WY FLAP CN10-277(1) Wiggins Bridge Stream Diversion Memorandum.pdf

To: Emilio Burgos, Project Manager, CFLHD, Lakewood CO

From: Luis Calderón, Hydraulics Engineer, CFLHD, Lakewood CO

CC: File N:\WY\cn10-277(1)\Hydraulics\9_Final-Report

Subject: Stream Diversion Recommendations for the WY FLAP CN10 - 277(1) – Replacement of the Wiggins Fork Bridge project

1 PROJECT BACKGROUND INFORMATION

This memorandum presents the hydrologic and hydraulic analysis to support the stream diversion recommendations for the WY FLAP CN10 - 277(1) – Replacement of the Wiggins Fork Bridge project. The project is located in Fremont County, Wyoming, see Figure 1. The project proposes to replace an existing bridge over Wiggins Fork, which is a tributary to the East Fork Wind River. Maintenance of traffic during construction is required and a temporary traffic diversion will be constructed over Wiggins Fork. Stream flows are required to be maintained through the crossing for the duration of the construction.

2 HYDRAULIC DESIGN CRITERIA

The Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands Highway 2012) provides criteria for temporary stream crossings as shown below:

• High Standard road: Culverts for temporary detours will convey runoff from the 10-year flood, unless seasonal construction justifies a lower standard.

• Low Standard road: Culverts for temporary detours will convey runoff from the 2-year flood, unless seasonal construction justifies a lower standard.

The bridge construction will take advantage of the seasonal low flow period on Wiggins Creek. It is assumed for the purposes of this analysis that this will take place between September and April. Due to the seasonal construction for this project, a flow duration analysis was conducted to the temporary crossing requirements as discussed in the following sections.

Technical Memorandum

Date: January 22, 2021

3 FLOW DURATION ANALYSIS

The project is located on Wiggins Creek, upstream of the confluence with the East Fork Wind River. The contributing drainage area to the bridge is approximately 212 square miles. There are no streamflow gages on Wiggins Creek near the project site. USGS streamflow station 06220500 - East Fork Wind River near Dubois, WY is located approximately 7 miles downstream of the confluence of Wiggins Creek with the East Fork Wind River. Information from this gage was used to conduct the flow duration analysis.

Figure 1 shows the gage location in relation to the project site.

Figure 1: USGS 06220500 East Fork Wind River near Dubois, WY

Daily streamflow information was collected at the gage. The gage has daily flow values for the period of May 1950 to September 1957, and October 1975 to September 1997. A plot of the daily streamflow information is shown in Figure 2. A flow duration analysis of the daily streamflow values was conducted using HEC-SSP (U.S. Army Corps of Engineers 2017). Flow duration curves for each month are shown in Figure 3. Table 1 shows the results in tabular format. The table shows flow values per month and the percentage of time exceeded. For example: in the month of February flows of 75 cubic feet per second were exceeded 1 percent of the time. A ratio of drainage areas was used to transfer the flow values to the project site. The contributing area to the USGS gage is 427 square miles, resulting in a 0.5 ratio of flows at the gage compared to flows at the bridge site. Table 2 shows the monthly flow values and percentage of time exceeded for the Wiggins bridge location.

USGS 06220500

Wiggins Fork Bridge

East Fork Wind River

Figure 2: USGS 06220500 Daily Streamflow

Figure 3: USGS 06220500 Flow Duration Analysis - Monthly

Table 1: Monthly Flow Duration Analysis at USGS 06220500 (DA = 427 mi2)

Percent Time Exceeded (%)

Flow (cfs) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

99 24 22 30 40 62 174 69 36 28 42 24 23 95 30 30 36 48 87 272 99 56 48 55 33 28 90 32 32 40 54 118 329 145 72 62 61 35 32 80 36 37 45 64 163 461 226 98 72 70 42 35 50 45 48 58 102 419 903 460 167 105 85 59 50 25 56 56 65 176 700 1,448 760 238 142 113 74 59 15 60 60 70 242 949 1,805 943 290 168 129 83 64 10 64 62 75 308 1,150 2,143 1,060 332 186 141 92 68 5 70 69 90 447 1,500 2,490 1,350 412 224 163 106 72 2 72 72 116 589 2,024 2,888 1,677 535 300 222 115 91 1 75 75 128 801 2,400 3,189 1,814 659 368 270 126 100

0.1 80 80 177 1,300 2,970 3,740 2,200 1,450 415 355 139 111

Table 2: Monthly Flow Duration Analysis at Wiggins Fork Bridge (DA = 212 mi2)

Percent Time Exceeded (%)

Flow (cfs) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

99 12 11 15 20 31 87 35 18 14 21 12 12 95 15 15 18 24 44 136 50 28 24 28 17 14 90 16 16 20 27 59 164 73 36 31 31 18 16 80 18 19 23 32 81 230 113 49 36 35 21 18 50 23 24 29 51 210 452 230 83 53 43 30 25 25 28 28 33 88 350 724 380 119 71 56 37 30 15 30 30 35 121 474 902 471 145 84 65 42 32 10 32 31 38 154 575 1,072 530 166 93 71 46 34 5 35 35 45 223 750 1,245 675 206 112 81 53 36 2 36 36 58 295 1,012 1,444 839 268 150 111 58 46 1 38 38 64 400 1,200 1,595 907 329 184 135 63 50

0.1 40 40 89 650 1,485 1,870 1,100 725 208 178 70 56

The construction season flows are highlighted in Table 2. For stream diversion sizing, the maximum flow during the construction period with a 10 percent time exceeded is recommended. The maximum value occurs in April and results in a design flow of 154 cubic feet per second. Note that this value is higher than the 0.1 exceedance value for the months of November to March.

4 HYDRAULIC ANALYSIS

A hydraulic evaluation to estimate proposed culvert sizes was conducted using HY-8 (Federal Highway Administration 2017). It is assumed that the culverts will be constructed matching the stream slope. The overtopping elevation shown is the road profile elevation near the culvert location, and was specified in the HY-8 model as a constant roadway elevation. Tailwater was assumed to be normal depth in the downstream channel. Two alternatives were evaluated: 1) standard corrugated metal pipes, and 2) embedded corrugated metal pipes to comply with environmental permitting requirements. For constructability of the embedded culvert a minimum culvert diameter of 60” is recommended. In addition, multi-barrel culverts are recommended for resiliency of the stream diversion. The proposed culvert alternatives are shown in Table 3. The hydraulic results are shown in Table 4.

Table 3: Proposed Culvert Characteristics

Alternative Type Embedment Depth (inI

Diameter (in)

Number of

Barrels

Assumed Length

(ft)

Assumed Slope (%)

Overtopping Elevation

(ft)

1 CMP 0 48 2 40 2.9 6,720

2 Embedded

CMP 12 60 2 40 2.9 6,720

Table 4: Proposed Culvert Hydraulic Results

Alternative Design

Discharge (cfs)

Headwater Elevation (ft)

Headwater Depth

(ft)

HW/D

Ratio

Roadway Overtopping Discharge

(cfs) 1 154 6,718.1 4.6 1.2 217 2 154 6,716.1 2.6 0.7 307

5 RECOMMENDATIONS

A summary of minimum stream diversion recommendations is provided in Table 5.

Table 5: Summary of Recommendations

Alterna tive Recommendation

1 • Double 48” CMP installed at streambed level

2 • Double 60” CMP installed a minimum of 1 foot below streambed level, backfilled with native streambed material sourced on site.

6 REFERENCES

Federal Highway Administration. 2017. HY-8 Culvert Analysis Program. Version 7.50.

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics." https://flh.fhwa.dot.gov/resources/design/pddm/.

U.S. Army Corps of Engineers. 2017. HEC-SSP, Hydrologic Engineering Center Statistical Software Package.

Version 2.1.1. Davis, CA.