WA_RIDGE_MAIN(1)_Hydraulic_Report.pdf

WA RIDGE MAIN (1)

1/30/2018

U.S. Department of Transportation Federal Highway Administration

WFLHD ii 1/30/18 WA RIDGE MAIN(1) Hydraulic Report

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Table of Contents

1 Introduction

2 Project Description

2.1 Location

3 Historic Creek Alignments

4 Field Reconnaissance

4.1 General Observations

4.2 Lateral Channel Stability

4.2.1 Gee Creek

4.2.2 Boutwell Creek

4.3 Vertical Channel Stability

4.3.1 Gee Creek

4.3.2 Boutwell Creek

4.4 Existing Scour

4.5 Bed Material

4.6 WDFW Fish Passage (Aquatic Organism Passage) Criteria

4.6.1 Culvert Span

4.6.2 Slope

5 Hydrology

6 Hydraulics

6.1 Gee Creek

6.2 Boutwell Creek

6.3 Design Criteria

6.4 Capacity Analysis

6.5 Proposed Culvert

7 Floodplain Model Results

7.1 Duplicate Effective Model

7.2 Existing Conditions

7.3 Proposed Conditions

8 Scour

8.1 Aggradation/ Degradation

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8.2 Scour Depth

8.3 Scour Protection

8.4 Riprap Sizing

8.5 Riprap Layout

9 References

Appendix A: Photographs

Appendix B: Hydrologic Analysis

Appendix C: Gee Creek Cross-Sections

Appendix D: Gee Creek HEC RAS Output

Appendix E Scour Calculations

Appendix F: Boutwell Creek Culvert

Appendix F: Main Avenue Access Plans

List of Figures Figure 1: Vicinity Map Figure 2: 1858 Cadastral Survey Map Figure 3: December 2007 Road Overtopped Figure 4: Gee Creek / Boutwell Creek Historic Confluence Figure 5: Gee Creek Particle Size Distribution Figure 6: Active Channel ( ) Measurements Figure 7: Cross-Section of Proposed Arch-Structure at Main Avenue Figure 8: Existing (CEM) and Proposed Water Surface profile at Main Ave Figure 9: Minimum Riprap Protection Dimenions Figure 10: East Side (upstream) from Main Avenue (December 2015) Figure 11: West side (downstream) from Main Avenue (December 2015) Figure 12: Unnamed Creek at Boutwell driveway (December 2015) Figure 13: Unnamed creek post high water event (December 2015)

Figure 14: Road overtopping evidence on the west side of Main Avenue (December 2015) Figure 15: Gee Creek downstream of Main Avenue (May 2016) Figure 16: Gee Creek west of Main Avenue (looking downstream)

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List of Tables Table 1: Gee Creek Minimum Stream-Simulation Culvert Width Table 2: Boutwell Creek Minimum Stream-Simulation Culvert Width Table 3: Gee Creek Peak Discharge

Table 4: Boutwell Creek Peak Discharge Table 5: Duplicate Effective Model Result (NAVD88)

Table 6: Corrected/ Existing Effective Model Result

Table 7: Proposed Condition Model (PEM) Results Table 8: Summary of Riprap Layout

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1 Introduction This report documents the results of the hydraulic engineering analysis carried out to support the hydraulic design for the drainages structures crossing Gee Creek and an unnamed tributary located on N. Main Avenue in rural Clark County near Ridgefield, Washington. For this report, the unnamed tributary will be referenced as Boutwell Creek. The existing culverts are undersized and barriers to fish passage.

The work reported includes:

Review of background information including applicable design standards and regulations

Field investigations to evaluate existing hydraulic conditions and channel stability

Hydrologic analysis to establish design flows Hydraulic analysis to support Gee Creek and unnamed tributary (Boutwell

Creek) culvert designs Scour analysis and any necessary scour countermeasures Design stream channel reconstruction at the structure and the design of scour countermeasures Development of hydraulic design recommendations for temporary water management to isolate in-stream work areas.

2 Project Description Western Federal Lands Highway Division (WFLHD), U.S. Fish and Wildlife Service (USFWS), City of Ridgefield, and Clark County are proposing to improve access along Main Avenue in the City of Ridgefield, Clark County, Washington. These improvements were proposed as part of management objectives in the Ridgefield National Wildlife Refuge (NWR) Comprehensive Conservation Plan (CCP) (USFWS 2010).

The Main Avenue Access Improvements Project is intended to provide a safer route for pedestrians and cyclists along Main Avenue between the City of Ridgefield and the Ridgefield National Wildlife Refuge (NWR) Carty Unit Headquarters (HQ). The existing road conditions within the project limits include two 11-foot travel lanes with no shoulder. These conditions force pedestrians and cyclists into the vehicle travel lanes along this narrow two-lane roadway.

Proposed work associated with this project includes construction of a sidewalk along Main Avenue, replacement of the culvert at Gee Creek with an Aquatic Organism Passage structure and realignment of Boutwell Creek to its original channel with an addition of a culvert under Main Avenue. In order to construct the new drainage

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structures to accommodate design flows; reconstruction of Main Avenue through the floodplain is required.

2.1 Location

Main Avenue is located in northwest Clark County and the City of Ridgefield, Washington (T4N, R1 S13). This roadway is classified as a Rural Major Collector running north-south with connections to Pioneer Street and NW 291st Street. This project is located between Depot Street and NW 291st Street (see Figure 1).

Figure 1: Vicinity Map

3 Historic Creek Alignments Cadastral survey maps and surveyor notes from 1858 (BLM 2016) indicate that no major roads or farms were present within the basin at this time. Boutwell Creek drained the area east of Main Avenue and south of NW 291st Street and the area to the north of NW 291st Street was drained by another unnamed tributary of Gee Creek.

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Figure 2: 1858 Cadastral Survey Map

By 1949, Clark County public works had developed construction plans for the existing Gee Creek culvert (Clark County). These plans indicate that a wood truss bridge had been previously constructed over Gee Creek. The construction of the present-day CMP culvert would remove a meander in the creek; resulting in a straight creek alignment. The construction plans also indicate that Boutwell Creek was rerouted to join Gee Creek east (upstream) of Main Avenue.

4 Field Reconnaissance Several field reconnaissance’s of Gee Creek and Boutwell Creek have been conducted by WFLHD staff. Observations were made to assess the general characteristics of the creeks, the configuration and condition of the existing culverts, the lateral and vertical stability of the Gee Creek channel, evidence of general and local scour, and bed material characteristics. Select photographs are included in Appendix A.

4.1 General Observations

Main Avenue crosses Gee Creek on a relatively straight reach approximately 1,650-feet upstream from the Burlington Northern Santa Fe railroad tracks near the confluence with the Columbia River. This reach is under backwater conditions of the Columbia River during the 100- year flood event and the hydraulics are greatly influenced by this condition.

N

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Immediately upstream of Main Avenue a small tributary (Boutwell Creek) enters Gee Greek through a CMP culvert. Boutwell Creek drains the area north of Gee Creek and east of Main Avenue and is cut-off by the existing road embankment and conveyed under an existing driveway through culvert. Under high water conditions, the road embankment impounds water due to the undersized culvert and occasionally overtops the roadway. In December 2007, the roadway was overtopped during a flood event. In December 2015, the road was overtopped again in a high-water event. Several pictures of are included in Appendix A.

Figure 3: December 2007 Road Overtopped

4.2 Lateral Channel Stability

4.2.1 Gee Creek

Under current conditions, Gee Creek appears to be laterally stable within the vicinity of the existing culvert. In 1949, Clark County replaced a truss bridge with the existing CMP culvert. Included in the county road project work was the realignment of the creek, which removed a large meander. Today there’s evidence of the original channel alignment, but the lateral channel appears stable. There is no evidence of the creek attempting to flow down its historic alignment.

The floodplain is well vegetated with ash, alder and cottonwood trees and the underbrush consists of Reed Canary Grass, stinging needles, blackberries, and

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ferns. There is little evidence of widespread lateral instability that would threaten the roadway and proposed arch-structure at Gee Creek.

4.2.2 Boutwell Creek

Boutwell Creek’s historic alignment is blocked by the existing Main Avenue road embankment. The creek was likely realigned during the original road construction over 68-years ago. Today, the creek flows at the toe of the embankment slope to Gee Creek before discharging through a 24-inch culvert under the Boutwell driveway.

During recent flood events it has been noted that the lowland area north of the existing culvert has been inundated with water; to the point Main Avenue is overtopped. There is no current lateral movement of channel banks.

4.3 Vertical Channel Stability

4.3.1 Gee Creek

Gee Creek appears to be vertically stable near the existing culvert with no signs of significant active aggradation or degradation. The channel appears to transport the available bed material supply through the reach with no significant scour or sedimentation deposition. Based on examination of the bed profile and observations of the channel upstream and downstream of the culvert, little downcutting or channel widening is likely.

4.3.2 Boutwell Creek

As discussed in Section 5.2.2, this project includes improvements to re-introduce flow back to its historic channel on the west side of Main Avenue. It can be expected that the creek profile will change within the Gee Creek floodplain due to the nature of the existing fine grain soil characteristics. During a site visit in May 2016, the confluence of the historic Boutwell Creek and Gee Creek was assessed.

Observations between the two creek beds were made and the elevation difference is as much as 5-feet (see photo). Since realigning Boutwell Creek, it appears that Gee Creek’s stream bed has generally lowered. The lowering is likely an adjustment caused by past channelization and land use changes.

To stabilize Boutwell Creek and protect any mitigation and infrastructure; it is recommended that grade control structures be installed at the confluence, at intermittent locations within the historic channel and immediately downstream and upstream of the new culvert crossing.

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Figure 4: Gee Creek / Boutwell Creek Historic Confluence

4.4 Existing Scour

There was no evidence of significant general or local scour in the vicinity of the existing culvert along Gee Creek.

4.5 Bed Material

The bed of Gee Creek near the culvert is a mix of sand and silt sized material. A pebble count (Wolman, 1954) was not conducted due to the fine-grained nature of the bed material. The project geotechnical engineer (Parsons Brinckerhoff) obtained a bulk soil sample of the Gee Creek bed material. The soil sample was submitted to a laboratory for a particle size analysis (PB, 2016). The D50 of sample was determined to be 0.195 mm (see figure below and appendix).

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Figure 5: Gee Creek Particle Size Distribution

4.6 WDFW Fish Passage (Aquatic Organism Passage) Criteria

The Washington Department of Fish and Wildlife (WDFW) published design requirements for fish passage and other aquatic organisms. The WDFW requirements for fish passage at roadway culverts contain specific criteria for passage, which includes the Stream-Simulation design option. This approach strives to duplicate the stream geometry and slope of the adjacent system to maintain natural stream processes in the culvert.

Once the natural stream width is determined, the culvert width is determined by the following equation:

4.6.1 Culvert Span

A field reconnaissance was conducted to measure bankfull width ( ) of Gee Creek and Boutwell Creek in the vicinity of Main Avenue. The details of the site visit are documented in the draft memo Field Reconnaissance of Gee Creek at Main Avenue (Davis, 2016). The following table summarizes the measured channel widths and corresponding Stream-Simulation culvert widths.

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Table 1: Gee Creek Minimum Stream-Simulation Culvert Width

Location WDFW

1 21-feet 28-feet 2 28-feet 36-feet 3 31-feet 40-feet 4 28-feet 36-feet 5 27-feet 35-feet

Average 27-feet 35-feet

Table 2: Boutwell Creek Minimum Stream-Simulation Culvert Width

Location WDFW

1 6-feet 9-feet 2 7-feet 10-feet

Average 6.5-feet 10-feet

Figure 6: Active Channel ( ) Measurements

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4.6.2 Slope

The culvert gradients were set to match the overall existing stream slopes at 0.3% and 0.0% for Gee and Boutwell, respectively. Therefore, the flow regime at fish passage flows would be the same as “normal flow” in an open channel.

5 Hydrology The Gee Creek watershed is approximately 11.6-square miles and primarily rural housing and agricultural land. However, due to the proximity of the City of Ridgefield and the I-5 corridor this area will continue to develop in the future.

The 2-, 10-, 25-, 50-, 100- and 500-year peak flows were estimated with the United States Geological Survey (USGS) web-based GIS program called “StreamStats”. The program uses a nationwide database to determine basin characteristics such as land slope, elevation and precipitation. Using these characteristics, the program then applies the appropriate regression equation discussed in “The National Flood-Frequency Program-Methods for Estimating Flood Magnitude and Frequency in Washington, 2001” (Knowles and Sumioka, 2001) to determine peak flows for events of various frequencies. The StreamStats output is included in Appendix B.

Table 3 compares Gee Creek peak flows from StreamStats to those reported in the Effective FIS for Clark County (FEMA, 2012). The table shows that the Effective FIS flows are similar those from StreamStats. To be consistent with the Effective FIS (e.g. for demonstrating “no-rise”) the Effective FIS flows were adopted for use in this analysis.

Table 3: Gee Creek Peak Discharge

Recurrence Intervals (years)

Exceedance Probability (Percent)

Peak Discharge (cfs) Gee Creek at Main

Avenue from StreamStats

Peak Discharge (cfs) Gee Creek at Main Avenue from FEMA

2 50 441 n/a 10 10 730 850 25 4 885 n/a 50 2 990 1010 100 1 1100 1080 500 0.2 1370 1260

Boutwell Creek has a 0.49-square mile drainage area. Peak flows were determined using regression equation discussed in “The National Flood-Frequency Program- Methods for Estimating Flood Magnitude and Frequency in Washington, 2001” (Knowles and Sumioka, 2001). StreamStats was not used due a discrepancy in

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drainage area. The drainage area defined in StreamStats does not include drainage infrastructure. This basin has several roadside ditches that required the recalculation of the drainage area. Below is a table summary of the design flows and supporting documentation is located in Appendix B.

Table 4: Boutwell Creek Peak Discharge

Recurrence Intervals (years)

Exceedance Probability (Percent)

Peak Discharge (cfs)

2 50 25 10 10 41 25 4 50 50 2 56 100 1 63 500 0.2 n/a

6 Hydraulics

6.1 Gee Creek

A steady flow, one-dimensional hydraulic analysis of Gee Creek was carried out to evaluate proposed hydraulic characteristics associated with the proposed culvert.

The analysis was conducted using Version 5.0.0 of the USACE HEC-RAS computer software (USACE, 2010). An existing HEC-RAS model of Gee Creek was originally created by WEST Consultants, Inc. (WEST) for the Flood Insurance Study (FIS) update to Gee Creek. The FIS model was modified using new survey data to more accurately model conditions adjacent to Main Avenue. The 2 FIS cross-sections adjacent to Main Avenue were updated and 10 additional cross-sections between RS 0.145 and RS 0.501 were used to describe the geometry of the channel and adjacent floodplain through the modeled reach. The field topography and model elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD29). The elevations within this report are corrected to the North American Vertical Datum of 1988 (NAVD88) to compare to the FIS. As described in the FIS, the conversion factor from NGVD29 to NAVD88 is 3.5-feet. The upstream and downstream limits of the study reach measured from Main Avenue centerline are 750 and 650, respectively. No changes were made to the FIS Model upstream or downstream of the culvert improvements. The portion of the model downstream of the study area was retained to minimize errors associated with the starting water-surface elevation.

In addition to providing fish passage, the new culvert design must have the capacity for the 100-year peak flow. Therefore, a steady-flow hydraulic analysis with backwater conditions was conducted to evaluate the hydraulic conditions of the

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proposed culvert. The modeling was based on a HEC-RAS model developed by West Consultant in the FEMA FIS Study and modified for this project.

6.2 Boutwell Creek

A hydraulic analysis of Boutwell Creek was carried out to evaluate proposed hydraulic characteristics associated with the proposed 10-ft diameter culvert. The analysis was conducted using Version 5.0.0 of the USACE HEC-RAS computer software (USACE, 2010). The tailwater condition was set to the Columbia River 100-year flood water surface elevation of 23.5-ft. The peak WSEL calculated was 23.54-ft.

6.3 Design Criteria

Per section 8.3 of the Clark County Stormwater Manual, the following criteria apply to this project:

Q100: Culverts with contributing drainage areas greater than 200 acres.

Q100: Culverts in areas of special flood hazard, as described in FEMA Flood

Insurance Rate Maps (FIRM) and reports for Clark County.

Per section 3-3 of the WSDOT Hydraulics Manual, Culvert spans over 20-feet are considered bridges and the guidance is outlined in section 3-3.1.2.

Per section 3-3.1 of the Hydraulics Manual, the following criterion applies to this project:

Q100: The depth of flow during the 100-year flow event should not exceed the height of the arch.

Per section 4-5 of the Hydraulics Manual, the following criterion is recommended for FEMA regulated floodways:

Q100: The rise in the culvert has a 3-foot vertical clearance between the bottom of the bridge and the 100-year water surface elevation.

6.4 Capacity Analysis

To demonstrate compliance with the Clark County Stormwater Manual and WSDOT Hydraulics Manual the HEC-RAS model was modified to include downstream boundary conditions. A steady flow simulation was run for the 100-year flow event.

The profile was run as a mixed profile regime (i.e., sub-critical and super-critical flow velocities are both computed). The downstream boundary condition was set at the FIS Columbia River 100-year water surface elevation of 23.5-ft (NAVD88).

The analysis computed the peak water surface elevation at the inlet of the culvert for the 100-year flow event with the new culvert. The results indicate that the water surface elevation will be 25.4 with a depth of 19.5-feet on the inlet side. To meet WSDOT Hydraulics Manual criteria for debris clearance, 3-feet of freeboard

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was provided between the water surface and the top of the arch during the 100-year flow event for potential debris clearance. Therefore, the top of the arch should be set at the minimum elevation of 28.4-ft (NAVD88).

The predicted 100-year storm surface elevation and depth is shown in

Figure 7.

Figure 7: Cross-Section of Proposed Arch-Structure at Main Avenue

6.5 Proposed Culvert

Based on the channel width required for the stream simulation design and to provide the culvert capacity for the 100-year flow event, the following minimum culvert dimensions are recommend for an open bottom arch:

Span – 40-Feet (minimum) Rise – 25-feet (minimum)

7 Floodplain Model Results

7.1 Duplicate Effective Model

The duplicate effective model (DEM) is a copy of the hydraulic analysis used in the effective FIS, referred to as the effective model. The effective model should be obtained and then reproduced on the applicant’s equipment to produce the duplicate effective model. This is required to ensure that the effective model’s input data has been transferred correctly to the applicant’s equipment and to ensure that

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the revised data will be integrated into the effective data to provide a continuous FIS model upstream and downstream of the revised reach. The DEM was obtained from Clark County and reproduced on the FHWA equipment to verify that the input data was transferred correctly and to ensure the revised data will be integrated into the an effective model that provides a continuous FIS model upstream and downstream of the revised reach.

The 1% annual chance water surface elevations (WSELs) for Without Floodway and With Floodway conditions were computed using the DEM and are summarized in Table 5. Table 5 also includes the water surface elevations documented in the FIS (FEMA, 2012) and obtained from the effective hydraulic model results. As shown in the table, the WSELs computed using the DEM is slightly different. Note that these WSELs are computed without the backwater effects of the Columbia River. The floodplain models and results are used to determine if this project complies with Clark County’s Floodplain ordinance. No additional revisions were made to the DEM.

Table 5: Duplicate Effective Model Result (NAVD88)

FIS Cross Section

Base Flood Water Surface Elevations Without Floodway With Floodway

Model

RS

Effective

FIS WSEL

(ft)

DEM

WSEL

(ft)

Delta (ft)

Effective

FIS WSEL

(ft)

DEM

WSEL

(ft)

Delta (ft)

0.000 - - 18.6 19.2 Railroad

0.022 - - 19.6 - - 20.3 -

0.037 A 20.3 20.3 0 21.0 21.0 0

0.145 - - 20.9 - - 21.5 -

0.319 - - 21.6 - - 22.6 -

0.328 Main Ave

0.337 B 27.5 27.5 0 28.2 28.2 0

0.501 - - 27.6 - 28.4 -

0.619 - - 27.7 - 28.6 -

0.624 C 27.7 27.7 0 28.7 28.7 0

0.727 - - 28.0 - 29.0 -

0.897 - - 29.1 - 29.8 -

0.911 D 29.7 29.7 0 30.3 30.3 0

1. Conversion factor from NGVD29 to NAVD88 is 3.5-feet

2. Elevation computed without consideration of backwater from Columbia River

7.2 Existing Conditions

The Duplicate Effective Model was modified to produce the Existing or Pre-Project Conditions Model to reflect any modifications that have occurred within the

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floodplain since the date of the Effective model but prior to the construction of the project for which the revision is being requested.

The model update included a total of 10 user-input cross-sections to describe the geometry of the channel and floodplain through the modeled reach. The new cross sections were developed from project survey data and Clark County lidar. The exiting culvert data was also updated into the model. The existing condition model results are summarized in the following table:

Table 6: Corrected/ Existing Effective Model Result (NAVD88)

FIS

Cross Section

Base Flood Water Surface Elevations Without Floodway

Model

RS

DEM

WSEL

(ft)

CEM

WSEL

(ft)

Delta (ft)

0.000 - 18.6 18.6 0.0 Railroad

0.022 - 19.6 19.6 0.0

0.037 A 20.3 20.3 0.0

0.145 - 20.9 20.9 0.0

0.317 - 21.6 22.4 0.8

0.328 Main

Ave

0.337 B 27.5 28.0 0.5

0.501 - 27.6 28.0 0.4

0.619 - 27.7 28.1 0.4

0.624 C 27.7 28.1 0.4

0.727 - 28.0 28.4 0.4

0.897 - 29.1 29.2 0.1

0.911 D 29.7 29.8 0.1

Table 6 shows an increase in water surface elevation between the Duplicate Effective Model and the Corrected Effective Model upstream of Main Avenue and one river station downstream. The delta is generated from the difference between the new survey data and associated cross-sections collected in Main Avenue for this project. Thus, the road overtops at a higher water surface elevation and the backwater extends upstream from the crossing. The downstream WSE increase is likely due to the additional ineffective flow areas that result in a loss of conveyance capacity.

7.3 Proposed Conditions

The proposed condition model was created by updating the corrected/ existing effective model (CEM) to include a 40-ft span arch-culvert and additional road fill.

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In addition, ineffective flows areas were adjusted on the new cross-sections bounding the culvert to account for the contraction and expansion of flow.

The results of the proposed condition hydraulic model demonstrate that this project will not increase the water surface elevation within the study reach. The figure and table below shows computed water-surface profiles output. The modeled profiles show the backwater caused by the culvert under existing conditions is eliminated.

Figure 8: Existing (CEM) and Proposed Water Surface profile at Main Ave

Table 7: Proposed Condition Model (PEM) Results

FIS

Cross Section

Base Flood Water Surface Elevations Without Floodway

Model

RS

CEM

WSEL

(ft)

PEM

WSEL

(ft)

Delta (ft)

0.000 - 18.6 18.6 0 Railroad 0

0.022 - 19.6 19.6 0

0.037 A 20.3 20.3 0

0.145 - 20.9 20.9 0

0.319 - 22.4 22.4 0

0.328 Main Ave 0

0.337 B 28.0 22.5 -5.5

0.501 - 28.0 24.0 -4

0.619 - 28.1 24.8 -3.3

0.624 C 28.1 24.9 -3.2

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0.727 - 28.4 25.9 -2.5

0.897 - 29.2 28.7 -0.5

0.911 D 29.8 29.5 -0.3

8 Scour To ensure that appropriate scour countermeasures are included with this project, scour depths were determined following the methodologies outlined in Hydraulic Engineering Circular-18, Evaluating Scour at Bridges. Section 6.9 provides guidance for calculating scour depths based on FHWA sponsored laboratory studies of scour for open-bottom culverts.

8.1 Aggradation/ Degradation

Based on several site visits and geotechnical findings, it is believed that the fine-grained sediment transported into this reach is transported as suspended load.

Therefore, the majority of sediment deposition occurs in the extensive floodplain areas adjacent to both channel banks. When flows are confined to the channel, the uniform trapezoidal cross section geometry and nearly straight alignment of the channel results in a greater ability to transport sediment which tends to limit sediment deposition within the channel.

Therefore, long-term degradation is assumed to be 0.0-ft over the lifespan of the proposed culvert.

8.2 Scour Depth

In 2007 FHWA sponsored a laboratory study of scour for open-bottom culverts. The study was completed under clear-water conditions and a resulting finding included a revised scour depth relationship which includes general and local scour.

For this project, scour was evaluated for the 1 percent flood discharge (100-yr flood) at the new arch-culvert using the methods described in the study. Because the study was completed with clear-water conditions, only similar conditions are applicable. To determine if live-bed or clear-water conditions would occur for this flow, Laursen's equation (FHWA, 2001) was used:

11.17 / /

Where y is the depth of the approach channel section (6.40-feet at RS 0.402), d50 is the median diameter of the bed material (0.195 mm, Parsons Brinckerhoff, 2016);

and Vc, the critical velocity for incipient motion of bed material in the approach section, is calculated to be 1.31 ft/s.

Under some cases, where the velocity in the approach section exceeds the critical velocity of the bed material, a live-bed scour condition may exist. However, it is

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possible that the sediment remains suspended, which acts as a clear-water scour condition. To determine if sediment settles out; the ratio of shear velocity to fall velocity must be is greater than 2.

For this project, the ratio is larger than 2 indicating that sediment remains suspended and clear-water scour calculations are appropriate for this design.

The maximum scour depth was calculated using the following equations:

Ku = 0.0077 English Units Q = Discharge through the culvert Dm = 1.25 D50 W = Bottom width of culvert, ft

Where ys is the flow depth at the culvert entrance corner including contraction scour, Q is the discharge through the culvert (1080 cfs), W is the width/ span of culvert (40-ft), d50 is the median diameter of bed material (0.195 mm), and Yo is the flow depth prior to scour (6.4-ft). The above calculations estimate the contraction scour to be 7.8-feet. This project is proposing to use the WSDOT specifications for Streambed Sediment. Using the bed particle size (d50 = 0.5 inches) for this material the expected scour depth is 0.0-ft

8.3 Scour Protection

Scour protection design guidelines outlined in HEC-23 include Riprap Protection for Bottomless Culverts (DG-18). DG-18 is intended to provide design considerations for the following conditions:

three-sided culvert free-surface flow clear-water flared wingwalls

This project is proposing to construct a bottomless culvert with wingwalls; and therefore, DG-18 guidelines are applicable.

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8.4 Riprap Sizing

An evaluation of the appropriate riprap class for the Gee Creek crossing was completed assuming HEC-23, Design Guideline 18 criteria using the 100-year flood and the following equation for sizing riprap on bottomless culverts:

Kr = 0.68 Yo = Average flow depth Sg = specific gravity of rock V = velocity in culvert g = acceleration of gravity

Where d50 is the median riprap diameter, Yo is the average flow depth of the at the culvert entrance before scour (11.12-feet), V is the average channel velocity plus safety factor (2.43 ft/s), S is the specific gravity of the riprap material (2.65), and g is the force of gravity (32 ft/s2). The above calculations estimate that the minimum median diameter of riprap for the Gee Creek arch-culvert be 1.2-feet (14.2-inches).

The riprap sizing for bottomless culverts requires the use of larger aggregate than the requirement for riprap calculated for bridge abutments. Based on the riprap size calculated from DG-18 equations, Class 4 riprap is recommended to protect the footings.

8.5 Riprap Layout

The layout dimensions suggested in DG-18 are used and summarized in the table and figure below:

Table 8: Summary of Riprap Layout

Dimension Riprap (Class 4)

Inlet Extent (ft) 22 Outlet Extent (ft) 22 YTOT (ft) 4 WT (ft) 5 WB (ft) 17 Thickness (ft) 2

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Figure 9: Minimum Riprap Protection Dimenions

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9 References Bureau of Land Management, 2016, Land Status and Cadastral Survey Records Available at:

http://www.blm.gov/or/landrecords/survey/ySrvy2.php?tr=00400N00100W&srt=A &ti=8&ri=1&ln=10000000

Federal Emergency Management Agency (FEMA), 2012. Flood Insurance Study, Clark County, Washington and Incorporated Areas. Community Number 530024.

Revised September 5

Federal Highway Administration (FHWA), 2012. Evaluating Scour at Bridges.

Hydraulic Engineering Circular No. 18, Fifth Edition. April.

Federal Highway Administration (FHWA), 2009. Bridge Scour and Stream Instability Countermeasures: Experience, Selection, and Design Guidance. Hydraulic Engineering Circular No. 23, Third Edition. September.

Federal Highway Administration (FHWA), 2009. Design Guideline 14 Rock Riprap at Bridge Abutments. Hydraulic Engineering Circular No. 23, Third Edition. September.

Federal Highway Administration (FHWA), 2009. Design Guideline 18 Riprap Protection for Bottomless Culverts. Hydraulic Engineering Circular No. 23, Third Edition. September.

Kerenyi, K., Jones, J.S., and Stein, S., 2007. “Bottomless Culvert Scour Study:

Phase II Laboratory Report,” Federal Highway Administration, Report No. FHWA-

HRT-07-026.

Knowles, S.M. and Sumioka. S.S., 2001, The National-Flood-Frequency Program – Methods for Estimating Flood Magnitude and Frequency in Washington, 2001: U.S.

Geological Survey Fact Sheet FS-016-01, 4p.

U.S. Army Corps of Engineers, 2010. HEC-RAS River Analysis System, User’s Manual, Version 4.1, Hydrologic Engineering Center, Davis, CA.

Washington Department of Fish and Wildlife (WDFW), 2013. Water Crossing Design Guidelines.

WEST Consultants, 2008. Geomorphology and Hydrology Assessment for Upper Gee Creek, prepared for Clark County, Washington, Department of Public Works, July.

SWCA Environnemental Consultants, 2016. Final Critical Areas Wetland and Waters Delineation Report for Main Avenue Access Improvements Project. June 17

WFLHD 10/7/16

Appendix A: Photographs Figure 9: East Side (upstream) from Main Avenue (December 2015)

Figure 10: West side (downstream) from Main Avenue (December 2015)

Figure 11: Unnamed Creek at Boutwell driveway (December 2015)

Figure 12: Unnamed creek post high water event (December 2015)

Figure 13: Road overtopping evidence on the west side of Main Avenue (December 2015)

Figure 14: Gee Creek downstream of Main Avenue (May 2016)

Figure 15: Gee Creek west of Main Avenue (looking downstream)

Appendix B: Hydrologic Analysis

Streamstats

Gee Creek @ Ridgefield National Wildlife Refuge

Hydrology

Reoccurrence Interval

Streamstats

2‐yr 441

10‐yr 730

25‐yr 885

50‐yr 990

100‐yr 1100

500‐yr 1370

Boutwell Creek Area = 312‐acres

REGION 3

WASHINGTON STATE HYDROLOGY

USGS REGRESSION EQUATIONS

Region 3 - 63 stations

Boutwell Creek Date:

Project: WA RIDGE MAIN(1) Made By:

Equations:

Q2yr = 0.817 x A^0.877 x (MAP)^1.02 (Standard Error = 57%)

Q10yr = 0.845 x A^0.875 x (MAP)^1.14 (Standard Error = 55%)

Q25yr = 0.912 x A^0.874 x (MAP)^1.17 (Standard Error = 54%)

Q50yr = 0.808 x A^0.872 x (MAP)^1.23 (Standard Error = 54%)

Q100yr = 0.801 x A^0.871 x (MAP)^1.26 (Standard Error = 55%)

Legend Limits Q = Flow (cfs) A = Drainage Basin Area (miles^2) (0.36 sq. miles < A < 2,198 sq. miles) MAP = Mean Annual Precipitation (inches) (42.0 in < MAP < 132 in)

Input Values Into Columns With Red Headings Return Q Qmetric

Description of Area Frequency A MAP (cfs) (cms) Tributary 2 0.49 52.1 25 0.70 Tributary 10 0.49 52.1 41 1.16 Tributary 25 0.49 52.1 50 1.41 Tributary 50 0.49 52.1 56 1.59 Tributary 100 0.49 52.1 63 1.77 usgseq2001

Appendix C: Gee Creek Cross-Sections

0.

0.

0.282

0.

0.241

0.

0.501

0.145

0.439

0.

M A

IN

1S T

R A

IL

R

O A

D

DEPOT

N. Main Avenue HEC-RAS Cross Sections£ 0 110 22055

Feet

Legend X-Sections

Gee Ceek

Appendix D: Gee Creek HEC-RAS Output

Duplicate Effective Model Without Columbia River Backwater

1.15269 1.12934*

1.106

1.051*

0.996

.9535*

0.911

.840333*

.783666*

0.727

0.624

0.501

0.337 0.319

0.145

0.037

0.011

0.000 davisj Typewritten Text Duplicate Effective Model Schematic davisj Typewritten Text

A (RS 0.037)

davisj Line davisj Line davisj Line davisj Typewritten Text

B (RS 0.337)

davisj Typewritten Text

C (RS 0.624)

davisj Line davisj Typewritten Text

E (RS 0.996)

davisj Line davisj Typewritten Text

D (RS 0.911)

davisj Line davisj Typewritten Text

MAIN AVE (RS 0.328)

HEC-RAS Plan: DEM River: Gee Creek Reach: Gee Creek Profile: 100-yr

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek 0.911 100-yr 1080.00 17.61 26.23 21.63 26.34 0.001054 2.94 518.30 132.94 0.19

Gee Creek 0.904 Bridge

Gee Creek 0.897 100-yr 1080.00 17.22 25.55 22.50 26.02 0.005059 5.89 237.59 264.85 0.39

Gee Creek .840333* 100-yr 1080.00 15.48 24.80 20.61 25.02 0.002176 4.23 428.79 342.32 0.26

Gee Creek .783666* 100-yr 1080.00 13.75 24.56 18.77 24.64 0.000749 2.76 781.71 401.83 0.16

Gee Creek 0.727 100-yr 1080.00 12.01 24.50 16.95 24.52 0.000223 1.66 1541.39 619.24 0.09

Gee Creek 0.624 100-yr 1080.00 10.83 24.21 16.48 24.33 0.000463 3.08 727.40 245.31 0.16

Gee Creek 0.622 Bridge

Gee Creek 0.619 100-yr 1080.00 10.83 24.18 16.48 24.28 0.000434 2.98 682.51 220.41 0.15

Gee Creek 0.501 100-yr 1080.00 9.44 24.14 16.04 24.15 0.000080 1.25 1807.08 394.58 0.06

Gee Creek 0.337 100-yr 1080.00 7.57 24.00 13.28 24.04 0.000190 2.02 883.46 360.48 0.09

Gee Creek 0.328 Culvert

Gee Creek 0.319 100-yr 1080.00 7.06 18.12 14.22 18.67 0.003857 6.04 217.38 475.39 0.38

Gee Creek 0.145 100-yr 1080.00 5.16 17.42 17.48 0.000493 2.57 928.99 296.14 0.14

Gee Creek 0.037 100-yr 1080.00 3.92 16.84 17.09 0.000902 4.06 292.89 48.02 0.23

Gee Creek 0.022 100-yr 1080.00 3.04 16.13 10.90 16.83 0.003643 6.74 165.50 17.88 0.36

Gee Creek 0.011 Culvert

Gee Creek 0.000 100-yr 1080.00 4.11 15.09 10.13 15.58 0.002001 5.62 195.54 81.42 0.32

Corrected Effective Model

1.106

1.051*

0.996

.9535*

0.911

.840333*

.783666*

0.727

0.624

0.501

0.456 0.439

0.402 0.328

0.298

0.282

0.241

0.145

0.037

0.011

0.000

Corrected Effective Model Schematic

A (RS 0.037)

MAIN AVE (RS 0.328)

B (RS 0.337)

C (RS 0.624)

E (RS 0.996)

D (RS 0.911)

davisj Line davisj Line davisj Line davisj Line davisj Line davisj Line

HEC-RAS Plan: CEM River: Gee Creek Reach: Gee Creek Profile: 100-yr

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek 0.911 100-yr 1080.00 17.61 26.34 21.63 26.44 0.000994 2.88 530.02 133.81 0.18

Gee Creek 0.904 Bridge

Gee Creek 0.897 100-yr 1080.00 17.22 25.70 22.50 26.14 0.004642 5.72 246.63 280.99 0.37

Gee Creek .840333* 100-yr 1080.00 15.48 25.08 20.61 25.26 0.001802 3.93 469.06 349.00 0.24

Gee Creek .783666* 100-yr 1080.00 13.75 24.89 18.77 24.96 0.000601 2.53 862.19 414.05 0.14

Gee Creek 0.727 100-yr 1080.00 12.01 24.85 16.95 24.86 0.000174 1.50 1705.75 624.54 0.08

Gee Creek 0.624 100-yr 1080.00 10.83 24.62 16.48 24.71 0.000376 2.84 826.49 258.77 0.14

Gee Creek 0.622 Bridge

Gee Creek 0.619 100-yr 1080.00 10.83 24.57 16.48 24.66 0.000350 2.73 766.88 227.99 0.14

Gee Creek 0.501 100-yr 1080.00 9.44 24.53 16.02 24.54 0.000068 1.18 1945.00 396.50 0.06

Gee Creek 0.456 100-yr 1080.00 7.57 24.50 24.52 0.000117 1.36 1437.25 263.78 0.07

Gee Creek 0.439 100-yr 1080.00 9.30 24.50 24.51 0.000073 1.14 1684.58 345.39 0.06

Gee Creek 0.420 100-yr 1080.00 5.79 24.49 24.50 0.000082 1.19 1727.74 353.54 0.06

Gee Creek 0.402 100-yr 1080.00 7.66 24.49 24.49 0.000048 0.92 2291.55 455.85 0.05

Gee Creek 0.368 100-yr 1080.00 3.79 24.48 24.49 0.000019 0.70 3057.59 530.37 0.03

Gee Creek 0.343 100-yr 1080.00 9.92 24.48 14.98 24.48 0.000055 1.07 2132.37 398.06 0.05

Gee Creek 0.337 100-yr 1080.00 7.86 24.47 13.37 24.48 0.000051 1.07 2029.03 361.61 0.05

Gee Creek 0.328 Culvert

Gee Creek 0.317 100-yr 1080.00 7.86 18.88 13.07 19.09 0.001065 3.65 296.55 571.50 0.22

Gee Creek 0.298 100-yr 1080.00 7.21 18.83 13.02 18.95 0.000737 2.93 446.88 546.55 0.19

Gee Creek 0.282 100-yr 1080.00 8.94 18.39 14.37 18.77 0.002796 4.98 228.49 344.93 0.34

Gee Creek 0.270 100-yr 1080.00 5.57 18.18 13.35 18.58 0.002885 5.07 226.53 348.94 0.33

Gee Creek 0.241 100-yr 1080.00 6.84 17.73 14.13 18.10 0.003157 4.86 235.61 388.45 0.36

Gee Creek 0.145 100-yr 1080.00 5.16 17.42 11.00 17.48 0.000509 2.62 930.27 296.17 0.14

Gee Creek 0.037 100-yr 1080.00 3.92 16.84 17.09 0.000902 4.06 292.89 48.02 0.23

Gee Creek 0.022 100-yr 1080.00 3.04 16.13 10.90 16.83 0.003643 6.74 165.50 17.88 0.36

HEC-RAS Plan: CEM River: Gee Creek Reach: Gee Creek Profile: 100-yr FW

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek 0.911 100-yr FW 1080.00 17.61 26.34 21.63 26.44 0.000994 2.88 530.02 133.81 0.18

Gee Creek 0.904 Bridge

Gee Creek 0.897 100-yr FW 1080.00 17.22 25.70 22.50 26.14 0.004642 5.72 246.63 280.99 0.37

Gee Creek .840333* 100-yr FW 1080.00 15.48 25.08 20.61 25.26 0.001802 3.93 469.06 349.00 0.24

Gee Creek .783666* 100-yr FW 1080.00 13.75 24.89 18.77 24.96 0.000601 2.53 862.19 414.05 0.14

Gee Creek 0.727 100-yr FW 1080.00 12.01 24.85 16.95 24.86 0.000174 1.50 1705.75 624.54 0.08

Gee Creek 0.624 100-yr FW 1080.00 10.83 24.62 16.48 24.71 0.000376 2.84 826.49 258.77 0.14

Gee Creek 0.622 Bridge

Gee Creek 0.619 100-yr FW 1080.00 10.83 24.57 16.48 24.66 0.000350 2.73 766.88 227.99 0.14

Gee Creek 0.501 100-yr FW 1080.00 9.44 24.53 16.02 24.54 0.000068 1.18 1945.00 396.50 0.06

Gee Creek 0.456 100-yr FW 1080.00 7.57 24.50 24.52 0.000117 1.36 1437.25 263.78 0.07

Gee Creek 0.439 100-yr FW 1080.00 9.30 24.50 24.51 0.000073 1.14 1684.58 345.39 0.06

Gee Creek 0.420 100-yr FW 1080.00 5.79 24.49 24.50 0.000082 1.19 1727.74 353.54 0.06

Gee Creek 0.402 100-yr FW 1080.00 7.66 24.49 24.49 0.000048 0.92 2291.55 455.85 0.05

Gee Creek 0.368 100-yr FW 1080.00 3.79 24.48 24.49 0.000019 0.70 3057.59 530.37 0.03

Gee Creek 0.343 100-yr FW 1080.00 9.92 24.48 14.98 24.48 0.000055 1.07 2132.37 398.06 0.05

Gee Creek 0.337 100-yr FW 1080.00 7.86 24.47 13.37 24.48 0.000051 1.07 2029.03 361.61 0.05

Gee Creek 0.328 Culvert

Gee Creek 0.317 100-yr FW 1080.00 7.86 18.88 13.07 19.09 0.001065 3.65 296.55 571.50 0.22

Gee Creek 0.298 100-yr FW 1080.00 7.21 18.83 13.02 18.95 0.000737 2.93 446.88 546.55 0.19

Gee Creek 0.282 100-yr FW 1080.00 8.94 18.39 14.37 18.77 0.002796 4.98 228.49 344.93 0.34

Gee Creek 0.270 100-yr FW 1080.00 5.57 18.18 13.35 18.58 0.002885 5.07 226.53 348.94 0.33

Gee Creek 0.241 100-yr FW 1080.00 6.84 17.73 14.13 18.10 0.003157 4.86 235.61 388.45 0.36

Gee Creek 0.145 100-yr FW 1080.00 5.16 17.42 11.00 17.48 0.000509 2.62 930.27 296.17 0.14

Gee Creek 0.037 100-yr FW 1080.00 3.92 16.84 17.09 0.000902 4.06 292.89 48.02 0.23

Gee Creek 0.022 100-yr FW 1080.00 3.04 16.13 10.90 16.83 0.003643 6.74 165.50 17.88 0.36

Gee Creek 0.000 100-yr FW 1080.00 4.11 15.09 10.13 15.58 0.002001 5.62 195.54 81.42 0.32

Proposed Effective Model

1.106

1.051*

0.996

.9535*

0.911

.840333*

.783666*

0.727

0.624

0.501

0.456 0.439

0.402 0.328

0.298

0.282

0.241

0.145

0.037

0.011

0.000

Proposed Effective Model Schematic

A (RS 0.037)

MAIN AVE (RS 0.328)

B (RS 0.337)

C (RS 0.624)

E (RS 0.996)

D (RS 0.911)

davisj Line davisj Line davisj Line davisj Line davisj Line davisj Line

HEC-RAS Plan: Low Arch: Scour River: Gee Creek Reach: Gee Creek Profile: 100-yr

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek 0.911 100-yr 1080.00 17.61 26.00 21.63 26.12 0.001200 3.07 493.24 131.08 0.20

Gee Creek 0.904 Bridge

Gee Creek 0.897 100-yr 1080.00 17.22 25.20 22.50 25.76 0.006193 6.31 217.60 227.91 0.42

Gee Creek .840333* 100-yr 1080.00 15.48 23.73 20.61 24.17 0.004701 5.66 283.37 216.70 0.37

Gee Creek .783666* 100-yr 1080.00 13.75 22.79 18.77 23.08 0.002840 4.69 380.60 274.89 0.30

Gee Creek 0.727 100-yr 1080.00 12.01 22.41 16.95 22.53 0.001114 3.24 670.34 421.75 0.19

Gee Creek 0.624 100-yr 1080.00 10.83 21.41 16.48 21.75 0.001631 4.83 280.29 54.98 0.28

Gee Creek 0.622 Bridge

Gee Creek 0.619 100-yr 1080.00 10.83 21.28 16.48 21.61 0.001660 4.83 267.67 53.92 0.28

Gee Creek 0.501 100-yr 1080.00 9.44 20.53 16.02 20.69 0.001130 3.77 586.34 266.44 0.22

Gee Creek 0.456 100-yr 1080.00 7.57 19.84 20.20 0.003109 5.00 293.88 183.95 0.33

Gee Creek 0.439 100-yr 1080.00 9.30 19.80 19.97 0.001307 3.36 369.43 147.86 0.24

Gee Creek 0.420 100-yr 1080.00 5.79 19.55 19.80 0.001928 4.05 287.43 98.56 0.27

Gee Creek 0.402 100-yr 1080.00 7.66 19.44 19.62 0.001474 3.49 386.90 145.90 0.24

Gee Creek 0.368 100-yr 1080.00 3.79 19.44 19.50 0.000244 1.93 676.64 210.93 0.11

Gee Creek 0.343 100-yr 1080.00 9.92 19.01 14.98 19.34 0.002299 4.80 282.99 91.43 0.31

Gee Creek 0.337 100-yr 1080.00 7.86 18.99 13.37 19.25 0.001429 4.08 278.25 170.87 0.25

Gee Creek 0.328 Bridge

Gee Creek 0.317 100-yr 1080.00 7.86 18.90 13.07 19.06 0.000931 3.33 396.23 572.03 0.20

Gee Creek 0.298 100-yr 1080.00 7.21 18.83 13.02 18.96 0.000746 2.94 460.49 546.41 0.19

Gee Creek 0.282 100-yr 1080.00 8.94 18.39 14.37 18.77 0.002796 4.98 228.49 344.93 0.34

Gee Creek 0.270 100-yr 1080.00 5.57 18.18 13.35 18.58 0.002885 5.07 226.53 348.94 0.33

Gee Creek 0.241 100-yr 1080.00 6.84 17.73 14.13 18.10 0.003157 4.86 235.61 388.45 0.36

Gee Creek 0.145 100-yr 1080.00 5.16 17.42 11.00 17.48 0.000509 2.62 930.27 296.17 0.14

Gee Creek 0.037 100-yr 1080.00 3.92 16.84 17.09 0.000902 4.06 292.89 48.02 0.23

Gee Creek 0.022 100-yr 1080.00 3.04 16.13 10.90 16.83 0.003643 6.74 165.50 17.88 0.36

Existing Conditions With Columbia River Backwater

HEC-RAS Plan: Existing Locations: User Defined Profile: 100-yr BW

River Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek Gee Creek 0.911 100-yr BW 1080.00 17.61 26.85 21.63 26.93 0.000758 2.63 587.26 137.98 0.16

Gee Creek Gee Creek 0.904 Bridge

Gee Creek Gee Creek 0.897 100-yr BW 1080.00 17.22 26.37 22.50 26.70 0.003213 5.04 289.42 335.05 0.31

Gee Creek Gee Creek .840333* 100-yr BW 1080.00 15.48 26.05 20.61 26.15 0.000984 3.12 616.57 375.11 0.18

Gee Creek Gee Creek .783666* 100-yr BW 1080.00 13.75 25.96 18.77 25.99 0.000316 1.96 1135.75 461.19 0.10

Gee Creek Gee Creek 0.727 100-yr BW 1080.00 12.01 25.94 16.95 25.94 0.000087 1.13 2225.25 642.58 0.06

Gee Creek Gee Creek 0.624 100-yr BW 1080.00 10.83 25.82 16.48 25.87 0.000201 2.21 1135.51 271.61 0.11

Gee Creek Gee Creek 0.622 Bridge

Gee Creek Gee Creek 0.619 100-yr BW 1080.00 10.83 25.80 16.48 25.84 0.000185 2.11 1046.69 248.35 0.10

Gee Creek Gee Creek 0.501 100-yr BW 1080.00 9.44 25.78 16.02 25.78 0.000035 0.91 2537.98 402.49 0.04

Gee Creek Gee Creek 0.456 100-yr BW 1080.00 7.57 25.76 25.77 0.000065 1.08 1774.79 272.90 0.05

Gee Creek Gee Creek 0.439 100-yr BW 1080.00 9.30 25.76 25.77 0.000040 0.91 2132.96 360.23 0.05

Gee Creek Gee Creek 0.420 100-yr BW 1080.00 5.79 25.75 25.76 0.000044 0.94 2185.22 369.82 0.05

Gee Creek Gee Creek 0.402 100-yr BW 1080.00 7.66 25.75 25.76 0.000026 0.72 2880.22 474.35 0.04

Gee Creek Gee Creek 0.368 100-yr BW 1080.00 3.79 25.75 25.75 0.000011 0.57 3733.21 536.07 0.02

Gee Creek Gee Creek 0.343 100-yr BW 1080.00 9.92 25.75 14.98 25.75 0.000030 0.84 2643.83 406.72 0.04

Gee Creek Gee Creek 0.337 100-yr BW 1080.00 7.86 25.74 13.37 25.75 0.000030 0.87 2518.36 403.09 0.04

Gee Creek Gee Creek 0.328 Culvert

Gee Creek Gee Creek 0.317 100-yr BW 1080.00 7.86 25.31 13.07 25.31 0.000005 0.34 6059.38 726.17 0.02

Gee Creek Gee Creek 0.298 100-yr BW 1080.00 7.21 25.31 13.02 25.31 0.000006 0.39 5558.44 700.86 0.02

Gee Creek Gee Creek 0.282 100-yr BW 1080.00 8.94 25.31 14.37 25.31 0.000013 0.55 3794.63 580.37 0.03

Gee Creek Gee Creek 0.270 100-yr BW 1080.00 5.57 25.31 13.35 25.31 0.000012 0.52 3897.89 497.73 0.02

Gee Creek Gee Creek 0.241 100-yr BW 1080.00 6.84 25.30 14.13 25.31 0.000009 0.44 4577.85 579.34 0.02

Gee Creek Gee Creek 0.145 100-yr BW 1080.00 5.16 25.30 11.00 25.30 0.000014 0.63 3495.71 355.29 0.03

Gee Creek Gee Creek 0.037 100-yr BW 1080.00 3.92 25.24 25.28 0.000082 1.84 836.07 77.54 0.08

Gee Creek Gee Creek 0.022 100-yr BW 1080.00 3.04 25.08 10.90 25.24 0.000390 3.31 403.29 75.77 0.13

Gee Creek Gee Creek 0.011 Culvert

Gee Creek Gee Creek 0.000 100-yr BW 1080.00 4.11 23.50 10.13 23.63 0.000224 2.88 397.46 472.36 0.12

Proposed Conditions With Columbia River Backwater

HEC-RAS Plan: Low Arch River: Gee Creek Reach: Gee Creek Profile: 100-yr BW

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

Gee Creek 0.911 100-yr BW 1080.00 17.61 26.68 21.63 26.78 0.000825 2.70 568.71 136.64 0.17

Gee Creek 0.904 Bridge

Gee Creek 0.897 100-yr BW 1080.00 17.22 26.16 22.50 26.53 0.003591 5.23 275.76 331.32 0.33

Gee Creek .840333* 100-yr BW 1080.00 15.48 25.78 20.61 25.90 0.001159 3.32 573.65 368.37 0.19

Gee Creek .783666* 100-yr BW 1080.00 13.75 25.67 18.77 25.71 0.000374 2.10 1057.78 448.62 0.11

Gee Creek 0.727 100-yr BW 1080.00 12.01 25.64 16.95 25.65 0.000104 1.21 2083.89 640.79 0.06

Gee Creek 0.624 100-yr BW 1080.00 10.83 25.50 16.48 25.56 0.000236 2.36 1052.79 268.99 0.11

Gee Creek 0.622 Bridge

Gee Creek 0.619 100-yr BW 1080.00 10.83 25.47 16.48 25.53 0.000218 2.26 971.14 244.13 0.11

Gee Creek 0.501 100-yr BW 1080.00 9.44 25.45 16.02 25.46 0.000043 0.99 2265.57 400.91 0.05

Gee Creek 0.456 100-yr BW 1080.00 7.57 25.43 25.44 0.000075 1.15 1684.92 270.50 0.06

Gee Creek 0.439 100-yr BW 1080.00 9.30 25.43 25.43 0.000046 0.97 2013.70 359.37 0.05

Gee Creek 0.420 100-yr BW 1080.00 5.79 25.42 25.43 0.000051 0.99 2063.11 365.58 0.05

Gee Creek 0.402 100-yr BW 1080.00 7.66 25.42 25.42 0.000030 0.77 2723.40 469.49 0.04

Gee Creek 0.368 100-yr BW 1080.00 3.79 25.42 25.42 0.000013 0.60 3555.18 534.57 0.03

Gee Creek 0.343 100-yr BW 1080.00 9.92 25.39 14.98 25.41 0.000086 1.40 1267.16 403.81 0.07

Gee Creek 0.337 100-yr BW 1080.00 7.86 25.36 13.37 25.40 0.000130 1.78 853.37 392.72 0.08

Gee Creek 0.328 Bridge

Gee Creek 0.317 100-yr BW 1080.00 7.86 25.31 13.07 25.33 0.000086 1.47 971.68 726.16 0.07

Gee Creek 0.298 100-yr BW 1080.00 7.21 25.31 13.02 25.32 0.000029 0.87 1957.17 700.87 0.04

Gee Creek 0.282 100-yr BW 1080.00 8.94 25.31 14.37 25.32 0.000047 1.04 1725.88 580.36 0.05

Gee Creek 0.270 100-yr BW 1080.00 5.57 25.30 13.35 25.31 0.000042 0.97 1930.07 497.73 0.04

Gee Creek 0.241 100-yr BW 1080.00 6.84 25.30 14.13 25.31 0.000009 0.44 4577.85 579.34 0.02

Gee Creek 0.145 100-yr BW 1080.00 5.16 25.30 11.00 25.30 0.000014 0.63 3495.71 355.29 0.03

Gee Creek 0.037 100-yr BW 1080.00 3.92 25.24 25.28 0.000082 1.84 836.07 77.54 0.08

Gee Creek 0.022 100-yr BW 1080.00 3.04 25.08 10.90 25.24 0.000390 3.31 403.29 75.77 0.13

Gee Creek 0.000 100-yr BW 1080.00 4.11 23.50 10.13 23.63 0.000224 2.88 397.46 472.36 0.12

Appendix E: Scour Calculations

Gee Creek at Main Avenue

HEC-23

Design Guideline-18 Riprap Protection for Bottomless Culverts

Where:

Qc= 1080 Flow in culvert, CFS Wc= 40 Width culvert, ft

Flow Area= Flow Area, ft^2 VAC = 2.43 Average velocity at culvert entrance (ft/s)

Y0 = 11.12 Water depth in culvert (ft)

Kr = 0.68 0.68 for design curve that envelops the lab data

Sg = 2.65 specific gravity of stone g = 32.2 acceleration due to gravity (32.2 ft/s2) d50 (ft) d50 Minimum (in)

1.2 14.2

Riprap Layout (DG 18-Bottomless Culverts)

Dimension Minimum Riprap

(Class 4) Length to extend riprap past upstream wall (ft) 22 22

Length to extend riprap past downstream wall (ft) 44 44

Embankment Riprap Thickness (ft)

2 2

YTOT (ft) 4 4

WT (ft) 5 5

WB (ft) 16 17 Ysc (ft) 7.8 7.8 (see Contraction Calculations)

Min. Required Riprap Size

Class 4 Riprap Size d50 (in)

15.5

Contraction Scour (Ysc) for Native Soils

Scour based on equations provided in HEC-18 Live-Bed Contraction Scour based on Laursen's Equation Clear-Water Contraction Scour based on Laursen's Equation Input paramaters based on 100-year flows in HEC-RAS

Input Parameters

Variable Description V*/w k1 ya 6.40 Average flow depth in main channel for approach section (i.e. hydraulic depth), ft 0 0.59 Va 3.49 Average velocity for approach section, ft/s 0.50 0.59 Qa 1080 Discharge in main channel for approach section, ft^3/s 0.5 0.64 Wa 0 Top width of main channel for approach section, ft 2 0.64 Sa 0.002…