0.5 -9,803 184.6 ----------
M 5,850 196 1,202 7.1 34.0 34.0 34.3 0.3 -9,426 179.5 ----------
N 6,485 119 1,131 10.6 34.3 34.3 34.6 0.3 Y 8,891 169.3 0.0 -0.5 383.2 1.5 0.0 0%0%28%22%0%
O 6,530 119 1,129 9.9 35.0 35.0 35.2 0.2 X 8,694 165.6 0.0 -0.3 1030.6 0.4 0.0 0%0%81%7%0%
P 6,708 117 1,139 10.1 35.2 35.2 35.5 0.3 --165.3 Pedestrian Bridge, Under I-405 ----------
Q 6,917 137 1,137 9.1 35.7 35.7 36.2 0.5 -8,664 165 ----------
R 6,961 149 1,149 7.4 37.5 37.5 38.1 0.6 W 8,443 160.8 0.0 -0.4 442.0 0.4 0.0 0%0%39%6%0%
S 7,658 119 1,128 9.4 38.2 38.2 38.8 0.6 --160.3 Houser Way Bridge ----------
T 7,736 119 1,128 8.8 39.1 39.1 39.7 0.6 V 8,383 159.7 0.0 -0.4 296.1 0.3 0.0 0%0%26%3%0%
U 8,011 130 1,134 8.0 39.8 39.8 40.3 0.5 U 8,011 153.1 0.0 0.3 363.2 0.3 0.0 0%0%32%3%0%
V 8,383 114 1,126 8.4 40.2 40.2 40.6 0.4 --151.3 Renton Library Bridge ----------
W 8,443 114 1,130 7.6 41.6 41.6 42.1 0.5 -7,848 149.5 ----------
X 8,694 171 1,269 5.2 42.3 42.3 43.3 1.0 T 7,736 147.4 0.0 -0.4 238.3 0.0 0.0 0%0%21%0%0%
Y 8,891 166 1,350 6.9 42.0 42.0 43.0 1.0 --146.7 Bronson Way Bridge ----------
Z 10,776 87 1,089 11.7 44.1 44.1 45.0 0.9 S 7,658 146 0.0 -0.4 151.4 0.0 0.0 0%0%13%0%0%
AA 12,173 120 1,235 8.7 48.3 48.3 49.0 0.7 -7,444 141.8 ----------
AB 12,741 95 1,183 11.5 48.7 48.7 49.5 0.8 -7,031 134.1 ----------
AC 13,187 125 1,297 9.0 50.8 50.8 51.3 0.5 R 6,961 132.8 0.0 0.0 468.2 0.9 0.0 0%0%41%12%0%
AD 13,726 92 1,514 12.0 51.3 51.3 51.8 0.5 --132.3 Wells Ave Bridge ----------
AE 14,467 113 1,458 8.7 54.1 54.1 54.5 0.4 Q 6,917 131.8 0.0 0.0 186.5 0.8 0.0 0%0%16%8%0%
AF 14,481 113 1,458 8.7 54.2 54.2 54.5 0.3 P 6,708 127.9 0.0 0.4 45.2 0.5 0.0 0%0%4%5%0%
O 6,530 124.5 0.0 0.3 81.9 0.3 0.0 0%0%7%3%0%
Comparison Description between Table 6 and HEC-RAS Model of Cedar River - 2003 FIS --124.1 Williams Ave Bridge ----------
(1) Floodway Width Comparison N 6,485 123.7 0.0 0.3 1.7 0.5 0.0 0%0%0%5%0%
(2) Floodway Sectional Area Comparison M 5,850 111.6 0.0 0.2 498.0 0.6 0.0 0%0%41%9%0%
(3) Floodway Mean Velocity Comparison L 5,746 109.5 0.0 31.4 628.5 0.8 0.0 0%21%54%13%0%
(4) Regulatory or without Floodway, 1% Annual Chance Flood Comparison --108.3 Logan Ave Bridge ----------
(5) With Floodway, 1% Annual Chance Flood Comparison K 5,636 107.1 -0.1 0.4 694.9 0.6 0.0 0%0%59%10%0%
J 5,565 106.3 0.0 -0.4 472.8 1.0 0.0 0%0%41%14%0%
I 5,255 100.2 0.0 5.4 98.2 0.6 0.0 0%4%8%7%0%
-4,719 90.2 ----------
H 4,344 84.2 0.0 0.5 69.7 0.0 0.0 0%0%6%0%0%
-4,178 80.4 ----------
G 4,063 77.7 0.0 0.2 193.2 0.0 0.0 0%0%17%0%0%
F 3,962 75.9 -0.1 -0.3 337.4 0.0 0.0 0%0%29%0%0%
-3,907 74.8 ----------
--70 Lat Struct ----------
E 3,364 64.6 0.0 -0.4 116.1 0.0 -0.1 0%0%9%0%0%
--50 Lat Struct ----------
D 2,438 46.9 0.0 -0.5 74.6 0.0 0.0 0%0%6%-1%0%
--40 Lat Struct ----------
C 1,640 31.7 0.0 0.3 90.1 0.0 0.0 0%0%7%0%0%
--20 Lat Struct ----------
B 975 19.2 0.0 -0.4 204.7 0.0 -0.1 0%0%17%0%0%
--10 Lat Struct ----------
A 119 3 0.0 -13.8 441.1 0.8 -0.1 0%-6%36%12%0%
--1.3 N. Boeing Bridge ----------
-0 0.1 ----------
--20 0.08 ----------
--320 0.03 ----------
FW
Floodway
Comparison Results
FW
Floodway
TABLE 6 - FLOODWAY DATA
FLOODING SOURCE FLOODWAY
1-PERCENT ANNUAL CHANCE FLOOD
WATER SURFACE ELEVATION
PLATE 1B15