HYD Report WY FLAP JOH 14(1).pdf

North Fork Crazy Woman Creek Bridge Johnson County, WY

WY FLAP JOH 14(1)

Final Hydraulics Report

Federal Highway Administration Central Federal Lands Highway Division

April 3, 2023 i | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Signature Sheet

Report prepared by: ____________________________________________________

Amanda Peters, Hydraulic Engineer

Report reviewed by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Approved for distribution by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Distribution

Electronic:

N:\WY\14(1)\Hydraulics\9_Final-Report Julia Dietsch, Project Management Jake Keithley, Project Development, Lead Designer Daniel Dell’Agnese, Environment Devin Dixon, Geotechnical Karl Eikermann, Bridge Phillip Clark, Bridge ii | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Executive Summary

Hydrologic and hydraulic analyses were conducted for the WY FLAP JOH 14(1) North Fork Crazy Woman Creek Bridge located near the Bighorn National Forest in Johnson County, WY. FHWA Project Development and Design Manual (PDDM) design requirements were used for the design of this bridge. The existing bridge is to be removed and replaced with a 14-ft wide, 51-ft long, single span bridge. A stream gage located downstream of the bridge location was used to estimate peak flows at the bridge through methodology set forth in the document Peak-Flow Characteristics of Wyoming Streams. These adjusted gage flows were adopted to represent flows at the bridge location and are used as the design flows.

Two-dimensional hydraulic modeling was completed using SRH-2D, which determined various water surface elevations, depths, and flow velocities near the existing bridge. Table 1 below provides maximum velocity and average water surface elevation data for various storm events. The values presented for the

100-yr and 200-yr storm event are from simulations including pressure flow on the bridge.

Table 1: Summary of North Fork Crazy Woman Creek Bridge Hydraulic Data

Q (cfs) V (fps) WSE (ft.) Scour Elevation (ft.)

Q2 230 11.2 5877.3 ---

Q50 1420 18.1 5882.1 ---

Q100 1790 18.8 5884.2 5867.9

Q200 2220 19.1 5885.1 5867.6

Notes:

The water surface elevations and velocities (V) are reported at the upstream bridge face.

50-year WSE used to determine freeboard = 5882.1-ft. (measured at the upstream face of the bridge).

Hydraulic capacity requirements: Bridge low chord provides a minimum 3.1-ft. of freeboard above the average 50-year water surface elevation at the upstream face of the bridge.

iii | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Table of Contents

1 Project Background Information

1.1 Project Information

1.2 Existing Bridge

1.2.1 Bridge Geometry

1.2.2 Inspection Reports

1.3 Flood Insurance Study

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting and Topographic Data

3.2 Basin Characteristics

3.3 Available Hydrologic Data

3.4 Regression Equation Estimates

3.5 Rainfall-Runoff Model Estimates

3.6 Gaged Site Flow Estimates

3.7 Adopted Design Flows

4 Hydraulic Analysis

4.1 Hydraulic Model Development

4.2 Topographic Information

4.3 Boundary Conditions

4.4 Land Cover

4.5 Existing Condition Model Results

4.6 Proposed Condition Model Results

4.7 Debris Check Condition

5 Bridge Scour

5.1 Site Observations

5.2 Long-Term Degradation and Channel Migration

5.3 Geotechnical Investigation

5.4 Scour Evaluation

5.5 Scour Estimate Results

6 Recommendations

6.1 Bridge Capacity

6.2 Bridge Scour

6.3 Bank Protection and Countermeasures

7 References

Tables Table 1: Summary of North Fork Crazy Woman Creek Bridge Hydraulic Data ............................................. ii

Table 2: PDDM Hydraulic Design Criteria

Table 3: Basin Characteristics

Table 4: Available Peak Streamflow Information

Table 5: Station 06314500 Annual Exceedance Probabilities

Table 6: Regression Equations Peak Flow Estimates

Table 7: HEC-HMS Model Inputs iv | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Table 8: HEC-HMS Results for Various CN Scenarios

Table 9: Estimated Peak Flows at Bridge Location based on Gage 06314500

Table 10: Recommended Design Flows

Table 11: Land Cover and Manning’s Roughness Coefficients

Table 12: Hydraulic Model Results, 50-yr (Existing)

Table 13: Hydraulic Model Results, 50-yr (Proposed)

Table 14: N. Fork Crazy Woman Creek Abutment Scour Estimates

Table 15: N. Fork Crazy Woman Creek Contraction Scour Estimates

Table 16: Scour Component Summary by Design Event

Figures Figure 1: Project Location Map

Figure 2: Existing Structure………………………………………………………………………………………………………………………1

Figure 3: Stream conditions

Figure 4: Basin Delineation

Figure 5: Gage and Bridge Locations

Figure 6: Regression and Rainfall-Runoff Analyses Results at Bridge Location

Figure 7: Regression Analyses and Flow Estimates at Bridge Based on Gage 06314500

Figure 8: Field Survey Merged with Lidar

Figure 9: Existing (LT) vs. Proposed (RT) Contours at Bridge Location

Figure 10: Mesh Limits with Contours and Boundary Conditions

Figure 11: Land Cover and Manning’s Roughness

Figure 12: Profile and Cross Section Locations

Figure 13: XS 1, Upstream Bridge Face Elevation View, Existing

Figure 14: XS 1, Upstream Bridge Face Elevation View, Proposed

Figure 15: XS2, 14-ft Upstream of Bridge Face, Proposed

Figure 16: XS3, 40-ft Upstream of Bridge Face, Proposed

Figure 17: Profile Cross Section Elevation View at Channel Thalweg for 50-yr Storm Event, Proposed

Appendices Appendix A: Hydrologic Analysis

Appendix B: HEC-HMS Information

Appendix C: Hydraulic Model Results

1 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

1 PROJECT BACKGROUND INFORMATION

1.1 PROJECT INFORMATION

The North Fork Crazy Woman Creek Bridge replacement is located in Johnson County, WY about 13 miles southwest of the town of Buffalo, WY. This project was chosen as a part of the Federal Lands

Access Program for the state of Wyoming. Crazy Woman Canyon Road is an access road to the Bighorn

National Forest. This road and bridge are maintained by Johnson County. The scope of the project involves removing and replacing the bridge with another single span structure. Additionally, the profile of the road is being raised slightly on the west side of the bridge.

Figure 1: Project Location Map

1.2 EXISTING BRIDGE

1.2.1 Bridge Geometry

The existing bridge is a 40-ft single span steel girder bridge built in 1997. The deck of the structure is timber and has a square footage of 612 with an existing width of 16-ft. This is a single lane bridge with a

15-ft clear roadway width. The figures below provide images of existing conditions.

Figure 2: Existing Structure Figure 3: Stream conditions

2 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

1.2.2 Inspection Reports

Multiple bridge inspections have been conducted on this bridge, the most recent on May 5, 2021 by the

Wyoming Department of Transportation. Per this report, the structural evaluation is intolerable, and the superstructure is in poor condition. In 2018 there was determined to be bank slumping in the channel as well as undermining of the grouted riprap on the east berm. Additionally, in 2016 an inspection was completed indicating that the bottom flanges of all girders have significant corrosion and pitting. In 2012 a scour analysis was conducted indicating that large amounts of debris needed to be removed as well as additional riprap added.

1.3 FLOOD INSURANCE STUDY

FEMA has not completed a study to determine flood hazards in the location of the North Fork Crazy

Woman Creek Bridge.

2 HYDRAULIC DESIGN CRITERIA

Hydraulic design criteria for the project were obtained from the Federal Lands Highway Project

Development and Design Manual (Federal Lands Highway, 2012) as well as the Johnson County Road &

Bridge Standards (Johnson County, 2008). North Woman Canyon Rd. had an ADT of 46 in 2019, is not a critical access road, and has an existing posted speed limit of 45 mph, designating it as a low standard road for hydraulic design purposes.

Table 2: PDDM Hydraulic Design Criteria

Low-Standard Roadway

Design Frequency

Check Frequency

Design Criteria

Bridges 50-Year

Greater of 100-Year and overtopping (≤ 500-Year)

Minimum 2 ft. of freeboard at the design flood

Woody debris potential is significant: 3.5 - 5.0 ft. of freeboard

Bridge Scour 100-Year 200-Year

Countermeasure design flood frequency: 200-Year

Use the worst case scour up to and including these events

Bridge foundation free standing at the check flood

Floodplain Encroachment

100-Year Overtopping (≤ 500-Year)

Unregulated base floodplain: rise ≤ 1.0 ft.

3 HYDROLOGY

3.1 HYDROLOGIC SETTING AND TOPOGRAPHIC DATA

This project is located within the Upper North Fork Crazy Woman Creek Watershed (HUC 12:

100902050101). North Fork Crazy Woman Creek generally runs from northwest to southeast with a headwater near 44.175101, -107.044159 and a confluence with Crazy Woman Creek near 44.064498, -

106.601426. The bridge is located at 44.1877778, -106.8308333. The contributing drainage basin was https://www.google.com/maps/place/44%C2%B010'32.9%22N+107%C2%B002'39.1%22W/@44.1774708,-107.0502223,15.75z/data=!4m5!3m4!1s0x0:0x8ab170071fa7d16b!8m2!3d44.175801!4d-107.044206 https://www.google.com/maps/place/44%C2%B003'52.2%22N+106%C2%B036'05.1%22W/@44.0645018,-106.6036147,17z/data=!3m1!4b1!4m5!3m4!1s0x0:0x50d2d48ad9e2529a!8m2!3d44.064498!4d-106.601426 https://www.google.com/maps/place/44%C2%B003'52.2%22N+106%C2%B036'05.1%22W/@44.0645018,-106.6036147,17z/data=!3m1!4b1!4m5!3m4!1s0x0:0x50d2d48ad9e2529a!8m2!3d44.064498!4d-106.601426 https://www.google.com/maps/place/44%C2%B011'16.0%22N+106%C2%B049'51.0%22W/@44.1876129,-106.8317937,17.27z/data=!4m5!3m4!1s0x0:0x2f793e8ce4f16e99!8m2!3d44.1877778!4d-106.8308333

3 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report delineated in WMS using Worldwide Elevation Data with a 6.9-meter resolution (U.S. Geological Survey

2018).

3.2 BASIN CHARACTERISTICS

The drainage basin that contributes flow at the North Fork Crazy Woman Creek Bridge was delineated using Watershed Modeling System (WMS) (Aquaveo 2021). The USGS application StreamStats (U.S.

Geological Survey 2016) has not been developed for the state of Wyoming. The curve number shown in the table below is for good land conditions as the area has not recently been impacted by fire or development. Additional general basin properties can be seen in Table 3 below and the basin can be seen in Figure 4 below.

Figure 4: Basin Delineation

Table 3: Basin Characteristics

Drainage Area

(sq. mi.)

Mean Basin Elevation (ft.)

Mean Basin Slope

Curve Number

(CN)

42.1 8,508 18.8 69

3.3 AVAILABLE HYDROLOGIC DATA

According to StreamStats, there are multiple stream gages in the vicinity of the bridge location. Station

06314000 shown below is located within the project limits. Although the period of record is from 1944-

1984, there is a gap in data collection from 1950-1974. Station 06314500 located downstream provides information on annual exceedance probabilities as can be seen in Table 5 below. Gage 06313950 is located upstream of the bridge crossing.

Table 4 below summarizes information on the three closest stations to the project.

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Table 4: Available Peak Streamflow Information

USGS Station Latitude Longitude

Drainage

Area

(mi2)

Period of

Record

Total Peak

Streamflow

Records

Status

06313950 44.18635946 -106.85394196 43.4 1974-

11 Inactive

06314000 44.18774877 -106.83060779 44.9 1944-

17 Inactive

06314500 44.19386111 -106.7803282 51.7 1949-

24 Inactive

Table 5: Station 06314500 Annual Exceedance Probabilities

Annual Exceedance Probability (%) Return Period

(Year) Peak Flow Estimate

(cfs)

50 2 270

20 5 590

10 10 890

4 25 1370

2 50 1810

1 100 2320

0.5 200 2920

0.2 500 3850

3.4 REGRESSION EQUATION ESTIMATES

The regression equations used to determine the peak flow for this watershed were from the USGS equations for peak-flow in Wyoming streams (U.S Geological Survey 2003). The project is located within the Rocky Mountain Region (Region 1). The regression equations for this region are based on the variables of basin area, mean basin elevation, and longitude of basin outlet. The analysis for these regression equations was conducted through WMS. In addition to regression equations, this document provides factors in which the lower and upper bounds of the 95% confidence interval relate to the peak flow estimates. Table 6 below shows the results from the regression analysis conducted.

Table 6: Regression Equations Peak Flow Estimates

Annual Exceedance

Probability (%)

Return Period (Year)

Lower Prediction Interval (cfs)

Peak Flow Estimate (cfs)

Upper Prediction Interval (cfs)

50 2 150 370 930

2 50 550 1100 2210

1 100 610 1260 2590

0.5 200 670 1430 3060

5 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

3.5 RAINFALL-RUNOFF MODEL ESTIMATES

Rainfall-runoff modeling using HEC-HMS (U.S. Army Corp of Engineers 2021) was also conducted to compare peak flow estimates with that of the regression equations described above. For this analysis, information was taken from NOAA Atlas 2. The state of Wyoming does not have updated information in

NOAA Atlas 14, making NOAA Atlas 2, Volume 2 (Miller, Fredrick and Tracy 1973) the current standard for precipitation frequency estimates. Collected precipitation data is available for the 2-yr and 100-yr, 6-hr and 24-hr storms. For all other return periods, the 6- and 24-hour storms were determined from isopluvials located in the NOAA Atlas 2, Volume 2 document. All other storm durations were determined through relationships with the 6- and 24-hour storms described in NOAA Atlas 2, Volume 2 as well as curves of best fit. Data was taken from the middle of the drainage basin as this is assumed to represent precipitation across the entire basin. Additional information and data can be found in Appendix A.

A composite curve number for the basin was found to be 69 using the SSURGO Soil Type information

(National Resources Conservation Service 2003) and the NLCD 2011 US National land Cover Database

(Multi-Resolution Land Conaracteristics Consortium 2018). The land cover throughout the basin is primarily forested area in a mountainous region.

The NRCS lag time equation and unit hydrograph were used to estimate peak flows for a comparison with the information from the regression equations described above. Model inputs and results can be seen in

Table 7 and Table 8, respectively.

Table 7: HEC-HMS Model Inputs

Storm Type A 24-hour storm based on NOAA Atlas 2-Volume 2 data dated 1973. Wyoming currently does not have updated precipitation-frequency information in NOAA Atlas 14.

Precipitation Data was obtained from NOAA Atlas 2

Soil Type Data was obtained from SSURGO. Majority are hydrologic soil group C.

Loss The Curve Number (CN) method was used. A CN of 69 was computed and utilized.

Time of Concentration

Time of concentration was computed as 5.68 hours. This equated to a lag time of 3.4 hours.

Table 8: HEC-HMS Results for Various CN Scenarios

Annual Exceedance Probability (%)

Return Period (Year)

Rainfall Runoff

50 2 850

2 50 3940

1 100 5640

0.5 200 6650

3.6 GAGED SITE FLOW ESTIMATES

In addition to the two methods described above, a third method was used to analyze flows at the bridge location. Gage 06314500, located just downstream of the bridge location, provides peak flow estimates for return periods of 2 to 500 years. The document Peak-Flow Characteristics of Wyoming Streams (U.S

6 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Geological Survey 2003) provides methodology to transpose the flows from a gaged site to an ungaged site on the same stream. This process involves creating a weighted peak flow value for the gaged location and relating that, through an area ratio, to the location in question. The gage and the project location are shown in Figure 5 below. The area of the ungaged site must be within 75-150% of the drainage area of the gaged site to utilize this methodology. The gaged site has a basin area of 51.7 square miles, and the drainage basin at the bridge location has an area of 42.1 miles, making the drainage area at the bridge location 81.41% of the drainage area at the gage location, allowing use of this method. Transposed peak flow rates for the bridge location based on the gage are shown in Table 9 below.

Figure 5: Gage and Bridge Locations

Table 9: Estimated Peak Flows at Bridge Location based on Gage 06314500

Annual Exceedance Probability

Return Period (Year)

Peak Flow (cfs)

50 2 230

20 5 500

10 10 730

4 25 1100

2 50 1420

1 100 1790

0.5 200 2220

0.2 500 2900

3.7 ADOPTED DESIGN FLOWS

As shown in figure 6 below, the flows found in the NRCS analysis were higher than that of the regression analysis’ upper bound at design flows of 50- and 100-year events, suggesting that the NRCS method is overestimating the peak flows with the assumptions that were made. The upper and lower bounds indicate the 95% confidence interval in which actual peak flows will likely occur for a given storm.

7 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Figure 6: Regression and Rainfall-Runoff Analyses Results at Bridge Location

In addition to this comparison, the gaged site (gage 06314500) flow estimates were compared to the regression analysis and NRCS results. This information also suggests that actual flows are lower than the results generated from the rainfall-runoff model. Although this gage is no longer active, 24 years of peak streamflow data was collected for the basin. The data collection ceased in 1974, however this area does not appear to have experienced any major changes in land use or cover since the data was collected. As described above, the flows at the gage were used to estimate flows at the bridge location in question.

These peak flows are more reflective of the regression equation analysis than the rainfall-runoff model results.

Figure 7 below shows the transposed peak flows at the bridge location based on gage 06314500. These results indicate the transposed peak flows are similar to the regression analysis or within the upper half of the 95% confidence interval. It is therefore recommended that the design flows be the transposed values from gage 06314500 to reflect the location of the North Fork Crazy Woman Creek Bridge. These values can be seen in Table 10 below.

0 100 200 300 400 500 600

P ea k Fl o w cf s)

Reccurance (year)

Peak Flow vs. Reccurance

Regression Equation Values Regression Equation Upper Bound

Regression Equation Lower Bound NRCS Good CN Values

8 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Figure 7: Regression Analyses and Flow Estimates at Bridge Based on Gage 06314500

Table 10: Recommended Design Flows

Annual Exceedance Probability

Return Period (Year)

Peak Flow (cfs)

50 2 230

20 5 500

10 10 730

4 25 1100

2 50 1420

1 100 1790

0.5 200 2220

0.2 500 2900

4 HYDRAULIC ANALYSIS

4.1 HYDRAULIC MODEL DEVELOPMENT

Water surface elevations, freeboard, and hydraulic capacity requirements were analyzed using two-dimensional hydraulic modeling utilizing SMS (Aquaveo 2022). Inputs, model development, and results are discussed in the following sections.

4.2 TOPOGRAPHIC INFORMATION

Survey information collected by CFLHD in February 2022 was utilized in the development of the hydraulic model. In addition, 2019 LiDAR information was taken from the USGS National Map (U.S. Geological Survey 2018) to merge with CFLHD survey data. All elevations are in units of feet and are referenced to the North American Vertical Datum of 1998 (NAVD 88). Figure 8 below shows the field survey information

0 100 200 300 400 500 600

P ea k Fl o w cf s)

Recurrance (years)

Peak Flow vs. Recurrance

Regression Analysis Values

Estimated Flow at Bridge Location based on Gage 06314500

Upper Bound Regression Values

9 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report merged with the 2019 LiDAR information. This topographic information was used for existing condition simulations. For proposed bridge conditions, LiDAR and survey information was merged with the proposed alignment. A comparison between the topographic information used for existing and proposed simulations at the bridge location can be seen in Figure 9.

To run SRH-2D, a computational mesh was created to solve the two-dimensional flow equations. The mesh used for existing condition simulations and the one used for proposed condition simulations can be found in Appendix C.

Figure 8: Field Survey Merged with Lidar

Figure 9: Existing (LT) vs. Proposed (RT) Contours at Bridge Location

Bridge Location

10 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

4.3 BOUNDARY CONDITIONS

The upstream boundary condition for all storms was modeled as a constant discharge using peak flow values. Downstream boundary conditions were specified as known water surface elevations obtained using Manning’s equation and an energy grade line slope assumed to be equal to the streambed slope at the downstream boundary. Figure 10 provides a visualization of the boundary conditions for all storm events. These boundary conditions apply to proposed conditions as well. Pressure flow boundary conditions are specified only for certain storm events.

Figure 10: Mesh Limits with Contours and Boundary Conditions

4.4 LAND COVER

Land cover on the project was assigned for locations in the channel, floodplain, and the gravel roadway.

The locations of the different land use parameters are shown in Figure 11 along with their respective Manning’s n values. These were used in the SRH-2D simulations run in SMS. Table 11 below provides information on land cover designations in the model. Material properties remain the same for both the existing and proposed condition simulations.

Inlet

Outlet

Pressure Flow

Boundary

Conditions (where applicable)

11 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Figure 11: Land Cover and Manning’s Roughness

Table 11: Land Cover and Manning’s Roughness Coefficients

Land Use Manning’s “n”

Main Channel 0.035

Gravel Roadway 0.023

Floodplain (Vegetated) 0.1

Floodplain (Canyon) 0.035

4.5 EXISTING CONDITION MODEL RESULTS

The results of the SRH-2D simulation are provided for the 2-, 50-, 100-, and 200-year storm events. The 50-yr event results are reported below in Table 12. The results for all other events can be found in Appendix C. Cross section elevation information was taken at the upstream face of the existing bridge, the point of maximum backwater (which is taken to be 40-ft upstream of the bridge face), and upstream of the bridge a distance equal to the width of the bridge (14-ft). Figure 12 below shows the locations of these cross sections. These cross section locations are the same for both existing and proposed conditions.

Figure 13 provides a cross section at the upstream bridge face with the results of the 50-yr event. Results shown in Table 12 provide information on average and maximum velocities for the 50-yr storm.

12 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Figure 12: Profile and Cross Section Locations

Figure 13: XS 1, Upstream Bridge Face Elevation View, Existing

Table 12: Hydraulic Model Results, 50-yr (Existing)

Location WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5882.1 5884.2 11.2 18.1 4.8 8.8

XS2 5884.0 5885.5 10.4 13.6 5.1 8.1

XS3 5886.0 5886.3 4.8 8.1 6.2 9.7

XS 3: 40 ft. US of

Bridge

XS 1: Upstream Face

Existing Streambed

50-year WSEL Bridge Location

XS 2: 14 ft. US of

Bridge

Channel Thalweg

13 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

4.6 PROPOSED CONDITION MODEL RESULTS

The proposed structure is to be a 51-ft single span modular steel bridge with steel girders and structural steel decking. Proposed grade as determined by roadway design was incorporated into the bridge model and subsequent simulations were run with the same boundary conditions and land use coverage as existing conditions. For the 100-yr and 200-yr storm events, pressure flow boundary conditions were utilized to determine hydraulic results.

Cross section locations were taken at the same locations as the existing condition results reported in the previous section. Figure 14 below provides a profile view of water surface elevations at the upstream bridge face. Similar results are provided for XS2 and XS3 in Figure 15 and Figure 16, respectively. Figure

17 below provides a profile view along the channel thalweg of proposed water surface elevations for the design storm event. As can be seen in Table 13, the proposed hydraulic results do not vary significantly from the existing conditions. Hydraulic capacity of the stream will be minimally impacted by the replacement of this bridge as the grouted riprap that is existing is recommended to remain untouched. A slight increase in hydraulic capacity will be accommodated due to the slight grade raise occurring on the west side of the bridge.

Figure 14: XS 1, Upstream Bridge Face Elevation View, Proposed

Figure 15: XS2, 14-ft Upstream of Bridge Face, Proposed

Existing Streambed

Existing Streambed

50-year WSEL

50-year WSEL

14 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Figure 16: XS3, 40-ft Upstream of Bridge Face, Proposed

Figure 17: Profile Cross Section Elevation View at Channel Thalweg for 50-yr Storm Event, Proposed

Table 13: Hydraulic Model Results, 50-yr (Proposed)

Location WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5882.1 5884.3 11.3 18.1 4.9 8.8

XS2 5884.0 5885.6 10.4 13.7 5.1 8.1

XS3 5886.0 5886.4 4.8 8.0 6.2 9.7

Freeboard estimates were taken using the average water surface elevation for the 50-yr return period at the upstream face of the bridge, per the PDDM. The assumed low chord of the bridge is 5885.2-ft.

Freeboard for the design storm can be found in Table 1. See Appendix C for additional information.

50-year WSEL

Existing Streambed

50-year WSEL

Existing Streambed

15 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

4.7 DEBRIS CHECK CONDITION

Per the PDDM, bridges with a high potential for woody debris should be designed with 3.5-ft to 5-ft of freeboard. The drainage basin to this bridge has not recently been impacted by any fires that may cause a higher debris load, and therefore the likelihood of woody debris is low. The bridge will accommodate

3.1-ft of freeboard for the average water surface elevation at the design storm event, which is sufficient for the likely debris load at the bridge location.

5 BRIDGE SCOUR

5.1 SITE OBSERVATIONS

A hydraulics team representative was not able to attend the site visit to the project. Site observations are taken from photos taken at the site visit by other CFL team members. There is evidence of undermining of the cobble/boulder bank configuration that exists on both abutments. The most recent bridge inspection report from 2018 does not indicate any scour or channel instability observations.

5.2 LONG-TERM DEGRADATION AND CHANNEL MIGRATION

Bridge inspection reports available for 1997, 2016, 2018, and 2020 provided channel cross sections. These cross sections do not indicate a pattern of degradation in the channel. Because of this, the value used for long term degradation in subsequent scour calculations for the N. Fork Crazy Woman Creek Bridge is 0.

5.3 GEOTECHNICAL INVESTIGATION

A geotechnical investigation was conducted in July 2022. The flow in N. Fork Crazy Woman Creek was too high to safely collect a streambed sample. During this site investigation multiple borings were taken near the east abutment of the bridge. Soil samples indicate a D50 size of 0.3-mm to 7.5-mm and classifications of GC-GM (clayey/silty gravels) and SC-SM (silty/clayey sands). Per visual observations during the geotechnical investigation, the majority of the streambed appeared to consist of cobbles. Because of these observations, multiple scenarios were conducted with differing D50 sizes to determine scour estimates.

5.4 SCOUR EVALUATION

Scour depths were estimated in accordance with HEC-18 (FHWA 2012) and were completed using the

Hydraulic Toolbox (FHWA 2021). Per the PDDM, the 100-yr storm event represents the scour design flood and the 200-yr storm event represents the scour check flood. All scour calculations were done using results from SRH-2D simulations in the Hydraulic Toolbox (FHWA 2021). Total scour is a combination of long-term degradation, contraction scour, and local (abutment) scour. Contraction scour can be characterized as live-bed or clear-water scour. The abutment scour values presented already include contraction scour using the NCHRP 24-20 abutment scour approach that was utilized in this analysis. Total scour was calculated as a combination of abutment scour and long-term degradation. As discussed, long term degradation is set to 0 for this evaluation.

Due to the observations of the geotechnical site investigation, multiple scour scenarios were investigated to determine scour estimates. D50 sizes of 6-in, 3-in, and 7.5-mm were used as different scenarios for comparison. All these three scenarios produced results in live-bed scour with very similar values. Because

16 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report the samples taken during the investigation were done at the abutment and do not necessary represent the streambed, a D50 of 3-in was chosen to be reported as this is the smallest particle size considered to be a cobble, consistent with the visual observations from the geotechnical investigation.

5.5 SCOUR ESTIMATE RESULTS

Scour results are presented in this section for both the scour design flood (100-yr) and check flood (200-yr). Table 14 below describes the abutment scour estimates for N. Fork Crazy Woman Creek. Table 15 presents the contraction scour estimates. The larger of the left and right abutment is taken as the recommended scour depth as the channel thalweg could migrate towards either abutment in time.

Additional information from the Hydraulic Toolbox can be found in Appendix C.

Table 14: N. Fork Crazy Woman Creek Abutment Scour Estimates

Parameter Left Abutment Right Abutment

100-yr 200-yr 100-yr 200-yr

D50 (ft) 0.25 0.25 0.25 0.25 q2/q1 1.76 1.86 1.76 1.86

Amplification Factor 1.38 1.31 1.38 1.31

Average Velocity Upstream (ft/s) 13.6 13.7 13.6 13.7

Scour Condition Type A Live-Bed Type A Live-Bed Type A Live-Bed Type A Live-Bed

Abutment Scour Depth (ft) 6.4 6.7 4.8 4.4

Adopted Abutment Scour Depth

(ft)

6.4 6.7 4.8 4.4

Table 15: N. Fork Crazy Woman Creek Contraction Scour Estimates

Parameter 100-year 200-year

D50 (ft) 0.25 0.25

Average Flow Depth Upstream of

Contraction (ft)

3.1 3.4

Critical Velocity (ft/s) 8.5 8.6

Average Velocity Upstream (ft/s) 13.6 13.7

Scour Condition Live-Bed Live-Bed

Contraction Scour Depth (ft) -1.5 -1.4

Adopted Contraction Scour Depth (ft) 0 0

17 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

6 RECOMMENDATIONS

6.1 BRIDGE CAPACITY

Hydrologic and hydraulic analyses were conducted for the North Fork Crazy Woman Creek Bridge as described in previous sections of this report. As can be seen in Table 1, the 2-ft of freeboard is met for the average water surface elevation for the 50-year design event. All information provided in this table is taken from the upstream face of the bridge per the PDDM section 7.4.3.4.1. This is based on an assumed low chord elevation of 5885.2-ft. At the design storm event, the average water surface elevation provides

3.1-ft of freeboard.

6.2 BRIDGE SCOUR

A summary of individual scour estimates for each of the scour components, utilizing the methodology outlined above across the two scour flow events of interest, is summarized in Table 16. Based on the critical velocity of the streambed materials, a live bed scour condition can be expected.

Table 16: Scour Component Summary by Design Event

Design Flood Long Term

Degradation

(ft)

Contraction

Scour (ft)

Abutment

Scour (ft)

Total Scour

(ft)

Thalweg

Elevation

(ft)

Total Scour

Elevation

(ft) 100-year

Scour Design

Flood

0 0 6.4 6.4 5874.3 5867.9

200-year

Scour Check

Flood

0 0 6.7 6.7 5874.3 5867.6

6.3 BANK PROTECTION AND COUNTERMEASURES

Bridge foundations for the N. Fork Crazy Woman Creek Bridge will be designed for the estimated scour depths described in this report. No additional bank protection or countermeasures are recommended.

Proposed bridge abutments will be placed behind existing, causing no impact to the existing bank protection that is in place in the form of grouted cobbles and boulders. This is recommended to remain in place with no additional countermeasures.

18 | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

7 REFERENCES

Aquaveo. 2021. Surface-water Modeling System (SMS), version 13.0.5. Provo, UT.

Aquaveo. 2021. Watershed Modeling System (WMS), version 11.0.2. Provo, UT.

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

J.F. Miller, R.H. Fredrick, R.J. Tracey. 1973. NOAA Atlas 2. Precipitation-Frequency Atlas of the Western

United States, Volume II-Wyoming. https://hdsc.nws.noaa.gov/hdsc/files25/Atlas2_Volume2.pdf

Johnson County, WY. 2008. Johnson County, WY County Road & bridge Standards, Subdivision Road &

Bridge Standards. http://www.johnsoncountywyoming.org/jcco/wp-content/uploads/2017/09/jc_road_bridge_standards_1.pdf

Multi-Resolution Land Characteristics Consortium. 2018. National Land Cover Database 2011 (NLCD 2011). Multi-Resolution Land Characteristics Consortium (MRLC).

https://data.nal.usda.gov/dataset/national-land-cover-database-2011-nlcd-2011.

Natural Resources Conservation Service. 2003. Soil Survey Geographic (SSURGO) database. Fort Worth, TX. http://websoilsurvey.nrcs.usda.gov.

U.S. Army Corps of Engineers. 2021. HEC-HMS, Hydrologic Engineering Center Hydrologic Modeling System. Version 4.8. Davis, CA.

U.S. Department of Transportation Federal Highway Administration. 2002. Hydraulic Design Series No.2, Second Edition. https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hif02001.pdf

U.S. Geological Survey. 2003. Water-Resources Investigations Report 03-4107 “Peak-Flow Characteristics of Wyoming Streams.” https://pubs.usgs.gov/wri/wri034107/pdf/wri034107.pdf

U.S. Geological Survey. 2016. StreamStats Program. http://streamstats.usgs.gov.

https://flh.fhwa.dot.gov/resources/design/pddm/ https://hdsc.nws.noaa.gov/hdsc/files25/Atlas2_Volume2.pdf http://www.johnsoncountywyoming.org/jcco/wp-content/uploads/2017/09/jc_road_bridge_standards_1.pdf http://www.johnsoncountywyoming.org/jcco/wp-content/uploads/2017/09/jc_road_bridge_standards_1.pdf https://data.nal.usda.gov/dataset/national-land-cover-database-2011-nlcd-2011 http://websoilsurvey.nrcs.usda.gov/ https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hif02001.pdf https://pubs.usgs.gov/wri/wri034107/pdf/wri034107.pdf

A | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Appendix A

Hydrologic Analysis

A1 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

Precipitation Frequency Data Server Information

Calculated Precipitation Data (per NOAA Atlas 2)

Duration Return Period

1 2 5 10 25 50 100 200 500

5-min 0.22 0.21 0.23 0.30 0.34 0.39 0.54 0.55 0.55

15-min 0.44 0.41 0.45 0.59 0.66 0.77 1.05 1.08 1.08

60-min 0.76 0.71 0.79 1.03 1.16 1.35 1.85 1.90 1.90

2-hr 0.91 0.88 0.99 1.25 1.42 1.64 2.10 2.19 2.26

3-hr 1.03 1.02 1.17 1.44 1.65 1.89 2.31 2.44 2.56

6-hr 1.33 1.36 1.60 1.90 2.20 2.50 2.85 3.06 3.32

12-hr 1.75 1.88 2.26 2.55 3.02 3.35 3.90 4.25 4.76

24-hr 2.16 2.40 3.00 3.20 3.80 4.20 5.00 5.53 6.50

A2 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A3 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

StreamStats Streamgage Information

A4 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A5 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A6 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A7 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A8 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A9 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A10 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A11 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A12 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A13 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

A14 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

Regression Equation Estimates

Recurrence Peak (CFS)- Regression

Analysis Equivalent

Lower Limit

Factor

Upper Limit

Factor Lower Bound Upper Bound

2 370 1.2 0.396 2.53 150 930 5 600 2.4 0.476 2.1 280 1250

10 750 3.8 0.503 1.99 380 1500 25 960 5.4 0.509 1.96 490 1880 50 1100 6.3 0.5 2 550 2210

100 1260 6.9 0.486 2.06 610 2590 200 1430 7.2 0.467 2.14 670 3060 500 1650 7.3 0.44 2.28 730 3770

A15 | Hydrology WY FLAP JOH 14(1) – Final Hydraulics Report

Bridge Location Gage Flow Estimates

Recurrence (years)

Gaging Station Peak Flow (Qts)

(cfs)

Average Equivalent Years of Record

Peak Flow of Gaged Station from Regression Equation (Qtr)

(cfs)

Weighted peak Flow (Qtw) (cfs)

Exponent

Peak Flow of Ungaged Site

(Bridge Location) (cfs)

2 274 1.2 320 280 0.866 230

5 593 2.4 560 590 0.829 500

10 889 3.8 720 870 0.81 730

25 1370 5.4 950 1290 0.79 1100

50 1810 6.3 1120 1670 0.776 1420

100 2320 6.9 1300 2090 0.764 1790

200 2920 7.2 1500 2590 0.752 2220

500 3850 7.3 1770 3360 0.738 2900

Note: These calculations pertain to equations 4 and 5 in the document Peak Flow Characteristics of Wyoming Streams

B | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Appendix B

HEC-HMS Information

B1 | HEC-HMS Information WY FLAP JOH 14(1) – Final Hydraulics Report

Curve Number Report

HEC-HMS Information

Meteorologic Models:

B2 | HEC-HMS Information WY FLAP JOH 14(1) – Final Hydraulics Report

B3 | HEC-HMS Information WY FLAP JOH 14(1) – Final Hydraulics Report

Results:

C | P a g e WY FLAP JOH 14(1) – Final Hydraulics Report

Appendix C

Hydraulic Model Results

C1 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

SRH-2D Computational Mesh, Existing

Selected SRH-2D Results, Existing

2-yr WSEL

C2 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

50-yr WSEL

100-yr WSEL

C3 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr WSEL

2-yr Velocity Magnitude and Vectors

C4 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

50-yr Velocity Magnitude and Vectors

100-yr Velocity Magnitude and Vectors

C5 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr Velocity Magnitude and Vectors

50-yr, XS2, 14-ft US of Bridge Face

50-yr, XS3, 40-ft US of Bridge Face

WSEL

WSEL

WSEL

Existing Ground

C6 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

50-yr, Profile Cross Section Elevation at Channel Thalweg

Model Results – 2-yr

WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5877.3 5878.1 7.9 11.2 2.0 3.1

XS2 5878.2 5878.2 8.3 9.6 2.1 2.7

XS3 5879.2 5879.2 4.7 7.5 2.2 2.8

Model Results – 100-yr

WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5884.2 5887.3 9.6 18.9 3.9 9.6

XS2 5885.4 5886.9 12.0 14.4 6.0 9.1

XS3 5887.4 5887.7 5.5 8.2 7.2 11.1

Model Results – 200-yr

WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5885.4 5888.4 10.9 17.8 4.9 10.5

XS2 5886.5 5887.9 11.6 13.5 7.2 10.6

XS3 5888.4 5888.8 5.9 7.9 8.2 12.1

WSEL

C7 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

SRH-2D Computational Mesh, Proposed

Selected SRH-2D Results, Proposed

2-yr WSEL

C8 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

50-yr WSEL

100-yr WSEL

C9 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr WSEL

2-yr Velocity Magnitude and Vectors

C10 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

50-yr Velocity Magnitude and Vectors

100-yr Velocity Magnitude and Vectors

C11 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr Velocity Magnitude and Vectors

2-yr XS1, Upstream Bridge Face

100-yr XS1, Upstream Bridge Face, with Pressure Flow

2-year WSEL

Existing Streambed

Bridge Location

100-year WSEL

Bridge Location

Existing Streambed

100-year

WSEL+Pressure

C12 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr XS1, Upstream Bridge Face, with Pressure Flow

Model Results – 2-yr

WSEL (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5877.3 5878.1 7.9 11.2 2.0 3.1

XS2 5878.2 5878.2 8.3 9.6 2.1 2.7

XS3 5879.1 5879.2 4.7 7.5 2.2 2.8

Model Results – 100-yr

WSEL + Pressure (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5884.2 5887.4 9.6 18.8 3.9 9.5

XS2 5885.4 5886.8 11.5 13.8 6.1 9.5

XS3 5887.3 5887.7 5.5 8.1 7.2 11.0

Model Results – 200-yr

WSEL + Pressure (ft) Velocity (fps) Depth (ft)

Average Maximum Average Maximum Average Maximum

XS1 5885.1 5888.4 10.2 19.1 4.6 10.2

XS2 5886.7 5889.6 10.4 13.9 6.2 10.6

XS3 5888.4 5888.7 5.8 8.2 8.2 12.0

200-year WSEL

200-year

WSEL+Pressure Existing Streambed

C13 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

Scour Estimates

100-yr Left Abutment Scour 100-yr Right Abutment Scour

100-yr Contraction Scour

C14 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr Left Abutment Scour 200-yr Right Abutment Scour

200-yr Contraction Scour

C15 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

Scour Summary

100-yr Scour Plot

C16 | Hydraulic Model Results WY FLAP JOH 14(1) – Final Hydraulics Report

200-yr Scour Plot