Hydraulic_Design_Memo_Cowlitz_Valley_Road_Repairs.pdf

Cowlitz Valley Road Repairs

WA FS ERFO 2016(1)-22(1)

Hydraulic Design Memorandum

Federal Highway Administration Western Federal Lands Highway Division

Project Number: 60519512

January 25, 2017

Hydraulic Design Memorandum

Prepared for: Federal Highway Administration - Western Federal Lands Highway Division AECOM

Quality information

Prepared by Checked by

Stephen Blanton T. Gut

Revision History

Revision Revision date Details Authorized Name Position

Distribution List

Susan Ellis, FHWA

Project File

Prepared for:

Western Federal Lands Highway Division 610 East Fifth Street Vancouver, WA 98661-3801

Prepared by:

Stephen Blanton

AECOM

1111 Third Avenue Suite 1600 Seattle WA, 98101 aecom.com

Table of Contents

1. Introduction

2. Project Description

3. Base Data and Sources

4. Analytical Approaches, Methods, and Results

5. Final Design Recommendations

6. Supporting Information

Figures Table 1. GPNF Identified Sites Table 2. Peak Flows for GPNF ERFO Culvert Crossings Table 3. HY-8 Hydraulic Capacity Results for the GPNF Sites Table 4. Channel Geometry for East Canyon Creek at Site 23-23.6

Tables Figure 1. Preliminary HEC-RAS Modeled Flow Velocities Figure 2. Site Location Map

Prepared for: Federal Highway Administration - Western Federal Lands Highway Division

AECOM

5/23

1. Introduction A large storm event in the December 2015 resulted in the high stream flows and multiple landslides within the Gifford Pinchot National Forest (GPNF). Inadequate culvert capacity and culverts blocked by accumulated rocks and debris cause roads to be overtopped resulting in many road failures. High flows in the Cispus River and East Canyon Creek resulted in large sections of Forest Road 23 being eroded away.

This Hydraulics Design Memorandum is intended to support the final design of the selected alternative at each of the project sites and to fully document, to a level commensurate with project complexity and risk, the following:

• Project description

• Base data and sources

• Analytical approaches, methods, and results

• Design approaches and methods

• Final design recommendations

• Supporting information

The information provided in this report details the findings at the Gifford Pinchot National Forest Emergency Relief for Federally Owned Roads Program (ERFO) project sites related to issues associated with hydrologic or hydraulic conditions. In support of this effort, a three-day site reconnaissance was conducted from September 26, 2016 – September 28, 2016. The Hydraulic Reconnaissance Report based on that visit is attached.

2. Project Description The GPNF ERFO project consists of 12 sites. The sites can be categorized as; culverts, bridges and road failures. The issues associated with each of the sites are the result of a large rainfall event in December 2015 that caused high flows in streams and rivers and also initiated multiple landslides and debris flows.

The damage included multiple culverts failures where debris flows blocked the inlet of the culverts forcing flows over the road. The erosive force of the flows on the unprotected downstream face of the road-fill washed away the roads at the crossing locations. The abutments of two bridges experienced support material erosion that may limit the load capacity of the bridges. Also two sections of the Road 23 were eroded away by the channel migration of the Cispus River and East Canyon Creek. The project sites are listed in Table 1 and a location map (Figure 1) is provided in the Supporting Information section.

6/23

Table 1. GPNF Identified Sites

Site ID Structure Type Description of Issues Hydraulic Recommended Fix

25-25 Slope Failure

• Appears debris accumulation in the ditch forced flow onto the road surface and then onto the outer edge of the road, discharging onto the unprotected slope.

• Existing culvert appears adequately sized and undamaged.

The DSR did not suggest a fix based on the drainage conditions at the site. During the site reconnaissance it was determined to add a new culvert at the upgradient end of the site to convey ditch flows safely to the toe of the slope. A second new culvert is suggested downgradient of the existing culvert to provide for redundancy in case of culvert plugging.

Proposed culverts will be the same diameter as the existing culvert. No hydrologic-hydraulic analysis is required for this site. Periodic removal of accumulated debris from the ditch is recommended

88-19.7 Culvert

• Site evidence suggests a piping failure. There is no evidence impaired culvert capacity forced flow over the road. The culvert may have been damaged within the road fill area or water at the inlet seeped in between the pipe and the fill.

• Debris accumulation at the inlet did not appear to be a factor.

The DSR recommends replacing the downstream end section of the existing culvert. No other modifications to the culvert are suggested or required. If future site investigation finds evidence suggesting a piping failure due to seepage at the inlet then “seepage rings” may be recommended. No hydrologic-hydraulic analysis is required for this site.

90-28.0 Culvert

• Roads section has sunk likely due to high moisture content in the subgrade.

• Existing culvert appears to be damaged one segment in.

No new surface hydraulic structures requiring hydraulic analyses are recommended for this site.

Replacement of the damage inlet section is recommended but may not be required. The geotechnical engineer has suggested sub-surface drains on the upgradient side of the road to reduce

7/23 moisture content of the road sub-grade.

29-7.60 Culvert

• This site is on Camp Creek.

• A debris slide from the upper valley blocked the culvert inlet and sent flow over the road, which then eroded and failed.

• Stream is already developing a new channel through the reach.

• Accumulated woody debris needs to be removed.

Replace the 72 inch culvert with a 90 inch culvert. The road profile will be design to provide a low point at the culvert. This will contain potential future flows resulting from similar debris flows to a confined section of road. The downstream face of the road fill will be hardened to provide erosion protection if future, similar debris flows occur. The downstream channel will not require channel protection as the stream channel appears to be at bedrock. Existing debris flow material including the logs need to be removed. Due the existing mining claim upstream of the crossing, no upstream debris protection is proposed.

23-18.0 Culvert

• The site has two culverts. It is not known if both conveyed flow prior to the December 2015 flow event.

• Debris slide block culvert inlet.

• Road was overtopped and eroded the downstream face.

The DSR recommends the removal of the existing 48 inch and 36 inch culverts and replace with a single 66 inch culvert. The single larger culvert will provide required conveyance capacity and also increase the capacity to convey sediment. It is recommended to use available woody debris to construct debris racks immediately upstream of the inlet. The woody debris can be positioned with the root wads in an upstream direction to slow flow velocities and create a deposition zone upstream of the culvert inlet. The channel downstream of the culvert location is currently stable. No downstream scour protection is required.

23-22.3 Culvert • Debris slide damaged inlet of culvert, reducing the conveyance capacity.

The DSR recommends replacing the damaged 72 inch inlet culvert section. The channel downstream

8/23

• Road was overtopped and eroded the downstream face.

appears to be stable and no outlet protection is needed. Removal of accumulated material upstream of the culvert is suggested. No hydrologic-hydraulic analysis is required for this site.

23-23.4 Culvert

• Debris flow blocked culvert inlet and cause water to overtop the road.

• A portion of the road was damaged.

Remove the two existing culverts and replace with an open-top box culvert with a metal grate lid. The proposed road profile will include a lowered section at the culvert location with concrete slope protection on the downstream face. If the culvert is blocked, overtopping flows will be confined to the lowered road sections and concrete slope protection. The downstream channel is stable so no outlet protection is required. The proposed open box culvert will provide for greater capacity to convey sediment and debris during high flow event. The open top aspect will allow for easier maintenance access and removal of large material

23-23.5 Bridge

• Bridge with erosion under gabion footing issue.

• Large log is wedged under the bridge. Log may have been placed to deflect high flows.

Geotechnical approaches will be used to fix this site.

No hydrologic-hydraulic analysis is required for this site. It is proposed to leave the large log in place.

2324-0.1 Culvert

• Debris flow blocked culvert inlet, road overtopped and eroded.

• This site is immediately upstream of site 23-23.4.

Remove existing culvert and replace at the same location with an open-top box culvert with a metal grate lid. The proposed road profile will include a lowered section at the culvert location with concrete slope protection on the downstream face. If the culvert is blocked, overtopping flows will be confined to the lowered road sections and concrete slope protection. The downstream channel is stable so no outlet protection is required.

9/23

2322-0.2 Bridge

• Bridge with eroded gravel foundation at the abutment.

• A log is lodged in the narrow canyon trapping bed material and raising the water level in the stream reach upstream of the bridge.

Geotechnical approaches will be used to fix this site.

No hydrologic-hydraulic analysis is required for this site. It is recommended that the existing log blocking the upstream end of the channel be removed. The material trapped upstream of the log should be removed or flushed downstream to restore channel conveyance capacity.

23-23.6 Road Lost to bank erosion

• Channel migration eroded the road.

• An existing large log may have initiated localized flow conditions resulting the road failure.

• Stream appears to be stable both upstream and downstream of the site.

The stream will be re-established into the historic channel. The historic floodplain terrace will be restored and planted. Log vanes will be incorporated into the restored road alignment project to direct the high flow stream energy towards the re-established channel. The terrain restricts the potential to realign the road farther away from the stream. The realigned road would still require stream bank protection and floodplain restoration. A deflector woody debris structure will be established at the upstream end of the site and the large log currently found at the site will be moved and reused as part of the floodplain restoration.

23-12.6

Large section of road lost to bank erosion

• The Cispus River channel migrated and eroded the existing road.

• Lots of existing woody debris in the area.

• River reach is very active.

• Previous road washout about 1 mile downstream

(~1996) was successfully repaired and incorporated ELJs.

Woody material will be used to construct three log structures as part of the proposed re-establishment of the road alignment. The log structures will incorporate large rock and logs from the adjacent gravel bars. Similar structures have been incorporated to mitigate for past road erosion downstream of this site along the Cispus River.

10/23

3. Base Data and Sources The designs related to the GPNF site are based on limited existing data. No survey data is available for any of the sites so all analyses supporting the designs use field sketches, hand measurements, and publicly available data sets related to topography. Following is a list of the data used in the design efforts:

• The WFL provided a Damage Survey Report for each of the sites collected after the damaging flood event. The reports contain site photos, hand sketches with field measurements, and suggested repairs.

• Topographic data was limited to 2009 LiDAR for only the 23-12.6 site along the Cispus River.

The LiDAR data was provided by the Puget Sound LiDAR Consortium. USGS topography was used to supplement missing data at all the other sites.

http://pugetsoundlidar.ess.washington.edu/

• Flow data for each site is based on the appropriate regional regression equations that are available through the USGS StreamStat webpage. This GIS interface allows the user to locate the point of the interest, delineate the drainage area and then estimate flows for various return intervals. http://streamstatsags.cr.usgs.gov/v3_beta/viewer.htm?stabbr=WA

Due to the isolated nature of the GPNF sites and limited likelihood that future site failures will cause damage to people or property the limited detail of the data is adequate for the majority of the culverts designs.

The design at the two road washout sites would benefit from additional site specific survey. The Cispus River site (23-12.6) requires a scour analysis to determine the required depth of stream bank protection and the stability of the placed wood structures. River cross sections of the active channel can be incorporated into the LiDAR to create a detailed model of the site capable of assessing scour depth and shear stress.

4. Analytical Approaches, Methods, and Results The culverts and road repair sites required different design approaches. The culverts required solely a hydraulic analysis of the culvert to determine the required size to meet the conveyance capacity design storm and the headwater depth to diameter ratio. Based on the project USFS Decision Memo dated June 28, 2016 none of the culvert sites are located on fish bearing stream and will not require fish passage or instream restoration mitigation measures. For the two road repair sites the analysis required a hydraulic analysis as well as a geomorphic approach to restoring the stream bank and provide for woody placement.

The design criteria used for the GPNF projects are taken from Exhibit 7.1-A QUICK REFERENCE GUIDE from the PDDM. The exhibit provides guidance for all typical projects. The pertinent elements are presented below:

The hydraulic analysis for the culverts was carried out using regional regression equation to estimate the design flows required for the culverts The Design Flood is based on roadway classifications: High-Standard and Low-Standard. The design flood associated with each classification is provided:

• High-Standard: roadway culverts will be stable for the 50-year flood.

• Low-Standard: roadway culverts will be stable for the 25-year flood.

http://pugetsoundlidar.ess.washington.edu/ http://streamstatsags.cr.usgs.gov/v3_beta/viewer.htm?stabbr=WA

11/23

For the GPNF it is assumed each of the locations is associated with a High Standard road.

Although the design standards suggest using the 50-year flood, the WFL decided to use the 100-year flood, in order to be conservative in the conveyance capacity and potentially provide additional flow area for passing sediment/debris flows. For Site 88-19.7, there is no field evidence of sediment/debris flows so the 50-year flood was used for this site.

The USGS StreamStat website was used to verify the WFL estimated design flows provided in the DSRs. The website provides a GIS interface for the regional regression equations appropriate for the site. Table 2 contains the StreamStat generated estimated flows at each culvert site. The DSRs for sites 88-19.7 and 23-22.3 did not include flows estimates for comparison. The StreamStat results for the remaining culvert sites resulted in similar flow results. As the regional regression equations in StreamStat are based on selected basin area, if the estimated selected basin are not identical in size to the DSR basin size then the results will differ. This occurred for site 2324-0.1 where the DSR basin was selected to be 0.01 mi2 larger. At that the larger of the two flows was selected. Additional information related to the StreamStat effort is included in the Supporting Information section of this report.

Table 2. Peak Flows for GPNF ERFO Culvert Crossings.

Site ID Drainage

Area, mi2

Estimated Recurrence Interval Peak Flows, cfs

2-Year 10-Year 25-Year 50-Year 100-Year 500-Year

88 - 19.7 0.17 18.9 34.1 42.4 49.61 56.6 75

23 - 18.0 Twin Creek

0.59 48 85 105 121 137 179

29 - 7.60 Camp Creek

0.73 61 108 133 154 175 229

23 - 22.3 0.64 57 102 126 147 167 220

23 -23.4 0.86 78 139 172 201 229 302

2324 - 0.1 0.86 78 139 172 201 229 302

Note 1. Flow Rates used in the culvert analysis are shown in bold.

Using the appropriate design flows in Table 2, a hydraulic analysis of the proposed culverts at each of the project sites was conducted using the FHWA program HY-8. The HY-8 program requires culvert geometry as well as upstream and downstream channel condition to estimate how the design flow is conveyed through the culvert. The program calculates the water surface depth at the inlet, referred to as the Headwater Depth, as well the flow rate required to overtop the road. For culvert analyses, the FHWA provides design criteria related to the Headwater Depth

12/23 to Diameter Ratio (HW/D Ratio). The criteria are based on culvert size and debris blockage potential.

• Less than or equal to 48” [1200 mm] equivalent and smaller culverts: Limit ratio to 1.5

• Larger than 48” [1200 mm] equivalent culverts: Limit ratio to 1.2.

• Debris or Sediment: A ratio range of 0.8 to 1.0, depending on severity, is suggested where the potential for heavy debris or sediment bed loads are a concern.

For the GPNF project sites all sites where culverts are being replaced will assume a debris and sediment load and therefore will use the HW/D ratio of 0.8-1.0. Table 3 provides the results of the HY-8 analysis for each of the proposed culverts. The analyses are based on the proposed culvert geometry presented in the DSRs.

Table 3. HY-8 Hydraulic Capacity Results for the GPNF Sites

Site ID

Design Flows, cfs Culvert Diameter, ft HW/D Ratio Overtopping

Flows, cfs 88-19.7 49.6 (50Yr) 2.5 2.8 77.9

23-18.0 121 (50Yr) 137 (100Yr) 5.5 0.76

0.84 342

29-7.60 154 (50Yr) 175 (100Yr) 7.5 0.51

0.56 563

23-22.3 147 (50Yr) 167 (100Yr) 6.0 0.94

1.01 425

23-23.4 201 (50Yr) 229 (100Yr)

Open top box

8.5 ft wide

Freeboard: 11.03’ Freeboard: 10.67’ 722

2324-0.1 201 (50Yr) 229 (100Yr)

Open top box

8.5 ft wide

Freeboard 2.12’ Freeboard 1.73’ 359

Based on the HY-8 result it appears the existing culvert at site 88-19.7 exceeds the HW/D ratio limit of 1.5. For the two sites with proposed box culverts, the freeboard reflects the distance between the estimated water surface elevation in the culvert and the assumed top of road.

Outlet Protection –

Based on the condition of the stream channels downstream of each of the culvert project sites it does not appear that the outlets will require energy dissipation to control stream erosion. At each project site, the stream channels downstream of the culverts are stable with no visible signs of erosion or channel incision. It is assumed the proposed culverts will be placed at the grade of the historic channel thalweg so as to not have a drop at the outlet. Although scour protection does not appear to be required, it may be beneficial to place the larger material being removed from the site at the outlet instead of hauling it off.

For the Forest Road 23 site (23-12.6) on the Cispus River, hydraulic modeling using the US Army Corps of Engineers HEC-RAS program was used for the initial assessment of hydraulic conditions at the site. The Forest Road 23 site on E. Canyon Creek (23-23.6) was assessed using regional fluvial geomorphic analysis techniques based on drainage area.

Site 23-12.6

13/23

Using publicly available LiDAR from 2009, a 2D HEC-RAS model of the project reach was developed. The intent of the model was to estimated flow velocities at the project site. The modeling effort was also used to estimate the size of a proposed new river channel to be developed during the dewatering and construction phase of the project. It is important to remember that LiDAR does not penetrate the water surface so the actual river channel geometry is not represented in the HEC-RAS model.. Typically, LiDAR is collected periods of clear skies and this usually corresponds to low flow periods in Pacific Northwest rivers, so it is likely the LiDAR provides a reasonable modeling surface for most locations except for deep pools.

The HEC-RAS model was run with 20,500 cfs (100-year flow), based on the USGS StreamStat regional regression equation. Figure 1, illustrates the HEC-RAS model flow velocity results for the 100-year flow event. The model estimated the flow velocity near the project site to be 6-7 feet per second. The current site conditions are not represented in the 2009 LiDAR data but the model results provide estimated flow velocity and depth values that can be used for the preliminary design of the log structures. For final design related to scour potential at the site it is recommended that actual stream channel survey be conducted and incorporated into the model.

14/23

Figure 1. Preliminary HEC-RAS Modeled Flow Velocities

In Figure 1, the flow areas shown along the southern edge of the modeled area are remnants of the initial conditions in the model.

Site 23-23.6

No LiDAR topographic data is available for this site so developing a hydraulic model of the East Canyon Creek project reach was not feasible at this stage. The channel design at this location is based on the regional hydraulic geometry relationship developed for Pacific Northwest rivers and streams (Castro & Jackson, 2001).

The regional equations are shown in Table 4. The equations are for streams located in the Western Cordillera Eco-Region. Based on the values presented in the table below, the restored stream channel will be designed to be approximately 35 feet wide and 1.5 feet deep.

15/23

Table 4. Channel Geometry for East Canyon Creek at Site 23-23.6

Regression Equation Stream Parameter Result Units

A=0.817Q0.806 57.0 ft2 A=2.94DA0.857 32.8 ft2 Q=17.28DA0.86 194.5 cfs w=3.50Q0.44 35.5 ft w=9.40DA0.42 30.7 ft d=0.20Q0.39 1.56 ft d=0.61DA0.33 1.54 ft v=1.43Q0.17 3.50 fps

Nomenclature:

A Bankfull XS area, ft2 Q Bankfull discharge, cfs w bankfull width, ft d bankfull mean depth, ft v bankfull mean velocity, fps DA Drainage area, mi2

The restored floodplain elevation at this site will be set to match the conditions downstream of the site.

Along with the restored channel and floodplain, additional woods elements including deflector wood jams, vanes and root wads will be incorporated into the site. The intent of the deflector jam is to redirect the energy of the stream toward the historic channel alignment. The vanes and root wads are to provide flow resistance at the road fill interface to limit the likelihood of a stream avulsion resulting in the channel eroding the restored road alignment.

5. Final Design Recommendations For the sites covered in this Hydraulic Design Memorandum, additional survey data would provide for greater certainty in meeting the design criteria. Currently the culvert assessment uses assumed elevations for the culvert inlet, outlet and crown of the road based on WFL hand measurements. In some cases the damage at the existing sites makes it difficult to determine culvert parameters and channel locations. Inlets and outlets for each of the culvert locations will be designed similar to pre-project, in that no headwalls or wing-walls will be used. As the downstream channels appear to be geomorphically stable, outlet scour protection is not required. If available, the placement of existing rock material at the disturbed areas of the outlet may be recommended.

For the two road washout locations additional survey would be beneficial for the re-establishment of the stream channel and floodplain. At site 23-12.6 on the Cispus River, survey will be required to assess the potential scour on the bank protection as well as the proposed mitigation wood structures. The East Canyon Creek site 23-23.6, can be designed without survey, but being able to model the actual channel and floodplain would assist with designing the floodplain roughness elements such a root wads and vanes as well as establishing stable boulder sizes.

16/23

6. Supporting Information

Figure 2. Site Location Map

17/23

USGS StreamStat Results

88 – MP 19.7

Study Area: Washington NAD 1983 Latitude: 46.1882 ( 46 11 17) NAD 1983 Longitude: -121.6875 (-121 41 15)

Peak-Flow Basin Characteristics

100% Region 3 (0.17 mi2)

Parameter Value Regression Equation Valid Range

Min Max Drainage Area (square miles) 0.17 (below min value 0.36) 0.36 2198

Mean Annual Precipitation (inches) 99.9 42 132

Peak-Flow Statistics

Statistic Value Unit Prediction Error (percent) Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 18.9 cfs PK10 34.1 cfs PK25 42.4 cfs PK50 49.6 cfs PK100 56.6 cfs PK500 75 cfs

18/23

23 – MP 18 ----Twin Creek Study Area: Washington NAD 1983 Latitude: 46.3744 ( 46 22 28) NAD 1983 Longitude: -121.7262 (-121 43 35)

Peak-Flow Basin Characteristics

100% Region 3 (0.59 mi2)

Parameter Value Regression Equation Valid Range

Min Max Drainage Area (square miles) 0.59 0.36 2198 Mean Annual Precipitation (inches) 85.4 42 132

Peak-Flow Statistics

Statistic Value Unit Prediction Error (percent)

Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 48 cfs 57 1 PK10 84.8 cfs 55 1 PK25 105 cfs 54 2 PK50 121 cfs 54 2 PK100 137 cfs 55 3 PK500 179 cfs

29 – MP 7.60 Camp Creek

19/23

NAD 1983 Latitude: 46.3622 ( 46 21 44) NAD 1983 Longitude: -121.7996 (-121 47 59)

Peak-Flow Basin Characteristics

100% Region 3 (0.73 mi2)

Parameter Value Regression Equation Valid Range

Min Max Drainage Area (square miles) 0.73 0.36 2198 Mean Annual Precipitation (inches) 89.4 42 132

(percent)

Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 60.6 cfs 57 1 PK10 108 cfs 55 1 PK25 133 cfs 54 2 PK50 154 cfs 54 2 PK100 175 cfs 55 3 PK500 229 cfs

23 – MP 22.3 Watershed based on aerial photography

20/23

NAD 1983 Latitude: 46.3318 ( 46 19 54) NAD 1983 Longitude: -121.7201 (-121 43 13)

Peak-Flow Basin Characteristics

100% Region 3 (0.64 mi2)

Parameter Value Regression Equation Valid Range

Min Max Drainage Area (square miles) 0.64 0.36 2198 Mean Annual Precipitation (inches) 94.5 42 132

(percent)

Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 57.2 cfs 57 1 PK10 102 cfs 55 1 PK25 126 cfs 54 2 PK50 147 cfs 54 2 PK100 167 cfs 55 3 PK500 220 cfs

23 – MP 23.4

NAD 1983 Latitude: 46.3159 ( 46 18 57)

21/23

NAD 1983 Longitude: -121.7323 (-121 43 57)

Peak-Flow Basin Characteristics

100% Region 3 (0.86 mi2)

Parameter Value Regression Equation Valid Range

Min Max Drainage Area (square miles) 0.86 0.36 2198 Mean Annual Precipitation (inches) 98.8 42 132

Peak-Flow Statistics

Statistic Value Unit Prediction Error (percent)

Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 77.5 cfs 57 1 PK10 139 cfs 55 1 PK25 172 cfs 54 2 PK50 201 cfs 54 2 PK100 229 cfs 55 3 PK500 302 cfs

2324 – MP 0.1

NAD 1983 Latitude: 46.3161 ( 46 18 58) NAD 1983 Longitude: -121.7332 (-121 44 00)

22/23

Peak-Flow Basin Characteristics

100% Region 3 (0.85 mi2)

Parameter Value Regression Equation Valid Range

Min Max

Drainage Area (square miles) 0.85 0.36 2198 Mean Annual Precipitation (inches) 98.8 42 132

Peak-Flow Statistics

Statistic Value Unit Prediction Error (percent)

Equivalent years of record

90-Percent Prediction Interval

Min Max PK2 76.7 cfs 57 1 PK10 138 cfs 55 1 PK25 171 cfs 54 2 PK50 199 cfs 54 2 PK100 227 cfs 55 3 PK500 299 cfs

WA FS ERFO 2016(1)-22(1)

Hydraulic Reconnaissance Report

Western Federal Lands Highway Division

Project Number: 60519512

October 14, 2016

Quality information

Prepared by Checked by

Stephen Blanton T. Gut

Revision History

Revision Revision date Details Authorized Name Position

Distribution List

Susan Ellis, FWHA

Project File

Prepared for:

Western Federal Lands Highway Division 610 East Fifth Street Vancouver, WA 98661-3801

Prepared by:

Stephen Blanton

AECOM

1111 Third Avenue Suite 1600 Seattle

WA, 98101

USA

Table of Contents

1. Introduction

2. Data Collection

3. Needed Hydrologic and Hydraulic Analysis

4. Design Considerations of Baseline Hydraulic Conditions Appendix A FHWA Damage Survey Reports Appendix B Site Photos

Tables

• Table 1. GPNF Identified Sites

• Table 2. Required Hydrologic and Hydraulic Approaches for GPNF Sites

• Table 3. Design Considerations for the GPNF Sites

1/133

1. Introduction Large storms events in the January 2016 resulted in the high stream flows and multiple landslides. Inadequate culvert capacity and culverts blocked by accumulated rocks and debris cause roads to be overtopped resulting in many road failures. High flows in the Cispus River and East Canyon Creek resulted in large sections of Forest Road 23 being eroded away and damage to two bridges.

This Hydraulics Reconnaissance report is intended to summarize the following hydrologic/ hydraulic tasks associated with the site inspection of the project sites:

• Data collection

• Needed hydrologic and hydraulic analyses

• Definition of baseline hydraulic conditions

The information provided in this report details findings at the Gifford Pinchot National Forest (GPNF) ERFO project sites related to issues associated with hydrologic or hydraulic conditions. A three-day site reconnaissance was conducted from September 26, 2016 – September 28, 2016.

Prior to the site visit, WFL staff had conducted field investigations and prepared Damage Survey Reports (Appendix A) providing additional information related dimension of existing structures, photos, and initial proposed mitigation improvements.

2. Data Collection The following table lists the visited project sites and includes a description of the existing site conditions and potential design issues. Site photos are provided in Appendix B

• Table 1. GPNF Identified Sites

Site ID Structure Type Description of Issues

25-25 Slope Failure Appears debris accumulation in the ditch forced flow onto the road surface and the other edge.

Existing culvert is likely adequately sized.

88-19.7 Culvert

Site evidence suggests a piping failure. The culvert may have been damaged within the road fill area or water at the inlet seeped in between the pipe and the fill.

Debris accumulation at the inlet did not appear to be a factor.

90-28.0 Culvert Roads section has sunk.

Existing culvert appears to be damaged one segment in.

29-7.60 Culvert Debris slide from the upper valley blocked the culvert and sent flow over the road, which then failed Log debris needs to be removed.

23-18.0 Culvert Debris slide block culvert inlet.

Road was overtopped and eroded the downstream face.

23-22.3 Culvert Debris slide damaged inlet of culvert, reducing the

2/133 conveyance capacity.

23-23.4 Culvert Debris flow blocked culvert inlet and cause water to overtop the road.

Road was damaged

23-23.5 Bridge Bridge with erosion under gabion footing issue.

Large log is wedged under the bridge.

2324-0.1 Culvert Debris flow blocked culvert inlet, road overtopped and eroded.

This site is immediately upstream of site 23-23.4.

2322-0.2 Bridge

Bridge with eroded gravel at the abutment.

A log is lodged in the narrow canyon grapping bed material and raising the water level in the stream reach upstream of the bridge.

23-23.6 Road Lost to bank erosion

Channel migration eroded the road.

Stream appears to be stable both upstream and downstream of the site.

23-12.6 Large section of road lost to bank erosion

The Cispus River channel migrated and eroded the existing road.

Lots of existing woody debris in the area.

River reach is very active.

Previous road washout about 1 mile downstream (~1996) was successfully repaired and incorporated ELJs.

At each of the failed culvert sites the field evidence suggests a debris flow of large cobbles, boulders, and woody material. It is likely the accumulation of the debris at the culvert inlet restricted the conveyance capacity and sent flows over the road crest. The flows then eroded the downstream face of road fill and the erosion cut back upstream through the road fill.

Accumulated material in the stream channels and adjacent to the failed culverts indicate material ranged in size from sand/gravel to large cobble with diameters greater than 1.5 feet.

The NF Road 23 wash out location on East Canyon Creek appears to be related to the accumulated woody material redirecting the stream flow. The stream energy eroded the existing vegetated floodplain terrace and the adjacent road fill. East Canyon Creek upstream and downstream of the site are in stable condition meaning the issues that created to the erosion are localized. With the reach boulder approximately 2-feet in diameter represent the D90 and the D50 is appears to be approximately 2-inches.

The NF Road 23 washout on the Cispus River is related to natural channel migration. The reach of the lower Cispus River at the project site is very dynamic. Field evidence related to vegetation growth suggests the river has occupied multiple channels over recent year. The lateral progression of the channel erosion has been restricted by the bedrock projection about mid way through the site. A similar road washout occurred downstream of the current site during a flood event in the late 1990s. The early site was mitigated using engineered logs jams. Currently the river has moved away for the log jams with the main channel more than 500-feet away.

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3. Needed Hydrologic and Hydraulic Analysis Based on the site findings and discussions in the field, the hydrologic and hydraulics needs for each site was assessed. Table 2 lists the data that will be required to be developed to complete the design for each site.

Estimate Design Flows – This activity requires the estimation of the anticipated flows to be used in determining the size of the culvert or channel geometry. The flows will be estimated using the appropriate regional regression equations for the sites. The USGS StreamStat webpage provides a GIS based process for delineating tributary areas and estimating flows.

Culvert Sizing – the Federal Highways program HY-8 will be used to determine the necessary culverts dimensions based on the design flows. The hydraulic characteristics of the culverts will be based on existing project sheets and field measurements. During design the need for additional inlet and outlet protection will be determined based on anticipated channel response to the new hydraulic character of the road crossing. The design of the protection will be based on FHWA Hydraulic Engineering Circulars.

Channel Hydraulics – If topographic data is available, a hydraulic model of the project reach will be developed to estimated flow depths and velocity. The results will provide information related to sizing channels, stability of in-stream structures, and depth of required protection. If no topographic data is available, then channel hydraulic analysis will focus on using regional hydraulic geometry relationships for Pacific Northwest rivers and streams.

• Table 2. Required Hydrologic and Hydraulic Approaches for GPNF Sites

Site ID Hydrologic Analysis Hydraulic Analysis

Estimate Design Flows Culvert Sizing Channel Hydraulics

25-25 • •

88-19.7 • •

90-28.0 No Anticipated H&H Analysis Required

29-7.60 • •

23-18.0 • •

23-22.3 No Anticipated H&H Analysis Required

23-23.4 • •

23-23.5 No Anticipated H&H Analysis Required

2324-0.1 • •

2322-0.2 No Anticipated H&H Analysis Required

23-23.6 • •

23-12.6 • •

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4. Design Considerations of Baseline Hydraulic Conditions Based on the information available from previous WFLHD site data gathering and the three-day site reconnaissance a design approach was developed for each of the GPNF sites. Table 3 contains the hydrologic and hydraulic modeling approaches to be used to guide the design and rehabilitation of the sites. Based on guidance provided by WFLHD, none of the culverts require fish passage considerations as part of the design process.

• Table 3. Design Considerations for the GPNF Sites

Site ID Potential Corrective Action(s)

25-25 Install two additional culverts – one near the up-gradient side of the project area and one down-gradient of the existing culvert.

88-19.7 Replace entire culvert with similar size and slope. May require seepage rings on proposed culvert.

90-28.0 The damaged section of the culvert will be replaced with the same diameter culvert section.

29-7.60 Design a spillway with culvert. Proposed having the logs removed this Fall.

Design outlet protection, if needed. Design inlet protection, if desired.

23-18.0 Replace the culvert. Potentially use existing woody debris to create a debris catcher. Regrade the stream alignment.

23-22.3 Replacing the inlet section of the existing culvert and removing some of the accumulate rock material. Replace the entire culvert as the outlet is also damaged.

23-23.4 Replace existing conveyance with an open-topped concrete box culvert and spillway/ford.

23-23.5 Provide protection of abutment.

2324-0.1 Remove existing 48” culvert and replace with new one along a new alignment. Best alternative may be a new open-topped box culvert.

2322-0.2 Remove log from slot canyon channel. Repair abutment foundation

23-23.6 Push stream back to historic flow path. Reconstruct and Revegetate floodplain terrace. Provide woody material to protect re-established road base.

23-12.6 Rebuild road alignment. Protect stream bank/road fill with large rock and woody debris. Bank protection will be similar to ELJ built in the late 1990s.

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Appendix A FHWA Damage Survey Reports

25-25 88-19.7 90-28.0 29-7.6 23-18.0 23-22.3 23-23.4 23-23.5 2324-0.1 2322-0.2 23-23.6 23-12.6

Sheet No: 1 of 8

DSR No:

Disaster No:

County: Latitude:

State: Longitude:

Facility Number: Mile Post:

Maint. Level:

Type: Traveled Way Width:

22-feet plus curve widening

Surface Type: ACP Thickness: 2.5-inches ADT:

ID#: Shoulder Width: 1 Surface Type: ACP Thickness: Inspection Date:

Unit Unit Price

Proposed:

Unit Unit Price

LS $180,000.00

LS $164,000.00

LS $1,000.00

LS $70.00

CY $20.00

CY $60.00

LS $25,000.00

CY $60.00

Ton $200.00

LS $5,000.00

Proposed:

20%

15%

0.00%

Eligible Ineligible

Eligible Ineligible

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

COST ESTIMATE for EMERGENCY REPAIRS Quantity Item Description Cost

6/1/2016

Classification:Road Data:Bridge Data:

W 121.96441

Skamania

WA

Applicant:

Agency:

$0 $0

Facility Name:

Gifford Pinchot NF

US Forest Service

$0

Description and Cause of Damage: Saturated soils failed along road embankment for 160-feet and undermined pavement shoulder.

Scope/Description of Repair: Emergency Repairs: Permanent Repairs: Subexcavate faile embankment materials and construct a reinforced soild embankment. Replace asphalt surfaced damaged during reconstruction. Provide subsurface drainage behind embankment.

Road 25

$0

$0

Total Estimated Emergency Repairs

$0 $0

$0 1 Moblization $180,000

$0

COST ESTIMATE for PERMANENT REPAIRS Quantity Item Description Cost

1 Remove and reset existing 18-inch culvert $70 18900 Excavation $378,000

1 FHWA contract items (survey, testing, quality control, schedule) $164,000 1 Temporary Soil Erosion Control $1,000

110 Asphalt Concrete $22,000

19800 Embankment - Reinforced soil $1,188,000 1 Underdrain $25,000

* Tribal transportation facilities and federal lands transportation facilities are at 100%. Other federally owned roads are at the sliding scale. See attached table.

N 46.26288

Signature: Date:

Reviewed By: (Name and Title) Signature: Date:

Submitted By: (Name and Title)

$396,574 $297,431

(amount from continuation sheet) $0

1 Permanent Erosion Control $5,000 $0

330 Roadway Aggregate $19,800

Preliminary Engineering (percent of permanent repair construction)

Construction Engineering (percent of permanent repair construction)

ERFO share of Permanent Repairs (Sliding Scale) * TOTAL EMERGENCY REPAIRS and ERFO SHARE of PERMANENT

REPAIRS

$0 $0

Recommended By: FLH ERFO Coordinator Signature: Date:

$1,982,870

$0 $0

Total Estimated Permanent Repairs - Construction

$0

$0

Identify Betterment and provide supporting documentation and economic justification on attached sheets.

Force Account Contract

Force Account Contract

NTTFI/NFLTFI

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Sheet No: 2 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post:0 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

Gifford Pinchot NF WA

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Sheet No: 3 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post: 25

WA

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

Gifford Pinchot NF

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Sheet No: 4 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post: 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

WA

Gifford Pinchot NF

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Sheet No: 5 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post:0 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

Gifford Pinchot NF WA

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Sheet No: 6 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post: 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

WA

Gifford Pinchot NF

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Sheet No: 7 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post:0 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

Gifford Pinchot NF WA

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Sheet No: 8 of 8

Disaster No:

Applicant: County: Skamania State:

Facility Name: Mile Post: 25

FEDERAL HIGHWAY ADMINISTRATION, Federal Lands Highway

DAMAGE SURVEY REPORT (Supplemental Sheet) 25-25

(Title 23, Federal-Aid System/Federal Domain) WA 2016-1 FS

WA

Gifford Pinchot NF

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Appendix B Site Photos 25-25 88-19.7 90-28.0 29-7.6 23-18.0 23-22.3 23-23.4 23-23.5 2324-0.1 2322-0.2 23-23.6 23-12.6

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122/144

Site Number: 25-25 Description: slope failure

Accumulated slope material in the ditch.

Failed slope and existing culvert.

123/144

Hillside ditch with evidence of accumulating material

Inlet of existing culvert. Vegetation suggests subsurface moisture

124/144

Site Number: 88-19.7 Description: Road failure at culvert, potential piping issue

Remaining road section at site.

Outfall of remain culvert section.

125/144

Site Number: 90-28.0 Description: Sunken road section

Sunken road section, no evidence of flows crossing road.

Existing culvert outlet is protected and in good shape.

126/144

Site Number: 29-7.60 Description: Road failure due to plugged culvert

Accumulated woody material. The jam is holding the grade of the upstream channel

Downstream channel. moss line illustrates historic bank.

127/144

Debris field upstream of the culvert.

Mining claim upstream of the culvert crossing

128/144

Site Number: 23-18.0 Description: Road failure due to debris slide

Accumulated material upstream of culvert. Limited large material.

Downstream of culvert. Large material may be from road fill.

129/144

Current stream channel through the deposited sediment.

Old debris screen. Logs with root wads shown in the background.

130/144

Site Number: 23-22.3 Description: Debris slide, blocked culvert

View of accumulated material upstream of culvert.

Streambed downstream of the culvert.

131/144

Damaged culvert inlet

Accumulated material within the culvert

132/144

Site Number: 23-23.4 Description: Debris blocked culvert, road overtopped

Downstream of failed culvert, looking upstream.

Accumulated debris flow material. angular material results from local sources

133/144

Culvert Inlets

Looking upstream from the culvert crossing

134/144

Site Number: 23-23.5 Description: Bridge abutment damaged

Gabion basket abutment with missing footing material.

Large log at upstream face of bridge. May have been placed.

135/144

Site Number: 2324-0.1 Description: blocked culvert, road failure

Looking downstream at Site 2324-0.1

136/144

Approximate location of culvert outlet

Culvert outlet buried in debris.

137/144

Buried culvert Inlet

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Bridge abutment with eroded footing material.

Site Number: 2322-0.2 Description: Bridge abutment needs repair

Trapped log retaining material upstream of bridge.

139/144

Site Number: 23-23.6 Description: Road lost to channel migration

Gravel bar remnant of previous bank location.

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Stable channel downstream of the site.

Existing eroded stream bank and current channel location

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Remain road surface and current channel location

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Site Number: 23-12.6 Description: Road lost to channel migration

Cispus River at NF 23 site.

143/144

Multiple flow channels upstream of NF 23 site.

Gravel bar at the project site.

144/144

Woody debris source at the downstream end of the site.

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PhotoLog

Hydraul Design Memo Cowlitz Valley Road Repairs