Red_Dirt_Bridge_Hydraulics_Report_FINAL.pdf

Submitted to:

US Department of Transportation Federal Highway Administration Central Federal Lands Highway Division 1200 West Dakota Avenue Lakewood, Colorado 80228

FINAL Hydraulics Report: Revision 1 Red Dirt Bridge

CO FLAP 301(1)

AECOM Project Number 60332793 March 7, 2016

AECOM FINAL Hydraulics Report: Revision 1 Red Dirt Bridge: CO FLAP 301 (1)

TOC-ii

Table of Contents

1 Introduction............................................................................................................................ 1-1

2 Project Summary ................................................................................................................... 2-1

2.1 Project Location ....................................................................................................... 2-1

2.2 Field Reviews .......................................................................................................... 2-2

2.3 Existing Drainage Features ...................................................................................... 2-2

3 Design Discussions ............................................................................................................... 3-1

3.1 Design Criteria......................................................................................................... 3-1

3.2 Wetlands and Waters of the US ............................................................................... 3-1

3.3 Cultural Resources .................................................................................................. 3-1

3.4 Future Land Use ...................................................................................................... 3-1

3.5 Dams ...................................................................................................................... 3-1

3.6 Ground Survey ........................................................................................................ 3-1

4 Hydrology ............................................................................................................................... 4-1

4.1 Soils ........................................................................................................................ 4-1

4.2 Flood History ........................................................................................................... 4-1

4.3 Precipitation ............................................................................................................ 4-1

4.4 Determining Peak Flows .......................................................................................... 4-1

5 Recommended Design .......................................................................................................... 5-1

5.1 Culverts ................................................................................................................... 5-1

5.2 Bridge Replacement ................................................................................................ 5-1

5.3 Bridge Scour and Scour Countermeasures .............................................................. 5-6

5.4 Pier Construction Approach and Cofferdams ........................................................... 5-7

5.5 Variances ................................................................................................................ 5-9

5.6 Summary ................................................................................................................. 5-9

6 References ............................................................................................................................. 6-1

Appendix Appendix A: References Appendix B: Hydrology Appendix C: Hydraulics Appendix D: Construction Plans

TOC-iii

Table of Figures

Figure 2-2. RDB looking upstream................................................................................................................................. 2-2 Figure 2-4. Both Bridges ............................................................................................................................................... 2-2 Figure 2-3. UPRR Bridge upstream of RDB ................................................................................................................... 2-2 Figure 2-5. Rock between bridges ................................................................................................................................. 2-2 Figure 2-6. Upstream channel ....................................................................................................................................... 2-3 Figure 2-7. Upstream bridges ........................................................................................................................................ 2-3 Figure 2-8. Downstream bridges ................................................................................................................................... 2-3 Figure 2-9. Downstream channel ................................................................................................................................... 2-3 Figure 2-10. RDB piers and debris racks ....................................................................................................................... 2-3 Figure 2-11. RDB riprap, D50 = 18” (Class 5) .................................................................................................................. 2-3 Figure 2-12. RDB north abutment .................................................................................................................................. 2-4 Figure 2-13. RDB south abutment ................................................................................................................................. 2-4 Figure 2-14. RDB north approach .................................................................................................................................. 2-4 Figure 2-15. RDB south approach ................................................................................................................................. 2-4 Figure 2-16. Debris flow channel ................................................................................................................................... 2-4 Figure 2-17. RDB bridge deck ....................................................................................................................................... 2-4 Figure 2-18. 3-Island Bridge .......................................................................................................................................... 2-5 Figure 2-19. 3-Island Bridge Piers ................................................................................................................................. 2-5 Figure 4-1. Proposed Cross Culvert at Red Dirt Creek Road Location ........................................................................... 4-2 Figure 4-2. Contributing Watershed of Proposed Cross Culvert at Red Dirt Creek Road ................................................ 4-3 Figure 5-1. Existing 50-yr HEC-RAS Profile ................................................................................................................... 5-3 Figure 5-2. Proposed 50-yr HEC-RAS Profile ................................................................................................................ 5-3 Figure 5-3. Existing Upstream HEC RAS Cross Section (675.6418) .............................................................................. 5-4 Figure 5-4. Existing Downstream HEC RAS Cross Section (675.6418) .......................................................................... 5-4 Figure 5-5. Proposed Upstream HEC RAS Cross Section (675.6418) ............................................................................ 5-5 Figure 5-6. Proposed Downstream HEC RAS Cross Section (675.6418) ....................................................................... 5-5 Figure 5-7. Proposed Profile for Cofferdam Construction ............................................................................................... 5-8 Figure 5-8. Cross Section at Upstream Face of Existing Bridge with Cofferdam ............................................................. 5-8

List of Tables

Table 4-1. Bridge Peak Flows........................................................................................................................................ 4-2 Table 4-2. TR-55 Input Parameters ............................................................................................................................... 4-3 Table 4-3. Cross Culvert at Red Dirt Creek Road .......................................................................................................... 4-3 Table 5-1. Culvert Improvement Summary .................................................................................................................... 5-1 Table 5-2. HEC-RAS Model Inputs for Red Dirt Bridge .................................................................................................. 5-2 Table 5-3. Existing and Proposed 50-yr WSEL and Velocities ....................................................................................... 5-2 Figure 5-1. Existing 50-yr HEC-RAS Profile ................................................................................................................... 5-3 Table 5-4. Freeboard at HEC-RAS Cross Section 704.2786 .......................................................................................... 5-6 Table 5-5. Scour Summary............................................................................................................................................ 5-6 Table 5-6. Cofferdam Summary Table ........................................................................................................................... 5-7

1-1

The Federal Lands Access Program (FLAP) is providing funding towards rehabilitation, restoration, and resurfacing (3R) projects. The scope of work for this project is to perform environmental, engineering, hydraulic, geotechnical, right-of-way, surveying, mapping, and project management services toward delivery of a 100% PS&E for the Federal Highway Administration (FHWA), Central Federal Lands Highway Division (CFL) for proposed improvements to Red Dirt Bridge (RDB).

This project includes reconstruction of RDB and both bridge approaches. RDB is on the Colorado River Road at approximate milepost 15.6, just north of Dotsero, Colorado in Eagle County (County). The County has completed similar bridge reconstructions downstream (3 Islands Bridge) and upstream (Burns Bridge and Catamount Bridge) across the Colorado River. RDB is downstream and parallel to a Union Pacific Railroad (UPRR) Bridge.

RDB, was constructed in 1945 and is a 200 ft long (back of face to back of face of abutments), 5 span steel bridge with a 16 ft cross section. The proposed bridge will have longer spans, eliminate piers in the river, and provide two 12 ft lanes, 4 ft wide shoulders with appropriate bridge rails. The overall length of the proposed bridge may change based on the final alignment of the roadway and is anticipated to be longer than the existing bridge.

This FINAL Hydraulics Report has been prepared to present a summary of the hydrologic analysis and hydraulic (H&H) for this project.

1 Introduction

2-1

The general scopes of improvements are programmed as reconstruction of the bridge and both bridge approaches. The goal of this bridge replacement project is to improve safety of this roadway, primarily allowing for two lanes of traffic with shoulders.

The proposed bridge will have longer spans, eliminate piers in the river, and provide two 11 ft lanes, 3 ft wide shoulders with appropriate bridge rails. The overall length of the proposed bridge will be longer than the existing bridge. The project includes replacement of shallow culverts, ditch re-grading to facilitate drainage, signing, striping, and removing and replacing guardrails, to meet current design practice.

Coordination with Eagle County and the Bureau of Land Management (BLM) are anticipated.

2.1 Project Location

The project area is located approximately 15.6 miles northeast of Dotsero, Colorado. RDB is located on the Colorado River Road (Eagle County Road 301) near the intersection with Red Dirt Road and is shown in Figure 2-

1. The Colorado River Road provides access to public land and recreation.

Figure 2-1. RDB Project Location

Provided by Map data © 2014 Google

2 Project Summary

Project Location

Colorado River

Dotsero

2-2

2.2 Field Reviews

In July 2013, AECOM and CFL conducting a scoping field review. This review evaluated the existing conditions of the project to produce a Scoping Report.

2.3 Existing Drainage Features

Drainage features within the project corridor include: culverts, channels, and bridges.

RDB is a 5 span, continuous rolled steel beam structure constructed in 1945. The existing bridge measures 200 ft from back face to back face of abutments and has a width of approximately 16 ft. Just upstream of RDB, Union Pacific Railroad (UPRR) has a bridge that spans the Colorado River. The UPRR Bridge has 2 piers with 3 spans.

The proposed bridge pier layout will be aligned with the existing UPRR Bridge to minimize bridge hydraulic impacts. The following figures document observations.

Figure 2-2. RDB looking upstream

Figure 2-4. Both Bridges

Figure 2-3. UPRR Bridge upstream of RDB

Figure 2-5. Rock between bridges

2-3

Figure 2-6. Upstream channel

Figure 2-7. Upstream bridges

Figure 2-8. Downstream bridges

Figure 2-9. Downstream channel

Figure 2-10. RDB piers and debris racks

Figure 2-11. RDB riprap, D50 = 18” (Class 5)

2-4

Figure 2-12. RDB north abutment

Figure 2-13. RDB south abutment

Figure 2-14. RDB north approach

Figure 2-15. RDB south approach

Figure 2-16. Debris flow channel

Figure 2-17. RDB bridge deck

2-5

The County prefers a design that matches a recently constructed downstream bridge (3-Island Bridge) and two proposed upstream bridges (Burns Bridge and Catamount Bridge). See Figure 2-18 and Figure 2-19 for the 3- Island Bridge and pier layouts.

Figure 2-18. 3-Island Bridge

Figure 2-19. 3-Island Bridge Piers

3-1

H&H design was conducted with the following considerations.

3.1 Design Criteria

Hydrologic and hydraulic analysis and design work associated with the proposed improvements are in accordance with the methods, guidelines, and criteria set forth with the following:

Federal Lands Highway Project Development and Design Manual (PDDM) Colorado Department of Transportation Drainage Design Manual

A summary of the applicable criteria can be found in the Hydrologic and Hydraulic Criteria and Computation Methods Memorandum, in Appendix A.

3.2 Wetlands and Waters of the US

A Wetlands and Waters of the U.S. Technical Report, presenting a formal delineation of wetlands and Other Waters of the U.S (OWUS) was prepared in July of 2015. A field survey was performed in October of 2014.

One permanent waterway occurs within the study area. The Colorado River is a jurisdictional waterway (OWUS 1) Classification of wetland system, subsystem, class, and subclass was based on the USFWS Cowardin et al.

(1979) classification system. Two Palustrine Scrub/Shrub (PSS) wetland areas were identified. The Categorical Exclusion (CatEx) summarizes the findings and describes potential effects and permit requirements. A Nationwide Permit (14 or 26) permit will be obtained, but mitigation for these impacts will likely not be required.

3.3 Cultural Resources

An intensive cultural Resources inventory was performed for the project and a report was prepared in July of 2015. A cultural resources investigation was completed for the project’s Area of Potential Effect to supplement past cultural resource inventories within a mile of the APE. An intensive pedestrian cultural resources inventory of approximately 4.99 total acres identified two historic cultural resources, the Red Dirt/Colorado River Bridge and a segment of the Dotsero Cutoff Railroad. More details can be found in the CatEx.

3.4 Future Land Use

Future land use is anticipated to remain the same as today.

3.5 Dams

The project area is located in the Upper Basins on the Colorado River System. The major reservoirs/dams that contribute to the project area are Dillion, Green Mountain, and Lake Granby. Detention/retention in the dams has not been considered in hydrologic analysis.

3.6 Ground Survey

While the existing conditions were being surveyed, there were a couple shots in the river cross sections that could not be obtained because of the high velocities of the Colorado River.

3 Design Discussions

4-1

Hydrology was determined using the following means and methods.

4.1 Soils

Soil types for the project area have been determined using the Natural Resources Conservation Service (NRCS) web based soil survey. The soils located in the project area consist of predominantly hydrologic soil Groups C and D, exhibiting a slow infiltration rate. For analysis, Group C will be used. See Appendix A for map of hydrologic soil groupings.

4.2 Flood History

There are no known documented records of flooding events at Red Dirt Bridge. The project improvements lie within a Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM) designation number 08037CO2000D that is a non printed flood map boundary. The proposed bridge will create a rise scenario of 0.01 ft downstream of the bridge, see Appendix A for more detailed information.

4.3 Precipitation

The National Oceanic and Atmospheric Administration (NOAA) from the online data server was used to determine point precipitation frequency estimates for use to create an intensity duration frequency (IDF) curve. This information for storm duration and precipitation depths were derived from NOAA Atlas 14, Volume 8, Version 2, see Appendix A for more detailed information..

4.4 Determining Peak Flows

Roadway hydrology will use the Rational Method as the anticipated contributing drainage areas will be less than 200 acres. For areas greater than 200 acres, regression equations will be used.

The bridge drainage area was calculated using United States Geological Survey (USGS) StreamStats Program, a web-based Geographic Information System (GIS). The contributing drainage area to RDB is 3138 sq mi. Upon completion, the program identified that the project is located with a gaged system and that regression equations are not applicable and other methods for determine peak flows is required.

Downstream of the RDB, near Dotsero, there is a USGS Gaging Station Number 09070500. Based on the location of this gaging station, two sources were reviewed and compared to determine peak flows at this station:

County’s Floodplain Information Report: Eagle River and Colorado River (Matrix 2003) Federal Emergency Management Agency (FEMA) Flood Insurance Study (FIS), (FEMA 2007)

Peak flows for each source are summarized in Table 4.1.

4 Hydrology

4-2

Table 4-1. Bridge Peak Flows

Storm Event (Year) Peak Flows at Station 09070500 2003 Report

(cfs)

Peak Flows

2007 FIRM

(cfs)

Peak Flows at RDB used for Calculations

(cfs)

10 16400 18950 15360

50 21600 24900 20180

100 23600 27140 21990

500 25500 31830 25790

Drainage Area (sq mi) 4394 4344 3138

Using the procedures outline in Water Resources Investigation Report (WRIR) 99-4190 (USGS 2000), peak flows for RDB were determined and are summarized in the above Table 4-1. This procedure uses the ratio of drainage areas for the gaged and project site to determine peak flows at the project site. Both sites must be located on the same stream. There is a difference in areas; however, these are from the previously mentioned reports by Matrix and FEMA FIS. More details are found in the Appendix.

A cross culvert at Red Dirt Creek Road is proposed. This culvert will convey flows across Red Dirt Creek Road.

Heavy sedimentation has been noted and will be considered in culvert sizing. The proposed culvert location is shown in Figure 4-1 below.

Figure 4-1. Proposed Cross Culvert at Red Dirt Creek Road Location

Proposed Culvert at Red Dirt Creek Road

4-3

The contributing drainage area is greater than 200 acres and not within the threshold of 5.5 to 988.0 square miles;

therefore, rational nor regression equations could be used to determine peak flows. The United States Department of Agriculture (USDA)’s Technical Release (TR-55) Curve Number approach was used to determine peak flows. Figure 4-2 shows the contributing watershed areas, input parameters are detailed in Table 4-2, and peak flows are summarized in Table 4-3. See Appendix B for more details.

Figure 4-2. Contributing Watershed of Proposed Cross Culvert at Red Dirt Creek Road

Table 4-2. TR-55 Input Parameters

Item Parameter

Drainage Area (sq mi) 0.62

Hydrologic Soil C

Weighted Curve Number (CN) Woods, Fair = 73

Rainfall Distribution Type II

Time of Concentration (hr) 1.053

Table 4-3. Cross Culvert at Red Dirt Creek Road

Storm Event (Year) Peak Flows (cfs)

10 16.15

25 35.91

50 55.40

100 80.51

5-1

Drainage improvements have been based on the County, CFL and AECOM field observations, maintenance recommendations, and proposed roadway design. Drainage improvements consist of additional culverts, ditch regrading, and a bridge replacement.

5.1 Culverts

One culvert is proposed across Red Dirt Creek Road. At this location, there is a significant amount of flow that is conveyed southerly across Red Dirt Creek Road into the Colorado River. Therefore, riprap is proposed at the upstream side of the culvert to capture sediment prior to culvert conveyance. This culvert will have end treatments and a riprap apron (Class 3 riprap) at the culvert entrance for sediment and debris capture and a riprap apron (Class 4 riprap) at the exit for energy dissipation.

FHWA’s HY8, Version 7.2 was used to analyze culvert capacity, velocity, and headwater to depth (HW/D) ratio.

See the Plan sheet in Appendix D and a summary of results below.

Table 5-1. Culvert Improvement Summary

Station Q25

(cfs) Roadway

Elev (ft)

HW Elev (ft)

HW Depth (ft)

Proposed Diameter

(in)

HW/D1 Velocity (fps)

Proposed Improvement Comments

Red Dirt Creek Road

35.91 6375.39 6374.65 2.94 36 0.98 17.63 Potential Sediment Transport

1 Headwater to Depth (HW/D) ratio = 0.8 to 1.0 range. Typically the governing criteria of 25 yr storm event, HW/D = 1.5 for D 48 in and HW/D = 1.2 for D > 48 in

An additional culvert is proposed that conveys flows from Colorado River Road to a ditch and culvert conveying flows through Red Dirt Creek Road. This culvert will go through a berm that is required to remain in place to mitigate flows from leaving the mountain side channel and over Colorado River Road. H&H analysis has not been conducted at this location. See Z Sheets for more details in Appendix D.

5.2 Bridge Replacement

An existing conditions and proposed conditions bridge model was prepared to determine proposed bridge recommendations. The 50 yr storm event was used for design.

The existing RDB is a 5 span, continuous rolled steel beam structure. US Army Corp of Engineers (USACE’s) Hydrologic Engineering Center River Analysis System (HEC-RAS) Version 4.1.0 was used to determine the 10, 50, 100, and 500 yr water surface elevation (WSEL) at the bridge using the mixed flow regime for bridge design.

The model limits extend roughly 710 ft downstream and 681 ft upstream of the proposed bridge improvements. A total of 14 cross sections were used to represent the channel geometry through the reach.

A fixed sediment elevation (6351.50-ft) was applied to 4 cross sections (847.29, 760.36, 730.68, and 704.28).

These were applied because there was a significant dip in the profile. Field survey also indicated that there were issues obtaining the stream bottom elevation because of the fast moving water. Upstream and downstream of these cross sections, the profile is constant; therefore the sediment application provides continuation of a smooth profile.

The proposed RDB is a 3 span bridge as shown in the construction plans in Appendix D. The piers are to be aligned with the existing UPRR Bridge. See Table 5-2 for proposed model inputs and Table 5-3 for a summary of WSEL and Velocities.

5 Recommended Design

5-2

Table 5-2. HEC-RAS Model Inputs for Red Dirt Bridge

Item Existing Conditions Proposed Conditions Comments

Channel Manning’s n 0.045 0.045 Bed material consists of gravel, sand, and cobbles

Bank Manning’s n Left=0.1, Right=0.08 Left=0.1, Right=0.08 Established vegetation

Bridge Deck Width 16.25’ 31’

Bridge Depth 15” Girder, 7” Deck 42” Girder, 8” Deck

Piers 4, 1 ft wide 2, 4.0 ft wide

Bridge Overtopping? No No

Low Chord Elevation 6371.82 6368.87

UPRR Low Chord Elevation 6366.98 6366.98 No improvements or impacts to this existing bridge

Table 5-3. Existing and Proposed 50-yr WSEL and Velocities

At cross section 575.17, there is a rise in the 0.01 ft rise in the 100 year water surface elevation. This cross section is located just downstream of the proposed bridge improvement and is negligible; however, a variance to the no rise in floodplain is required. All other cross sections either have a no rise or a decrease in WSEL. See Appendix C for more details.

HECRAS Cross Section

50-year Existing

WSEL

(ft)

50-year Proposed

WSEL

(ft)

Difference in WSEL from Existing (ft)

50-year Existing Velocity

(fps)

50-year Proposed Velocity

(fps)

Difference in Velocity from Existing (fps)

1396.682 6371.79 6371.79 0 6.75 6.75 0

1171.801 6371.63 6371.63 0 6.44 6.44 0

1013.45 6371.56 6371.56 0 5.88 5.88 0

847.2888 6368.86 6368.86 0 13.59 13.59 0

760.3641 6368.56 6368.56 0 13.35 13.35 0

745.9536 Existing UPRR Bridge

730.6773 6366.61 6366.26 -0.35 10.51 10.78 0.27

704.2786 6366.57 6366.22 -0.35 10.2 10.42 0.22

688.8398 6366.74 6366.4 -0.34 8.77 8.93 0.16

675.6418 Existing Proposed Bridge Existing Proposed Bridge

665.3367 6366.16 Removed Not Applicable 9.82 Removed Not Applicable

640.878 6366.46 6366.15 -0.31 7.21 8.36 1.15

575.1618 6362.42 6362.46 0.04 15.71 15.66 -0.05

428.3976 6358.22 6358.22 0 20.47 20.49 0.02

202.1478 6359.04 6359.04 0 9.08 9.08 0

0.730402 6358.73 6358.73 0 8.14 8.14 0

5-3

0 200 400 600 800 1000 1200 1400

RedDirtBridge Plan: 1) Exist 8/13/2015

Main Channel Distance (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

2.

8.

5.

0.

5.

4.

0.

5.

7.

.4

.8

.6

Colorado River Colorado River

0 200 400 600 800 1000 1200 1400

RedDirtBridge Plan: Proposed 8/13/2015

Main Channel Distance (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

2.

8.

5.

0.

5.

4.

0.

5.

7.

.4

.8

.6

Colorado River Colorado River

Figures 5-1 through 5-6 shows the profile and upstream cross section at RDB with the WSEL for the 50-year storm event highlighted in blue.

Figure 5-1. Existing 50-yr HEC-RAS Profile

Figure 5-2. Proposed 50-yr HEC-RAS Profile

Area of Sediment Fill

Area of Sediment Fill

5-4

0 100 200 300 400 500

RedDirtBridge Plan: Exist 8/13/2015 River = Colorado River Reach = Colorado River RS = 675.6418 BR

Station (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

Ineff

Bank Sta

.1 .045 .08

0 100 200 300 400 500

RedDirtBridge Plan: Exist 8/13/2015 River = Colorado River Reach = Colorado River RS = 675.6418 BR

Station (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

Ineff

Bank Sta

.1 .045 .08

Figure 5-3. Existing Upstream HEC RAS Cross Section (675.6418)

Figure 5-4. Existing Downstream HEC RAS Cross Section (675.6418)

5-5

RedDirtBridge Plan: Proposed 8/13/2015 River = Colorado River Reach = Colorado River RS = 675.6418 BR Proposed Bridge

Station (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

Ineff

Bank Sta

.1 .045 .08

0 100 200 300 400

RedDirtBridge Plan: Proposed 8/13/2015 River = Colorado River Reach = Colorado River RS = 675.6418 BR Proposed Bridge

Station (ft)

E le va tio n (ft

Legend

WS 100 yr

WS 50 yr

Ground

Ineff

Bank Sta

Figure 5-5. Proposed Upstream HEC RAS Cross Section (675.6418)

Figure 5-6. Proposed Downstream HEC RAS Cross Section (675.6418)

5-6

Freeboard requirements satisfy CFL’s (minimum 2’ of freeboard) for both the 50-yr (design) and 100-yr storm events.

Table 5-4. Freeboard at HEC-RAS Cross Section 704.2786

Storm Event (yrs)

Discharge (cfs)

Existing Freeboard

(ft)

Proposed Velocity

(fps)

Proposed Freeboard

(ft)

Comments

50 20180 5.60 10.42 2.65 Design Event

100 21990 5.01 10.86 2.06 For information only, this is not the design event

On April 30, 2015 a conversation with CDOT Hydraulics R3, Stuart Gardner confirmed that there is not an issue with debris flow. However, there is a concern with ice jams breaking loose. The UPRR Bridge, just upstream of the proposed bridge has a lower low chord than what is proposed for the RDB. Should ice jam occur, the UPRR Bridge would jam first Should the ice break free and moves down to RDB, it is anticipated that the ice would be smaller and pass through more easily with the reduce piers. The Three Island Bridge, located downstream of this bridge provides 5 ft of freeboard. Changing the existing 5 span bridge to a 2 span bridge should help to alleviate ice jam potential.

Raising the profile of the road is not feasible. Also, with the elimination of existing piers, the proposed bridge deck has increased. The proposed WSEL upstream, downstream, and through the bridge are lower than the existing WSEL. 2.65’ of freeboard is provided and a variance to the 5’ minimum is requested.

5.3 Bridge Scour and Scour Countermeasures

Scour analysis was evaluated using the 500-yr flood event using FHWA’s Hydraulic Toolbox, Version 4.20. Table 5-5 summarizes the results and more detailed information and calculations can be found in Appendix C.

Table 5-5. Scour Summary

Scour Type Depth (ft) Comments

Degradation 0 HEC 18

Contraction NA Included in Abutment Scour in the NCHRP Method Abutment 0 NCHRP Method

Pier 11 Not on the Scour Critical List Total 11

HEC 23 was used to determine riprap sizing and extents at RDB. Using the 500-yr flood event velocity and depths, Class 4 riprap, D50 = 15”, is recommended. Per HEC 22 the riprap extents should be the greater of 25ft or twice the water depth. Abutment riprap is placed. This bridge is not on the Scour Critical List and pier riprap is not required. Appendix C contains more detailed information and calculations for scour and scour countermeasures.

5-7

5.4 Pier Construction Approach and Cofferdams

During construction it is anticipated that 2 cofferdams will be required to construct the piers. This will require placing fill in the channel 5’ beyond the proposed piers. This is needed to create a dry area for constructing piers.

Construction activity will occur from August 15 to October 31st and January 1st to March 31st, during the channel low flow. The low flow discharge was determined using USGS gaged data downstream of this project’s site that provided the median daily statistic for over 75 years averages to be at or less than 2000 cfs.

For construction, it is assumed that both cofferdams are constructed and in place at the same time. The maximum cofferdam height is to be set at 6360 feet. At this height, it is anticipated that the low flow (2000 cfs) will yield the following which results in no impacts to the proposed cofferdams or existing Red Dirt or UPRR Bridge:

1. Cofferdam Freeboard: 2.72 feet prior to overtopping the cofferdams

2. Existing Red Dirt Bridge Freeboard: 14.54 feet prior to impacting the low chord

3. UPRR Bridge Freeboard: 9.05 feet prior to impacting the low chord

As a design check, the 10-yr storm event was used to verify that the constricted channel at the cofferdams could convey the storm without impacting the existing Red Dirt Bridge and the UPRR Bridge. Although the 2 cofferdams convey the 10 year storm event with adequate freeboard at both bridges, the constricted channel would overtop the cofferdams. Table 5-6 provides a cofferdam summary.

Table 5-6. Cofferdam Summary Table

Item Low Flow (Mean Daily) 10 year Flow Rate (cfs) 2000 15360

WSEL at Existing Bridge(ft) 6357.28 6364.52 Provided Cofferdam Freeboard 2.72 Overtops by 4.52 feet

Provided Existing Bridge Freeboard 14.54 7.30 WSEL at UPRR Bridge(ft) 6357.93 6365.29

Provided UPRR Bridge Freeboard 9.05 1.69 Maximum Cofferdam Height (ft) 6360 6360

Existing Bridge Low Chord: 6371.82 UPRR Bridge Low Chord: 6366.98 feet

It is recommended that construction activities:

1. Verify the low flow discharge and modify cofferdam design accordingly.

2. Have no impacts to the UPRR Bridge.

3. Cofferdam type and method of construction to be approved by the engineer prior to construction.

4. Contractor to obtain dewatering permit prior to construction, per the US Environmental Protection Agency

(EPA) Stormwater Pollution Prevention Plan (SWPPP) that has been provided for this project.

See Figure 5-7 for the profile of the stream centerline with obstructions placed at the upstream and downstream section of the proposed improvements and Figure 5-8 for a cross section at the upstream face of the exiting bridge.

5-8

Figure 5-7. Proposed Profile for Cofferdam Construction

Figure 5-8. Cross Section at Upstream Face of Existing Bridge with Cofferdam

RedDirtBridge Plan: ExistCoffer 3/1/2016

Main Channel Distance (ft)

E le va tio n (ft

Legend

WS 10 yr

WS Low Flow

Ground

2.

8.

5.

0.

5.

5.

4.

0.

5.

7.

.4

.8

.6

Colorado River Colorado River

0 100 200 300 400 500

RedDirtBridge Plan : ExistCoffer 3/3/2016 River = Colorado River Reach = Colorado River RS = 675.6418 BR

Station (ft)

E le va tio n (ft

Legend

WS 10 yr

WS Low Flow

Ground

Ineff

Bank Sta

.1 .045 .08

UPRR Bridge Existing Red Dirt Bridge

5-9

5.5 Variances

There are 2 areas where the proposed design does not adhere to criteria and a variance is requested/required:

1. At cross section 575.17, there is a rise in the 0.01 ft rise in the 100 year water surface elevation. This is a negligible difference. Also, in many areas the floodplain has been lowered with the proposed design.

2. At the proposed bridge, there is a concern for ice jams. The design freeboard is 2.65’; however, a minimum of 5’ is required by CFL for ice flows. Should ice jam occur, the UPRR Bridge would jam first Should the ice break free and moves down to RDB, it is anticipated that the ice would be smaller and pass through more easily with the reduce piers.

5.6 Summary

These hydraulic recommendations include reconditioning or adding ditches, adding culverts, riprap, and a bridge replacement.

6-1

USDOT, FHWA, Federal Lands Highway Project Development and Design Manual, January 2014.

USGS, Water Resources Investigations Report 99-4190: Analysis of the Magnitude and Frequency of Floods in Colorado, 2000.

NOAA Atlas 14, Volume 8, Version 2 Online Data Server, Point Precipitation Frequency Estimates, October 2014.

NRCS Online Web Soil Survey, October 2014.

CDOT, Drainage Design Manual, 2004.

USACE, HEC RAS, Version 4.1.0, January 2010

FHWA, HY-8, Version 7.2, January 2012

USGS’s web-based GIS tool, Streamstats, October 2014.

Matrix Design Group, Eagle County: Floodplain Information Report: Eagle River and Colorado River, 2003.

FEMA, Eagle County, Colorado and Incorporated Areas FIS, 2007.

AECOM, Hydrologic and Hydraulic Criteria Computation Methods Memorandum, November 2014.

USDOT, Hydraulic Engineering Circular No. 18: Evaluating Scour at Bridges, Fifth Edition, April 2012.

USDA, Urban Hydrology for Small Watersheds: Technical Release 55 (TR55), June 1986.

AECOM, Categorical Exclusion Memorandum, July 24, 2015.

6 References

Appendix A: References A-1 H&H Criteria and Computation Methods Technical Memorandum

A-2 NOAA Point Precipitation Frequency Estimates

A-3 NRCS Web Soil Survey

A-4 Rainfall Distribution Figure

Memorandum

Project: Red Dirt Bridge CO FLAP 301(1) AECOM Project Number 60332793 Subject: Hydrologic and Hydraulic Criteria and Computational Methods Technical

Memorandum Date: July 15, 2015

1.0 Introductions

The purpose of this Hydrologic and Hydraulic Criteria and Computational Methods Technical Memorandum is to provide a summary of the applicable criteria that will be applied to the proposed improvements to Red Dirt Bridge (RDB), which provides access to the White River National Forest, including the Flat Tops Wilderness, the Bureau of Land Management (BLM) Lands, and the Colorado River.

2.0 Background and Description

The Federal Lands Access Program (FLAP) is providing funding for public highways, roads, bridges, trails and transit systems that are located on, are adjacent to, or provide access to Federal Lands. The scope of work for this project is to perform environmental, engineering, hydraulic, geotechnical, right-of-way, surveying, mapping, and project management services toward delivery of a 100% PS&E for the Federal Highway Administration (FHWA), Central Federal Lands Highway Division (CFL) for proposed improvements to RDB.

This project includes reconstruction of RDB and both bridge approaches. RDB is on the Colorado River Road at approximate milepost 15.6, just north of Dotsero, Colorado in Eagle County (County). The County has completed similar bridge reconstructions downstream (3 Islands Bridge) and upstream (Burns Bridge and Catamount Bridge) across the Colorado River.

RDB is downstream and parallel to a Union Pacific Railroad (UPRR) Bridge.

RDB, was constructed in 1945 and is a 200 ft long (back of face to back of face of abutments), 5 span steel bridge with a 16 ft cross section. The proposed bridge will have longer spans, eliminate piers in the river, and provide two 12 ft lanes, 4 ft wide shoulders with appropriate bridge rails. The overall length of the proposed bridge may change based on the final alignment of the roadway and is anticipated to be longer than the existing bridge.

This project will include coordination with the County and BLM.

3.0 Criteria References

Hydrologic and hydraulic analysis and design work associated with the proposed improvements will be in accordance with the methods, guidelines, and criteria set forth with the following:

Federal Lands Highway Project Development and Design Manual (FLH PDDM) Colorado Department of Transportation (CDOT) Drainage Design Manual kirkbridet Typewriter A1.01

Hydrologic and Hydraulic Criteria and Computational Methods Technical Memorandum Red Dirt Bridge

Per CFL classification, the roads are designated as a High-Standard Road if any of the following criteria are satisfied:

Design Speed > 45 miles per hour (mph) Design Average Daily Traffic (ADT) > 1500 Designated as a “critical access road” Emergency evacuation routes, sole access to community/critical facilities (hospitals, power plants, water supply, wastewater treatment facilities).

Table 3.1: Roadway Classification

Criteria CFL CDOT Functional Classification Rural Local Road Rural Areas Design Speed (miles per hour) 35 35

ADT < 400 < 400

Critical Access Road Designation No No Roadway Classification Low Low

4.0 Hydrology

Roadway hydrology will use the Rational Method as the anticipated contributing drainage areas will be less than 200 acres. For areas greater than 200 acres, regression equations will be used.

The bridge drainage area was calculated using United States Geological Survey (USGS) StreamStats Program, a web-based Geographic Information System (GIS). The contributing drainage area to RDB is 3138 sq mi. Upon completion, the program identified that the project is located with a gaged system and that regression equations are not applicable and other methods for determine peak flows is required.

Downstream of the RDB, near Dotsero, there is a USGS Gaging Station Number 09070500.

Based on the location of this gaging station, two sources were reviewed and compared to determine peak flows at this station:

County’s Floodplain Information Report: Eagle River and Colorado River (Matrix 2003) Federal Emergency Management Agency (FEMA) Flood Insurance Study (FIS), (FEMA

2007)

Using the procedures outline in Water Resources Investigation Report (WRIR) 99-4190 (USGS 2000), peak flows for RDB were determined and are summarized in Table 4.1 below. This procedure uses the ratio of drainage areas for the gaged and project site to determine peak flows at the project site. Both sites must be located on the same stream. More details are found in the Appendix.

kirkbridet

A1.02

Table 4.1: Bridge Peak Flows Storm Event Peak Flows at

Station 09070500 2003 Report

(cfs)

Peak Flows at Station 09070500

2007 FIRM

(cfs)

Peak Flows at RDB

(cfs)

10-yr 16400 18950 15360 50-yr 21600 24900 20180

100-yr 23600 27140 21990 500-yr 25500 31830 25790

Drainage Area (sq mi) 4394 4344 3138

Table 4.2 summarizes the storm frequencies to be used for this project. The more stringent criteria typically will be used.

Table 4.2: Storm Frequencies Drainage Classification Frequency

Roadway Classification Low Cross Drainage: Culverts 25 yr Roadside Ditches Conveyance: 10 yr

Permanent Linings: 10 yr Temporary Linings: 2 yr

Pavement Drainage On-grade: 10 yr Sumps: 50 yr

Minimum Time of Concentration1

10 min

Bridge Design: 50 yr Check: Greater of overtopping or 100 yr. Not to exceed 500 yr

1 CDOT Criteria

5.0 Hydraulics

The hydraulics for culverts, ditches, bridges, and scour analysis/countermeasures are summarized in Tables 5.1 through 5.4. Storm drainage and pavement drainage is not anticipated for this project. FLH PDDM criteria will be used as it generally proves to be more stringent.

Table 5.1: Ditches

Item Criteria Maximum Flows For Q > 50 cfs, Refer to PDDM River Hydraulics Section 7.4 Depth New Ditch: Depth < Bottom of the Aggregate Base Layer

Existing Ditch: Design < Shoulder Hinge Point

Slope Preferred: 1.0% Minimum: 0.5% for lined or paved ditches

Shear Stress Shear Stress < Permissible Shear Stress

A1.03

Table 5.2: Culvert Criteria Item Criteria

Headwater (HW) Elevation

Existing: Water surface elevation (WSEL) Shoulder Hinge Point New: WSEL Bottom of Aggregate Base Layer

Maximum HW to Depth (HW/D) Ratio

Diameter (D) 48 in, HW/D = 1.5 D > 48 in, HW/D = 1.2 Debris/Sediment Concern: A range of 0.8 to 1.0

Minimum Size Cross Culvert: 24 in All others: 18 in

Slope Preferred: 2% Minimum: 0.5% Minimum Not to exceed 10% for concrete and 25% for metal pipes

Cover Refer to FLH Standard Drawings: 602-1, 602-5, 602-7

Pipe Material Reinforced Concrete Pipe (RCP) Corrugated Metal Pipe (CMP)

Entrance and Outlet Treatments

Diameter 48 in, Flared End Section (FES) Diameter > 48 in, Headwalls and Wingwalls

Velocity1 Minimum: 3 fps Maximum: 16 fps

Table 5.3: Bridges

Item Criteria Freeboard High Debris1: 4 ft

Low Debris1: = 0.1Q 0.3 + 0.008V2

If V > 16fp, then bridge must be widened1

Refer to Figure 5.1 and 5.2 for more consideration

Minimum: 2 ft Wood Debris: 3.5 to 5 ft Ice Flows: 5 to 10 ft

Scour Abutments: 500 yr Foundation: 500 yr Roadway Overtopping: minimum 100 yr

A1.04

Figure 5.1: Freeboard for Bridges with Crest Vertical Curve

Figure 5.2: Freeboard for Bridges on Continuous Grade

Figures from CDOT’s Drainage Design Manual, Chapter 10 (10-9)

Table 5.4: Scour Countermeasures Analysis: Using HEC-RAS, Hydraulic Toolbox

Item Criteria General Scour: Aggradation and Degradation

HEC-RAS or Hydraulic Toolbox 4.2

Lateral Channel Movement Not considered:

Contraction Scour Clear-Water or Live-bed Local Scour: Pier HEC 18 Local Scour: Abutment NCHRP Project 24-20 Method: Use Hydraulic Toolbox 4.2

A1.05

6.0 Erosion Control Measures

Erosion control measures will be used during and post construction activities in the form of silt fence, sediment control fiber rolls, check dams, riprap, riprap rundowns, seeding, and mulching.

Energy dissipation will adhere to HEC-14.

7.0 Summary

The information contained in this memorandum is only a summary of the applicable criteria. All criteria will be reviewed and adhere to by the project engineer. Any changes to the design/planning criteria will be noted in future memorandums.

8.0 References

USDOT, FHWA, Federal Lands Highway Project Development and Design Manual, January 2014.

USGS, Water Resources Investigations Report 99-4190: Analysis of the Magnitude and Frequency of Floods in Colorado, 2000.

NOAA Atlas 14, Volume 8, Version 2 Online Data Server, Point Precipitation Frequency Estimates, October 2014.

NRCS Online Web Soil Survey, October 2014.

CDOT, Drainage Design Manual, 2004.

USGS’s web-based GIS tool, Streamstats, October 2014.

Matrix Design Group, Eagle County: Floodplain Information Report: Eagle River and Colorado River, 2003.

FEMA, Eagle County, Colorado and Incorporated Areas FIS, 2007.

FHWA, Hydraulic Toolbox 4.2, August 2014.

USDOT, Hydraulic Engineering Circular No. 18: Evaluating Scour at Bridges, Fifth Edition, April 2012.

kirkbridet

A1.06

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 99–4190

Analysis of the Magnitude and Frequency of Floods in Colorado

By J.E. Vaill

Denver, Colorado

Prepared in cooperation with the

COLORADO DEPARTMENT OF TRANSPORTATION

and the BUREAU OF LAND MANAGEMENT kirkbridet

A1.07

10 Analysis of the Magnitude and Frequency of Floods in Colorado interval of interest is selected, a weighted estimate of the peak discharge can be computed for a site using the regression equation for the appropriate region and the peak-discharge value from the ood-frequency curve.

Weighted estimates are used for unregulated streams to reduce the time-sampling error that may occur in a station ood-frequency estimate. This time-sampling error is associated with the length of record for a gaging station. A station with a short period of record may have a large time-sampling error because its record may not be representative of the actual ood history of the site based on a large number of years.

The observed period of record has the possibility of falling within a wet or dry climatic cycle. The weighted estimate of ood frequency should be a better indicator of the true value because the regres-sion estimate is an average of the ood histories of many gaging stations over a long period of time (Thomas and Lindskov, 1983).

Sites near Gaging Stations on the Same Stream

Peak discharges for sites near gaging stations on the same stream can be estimated by using a ratio of drainage area for the sites near the ungaged sites and the gaged sites. This method is considered to be reli-able when the drainage-area ratio is between about

0.5 and 1.5 and when the two sites have similar drainage-basin and climatic characteristics. If the sites of interest have similar basin and climatic characteris-tics and meet the drainage-area-ratio requirement, peak discharges can be computed by the following equation:

(3) where QT(u) is the peak discharge, in cubic feet per second, at the ungaged site for T-year recurrence interval;

QT(g) is the weighted peak discharge, in cubic feet per second, at the gaged site for T-year recurrence interval;

Au is the drainage area, in square miles, at the ungaged site;

Ag is the drainage area, in square miles, at the gaged site; and x is the average exponent for drainage area for each ood region as follows:

The following is an example calculation to determine the 100-year peak discharge for an ungaged site near a gaged site on the same stream in the moun-tain region. The drainage area at the ungaged site is given as 350 mi2 and at the gaged site is 450 mi2. The weighted discharge for the 100-year peak at the gaged site is given as 11,500 ft3/s.

1. Check that the drainage area ratio Au/Ag is between

0.5 and 1.5. That ratio is as follows:

which meets the ratio requirement.

2. Compute the discharge at the ungaged site using the speci ed values in equation 3:

ft3/s.

Ungaged Sites

Peak discharges at ungaged sites can be computed using the appropriate regional equation shown in table 1. For sites on streams that cross regional boundaries, results from more than one of the regional equations need to be weighted as described below.

Table 2. Basin characteristics and the range of values used in the analysis

Basin characteristics Range of values Drainage-basin area, in square miles 5.5 to 988.0 Mean annual precipitation, in inches 7.0 to 49.0 Mean drainage-basin elevation, in feet 2.805 to 12,200 Mean drainage-basin slope, in foot per foot 0.081 to 0.562

QT u QT g Au Ag x,=

Flood region Exponent Mountains 0.69 Rio Grande 0.88 Southwest 0.71 Northwest 0.64 Plains 0.40

Au Ag 350 450 0.78= =

Q100 u 11 500 350 450 0.69 9 670= = kirkbridet

A1.08

Ea gl e an d C ol or ad o

Ri ve rs

Fl oo dp la in In fo rm at io n Re po rt

Ea gl e Co un ty

, C ol or ad o

Pa ge

A ug us t 2

2, SE

C

T

IO

N

FL

O O

D H

IS

TO

R Y

Th er e is n ot a lo ng h is to ry o f s tre am g ag e re co rd s on th e Ea gl e

Ri ve r.

Th e ga ge o n th e Ea gl e

R iv er w ith th e lo ng es t p er io d of re co rd is lo ca te d ou tsi de th is st ud y ar ea

. T he

E ag le R iv er a t R ed cl iff g ag e is lo ca te d up st re am fr om th is fl oo dp la in s tu dy a re a as h as ye ar s of re co rd

. T he p ea k flo od o f r ec or d oc cu rre d in

. T he

E ag le R iv er b el ow G yp su m g ag e ha s t he n ex t l on ge st p er io d of re co rd a nd a s be en in e xi st en ce si nc e

. T hi s ga ge h as a d ra in ag e ba si n of s qu ar e m ile s.

Th e U

SG

S ga ge re co rd s do n ot s ho a si gn ifi ca nt f lo od d ur in g th is pe rio d of r ec or d.

H ow ev er

, h ig h flo w s oc cu rr ed o n th e

Ea gl e Ri ve r in th e ye ar s 1

2, 7, 3, 4, 5, an d

3.

G ag e R ec or ds

Th er e ar e fiv e ac tiv e

U

SG

S ga ge s lo ca te d on t he m ai n ste m o f th e

Ea gl e R iv er a nd th e po rti on o f th e C ol or ad o

Ri ve r in th is s tu dy a re a.

Tw o ot he r ga ge s ha ve e xi ste d in th e pa st, b ut a re n o lo ng er a ct iv e, al ou gh re co rd s f ro m th at g ag es a re u se fu l i n sta tis tic al g ag e an al ys is

Th e ga ge s ar e lis te d in o rd er fr om up st re am to d ow ns tre am

T A

B

LE

U

SG

S G

A G

IN

G

S T

A T

IO

N

S

St at io n

N um be r

St at io n

N am e D ra in ag e

A re a (s q.

m i.)

G ag e E le va tio n

(f ee t)

Pe ri od o f R ec or d St at us

Pe ak

D is ch ar ge

(c fs e R iv er a t R ed cl iff

-1

-p re se nt ct iv e 1, e

R iv er n ea r M in tu rn

-p re iv e

1, e Ri ve r a t A vo n

-1

In ac tiv e 3, e

Ri ve r W W

TP

a t A vo n

-p re iv e 3, e

Ri ve r a t E ag le

-1

In ac tiv e 6, e

Ri ve r b el ow G yp su

-p re iv e

7, Co lo ra do

R iv er n ea r D ot ro

-p re iv e

,2

3.

F lo od P ro te ct io n M ea su re s

H om es ta ke R es er vo ir da m c on st ru ct ed o n

H om es ta ke C re ek i n f or w at er d iv er si on t o

C ol or ad o Sp rin gs a nd

A ur or a ha s ac te d to in ad ve rte nt ly re du ce th e pe ak fl oo d di sc ha rg es o n th e lo w er

E ag le R iv er

Th e da m w as n ot c on str uc te d fo r f lo od c on tro l, bu t a ct s to fi ll du rin g th e sp rin g ru no ff a nd h as re du ce d pe ak fl oo di ng o n th e Ea gl e

R iv er

Ea gl e an d C ol or ad o

Ri ve rs

Fl oo dp la in In fo…