ND FLAP 704(1) 795(1) Magpie_Whitetail_Final_Hydraulics_Report.pdf

Dakota Prairie Grasslands US Forest Service

Billings County, ND

ND FLAP 704(1) 795(1)

Magpie Creek and Whitetail Creek Crossings

Final Hydraulic Report

Federal Highway Administration

Central Federal Lands Highway Division

23 February 2023 i ND FLAP 704(1) 795(1) – Final Hydraulic Report

Executive Summary

Hydrologic and hydraulic analyses were conducted for the ND FLAP 704(1) 795(1) Magpie Creek and Whitetail Creek Crossings Project. The objective of the project is to elevate the crossings out of the stream to provide safe vehicular passage during frequent stream flow. To achieve this, the existing natural surface low water crossings will be replaced with a bridge crossing at Magpie Creek and a culvert crossing at Whitetail Creek.

The design peak flow values for the project were estimated using USGS regression equations for North Dakota. For Magpie Creek, the 50-year flow was used to hydraulically size the crossing in accordance with Federal Lands Highway PDDM criteria. Scour depth estimates were conducted in accordance with HEC-18 using a 100-year scour design flood and 200-year scour check flood.

For Whitetail Creek a 25-year design flood was used to size the crossing in accordance with PDDM low standard hydraulic criteria for culverts.

Two-dimensional hydraulic modeling using SRH-2D was conducted to estimate water surface elevations (WSEL), depths, and flow velocities at the project site. At Magpie Creek the proposed configuration is a 114-foot bridge with 2H:1V spill-through abutment slopes. Abutment toes will be located near existing channel banks to allow conveyance of bankfull flows. The proposed low chord is 2,144.91 feet and provides a minimum 2 feet of freeboard above the 50-year WSEL.

At Whitetail Creek the proposed configuration is a two-barrel 12’ x 10’ concrete box culvert, embedded a minimum of 1-foot. The hydraulic recommendations for the Magpie Creek and Whitetail Creek crossings are shown in the following table:

Summary of Hydraulic Recommendations

Site Location Proposed Structure Type

Geometric Parameters Remarks

704 Magpie Creek 3-Span Bridge Bridge Length = 114 feet

Bridge Low Chord = 2,144.91 • Class 3 riprap abutment protection

795 Whitetail Creek

Concrete Box Culvert

Number of Barrels = 2 Span x Height = 12-ft x 10-ft

• Culvert embedded 1-foot minimum.

• Class 2 riprap outlet protection

The Magpie Creek bridge hydraulic data is summarized in the following table:

ii ND FLAP 704(1) 795(1) – Final Hydraulic Report

Summary of Magpie Creek Bridge Hydraulic Data Q (cfs) V (ft/s) WS El. (ft) Scour El. (ft)

Q2 397 3.9 2,138.52 --- Q50 3,400 10.3 2,142.13 --- Q100 4,170 10.7 2,142.91 2,127.21 Q200 4,890 11.0 2,143.21 2,126.42

Notes:

Water surface elevations are at upstream face of bridge.

50-year WS. El. used to determine freeboard = 2,142.6’ (measured 28 feet upstream of bridge).

Hydraulic capacity requirements: Bridge low chord provides a minimum 2.0 feet of freeboard above 50-year water surface elevation.

iii ND FLAP 704(1) 795(1) – Final Hydraulic Report

Table of Contents

1 Project Background Information

2 Hydraulic Design Criteria

3 Hydrology

3.1 Hydrologic Setting

3.2 FEMA Flood Insurance Study

3.3 Available Hydrologic Data

3.4 Regression Equation Estimates

4 Hydraulic Analysis

4.1 Topographic Information

4.2 Hydraulic Model Development

4.3 Hydraulic Model Results

4.3.1 Magpie Creek Existing Conditions

4.3.2 Magpie Creek Proposed Conditions

4.3.3 Whitetail Creek Existing Conditions

4.3.4 Whitetail Creek Proposed Conditions

4.4 Magpie Creek Scour Assessment

4.4.1 Geotechnical Investigation

4.4.2 Scour Estimates

5 Summary of Hydraulic Recommendations

6 References

Tables Table 1: FLH Hydraulic Design Criteria Table 2: Stream Crossing Standards Article 89-14 ND Administrative Code Table 3: Basin Properties Table 4: Available Peak Streamflow Information Table 5: Magpie Creek Creek Regression Peak Flow Estimates Table 6: Whitetail Creek Regression Peak Flow Estimates Table 7: Project Land Cover Types and Manning’s Roughness Table 8: Magpie Creek 2-year Proposed Conditions Hydraulic Results Table 9: Magpie Creek 50-year Proposed Conditions Hydraulic Results Table 10: Magpie Creek 100-year Proposed Conditions Hydraulic Results iv ND FLAP 704(1) 795(1) – Final Hydraulic Report

Table 11: Magpie Creek 200-year Proposed Conditions Hydraulic Results Table 12: 50-year Proposed Conditions Freeboard Table 13: Whitetail Proposed Culvert Characteristics Table 14: Whitetail Creek 2-year Proposed Conditions Hydraulic Results Table 15: Whitetail Creek 15-year Proposed Conditions Hydraulic Results Table 16: Whitetail Creek 25-year Proposed Conditions Hydraulic Results Table 17: Whitetail Creek 100-year Proposed Conditions Hydraulic Results Table 18: Magpie Creek Contraction Scour Estimates Table 19: Magpie Creek Abutment Scour Estimates Table 20: Magpie Creek Pier Scour Estimates Table 21: Magpie Creek Total Abutment Scour Results Table 22: Summary of Hydraulic Recommendations

Figures Figure 1: Magpie Creek Location Map Figure 2: Whitetail Creek Location Map Figure 3: Magpie Creek Topographic Surface, Elevations in feet (NAVD88) Figure 4: Whitetail Creek Topographic Surface, Elevations in feet (NAVD88) Figure 5: Magpie Creek Existing SRH-2D Mesh Figure 6: Whitetail Creek Existing SRH-2D Mesh Figure 7: Magpie Creek Land Cover Types and Manning’s Roughness Figure 8: Whitetail Creek Land Cover Types and Manning’s Roughness Figure 9: Magpie Creek 2-Year Water Depth Figure 10: Magpie Creek 10-Year Water Depth Figure 11: Magpie Creek Proposed Conditions SRH-2D Mesh Figure 12: Magpie Creek Cross Sections and Profile Baseline Figure 13: Proposed Magpie Creek Water Surface Profiles Figure 14: Magpie Creek 100-Year WSEL Difference (Proposed – Existing) Figure 15: Whitetail Creek 2-Year Water Depth Figure 16: Whitetail Creek 10-Year Water Depth Figure 17: Whitetail Creek Proposed SRH-2D Mesh Figure 18: Whitetail Creek Cross Sections and Profile Baseline Figure 19: Proposed Whitetail Creek Water Surface Profiles Figure 20: WSEL - Embankment Cross Section Figure 21: Whitetail Creek 100-Year WSEL Difference (Proposed – Existing) Figure 22: Recommended Abutment Protection

Appendix A: Hydrology Information Appendix B: Hydraulic Information

ND FLAP 704(1) 795(1) – Final Hydraulic Report

1 PROJECT BACKGROUND INFORMATION

The purpose of this project is to provide safe travel and allow consistent access across Magpie Creek (Magpie Road) and Whitetail Creek (Whitetail Road). The scope of this project will include the construction of structures across Magpie Creek and Whitetail Creek to allow the passage of vehicles. Work will also include roadway work for the stream crossing approaches as appropriate.

Figure 1: Magpie Creek Location Map

Magpie Creek Crossing

Figure 2: Whitetail Creek Location Map

2 HYDRAULIC DESIGN CRITERIA

Hydraulic design criteria for the project were obtained from the Federal Lands Highway Project Development and Design Manual (PDDM) (Federal Lands Highway 2012). Based on the project scoping summary, both the Magpie Creek and Whitetail Creek roads have an average daily traffic (ADT) of less than 200 vehicles. Based on these parameters, the road is classified as low standard for hydraulic design purposes according to the PDDM. The applicable FLH design criteria are listed in Table 1. Additional capacity design criteria based on ND Article 89-14 Public Highway Stream Crossings are shown in Table 2.

Table 1: FLH Hydraulic Design Criteria Road Classification: Low-Standard Road (ADT < 200 vpd)

Bridges

Design Frequency Check Frequency Freeboard

50-year flood

Greater of 100-year or overtopping flood

• Minimum of 2 feet

• 3.5 feet to 5 feet when woody debris potential is significant

• 5 feet to 10 feet when ice flow potential is significant

Scour

Scour Design

Frequency Scour Check Frequency Scour Countermeasure Design Frequency

100-year flood 200-year flood 200-year flood

Culverts Design Frequency Check Frequency Allowable Headwater

Whitetail Creek Existing Crossing

25-year flood

Overtopping flood or 100-year

Minimum of:

• Bottom of aggregate base layer

• HW/D ratio of 1.2 for D > 48", 1.5 for D ≤ 48”

• Heavy debris or sediment load concerns:

0.8 ≤ HW/D ≤ 1.0

• Unacceptable hazard to human life or property

Table 2: Stream Crossing Standards Article 89-14 ND Administrative Code

Road Classification: County, Rural System, Off System

Bridges & Reinforced

Concrete Boxes

Design Frequency Check Frequency Remarks

15-year flood Not specified

Discharges must be computed using United States geological survey report 92-4020 or other recognized hydrologic methods.

3 HYDROLOGY

3.1 HYDROLOGIC SETTING

The project is located within the Middle Little Missouri watershed (HUC 8: 10110203) and the Lower Little Missouri watershed (HUC 8: 10110205), a right bank tributary to the Little Missouri River. Whitetail Creek and Magpie Creek generally flow from south-east to north-west to their confluence with the Little Missouri River. The contributing drainage basins to the crossings were delineated using available 10-meter digital elevation model (DEM) and StreamStats (U.S. Geological Survey 2016). A summary of general basin properties is shown in Table 3.

Table 3: Basin Properties

Site Drainage Area (mi2)

Mean Basin Elevation (ft)

Mean Basin Slope (%)

Mean Annual Precipitation (in)

Magpie Creek Crossing 87.9 2,507 15.8 15.2 Whitetail Creek Crossing 16.7 2,722 5.37 14.9

3.2 FEMA FLOOD INSURANCE STUDY

According to FEMA Flood Insurance Rate Map (FIRM) Panel 380005 there is no FIRM data available for this region and is yet to be mapped.

3.3 AVAILABLE HYDROLOGIC DATA

According to the USGS National Water Information System (NWIS) there are no active USGS peak streamflow stations within the project limits. The closest USGS active station is located on Little Missouri River approximately 21 miles north-east of the confluence with Magpie Creek. Peak streamflow data from this station was included in the development of the USGS regression equations for North Dakota described in Section 3.4. Table 4 summarizes the station location and period of record.

Table 4: Available Peak Streamflow Information

USGS

Station Location Latitude Longitude Drainage

Area Period of Record

Total Peak Streamflow

Records Status

06337000 Little Missouri River NR Watford City, ND 47°35'43" 103°15'48" 8,310 mi2 1935-

2021 86 Active

3.4 REGRESSION EQUATION ESTIMATES

Regression Equations were used to estimate peak flows for the project basins. The equations for North Dakota are based on USGS Report 2015-5096 (Williams-Sether 2015). The site is located in the North Dakota hydrologic region B. The equations developed for region B relate peak discharge to drainage area, ruggedness number, and compactness ratio. The StreamStats web application (U.S. Geological Survey 2016) was used to perform the peak discharge estimates. 15-year and 200-year peak flows were estimated by fitting a logarithmic function to the regression data. The peak flow results and prediction errors for the project basins are shown in Table 5 and Table 6 for Magpie Creek and Whitetail Creek, respectively.

Table 5: Magpie Creek Creek Regression Peak Flow Estimates Percent Chance Exceedance (%) Return Period (year)

Peak Flow Estimate Average Standard Error of Prediction (ASPe) (cfs)

50 2 397 75.3 20 5 1,110 60.3 10 10 1,730 58.0

6.7 15 2,253 N/A 4 25 2,660 58.8 2 50 3,400 60.7 1 100 4,170 63.5 .5 200 4,892 N/A

Table 6: Whitetail Creek Regression Peak Flow Estimates Percent Chance Exceedance (%) Return Period (year)

Peak Flow Estimate Average Standard Error of Prediction (ASPe) (cfs)

50 2 119 75.3 20 5 340 60.3 10 10 538 58.0

6.7 15 708 N/A 4 25 836 58.8 2 50 1,070 60.7 1 100 1,320 63.5 .5 200 1,555 N/A

4 HYDRAULIC ANALYSIS

Hydraulic analyses were conducted for two crossing locations. The objective of the analyses was to establish the hydraulic capacity requirements using the available data and two-dimensional hydraulic modeling. The input data, model development, and results are discussed in the following sections.

4.1 TOPOGRAPHIC INFORMATION

Field survey information collected by Central Federal Lands was used to develop the hydraulic models for the sites. The survey information was processed to create triangular irregular network (TIN) surfaces to represent the topography in the streambed and floodplain areas near the existing crossings as shown in Figure 3 and Figure 4 for Magpie Creek and Whitetail Creek, respectively. LiDAR data obtained from the National Map was used to supplement the survey information where necessary. All elevations for the study are in units of feet and are referenced to the North American Vertical Datum of 1988 (NAVD 88).

Figure 3: Magpie Creek Topographic Surface, Elevations in feet (NAVD88)

Crossing Site

Figure 4: Whitetail Creek Topographic Surface, Elevations in feet (NAVD88)

4.2 HYDRAULIC MODEL DEVELOPMENT

Two-dimensional hydraulic simulations were conducted using SRH-2D (U.S. Bureau of Reclamation 2017) to estimate water surface elevations, water depth and flow velocities at the project site. The SRH-2D computational mesh generation and model pre- and post-processing was performed using the SMS 13.1 interface (Aquaveo 2022). SRH-2D uses a computational mesh to solve the two-dimensional flow equations (i.e., the depth-averaged St. Venant equations). The mesh defines the underlying topography and geometric properties of each computational element. The existing conditions SRH-2D computational meshes for Magpie Creek and Whitetail Creek are shown in Figure 5 and Figure 6, respectively.

Figure 5: Magpie Creek Existing SRH-2D Mesh

Crossing Site

Figure 6: Whitetail Creek Existing SRH-2D Mesh

The upstream boundary conditions in the model were specified as a constant discharge using the peak flow values discussed in section 3.4. The downstream boundary conditions were specified as known water surface elevations obtained using Manning’s equation and a energy grade line slope assumed to equal the streambed slope near the model downstream boundary.

SRH-2D uses Manning’s “n” values to calculate bed friction. The land use types were delineated using a combination of field assesment and aerial imagery as shown in Figure 7 and Figure 8 for Magpie and Whitetail Creek, respectively. The roughness values used in the model are shown in Table 7.

Table 7: Project Land Cover Types and Manning’s Roughness Land Use Manning's "n"

Main Channel 0.03 Floodplain Brush 0.05 Floodplain Trees 0.08

Gravel Road 0.025

Figure 7: Magpie Creek Land Cover Types and Manning’s Roughness

Figure 8: Whitetail Creek Land Cover Types and Manning’s Roughness

Crossing Site

4.3 HYDRAULIC MODEL RESULTS

4.3.1 Magpie Creek Existing Conditions

The existing crossing at Magpie Creek is a natural bottom low water crossing, the crossing becomes impassable during flow periods and is a safety and mobility problem. Existing conditions model results show a depth greater than 2 feet at the stream thalweg for the 2-year flow and greater than 4 feet for the 10-year flow. The 10-year flow exhibits significant overbank flooding as expected. Depth results are graphically shown in Figure 9 and Figure 10 for the 2-year and 10-year events, respectively.

Figure 9: Magpie Creek 2-Year Water Depth

Figure 10: Magpie Creek 10-Year Water Depth

4.3.2 Magpie Creek Proposed Conditions

For Magpie Creek, the proposed crossing is a 114-feet three-span bridge with 2H:1V spill-through abutment slopes supported on groups of cylindrical piers. The proposed roadway will be raised to an approximate elevation of 2,148 feet. The waterway bottom width is approximately 70-feet. The SRH-2D mesh was modified to include the roadway embankment. The bridge low chord allows conveyance of the 200-year peak flow without pressure flow; therefore, a pressure flow boundary condition was not used in the model. The piers were modeled as holes in the mesh to obtain detailed hydraulic results to be used in the pier scour equations discussed in the following sections. An excerpt of the proposed SRH-2D mesh near the bridge is shown in Figure 11.

Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 12. The water surface profile is shown in Figure 13. Due to the two-dimensional model domain, the profiles do not represent the maximum water surface elevations. Average and maximum hydraulic results at the selected cross sections are shown in Table 8 to Table 10 for 2-year, 50-year, 100-year, and 200-year return periods, respectively. Maps showing water surface elevations for various return periods are included in Appendix B.

Figure 11: Magpie Creek Proposed Conditions SRH-2D Mesh

Bridge piers (holes in the mesh)

Bridge Schematic

Figure 12: Magpie Creek Cross Sections and Profile Baseline

Figure 13: Proposed Magpie Creek Water Surface Profiles

100-year 50-year

2-year

200-year

Streambed

Table 8: Magpie Creek 2-year Proposed Conditions Hydraulic Results

Station Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 13 2.2 3.6 1.5 2.3 2,138.0 2,138.0

104 2.4 4.1 1.3 2.0 2,138.2 2,138.5 164 2.6 3.9 1.3 1.9 2,138.5 2,138.6 264 2.7 4.3 1.5 2.0 2,138.6 2,138.6

Table 9: Magpie Creek 50-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 13 2.6 8.1 1.7 5.4 2,140.3 2,141.1

104 3.1 9.9 2.1 5.1 2,140.7 2,141.7 164 1.8 7.5 2.9 5.6 2,142.6 2,143.2 264 2.7 6.8 2.9 6.0 2,142.9 2,143.6

Table 10: Magpie Creek 100-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 13 3.1 9.8 2.1 6.1 2,140.9 2,141.9

104 3.6 12.3 2.5 5.9 2,141.2 2,142.5 164 2.2 7.8 3.8 7.0 2,144.1 2,144.7 264 2.9 6.2 4.1 7.5 2,144.2 2,144.7

Table 11: Magpie Creek 200-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 13 2.9 9.0 1.9 5.8 2,140.6 2,141.5

104 3.4 11.4 2.4 5.5 2,140.9 2,142.1 164 2.1 7.6 3.4 6.3 2,143.4 2,144.1 264 2.8 6.4 3.5 6.8 2,143.6 2,144.2

To estimate freeboard requirements, the average 50-year water surface elevation was extracted 28 feet upstream of the bridge to approximate the point of maximum backwater and avoid uncertainty associated with the rapid drawdown of water at the bridge opening. Table 12 shows the minimum low chord elevation to meet 2 feet of freeboard requirement.

Table 12: 50-year Proposed Conditions Freeboard

Proposed Bridge Return Period (year)

Maximum WSEL (ft) (28 feet upstream)

Minimum Freeboard (ft)

Minimum Low Chord (ft)

114’ Bridge 50 2,142.6 2 2,144.6

While the project is not in a special flood hazard area mapped by FEMA, the impact of the proposed crossing on 100-year water surface elevations was evaluated. Figure 14 shows proposed minus existing 100-year water surface elevation. The results show that upstream of the proposed bridge the increase in 100-year water surface varies from 1 to 2.4 feet, shaded yellow and orange in the figure, for approximately 200 feet upstream. Beyond 200 feet the increase is less than 1-foot, shaded green in the figure, which is the PDDM backwater increase requirement in unmapped zones. At the upstream limit of the model domain the difference in water surface elevation is approximately 0.07 feet.

Figure 14: Magpie Creek 100-Year WSEL Difference (Proposed – Existing)

4.3.3 Whitetail Creek Existing Conditions

The existing crossing at Whitetail Creek is a natural bottom low water crossing, the crossing becomes impassable during flow periods and is a safety and mobility problem. Existing conditions model results show a depth greater than 2 feet at the stream thalweg for the 2-year flow and approximately 6 feet for the 10-year flow. Although Whitetail Creek is in a more confined setting, the 10-year flow exhibits shallow overbank flooding as expected. Depth results are graphically shown in Figure 15 and Figure 16 for the 2-year and 10-year events, respectively.

Figure 15: Whitetail Creek 2-Year Water Depth

Figure 16: Whitetail Creek 10-Year Water Depth

4.3.4 Whitetail Creek Proposed Conditions

For Whitetail Creek, the proposed crossing will be elevated to maintain vehicles out of the flowing stream.

Curve straightening will be required to meet the roadway geometric requirements and to locate the proposed crossing in a hydraulically favorable location. The bankfull width has been identified in previous reports as approximately 19 feet. The proposed crossing is a two-barrel concrete box culvert (CBC) that will convey the 25-year flow without overtopping of the roadway embankment. The proposed CBC consists of 12’ span x 10’ height barrels embedded a minimum of 1 foot. Proposed culvert characteristics are shown in Table 13.

Table 13: Whitetail Proposed Culvert Characteristics

Location Type Size (ft) (Span x height)

Number of

Barrels

Length (ft)

Upstream Channel

Invert (ft)

Downstream Channel

Invert (ft)

Upstream Culvert

Invert (ft)

Downstream Culvert

Invert (ft)

Overtopping Elevation

(ft)

Whitetail Creek

Concrete Box

Culvert 12 x 10 2 34 2,519.4 2,519.2 2,518.4 2,518.2 2,529.3

The SRH-2D mesh was modified to include the proposed roadway embankment. The culvert was modeled as a pressure flow boundary condition. The barrel wall was modeled as a 1-ft wide obstruction. An excerpt of the SRH-2D mesh in the vicinity of the crossing is shown in Figure 17.

Figure 17: Whitetail Creek Proposed SRH-2D Mesh

Summary hydraulic results and water surface profiles were extracted along cross sections and profile baseline as shown in Figure 18. The water surface profile is shown in Figure 19. Due to the two-dimensional model domain, the profiles do not necessarily represent the maximum water surface elevations. Average and maximum hydraulic results at the selected cross sections are shown in Table 14 to Table 17 for 2-year, 15-year, 25-year, and 100-year return periods, respectively. Maps showing water surface elevations for various return periods are included in Appendix B.

Pressure Flow boundary conditions simulate culvert

Figure 18: Whitetail Creek Cross Sections and Profile Baseline

Figure 19: Proposed Whitetail Creek Water Surface Profiles

Table 14: Whitetail Creek 2-year Proposed Conditions Hydraulic Results

Station Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 2.4 3.7 1.5 3.1 2,523.1 2,523.1

164 1.8 2.4 3.0 3.8 2,523.0 2,523.0 247 1.5 2.3 2.0 3.7 2,522.9 2,523.0 388 0.8 2.4 1.3 3.3 2,522.7 2,522.7

Table 15: Whitetail Creek 15-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 1.7 4.9 1.8 7.0 2,527.0 2,527.1

164 1.0 4.9 2.1 7.5 2,526.8 2,526.9 247 1.2 4.9 2.4 7.2 2,526.3 2,526.6 388 0.8 4.1 2.5 6.8 2,526.3 2,526.3

Table 16: Whitetail Creek 25-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 1.8 4.7 2.1 7.4 2,527.4 2,527.5

164 1.1 5.2 2.4 7.9 2,527.2 2,527.3 247 1.3 5.5 2.6 7.4 2,526.6 2,526.9 388 0.9 4.4 2.8 7.1 2,526.5 2,526.5

Proposed Culvert

25-year

2-year 15-year

Table 17: Whitetail Creek 100-year Proposed Conditions Hydraulic Results

Velocity (ft/s) Depth (ft) WSEL (ft)

Average Maximum Average Maximum Average Maximum 0 1.9 4.2 2.9 8.8 2,528.8 2,528.9

164 1.3 5.6 3.2 9.3 2,528.7 2,528.7 247 1.7 7.0 3.0 8.3 2,527.4 2,527.8 388 1.4 5.7 3.5 7.9 2,527.3 2,527.4

For the 25-year event the maximum headwater elevation is 2,527.3 feet which results in a headwater to depth ratio (HW/D) of 0.88 assuming a 9-foot opening height after embedment. For the 100-year event the maximum headwater elevation is 2,528.7 feet which results in a headwater to depth ratio (HW/D) of

1.03. There is no embankment overtopping for the 25-year or 100-year events. Figure 20 shows a sample embankment cross section taken approximately 50-feet west of the culvert. The cross section shows approximately 1.4 feet of freeboard with respect to the edge of shoulder for the 25-year event. The 100-year event reaches the edge of shoulder but doesn’t encroach into the traveled way.

Figure 20: WSEL - Embankment Cross Section

While the project is not in a special flood hazard area mapped by FEMA, the impact of the proposed crossing on 100-year water surface elevations was evaluated. Figure 21 shows proposed minus existing 100-year water surface elevation. The results show that upstream of the proposed culvert the increase in 100-year water surface varies from 0 to 1-foot, shaded green in the figure, for approximately 500 feet.

Beyond 500 feet water surface elevation decreases from 0 to 1-foot. The proposed crossing meets the PDDM backwater requirement for unmapped zones.

25-year

Figure 21: Whitetail Creek 100-Year WSEL Difference (Proposed – Existing)

4.4 MAGPIE CREEK SCOUR ASSESSMENT

4.4.1 Geotechnical Investigation

The geotechnical investigation was conducted in October 2018. For the Magpie Creek site, streambed soils are generally classified as well graded sand with silt (SW-SM). Based on the laboratory results, the median particle size (D50) of the streambed material is 4.1 mm (0.013 ft). For the scour evaluation a D50=

0.2 mm was chosen, this value represents the lower bound of the contraction scour equations. Based on the boring logs there is the potential for finer material to be present in the soil column. Additional details can be found in the project Geotechnical Report.

4.4.2 Scour Estimates

Scour depth estimates were conducted in accordance with HEC-18 (Federal Highway Administration 2012) for the 100-year scour design flood and the 200-year scour check flood. Total scour is the combination of long-term degradation, contraction scour and local scour (abutment scour and pier scour). For this study, abutment scour was estimated using the NCHRP 24-20 method. Long-term degradation was assumed to be zero.

Contraction scour can occur under two conditions: live-bed and clear-water. Live-bed scour occurs when there is sediment transport of bed material from the upstream reach into the bridge section. Clear-water scour occurs when there is no transport of bed material into the bridge section. The applicable scour case is determined by comparing the mean velocity of the channel with the critical velocity for initiation of motion using the median size (D50) of the streambed materials. Based on the materials observed on site and the results of the geotechnical investigation a live bed scour condition can be expected. A summary of contraction scour depths is shown in Table 18. In these tables negative scour values imply that zero scour is expected.

Table 18: Magpie Creek Contraction Scour Estimates

Parameter 100-Year 200-Year D50 (ft) 0.0007

Average Flow Depth Upstream of Contraction(ft) 6.65 7.12

Critical Velocity (ft/s) 1.33 1.35 Average Velocity Upstream (ft/s) 6.25 6.68

Scour Condition Live Bed Live Bed Contraction Scour Depth (ft) 0.88 1.04

Adopted Contraction Scour Depth (ft) 0.88 1.04

Abutment scour was estimated using the NCHRP 24-20 method which applies an amplification factor to the contraction scour at the abutments, i.e., it includes contraction scour at each abutment as part of the estimate. A type a (main channel) scour condition was assumed in accordance with HEC-18. A summary of abutment scour depths is shown in Table 19.

Table 19: Magpie Creek Abutment Scour Estimates

Parameter Left Abutment (Abut.1) Right Abutment (Abut. 2)

100-Year 200-Year 100-Year 200-Year D50 (ft) 0.0007 0.0007 q2/q1 1.46 1.47 1.46 1.47 Amplification Factor 1.52 1.50 1.52 1.50

Average Velocity Upstream (ft/s) 6.25 6.68 6.25 6.68

Scour Condition Type a Live Bed Type a Live Bed Type a Live Bed Type a Live Bed Abutment Scour Depth (ft) 8.45 8.94 9.23 9.73

Adopted Abutment Scour Depth (ft) 8.45 8.94 9.23 9.73

Pier scour was estimated using the HEC-18 pier scour equation.

Table 20: Magpie Creek Pier Scour Estimates

Parameter Pier 1 Pier 2

100-Year 200-Year 100-Year 200-Year Depth Upstream (ft) 6.30 6.86 6.30 6.86

Velocity Upstream (ft/s) 7.88 8.18 7.88 8.18 Width of Pier 1.50 1.50 1.50 1.50

Angle of Attack (°) 32.79 33.48 17.23 15.89 Column Spacing (ft) 7.50 7.50 7.50 7.50 Number of Columns 3 3 3 3 Pier Scour Depth (ft) 7.60 7.86 6.29 6.33

Total Pier Scour Depth Including Contraction Scour (ft) 8.48 8.90 7.17 7.37

It is recommended that the maximum scour elevations are applied to both abutments and that they are referenced to the channel thalweg. In addition, it is recommended that these elevations are also applied to the channel piers due to the potential for overlapping scour holes and uncertainty with the angle of attack estimate. A summary of total scour depths and recommended scour elevations are shown in Table 21.

Table 21: Magpie Creek Total Abutment Scour Results

Design Flood Long Term

Degradation (ft)

Contraction Scour (ft)

Adopted Pier/Abutment Scour Depth (ft)

Thalweg Elevation (ft)

Total Scour Elevation (ft)

100-year Scour Design Flood 0 0.88 8.94 2,136.15 2,127.21

200-year Scour Check Flood 0 1.04 9.73 2,136.15 2,126.42

Embankment abutment protection was designed in accordance with HEC-23 Design Guideline 14 (Federal Highway Administration 2009). Class 3 riprap is recommended based on the results of the hydraulic model. The recommended abutment protection layout is shown in Figure 22.

Figure 22: Recommended Abutment Protection

5 SUMMARY OF HYDRAULIC RECOMMENDATIONS

Hydrology and hydraulics analyses were conducted for the Magpie Creek and Whitetail Creek crossings as discussed in the preceding sections. Table 22 shows the summary of hydraulic recommendations.

Table 22: Summary of Hydraulic Recommendations

Site Location Proposed Structure Type

Geometric Parameters Remarks

704 Magpie Creek 3-Span Bridge Bridge Length = 114 feet

Bridge Low Chord = 2,144.91 • Class 3 riprap abutment protection

795 Whitetail Creek

Concrete Box Culvert

Number of Barrels = 2 Span x Height = 12-ft x 10-ft

• Culvert embedded 1-foot minimum.

• Class 2 riprap outlet protection

6 REFERENCES

Aquaveo. 2022. Surface-water Modeling System (SMS), version 13.1.15. Provo, UT.

Federal Highway Administration . 2009. "Bridge Scour and Stream Instability Countermeasures - Experience, Selection, and Design Guidelines, Hydraulic Engineering Circular No. 23, Third Edition, FHWA-NHI 09-111 (Vol. 1), FHWA-NHI-09-112 (Vol. 2)." Federal Highway Administration, Washington, DC.

Federal Highway Administration. 2012. "Evaluating Scour at Bridges, Hydraulic Engineering Circular No.

18, Fifth Edition, FHWA-HIF-12-003." Washington D.C.

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

U.S. Bureau of Reclamation. 2017. SRH-2D, Sedimentation and River Hydraulics – Two-Dimensional model.

Version 3.2.

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

Williams-Sether, Tara. 2015. "Regional Regression Equations to Estimate Peak-Flow Frequency at Sites in North Dakota using Data Through 2009." U.S. Geological Survey Scientific Investigations Report 2015-5096.

Appendix A: Hydrology

Appendix B: Hydraulics

ND FLAP 704(1) 795(1) – Draft Hydraulic Report

Appendix A: Hydrology

1/10/22, 2:32 PM StreamStats https://streamstats.usgs.gov/ss/ 1/4

Magpie Creek StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 87.9 square miles

RUGGED Ruggedness number computed as stream density times basin relief

1770 feet per mi

COMPRAT A measure of basin shape related to basin perimeter and drainage area

2.17 dimensionless

AG_OF_DA Agricultural Land in Percentage of Drainage Area (Idaho Logistic Regression Equations SIR 2006-

3.45 percent

Region ID: ND Workspace ID: ND20220110212755476000 Clicked Point (Latitude, Longitude): 47.32571, -103.53877 Time: 2022-01-10 14:28:19 -0700 https://streamstats.usgs.gov/ss/ 2/4

Parameter Code Parameter Description Value Unit

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262

72.1 miles

BSLDEM10M Mean basin slope computed from 10 m DEM 15.8 percent

CSL1085LFP Change in elevation divided by length between points 10 and 85 percent of distance along the longest flow path to the basin divide, LFP from 2D grid

17.13 feet per mi

ELEV Mean Basin Elevation 2507 feet

ELEVMAX Maximum basin elevation 2817 feet

ISOLAKEDA Percent of total drainage area to isolated lakes 0.46

ISOLAKESUM Drainage area of isolated lakes 0.4 square miles

LAKEAREA Percentage of Lakes and Ponds 0.0109 percent

LAKEAREASU Total area of isolated lakes and ponds 0.00957 square miles

LC11DEV Percentage of developed (urban) land from NLCD 2011 classes 21-24

0.41 percent

LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset

0.16 percent

LFPLENGTH Length of longest flow path 30.2 miles

MINBELEV Minimum basin elevation 2139 feet

PRECIP Mean Annual Precipitation 15.2 inches

SLOPERAT Slope ratio computed as longest flow path (10-85) slope divided by basin slope

0.0206 dimensionless

SOILPERM Average Soil Permeability 1.65 inches per hour

STRMTOT total length of all mapped streams (1:24,000-scale) in the basin

229 miles

Peak-Flow Statistics Parameters [Peak Region B 2015 5096]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 87.9 square miles 0.11 8343

RUGGED Ruggedness_Number 1770 feet per mi 68 7820 https://streamstats.usgs.gov/ss/ 3/4

Parameter Code Parameter Name Value Units Min Limit Max Limit

COMPRAT Compactness Ratio 2.17 dimensionless 1.4 3.48

Peak-Flow Statistics Flow Report [Peak Region B 2015 5096]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, ASEp: Average Standard Error of Prediction, SE: Standard Error (other -- see report)

Statistic Value Unit ASEp

50-percent AEP flood 397 ft^3/s 75.3

20-percent AEP flood 1110 ft^3/s 60.3

10-percent AEP flood 1730 ft^3/s 58

4-percent AEP flood 2660 ft^3/s 58.8

2-percent AEP flood 3400 ft^3/s 60.7

1-percent AEP flood 4170 ft^3/s 63.5

0.2-percent AEP flood 5970 ft^3/s 70.1

Peak-Flow Statistics Citations

Williams-Sether, T.,2015, Regional regression equations to estimate peak-flow frequency at sites in North Dakota using data through 2009: U.S. Geological Survey Scientific Investigations Report 2015–5096, 12 p. (http://dx.doi.org/10.3133/sir20155096)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.6.2

StreamStats Services Version: 1.2.22

NSS Services Version: 2.1.2 http://dx.doi.org/10.3133/sir20155096 https://streamstats.usgs.gov/ss/ 4/4

1/10/22, 2:51 PM StreamStats https://streamstats.usgs.gov/ss/ 1/3

Whitetail StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 16.7 square miles

RUGGED Ruggedness number computed as stream density times basin relief

892 feet per mi

COMPRAT A measure of basin shape related to basin perimeter and drainage area

1.94 dimensionless

AG_OF_DA Agricultural Land in Percentage of Drainage Area (Idaho Logistic Regression Equations SIR 2006-5035

15.3 percent

BASINPERIM Perimeter of the drainage basin as defined in SIR 2004-5262

28.1 miles

Region ID: ND Workspace ID: ND20220110214826590000 Clicked Point (Latitude, Longitude): 47.19845, -103.30230 Time: 2022-01-10 14:48:50 -0700 https://streamstats.usgs.gov/ss/ 2/3

Parameter Code Parameter Description Value Unit

BSLDEM10M Mean basin slope computed from 10 m DEM 5.38 percent

CSL1085LFP Change in elevation divided by length between points 10 and 85 percent of distance along the longest flow path to the basin divide, LFP from 2D grid

19.58 feet per mi

ELEV Mean Basin Elevation 2722 feet

ELEVMAX Maximum basin elevation 2896 feet

ISOLAKEDA Percent of total drainage area to isolated lakes 0

ISOLAKESUM Drainage area of isolated lakes 0 square miles

LAKEAREA Percentage of Lakes and Ponds 0 percent

LAKEAREASU Total area of isolated lakes and ponds 0 square miles

LC11DEV Percentage of developed (urban) land from NLCD 2011 classes 21-24

1.67 percent

LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset

0.37 percent

LFPLENGTH Length of longest flow path 11.1 miles

MINBELEV Minimum basin elevation 2535 feet

PRECIP Mean Annual Precipitation 14.9 inches

SLOPERAT Slope ratio computed as longest flow path (10-85) slope divided by basin slope

0.069 dimensionless

SOILPERM Average Soil Permeability 1.34 inches per hour

STRMTOT total length of all mapped streams (1:24,000-scale) in the basin

41.3 miles

Peak-Flow Statistics Parameters [Peak Region B 2015 5096]

Parameter Code Parameter Name Value Units Min Limit Max Limit

DRNAREA Drainage Area 16.7 square miles 0.11 8343

RUGGED Ruggedness_Number 892 feet per mi 68 7820

COMPRAT Compactness Ratio 1.94 dimensionless 1.4 3.48

Peak-Flow Statistics Flow Report [Peak Region B 2015 5096] https://streamstats.usgs.gov/ss/ 3/3

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, ASEp: Average Standard Error of Prediction, SE: Standard Error (other -- see report)

Statistic Value Unit ASEp

50-percent AEP flood 119 ft^3/s 75.3

20-percent AEP flood 340 ft^3/s 60.3

10-percent AEP flood 538 ft^3/s 58

4-percent AEP flood 836 ft^3/s 58.8

2-percent AEP flood 1070 ft^3/s 60.7

1-percent AEP flood 1320 ft^3/s 63.5

0.2-percent AEP flood 1910 ft^3/s 70.1

Peak-Flow Statistics Citations

Williams-Sether, T.,2015, Regional regression equations to estimate peak-flow frequency at sites in North Dakota using data through 2009: U.S. Geological Survey Scientific Investigations Report 2015–5096, 12 p. (http://dx.doi.org/10.3133/sir20155096)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.6.2

StreamStats Services Version: 1.2.22

NSS Services Version: 2.1.2 http://dx.doi.org/10.3133/sir20155096

ND FLAP 704(1) 795(1) – Draft Hydraulic Report

Appendix B: Hydraulics

Magpie Creek SRH-2D Information

Scatter Data (Topographic Surface)

Magpie Creek Crossing

Magpie Creek SRH-2D Information (cont.)

SRH-2D Computational Mesh and Elevations

Magpie Creek Bridge

Land Use – Manning’s Roughness Coefficients

MagpieCreek SRH-2D Information (cont.)

2-Year Water Surface Elevation – Existing Conditions

50-Year Water Surface Elevation – Existing Conditions

MagpieCreek SRH-2D Information (cont.)

100-Year Water Surface Elevation – Existing Conditions

200-Year Water Surface Elevation – Existing Conditions

2-Year Water Surface Elevation – Proposed Conditions

50-Year Water Surface Elevation – Proposed Conditions

100-Year Water Surface Elevation – Proposed Conditions

200-Year Water Surface Elevation – Proposed Conditions

Whitetail Creek SRH-2D Information

Scatter Data (Topographic Surface)

Whitetail Creek SRH-2D Information (cont.)

SRH-2D Computational Mesh and Elevations

Whitetail Creek Culvert

Land Use – Manning’s Roughness Coefficients

WhitetailCreek SRH-2D Information (cont.)

2-Year Water Surface Elevation – Existing Conditions

Whitetail Creek Crossing

15-Year Water Surface Elevation – Existing Conditions

WhitetailCreek SRH-2D Information (cont.)

25-Year Water Surface Elevation – Existing Conditions

100-Year Water Surface Elevation – Existing Conditions

2-Year Water Surface Elevation – Proposed Conditions

15-Year Water Surface Elevation – Proposed Conditions

25-Year Water Surface Elevation – Proposed Conditions

100-Year Water Surface Elevation – Proposed Conditions