Hydraul Design Memo WA NPS OLYM 2017(1) Spruce Trail Segment B 03_2018.pdf

Spruce Railroad Trail Segment B

WA NPS OLYM 2017(1)

Hydraulics Design Memorandum

Federal Highway Administration

Western Federal Lands Highway Division

Project Number: 60547135

March 29, 2018

Hydraulic Design Memorandum

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

March 2018

AECOM

Quality information

Prepared by Checked by

Stephen Blanton, P.E. T. Gut, P.E.

Revision History

Revision Revision date Details Authorized Name Position

Distribution List

Kirk Loftsgaarden, FHWA

Project File

Prepared for:

Federal Highway Administration

Western Federal Lands Highway Division

610 East Fifth Street

Vancouver, WA 98661-3801

Prepared by:

Stephen Blanton, P.E.

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

Tables

Table 1. Spruce Trail Segment B Identified Existing and Proposed Hydraulic Conveyance Sites

Table 2. Culvert Design Criteria for Spruce Trail Segment B

Table 3. Drainage Area Characteristics for Regional Regression Equations

Table 4. Peak Flows for the Spruce Trail Segment B Major Culvert Crossings

Table 5. Flow Rates Used for Spruce Trail Segment B Culvert Sizing

Table 6. Design Criteria and Proposed Culvert Size for Spruce Trail Segment B

Table 7. Outfall Protection Sizing

Table 8. Preliminary Cost Estimate

Figures

Figure 1. Location Map

Figure 2. Drainage Basin for Station 132+11 Culvert Location

Figure 3. Drainage Basin for Station 90+70 Culvert Location

Figure 4. Relationship Between Drainage Area and Peak Flow Rate for Spruce Trail

Figure 5. Headwater Depth Based on Culvert Diameter

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1. Introduction

The historic Spruce Railroad ran along the north edge of Crescent Lake in what is now the

Olympic National Park. The abandoned railroad alignment has become a popular hiking trail. The trial is being incorporated into the 140 mile Olympic Discovery Trail (ODT). The ODT is a multi-use trail for biking, hiking, and horseback riding. Improvements to the Spruce Railroad alignment are required to meet the design guidelines for the ODT. These include widening the trail, repairing slide damage, and re-establishing a historic tunnel.

This Hydraulics Design Memorandum is intended to support the final design of the Segment B trail improvements related to surface water conveyance. The design memorandum fully documents, 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

2. Project Description

Segment B of the Spruce Railroad Trail improvements is an approximately 1.8 mile alignment along the northern shore of Crescent Lake in the Olympic National Park. Multiple culverts are to be used to safely convey surface flows and stormwater runoff from the hillslopes to the lake. Site reconnaissance only identified one existing culvert although there appears to be multiple other minor drainages associated with trail segment.

A project location map (Figure 1) and Identified drainage crossings (Table 1) are provided below.

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Figure 1. Location Map

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Table 1. Spruce Trail Segment B Identified Existing and Proposed Hydraulic Conveyance Sites

Site ID Structure

Type Site Description Hydraulic Recommended Fix

STA 134+68

Existing

Stream/

Proposed

Culvert

Perennial stream crossing the trail, currently occupying the topographic highpoint of an assumed alluvial fan.

Stream is maintained in place using rocks and logs.

After crossing the trail alignment, the stream flows toward the west and discharges to the lake.

Historically, this flow may have been conveyed to the existing culvert at Station 132+11.

Two 24 inch culverts will be placed at Station 134+68. The culverts will discharge into the existing channel flowing along the lake side of the trail. Will require regrading of outfall to catch grade.

STA 132+11

Existing

Culvert

Wood culvert.

There is a depression across the trail above the culvert alignment which may indicate the culvert has collapsed and is no longer functioning as designed.

Fill in the existing wood culvert. Place a 24 inch culvert on the western side of existing wooden culvert at Station

131+30, coincident with a low point in the trail profile.

STA 90+70

Existing

Culvert –

Potentially

Buried

Site evidence suggests an alluvial fan has deposited materials blocking the historic flow path. There is no evidence of a defined flow path from the upstream drainage area.

Provide for flow conveyance to the west. A single 24 inch culvert will be placed at Station 90+14, coincident with a low point in the trail profile.

STA 66+39

STA 76+75

STA 90+14

STA 102+68

STA 122+87

STA 131+30

STA 138+25

STA 148+52

Proposed

Culvert

Low point of trail alignment. Culverts are required to convey accumulated flows under the trail.

It is proposed that 24-inch HDPE culverts will be used as the minimum diameter culvert. The larger than hydraulically needed culverts allows for most rocks to be conveyed through the culverts. The culverts should be placed at a slope that generates enough velocity to convey the material through the culverts.

At Station, 131+30, two 24 inch culverts are required.

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3. Base Data and Sources

The designs related to the Segment B site are based on limited existing data. Survey data of the trail alignment provided an approximately 80-ft wide swath of terrain data. Additionally the analyses supporting the designs used 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 Western Washington Continuous Simulation Hydrology Model (WWHM).

http://www.ecy.wa.gov/programs/wq/stormwater/wwhmtraining/index.html

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

4. Analytical Approaches, Methods, and Results

The culvert’s design approach required 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 FHL PDDM requirements (Table 2).

Table 2. Culvert Design Criteria for Spruce Trail Segment B

Design Parameter Classification Design Criteria

Capacity Design

High-Standard Roads 50-Year Flood

Low-Standard Roads 25-Year Flood

Roadside Ditch 10-Year Flood

Headwater Ratio (HW/Diam)

48” Diameter or Smaller 1.5

Larger than 48” Diameter 1.2

Heavy Debris/Sediment 0.8-1.0

Minimum Size (Diameter) Cross Road 24-inch

Slope Stream Crossings Match Streambed http://www.ecy.wa.gov/programs/wq/stormwater/wwhmtraining/index.html http://streamstatsags.cr.usgs.gov/v3_beta/viewer.htm?stabbr=WA

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Hydrology

The Spruce Trail Segment B alignment crosses multiple drainage paths requiring the placement of culverts to convey the from the upslope side of the trail to the Crescent Lake. The design flows for each of the culvert locations was estimated using the USGS regional regression equations and the Western Washington Hydrologic Model (WWHM).

The USGS StreamStats website provides automated watershed delineation and estimated flows for identified locations. The StreamStats site will only delineate watershed with a minimum drainage area of approximately 50 acres. Along the Segment B alignment only two locations met the criteria: Station 132+11 and 90+70. Station 132+11 is the location of an existing wooden culvert and Station 90+70 is where an alluvial fan was identified at the bottom of a dry stream channel. Figure 2 illustrates the delineation of the drainage area for Station 132+11 and Figure 3 illustrates the Station 90+70 drainage area. It can be assumed that all other drainage areas along the alignment are less than 50 acres.

Figure 2. Drainage Basin for Station 132+11 Culvert Location

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Figure 3. Drainage Basin for Station 90+70 Culvert Location

Table 3 lists the area associated with the two largest culverts crossings along with the average annual precipitation in each. The precipitation value is a required parameter for the regional regression equations. For selection of the appropriate regional regression equations, Crescent

Lake is located within Hydrologic Region 3.

Table 3. Drainage Area Characteristics for Regional Regression Equations

Basin Drainage Basin Area Annual Precip

Mi2 Acres Inches

Sta 132+11 0.14 89.6 85.3

Sta 90+70 0.11 70.4 88.3

The two subbasin areas shown in Table 3, are on the very near the lower limit of the recommend drainage area for using the regional regression equation (0.08 mi2). Using the regional regression equations has the potential to over-estimate the peak flows associated with each of the design storms. For comparison, the Western Washington Hydrologic Model (WWHM) was also used to estimate peak flow rates associated with the two delineated subbasins.

WWHM uses scaled local precipitation gages along with basin area, land use, and soil type to estimate a 50 year continuous surface water runoff hydrograph. Using the annual peaks

7/12 generated by the model for each of the drainage areas the WWHM conducts a flood frequency analysis to determine the peak flows associate with the annual recurrence intervals.

Table 4 contains the estimated peaks flows for the two larger drainage basins based on the two hydrologic approaches: Regional Regression Equations and WWHM. As indicated by the flow values in the table, the WWHM approach results in lower peak flows for the more recurring storm events but the WWHM estimates higher flows for the larger storm events. The WWHM are likely the more accurate but for this analysis the more conservative flows from the regional regression equations were used.

Table 4. Peak Flows for the Spruce Trail Segment B Major Culvert Crossings

Design

Storm

Estimated Flows, cfs

Regional Regression WWHM

Sta 132+11 Sta 90+70 Sta 132+11 Sta 90+70

2 12.0 10.3 2.0 1.6

5 18.6 15.9 6.3 4.9

10 23.0 19.6 11.9 9.3

25 28.2 24.1 23.9 18.7

50 32.0 27.3 38.3 30.0

100 36.1 30.7 59.1 46.2

200 40.1 34.0

500 45.5 38.6

Using the regional regression equation for Region 3, the relationship between drainage area and peak flow rates was developed. Figure 4 illustrates the resulting relationships for the 10, 25, and

50 year flow rates. It must be restated, the regional regression equations are not valid for drainage areas under 50 acres but they likely result in conservative flows requiring larger culverts. For the two larger drainage areas associated with Station 132+11 and 90+70 culverts the 10 year design storm flows in Table 4 will be used. For the other culverts, Figure 4 was used to estimate design flows for each proposed culverts, assuming 50 acres drainage areas. The final design flows for each fo the culvert are shown in Table 5.

Table 5. Flow Rates Used for Spruce Trail Segment B Culvert Sizing

Culvert Locations Drainage Area

(acres)

Estimated 10 – Year Flow

Rate

132+11 89.6 23.0 cfs

90+70 70.4 19.6 cfs

STA 66+39

STA 76+75

STA 102+68

STA 122+87

STA 138+25

STA 148+52

50 (assumed) 14 cfs

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Culvert locations Sta 132+11 and Sta 90+70 are being moved to Sta 131+30 and Sta 90+14 to match culvert crossings to low points in the trail profile. The proposed culvert locations were sized based on the original location flows.

Figure 4. Relationship Between Drainage Area and Peak Flow Rate for Spruce Trail

Culvert Analysis

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.

To facilitate the design of the culverts the HY-8 program was used to model a series of flow rates and pipe sizes to estimate the headwater depth of the culverts. The resulting relationships in

Figure 5 assume a culvert slope of 5% for each of the diameter culverts.

For the culvert analyses, the FHWA design criteria are provided in Table 2. For the Spruce Trail

Segment B project all sites where culverts are being placed will assume a debris and sediment load and therefore will use the HW/D ratio of 0.8-1.0. Therefore the headwater depth for each culvert cannot exceed the diameter of the proposed culvert.

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Figure 5. Headwater Depth Based on Culvert Diameter

Using the estimated design flows (Table 5) and the relationship shown in Figure 5, the project culverts were sized. Table 6 lists the proposed culvert locations, the estimated design flows and the proposed culvert diameters.

Table 6. Design Criteria and Proposed Culvert Size for Spruce Trail Segment B

Site ID Structure Type Design Flow

(cfs)

Proposed Diameter

(inches)

STA 134+68 Culvert 23 24 (x 2)

STA 90+14 Culvert 19.6 24

STA 66+39

STA 76+75

S

STA 102+68

STA 122+87

STA 131+302

STA 138+25

STA 148+52

Culvert 141 24 (Minimum Diam.)

Note 1: Assumed drainage area is 50 acres.

Note 2:. Station 131+30 is being used at the low point near station 132+11 but will not receive flows from the tributary (see Sta

134+68).

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Outlet Protection

The culverts outlets require protection against erosion. The design of the outlet protection was based on the FHWA HEC 14, Hydraulic Design of Energy Dissipators for Culverts and Channels, FHWA NHI-06-086, 2006. Based on the available approaches provided in HEC-14 and the previous experience with Segments A and C of the Spruce Trail, the outlets will provide erosion protection using Rip Rap Aprons.

The culverts outlet will use a standard end section expansion fitting and will not discharge to a ditch. Table 7 lists the final sizing for each of the culvert outfall using Rip Rap Aprons.

Table 7. Outfall Protection Sizing

Site ID

Proposed

Diameter

(inches)

Riprap

Class

Outfall Apron

Length

(ft)

Outfall Apron Width

(ft)

At Outlet At End of

Apron

STA 134+68 24 (x2) 2 8 9 14.5

STA 90+14 24 2 8 6 11

STA 76+75

STA 102+68

STA 122+87

STA 131+30

STA 138+25

STA 148+52

24 2 8 6 11

The apron design thickness is based on the riprap size. For Class 2 the depth will be 18 inches

(1.5 ft).

5. Final Design Recommendations

Site investigations along Segment B of the Spruce Trail found only one location with surface flows (Station 132). There were no other recorded sites showing evidence of surface flows along

Segment B. In many natural forest environments in the Pacific Northwest, precipitation associated with storm event smaller than the 10 to 20 year events are completely infiltrated and conveyed subsurface. This may explain why so few flow paths were identified across the trail alignment.

The proposed culverts under the Spruce Trail have been sized to convey the 10 year design storm. The design hydraulics of the culverts has been assessed to provide for the conveyance of sediment and rock materials. This design approach is intended to limit the need for maintenance required to unblock culvert inlets. Based on the analysis presented, the culverts required to convey flow safely from the upslope side of the Spruce Trail to the lake side are summarized below:

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Station 134+68:

This site will use two 24 inch diameter culverts. The outlet of the culvert will discharge into the existing stream alignment. The stream channel will need to be reconstructed to address the outlet elevation of the culverts. The final outlet elevation will dictate the extent of the channel reconfiguration along the trail.

Station 132+11 and 131+30:

The existing wooden box culvert will be dug out and backfilled. A new 24 inch culvert will be placed at Sta 131+30 to provide drainage for localized flows.

Station 90+70 and 90+14

A 24 inch culvert will be placed to convey the design flows under the trail at the proposed sag location at Sta 90+14. Flows from the Sta 90+70 will be conveyed to Sta 90+14 using a ditch along the upstream side trail. The inlet and outlet elevations will be based on actual site conditions related to the ability to excavate.

All other Culverts

All other culverts have been assumed to convey flows generated by drainage areas of less than

50 acres. Each low point requiring a culvert will use a 24 inch culvert. This diameter is the minimum required diameter and will be able to convey 14 cfs with a headwater to diameter ratio of 1.

Each of the culverts will require an outlet erosion protection apron. Riprap aprons will be used for energy dissipation and erosion control at the culvert outfalls. The aprons with be constructed with end sections. The length and width of the aprons is based on the culvert diameter using

HEC-14 design guidance.

Table 8 lists the estimated costs associated with each of the culvert location for the Spruce Trail

Segment B project.

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Table 8. Preliminary Cost Estimate

Site ID Cost

STA 134+68 $10,100

STA 131+30 $5,950

STA 90+14 $4,250

STA 76+75

STA 102+68

STA 122+87

STA 138+25

STA 148+52

$5,850

$3,950

$4,150

$3,750

$4,550

$4,450

Total: $47,000

6. Supporting Information

Mastin, M.C., Konrad, C.P., Veilleux, A.G., and Tecca, A.E., 2016, Magnitude, frequency, and trends of floods at gaged and ungaged sites in Washington, based on data through water year 2014

(ver 1.1, October 2016): U.S. Geological Survey Scientific Investigations Report 2016–5118, 70 p., http://dx.doi.org/10.3133/sir20165118.

U.S. Geologic Survey – StreamStats Webpage https://streamstats.usgs.gov/ss/ http://dx.doi.org/10.3133/sir20165118 https://streamstats.usgs.gov/ss/