Hyd_6WX(1)_Final.pdf

HYDRAULIC REPORT

SOUTHFORK ROAD BRIDGES

PARK COUNTY, WY

WY 6WX(1), SOUTHFORK ROAD

Prepared by:

Megan Frye

Hydraulic Engineer

Central Federal Lands Highway Division

January 2018 ii

TABLE OF CONTENTS

Introduction

Project Background and Objectives

Site Visit

Bridge Design Criteria

Project Data

Project Area Description

Hydrologic Analysis

Hydraulic Analysis

Proposed Condition Model

Scour Analysis

Abutment Protection

Summary of Recommendations

References

APPENDICIES

Site Visit Photos, Hydraulic Analysis Results

INTRODUCTION

This report provides a summary of the hydrologic and hydraulics analyses completed in conjunction with the proposed roadway project. The intent is to provide information to support the selected bridge type, size, and location for the bridge over the South Shoshone River (EGF) and bridge over Little Boulder Creek (EGR) on Hunter Creek Road. Scour calculations and scour countermeasure recommendations are also provided for the Legg Creek Bridge (LXD).

PROJECT BACKGROUND AND OBJECTIVES

The Central Federal Lands Highway Division, in cooperation with Park County and the Shoshone National Forest, plan to widen/reconstruct a portion of the Southfork Road. The proposed project is 13.6 miles long and is located approximately

30 miles southwest of Cody, Wyoming. Figure 1 shows the project location and surrounding area.

Figure 1. WY 6WX(1) – Project Location Map

There are three bridges along the route and one bridge within the vicinity. The three bridges on the route are the South

Fork Shoshone River bridge (EGF), Legg Creek bridge (LXD), and the Deer Creek bridge (EGP). The bridge off the route but in the vicinity is the Little Boulder Creek bridge (EGR). Figure 2 shows an aerial of the route with the bridge locations identified.

Proposed project

Figure 2. WY 6WX(1) – Aerial Map

The scope of the project includes reconstruction, resurfacing, restoration, and rehabilitation throughout the route as well as two bridge replacements (EGR and EGF). During the scoping trip, some concerns with scour at the abutments of the

LXD bridge were identified. Scour calculations and countermeasure recommendations are provided for future use by Park

County when funding is available.

The objective of this report is to evaluate the existing hydraulic conditions and provide recommendations for two new bridges with sufficient capacity to meet the design criteria.

SITE VISIT

The Central Federal Lands Highway Division (CFLHD) visited the project site in November 2017 and June 2018 to review the existing site conditions and define the scope of work for the design of replacement bridges. Photos from the site visit are included in the Appendix A.

BRIDGE DESIGN CRITERIA

According to the bridge inspection reports, the average daily traffic across EGF bridge is 220 vehicles and the average daily traffic across the EGR bridge is 200. The CFLHD capacity design standard for bridged waterways is conveyance of the 50-year hydraulic design flood with a minimum of 2 feet of freeboard below the low chord. The foundation stability design standard is the 100-year scour design flood with a 200-year scour check flood.

PROJECT DATA

Ground survey data was collected by the CFL survey team in March 2018. Supplemental survey at the EGF bridge was collected by Park County through a consultant in May 2018. The County also collected additional survey through a consultant at EGR bridge in October 2018.

The USGS has a gaging station approximately 4 miles upstream of the EGF bridge on the South Fork Shoshone River.

Information from this gage station was used in the hydrologic analysis.

PROJECT AREA DESCRIPTION

The existing South Fork Shoshone River Bridge (EGF) is a two lane, two span bridge built in 1978. The bridge is 132 feet long (each span is 66 feet) and 26 feet wide (out-to-out). Significant channel migration has led to an undesirable angle of attack on the pier causing scour along the pier. The migration has also resulted in embankment failure around the west abutment which has been temporarily filled with riprap as shown in Figure 3.

Figure 3. EGF Existing Conditions – From upstream, looking downstream at bridge

It appears the channel migration may be a result of heavy sediment loads depositing at the confluence of Aldrich Creek and South Fork Shoshone River approximately 500 feet upstream of the bridge. Figure 4 depicts the progression of the channel migration from Google Earth imagery from September 2006 to June 2015.

September 2006 June 2014 June 2015

Figure 3. EGF Existing Conditions – From upstream, looking downstream at bridge

The scope of work at the bridge includes replacement of the existing structure along with flow-training structures upstream of the proposed bridge to mitigate channel migration.

The existing Legg Creek Bridge (LXD), is a two lane, single span bridge built in 2005. The bridge is 65 feet long and 26 feet wide (out-to-out). A scour analysis and countermeasure design recommendations were completed for this structure if funding becomes available in the future. The existing structure is shown in Figure 4.

Figure 4. LXD Existing Conditions – From downstream, looking upstream at bridge

The existing Deer Creek Bridge (EGP), is a one lane, single span bridge built in 1973. The bridge is 72 feet long and 15.4 feet wide (out-to-out). The bridge foundations were evaluated in 1990 for scour-ability and the material the abutments is founded on was determined to be non-scourable. For this reason, no analysis was completed for EGP. The existing structure is shown in Figure 5.

Figure 5. EGP Existing Conditions –From upstream, looking downstream at bridge

The existing Little Boulder Creek Bridge (EGR), is a one lane, single span bridge built in 1956. The bridge is 28 feet long and 15.3 feet wide (out-to-out). If funding is available, the County expressed an interest in replacing the existing structure.

The existing timber structure is shown in Figure 6.

Figure 6. EGR Existing Conditions – From downstream, looking upstream at bridge

HYDROLOGIC ANALYSIS

A flood frequency analysis was performed for each crossing using one of two methods. An existing USGS gage station on the South Fork Shoshone River was used to approximate the peak discharges at the EGF bridge. The peak discharges at the remaining crossings were approximated using USGS regional regression equations.

The Watershed Modeling System (WMS v. 10.1) was used to delineate drainage basins. Figure 7 shows the four drainage basins coinciding with the bridge crossings.

Figure 7. Bridge Crossing Drainage Area Delineation

The drainage basin area for each crossing is shown in Table 1.

Site Drainage Area (sq. miles)

Bridge EGF 334.5

Bridge LXD 2.5

Bridge EGP 19.0

Bridge EGR 38.0

Table 1. Regional Regression Parameters

For the EGF bridge, a Log-Pearson Type III analysis of the upstream gage station (USGS 06280300) was completed. The peak flow values computed for the gage station were used to estimate the peak flow at the EGF bridge using the method detailed in the USGS publication, Peak Flow Characteristics of Wyoming Stream. A summary of the peak flow estimations from the Log-Pearson Type III analysis at the gage and the interpolated peak flow estimations at the bridge are shown in

Table 2.

Flood Event USGS Gage

(cfs) Bridge EGF

(cfs)

2-year 3,950 4,260

10-year 5,920 6,350

50-year 7,580 8,110

100-year 8,290 8,870

200-year 9,025 9,640

500-year 10,020 10,690

Table 2. Bridge EGF Peak Flow Estimates

EGR

EGF

EGP

LXD

Using the same USGS report, the regional regression equations for ungagged streams were used to estimate the peak flow at the remaining bridge sites. The remaining bridges fall within the Rocky Mountain region where the parameters used to compute the peak discharge are drainage area, mean basin elevation, and longitude of basin outlet. A summary of the regional regression parameters is shown in Table 3.

Bridge Site Drainage Area

(sq. miles) Mean basin elevation (ft.)

Longitude of basin outlet (decimal degrees)

LXD 2.5 9538.2 109.5825

EGP 19.0 9562.7 109.6118

EGR 38.0 9730.8 109.5582

Table 3. Regional Regression Parameters

The summary of the discharges is in Table 4.

Flood Event Bridge LXD

(cfs) Bridge EGP

(cfs) Bridge EGR

(cfs)

2-year 50 270 525

10-year 90 465 850

50-year 130 615 1,085

100-year 145 675 1,180

200-year 165 740 1,280

500-year 190 825 1,400

Table 4. Peak Flow Estimation

HYDRAULIC ANALYSIS

Hydraulic modeling of the EGF, LXD, and EGR bridges was performed using the Surface-water Modeling System, Sedimentation and River Hydraulics 2D (SMS-SRH2D) Version 12.3.1 provided by Aquaveo. For the EGF and EGR bridges, the existing and proposed conditions were modeled. For the LXD bridge, the existing conditions were modeled.

Because no work was proposed at the EGP bridge, no modeling or hydraulic analysis was completed for that site.

BRIDGE EGF

The existing and proposed bridges were modeled in SMS for the 2, 10, 50, 100, 200, and 500-year design flows. Based on coordination with the CFL cross functional team and partners on the project, the proposed bridge is a 150 feet long, single span structure. The existing pier will be removed as part of the demolition. The abutment foundations for the new bridge will be installed behind the existing abutment walls which will remain in place.

The design standard for bridged waterways is conveyance of the 50-year hydraulic design flood with a minimum of 2 feet of freeboard below the low chord. The proposed low chord elevation at each abutment is shown in Table 5.

Proposed Bridge Foundation Low Chord Elev. –

Proposed Bridge (ft)

Abutment 1 6091.02

Abutment 2 6088.84

Table 5. Low Chord Elevations

The 2-dimensional model was developed using the CFL survey and consultant survey. Aerial photos were used to delineate areas of like materials and Manning’s n values were assigned to each material area. Figure 8 shows the materials areas in the model.

Figure 8. Materials Areas

The initial Manning’s n values were selected using the values listed in Open Channel Hydraulics by Ven Te Chow. Those values were then varied to calibrate the model to one observed flow rate and depth conditions during the bathymetric survey. The final Manning’s n values used for the model are represented in Table 6. The unassigned material coverage was used in the existing conditions model to represent the pier.

Material Area Symbol Manning’s n Value

Unassigned

Channel

0.03

Point Bar

0.04

Floodplain

0.08

Hillside

0.10

Table 6. Manning’s n values.

The boundary condition at the upstream limit assumed a subcritical inflow equal to the flow rate for each design event.

The downstream boundary condition was set at a constant water surface elevation using a channel cross section, composite Manning’s n value, and channel slope. The model limits extend approximately 1000 feet upstream and 450 feet downstream of the existing bridge.

Table 7 presents the hydraulic modeling results for the water surface elevations at the cross sections immediately upstream of the bridge for the existing and proposed conditions.

Flow Profile Flow Rate

(cfs) Water Surface Elev. –

Existing (ft) Water Surface Elev. –

Proposed (ft)

2-year 4,260 6085.4 6085.0

10-year 6,350 6086.4 6085.8

50-year 8,110 6087.3 6087.3

100-year 8,870 6087.6 6087.6

200-year 9,640 6088.0 6088.0

500-year 10,690 6088.4 6088.4

Table 7. Hydraulic Modeling Results – Water Surface Elevations

The results from the model show that the proposed bridge provides a minimum of 1.1 feet of freeboard for the 50-year peak flow. This does not meet the proposed design criteria for bridged waterways. The variance in design standards was deemed acceptable given the significant right-of-way impacts associated with raising the bridge elevation. Given the slope of the bridge, a 50-foot section of the bridge provides less than 2 feet of freeboard for the 50-year event while 100 feet of the bridge provides adequate freeboard. The cross-functional team and partner agency determined that the risk associated with less than 2 feet of freeboard for a portion of the structure did not outweigh the cost to raise the profile.

Figure 9 demonstrates the water surface elevations for the 10, 50, 100, 200, and 500-year design event for the proposed bridges in the main channel. The proposed bridge in the figure represent the minimum low chord elevation above the main channel.

Figure 9. Water Surface Elevations along Main Channel

A cross section at the upstream face of the proposed bridge is shown in Figure 10.

Flow

Proposed bridge

Figure 10. Upstream Cross Section – Proposed Bridge

SCOUR ANALYSIS

A scour analysis was performed using the results from the SMS-SRH2D model. Based on material gradations from the geotechnical investigation, the bed material of the South Fork Shoshone River was classified as coarse sand with a D50 of

2mm. Long term degradation at the site was assumed to be zero.

The total scour depth at the abutments is a combination of contraction scour and local scour. The local scour depths at the abutments were calculated using the NCHRP Method outlined in HEC-18 (2012). The NCHRP Method combines contraction scour calculations with an amplification factor based on the abutment configuration and scour condition to determine the local scour depth at the abutment. Both abutments are close to the main channel, therefore abutment scour condition (a) was used to determine the local scour at the abutments. The proposed abutments are vertical walls with wingwalls. Table 8 summarizes the local scour at the abutments for the scour design flow event and the scour check flow event. The variables used in the scour calculations can be found in Appendix B.

Event 100-yr 200-yr

Abutment Scour (ft.)

Abutment Scour (ft.)

Abutment 1 (West) 6.3 10.3

Abutment 2 (East) 6.3 10.3

Table 8. Abutment Scour Depths – Proposed Bridge

The contraction scour at the proposed bridge was also calculated. The main channel scour depths were calculated using live bed conditions. The contraction scour depths for the main channel are presented in Table 9.

Event 100-yr 200-yr

Contraction Scour

(ft.)

Contraction Scour

(ft.)

Main Channel 1.0 2.0

Table 9. Contraction Scour Depths – Proposed Bridge

The total scour at each foundation element is summarized in Table 10. The scour elevations were determined using the minimum main channel elevation and subtracting the scour depth.

100-yr 200-yr

Total Scour

(ft.)

Scour Elev.

(ft.)

Total Scour

(ft.)

Scour Elev.

(ft.)

Abutment 1 (West) 6.3 6071.7 10.3 6067.7

Abutment 2 (East) 6.3 6071.7 10.3 6067.7

Table 10. Total Scour Depths and Elevations – Proposed Bridge

ABUTMENT PROTECTION

Class 6 riprap, to be placed along the abutments, was selected based on the methodology presented in HEC-23 Volume

2, Design Guideline 14 and for consistency with the proposed riprap sizing of the flow training structures.

The riprap around the bridge abutments should be toed into the channel bed by extending the riprap 4 feet below the bed elevation and extending it horizontally into the floodplain 8 feet. The side slope is a 1.5(h):1(v) with the top elevation at

6090 feet at Abutment #1 and 6088 feet at Abutment #2. Figure 10 shows the profile view of the abutment riprap.

Figure 10. Proposed Riprap Profile

FLOW TRAINING DESIGN

The intent of the flow-training structures upstream of the bridge is to redirect the main flow back into the middle of the channel and away from the eroding west bank. To mitigate the main channel migration, a series of six weirs are proposed along the west bank upstream of the bridge crossing. The weirs are oriented such that the flow is redirected to the middle of the main channel which will result in reduced velocities along the west bank which will allow for sediment deposition between the spurs. Sediment deposition will continue in future events which will continue to push the main flow path towards the middle of the channel. The preferred material for the weirs is Class 6 angular riprap with a D50 of 20 inches.

Each weir is 30 feet long and 3-4 feet high with a 12-foot key into the bank. See Figure 12 for design details for the spurs.

Figure 12. Bendway weir and revetment detail

Figures 13 illustrating the existing flow depth and velocity vectors for the 2-year and 10-year flow conditions.

2-year Flow Depth 10-year Flow Depth

Figure 13. Existing Conditions – Flow Depth with velocity vectors

The existing conditions model shows the adverse flow path from upstream through the bridge section. The majority of the flow is pointing directly at the existing pier causing significant scour concern at the pier.

Figures 14 illustrating the existing velocity magnitude and vectors for the 2-year and 10-year flow conditions.

2-year Velocity 10-year Velocity

Figure 14. Existing Conditions – Velocity Magnitude with vectors

Figures 15 illustrating the proposed flow depth and velocity vectors for the 2-year and 10-year flow conditions.

Figure 15. Proposed Conditions – Flow Depth with velocity vectors

Figures 16 illustrating the proposed velocity magnitude and vectors for the 2-year and 10-year flow conditions.

Figure 16. Proposed Conditions – Velocity Magnitude with vectors

The addition of the weirs upstream of the bridge improves the flow path upstream and through the bridge section. The primary direction of the flow is not perpendicular to the bridge cross section but the angle is improved from the existing conditions and the scour concerns at the pier eliminated as the pier will be removed.

The differences between the existing and proposed conditions were considered to identify any undesirable conditions created with the proposed upstream improvements. Figure 15 illustrating the difference in flow depth from the existing to the proposed conditions for the 2-year and 10-year flows. Increases in flow depth are represented by the yellow to red hues while the decreases in flow depth are represented by the blue hues. The light yellow hue represented minimal changes to flow depth.

Figure 15. Difference in Depth from Existing to Proposed Conditions

The majority of the increases in flow depth are seen upstream of the bridge within the influence of the weirs. This indicates that the weirs are redirecting flow into the center of the main channel and better aligning the flows with the bridge cross section.

Figure 16 illustrating the difference in velocity magnitude from the existing to the proposed conditions for the 2-year and

10-year flows. Increases in velocity are represented by the yellow to red hues while the decreases in velocity are represented by the blue hues. The light yellow hue represented minimal changes.

Figure 15. Difference in Velocity from Existing to Proposed Conditions

The heat maps demonstrate the reductions in velocity along the west bank as a result of the weir installation with increased velocities in the center of the main channel. The reduced velocities along the west bank will promote sediment deposition which will help mitigate the erosion along the west bank. The increases in velocity on the large point bar along the east bank should increase the transport of materials from this deposition. Increasing the mobility of this material will help reduce the constriction of the main channel that has occurred with the increased deposition from Aldrich Creek. The strip of increased velocity through the bridge section and immediately downstream is a result of the removal of the pier from the channel.

BRIDGE EGR

The existing and proposed bridges were modeled in SMS for the 2, 10, 50, 100, 200, and 500-year design flows. Based on coordination with the CFL cross functional team and partners on the project, the proposed bridge is a 50 feet long, single span structure. The existing timber abutments will be removed to increase the capacity of the channel beneath the bridge.

The 2-dimensional model was developed using the CFL survey and consultant survey. Aerial photos were used to delineate areas of like materials and Manning’s n values were assigned to each material area. Figure 16 shows the materials areas in the model.

Figure 16. Materials Areas

The Manning’s n values were selected using the values listed in Open Channel Hydraulics by Ven Te Chow and represented in Table 9.

0.06

Floodplain

0.09

Table 9. Manning’s n values.

The boundary condition at the upstream limit assumed a subcritical inflow equal to the flow rate for each design event.

The downstream boundary condition was set at a constant water surface elevation using a channel cross section, composite Manning’s n value, and channel slope. The model limits extend approximately 170 feet upstream and 100 feet downstream of the existing bridge.

Table 10 presents the hydraulic modeling results for the water surface elevations at the cross sections immediately upstream of the bridge for the existing and proposed conditions.

Flow Profile Flow Rate

(cfs) Water Surface Elev. –

Existing (ft) Water Surface Elev. –

Proposed (ft)

2-year 525 6425.6 6425.4

10-year 850 6427.2 6426.6

50-year 1000 6427.8 6427.1

100-year 1180 6428.2 6427.4

200-year 1280 6428.5 6427.6

500-year 1,400 6428.8 6427.9

Table 10. Hydraulic Modeling Results – Water Surface Elevations

The results from the model show that the proposed bridge provides the minimum freeboard for the 50-year peak flow. The minimum low chord elevation of the proposed bridge will be set at or above 6429.1 feet.

Figure 17 demonstrates the water surface elevations for the 10, 50, 100, 200, and 500-year design event for the proposed bridges in the main channel. The proposed bridge in the figure represent the minimum low chord elevation above the main channel.

Figure 17. Water Surface Elevations along Main Channel

A cross section at the upstream face of the proposed bridge is shown in Figure 17.

Proposed bridge

Figure 17. Upstream Cross Section – Proposed Bridge

A scour analysis was performed using the results from the SMS-SRH2D model. Based on material gradations from the geotechnical investigation, the bed material of Little Boulder Creek was classified as coarse gravel with a D50 of 75mm.

Long term degradation at the site was assumed to be negligible.

The total scour depth at the abutments is a combination of contraction scour and local scour. The local scour depths at the abutments were calculated using the NCHRP Method outlined in HEC-18 (2012). The NCHRP Method combines contraction scour calculations with an amplification factor based on the abutment configuration and scour condition to determine the local scour depth at the abutment. Both abutments are close to the main channel, therefore abutment scour condition (a) was used to determine the local scour at the abutments. The proposed abutments are vertical walls with wingwalls. The variables used in the scour calculations can be found in Appendix B.

The total scour at each foundation element is summarized in Table 11. The scour elevations were determined using the minimum main channel elevation and subtracting the scour depth.

100-yr 200-yr

Total Scour (ft.)

Scour Elev.

(ft.)

Total Scour (ft.)

Scour Elev.

(ft.)

Abutment 1 (West) 1.26 6419.74 1.28 6419.72

Abutment 2 (East) 1.26 6419.74 1.28 6419.72

Table 11. Total Scour Depths and Elevations

ABUTMENT PROTECTION

Min. low chord

Given the relatively large boulders existing in the channel, it was assumed that an adequate number of large boulders could be conserved during excavation for the bridge. Those conserved boulders will be placed along the abutments. See

Figure 18 for the plan detail.

Figure 18. Proposed Riprap Profile

BRIDGE LXD

The most recent bridge inspection report from March 2017 includes a NBIS Rating Worksheet for Item 113 (Scour) and lists the foundations as spread footings with sub-surface materials unknown. In a memo from an Engineering Geologist from WYDOT to the State Bridge Engineer dated December 22, 2005, a report-out on a scour investigation is outlined. In

2005, a 3-foot scour hole was observed at Abutment 1. Based on the geotechnical assessment of the site, the material is generally consistent to a 20-foot depth. The memo sites the potential for 18-20 feet of scour at the abutments.

As part of the hydraulic analysis completed for this project, the conditions at LXD were analyzed and an abutment scour analysis was completed. Scour countermeasure design recommendations were completed for this structure if funding becomes available in the future.

The 2-dimensional model was developed using the CFL survey. Aerial photos were used to delineate areas of like materials and Manning’s n values were assigned to each material area. Figure 15 shows the materials areas in the model.

Figure 15. Materials Areas

The Manning’s n values were selected using the values listed in Open Channel Hydraulics by Ven Te Chow and represented in Table 11.

0.04

Overbank

0.06

Wooded Area

0.09

Road

0.02

Concrete Slopes

0.02

Table 11. Manning’s n values.

The boundary condition at the upstream limit assumed a subcritical inflow equal to the flow rate for each design event.

The downstream boundary condition was set at a constant water surface elevation using a channel cross section, composite Manning’s n value, and channel slope. The model limits extend approximately 200 feet upstream and 215 feet downstream of the existing bridge.

Table 12 presents the hydraulic modeling results for the water surface elevations at the cross sections immediately upstream of the bridge for the existing condition.

Flow Profile Flow Rate

(cfs) Water Surface Elev. –

Existing (ft)

2-year 50 6287.0

10-year 90 6287.3

50-year 130 6287.4

100-year 150 6287.4

200-year 165 6287.5

500-year 190 6287.5

Table 12. Hydraulic Modeling Results – Water Surface Elevations

Figure 16 demonstrates the water surface elevations for the 2, 10, 50, 100, 200, and 500-year design event for the proposed bridges in the main channel. The proposed bridge in the figure represent the minimum low chord elevation above the main channel.

Figure 16. Water Surface Elevations along Main Channel

A cross section at the upstream face of the existing bridge is shown in Figure 17.

Existing bridge (approx. low chord @ 6293’)

Figure 17. Upstream Cross Section – Proposed Bridge

A scour analysis was performed using the results from the SMS-SRH2D model. Based on material gradations from the geotechnical investigation cited in the bridge inspection report, the bed material of Little Boulder Creek was classified as poorly graded gravel with a D50 of 2 inches. Long term degradation at the site was assumed to be negligible.

The total scour depth at the abutments is a combination of contraction scour and local scour. The local scour depths at the abutments were calculated using the NCHRP Method outlined in HEC-18 (2012). The NCHRP Method combines contraction scour calculations with an amplification factor based on the abutment configuration and scour condition to determine the local scour depth at the abutment. Both abutments are close to the main channel, therefore abutment scour condition (a) was used to determine the local scour at the abutments. The existing abutments are sloping abutments.

The total scour at each foundation element is summarized in Table 13. The scour elevations were determined using the minimum main channel elevation and subtracting the scour depth.

100-yr 200-yr

Total Scour (ft.)

Scour Elev.

(ft.)

Total Scour (ft.)

Scour Elev.

(ft.)

Abutment 1 (West) 1.1 6285.0 1.0 6285.1

Abutment 2 (East) 1.1 6285.0 1.0 6285.1

Table 10. Total Scour Depths and Elevations

Approx. low chord

ABUTMENT PROTECTION

If funding becomes available, the abutments should be protected against scour using riprap designed using the methodology presented in HEC-23 Volume 2, Design Guideline 14.

The Class 1 riprap around the bridge abutments should be toed into the channel bed by extending the top of the riprap to the deepest scour elevation reported in Table 10. The channel opening under the bridge is narrow therefore the riprap protection should extend across the full channel. The protection should extend 25 feet downstream of the abutments and should wrap around the abutment as shown in Figure 18. The side slope is a 2(h):1(v) with the top elevation at 6288.5 feet.

Figure 11. Proposed Riprap Layout

REFERENCES

Chow, Ven Te, Open Channel Hydraulics, 1959

Federal Highway Administration (2008) “Project Development and Design Manual” Federal Lands

Highway Division. US Department of Transportation. Chap 7.

Federal Highway Administration HEC-18, Evaluating Scour at Bridges, Fifth Edition, April 2012.

Federal Highway Administration HEC-23, Bridge Scour and Stream Instability Countermeasures:

Experience, Selection, and Design guidance-third Edition, Volume2, September 2009.

APPENDIX A

Site Visit Photos

Figure A.1. Upstream EGF bridge face (looking at left abutment)

Figure A.2. Upstream EGF bridge face (looking towards right abutment)

Figure A.3. From EGF bridge, looking upstream

Figure A.4. From EGF bridge, looking downstream

Figure B.1. Upstream EGR bridge face (looking at left abutment)

Figure B.2. Downstream of EGR bridge, looking upstream

Figure B.3. From EGR bridge, looking upstream

Figure B.4. From EGR bridge, looking downstream

Figure C.1. Under LXD bridge (looking at left abutment)

Figure C.2. Under LXD bridge (looking towards right abutment)

Figure C.3. From LXD bridge, looking upstream

Figure C.4. From LXD bridge, looking downstream

Figure D.1. Upstream EGP bridge face (looking at left abutment)

Figure D.2. Upstream EGP bridge face (looking towards right abutment)

Figure D.3. From EGP bridge, looking upstream

Figure D.4. From EGP bridge, looking downstream

Figure D.5. EGP bridge, upstream left irrigation intake structure

Figure D.6. EGP bridge, downstream right irrigation intake structure

APPENDIX B

Hydraulic Analysis

Scour Analysis – EGF

Contraction Scour – Proposed Bridge

Input

Output

Abutment Scour, NCHRP Scour Condition (a) – Proposed Bridge

Riprap Abutment Protection Sizing

Scour Analysis – EGP

Contraction Scour – Proposed Bridge

Input

Output

Abutment Scour, NCHRP Scour Condition (a) – Proposed Bridge

Scour Analysis – LXD

Abutment Scour, NCHRP Scour Condition (a) – Existing Bridge

Riprap Abutment Protection Sizing