Hydraulic Report - 10.2 WV ERFO FS MNGAH921 2018-1(1) Appendix B.pdf

APPENDIX B

SMS Major Culverts Analysis

TR 312 – MP 1.0

DSR 2018-2.8

STA 81+94.56

Hydraulics Report TR 312 – MP 1.0

WV ERFO FS MNGAH921 2018-1(1) DSR 2018-2.8 – STA 81+94.56

TABLE OF CONTENTS

1. Purpose

2. Existing Structure

2.1. Location

2.2. Existing Geometry

2.3. Proposed Geometry

3. Hydrology

4. Structure Selection

5. Hydraulic Analysis

5.1. Modeling Method and Program Used

5.2. Topographic and Bathymetric Data

5.3. Model Geometry

5.4. Roughness Assignments

5.5. Boundary Conditions

5.6. Modeling of Proposed Structure

5.7. Model Run Control Parameters

6. Results

7. Riprap Analysis – Culvert Outlet Protection

LIST OF FIGURES

Figure 1: Project Location Map Figure 2: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours Figure 3: Mesh Elements Figure 4: ARR Mesh Quality Plot Figure 5: Annotated Plot Showing all Boundary Conditions Figure 6: 3D UGrid Proposed RCP 60-inch Culvert Figure 7: HEC-14 Equation 10.4 Figure 8: HEC-14 Equation 10.5 Figure 9: HEC-14 Table 10.1

LIST OF TABLES

Table 1: Culvert parameters Table 2: Culvert parameters Table 3: StreamStats Peak Discharge Data Table 4: Capacity Design, Scour Design, and Countermeasure Design Standards Table 5: Proposed Conditions Hydraulic Results (Design Flood Event – 25-Year) Table 6: Proposed Conditions HW/D Results (Design Flood Event - 25-Year) Table 7: Outlet Protection Analysis Inputs and Results

1. Purpose The purpose of this report is to assess the proposed hydraulic conditions at DSR 2018-2.8– Trail 312, which conveys flows of an unnamed tributary to the West Fork Glady Fork under West Fork Trail.

2. Existing Structure

2.1. Location

Figure 1: Project Location Map

2.2. Existing Geometry

Existing culvert through trail embankment is formed from rough-cut boulders. Survey data provides an invert elevation and approximate dimensions for the rectangular culvert opening at the upstream end. The downstream end of the culvert has collapsed and is buried as part of the slope failure of the trail embankment, so no data for invert or dimensions are provided in the survey. Downstream invert was

Project Location:

LAT: 38.7829310

LONG: -79.7294650

assumed from the elevations at the outfall location, and downstream dimensions were assumed to match the upstream opening dimensions.

The existing culvert has the following parameters:

Table 1: Culvert parameters

Material Opening Height

(FT)

Opening Width (FT) Length (FT) Upstream

Invert Downstream

Invert

Boulders 4.0 3.0 120.2 2921.00 2913.00

2.3. Proposed Geometry

The culvert will be replaced with a 60-inch (5.0-foot) circular Reinforced Concrete Pipe (RCP) through the embankment. The existing headwall structures will be replaced, and the embankment will be repaired and stabilized.

Table 2: Culvert parameters

Material Shape Inner Diameter (FT) Length (FT) Upstream

Invert Downstream

Invert RCP Circular 5.0 88.0 2919.85 2914.01

3. Hydrology The unnamed tributary (Tributary) to West Fork Glady Fork is an unregulated and ungaged stream. Peak discharges were estimated using USGS Stream Stats. The drainage area delineated using StreamStats was found to be 0.20 mi2. The resulting peak discharge data produced using StreamStats is presented below:

Table 3: StreamStats Peak Discharge Data

Frequency Flow Rate (ft3/s)

2-YR 17.0

25-YR 55.4

50-YR 68.2

100-YR 82.0

200-YR 96.8

500-YR 119.0

As West Fork Trail (Trail) is considered a Low-Standard Road. Design flood standards for this type of roadway are presented in Table 4.

Table 4: Capacity Design, Scour Design, and Countermeasure Design Standards

Capacity Design Flood Frequency

Scour Design Flood Frequency

Scour Check Flood Frequency

Countermeasure Design Flood Frequency

Q25 Q50 Q100 Q100

4. Structure Selection As outlined in the design scoping report, this site will receive embankment slope repair with soldier walls, guard rail installation, aggregate trail reconstruction as needed, removal of the failed boulder culvert, and replacement with a 60-inch RCP culvert.

5. Hydraulic Analysis

5.1. Modeling Method and Program Used

WSP developed a two-dimensional model of the 2018-2.8 crossing using the Sedimentation and River Hydraulics model (SRH-2D) within the Surface-water Modeling System (SMS Version 13.4.8) graphical user interface. SRH-2D was developed by the US Bureau of Reclamation (USBR), with cooperating technical development from the Federal Highway Administration (FHWA). SRH-2D is the preferred river modeling approach by FHWA for river crossing structures.

SRH-2D is a depth-averaged two-dimensional hydraulic model that uses a flexible mesh based finite element analysis of hydraulic systems. The model provides robust analysis of 2D dominated flow fields such as flows with in-stream structures, through bends, perched rivers, side channel and agricultural returns, and braided channel systems.

5.2. Topographic and Bathymetric Data

Field topographic and bathymetric survey data was collected by JMT in 2022. This survey data extended approximately 150 feet upstream and 130 feet downstream of the roadway crossing. However, due various issues with survey data, WSP utilized secondary data source from Tucker County FEMA 2018-2019 dataset, available through West Virginia University, for use as the terrain data for the model. The vertical datum for all sources is NAVD 88, the horizontal datum for all sources is NAD 83. Projection was set to State Plane Coordinate System, Zone: West Virginia North (FIPS 4701).

Figure 2: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours

5.3. Model Geometry

The modeling mesh is a collection of vertices, edges, and faces defining the three-dimensional spatial information of the ground surface. SRH-2D uses a finite element mesh to define the geometric surface and set the modeling limits. The SRH-2D modeling site extends from approximately 630 feet upstream of the crossing to approximately 660 feet downstream. The model domain width was sized to extend a conservative distance to capture the anticipated flood boundaries.

Both the patch and paving mesh type were utilized to create the model mesh. Triangular paving was primarily used in the overbank regions while rectangular patching was used throughout the upstream channel and the crossing. The mesh contains roughly 23,200 elements.

The mesh extents and total number of elements was developed to best capture geometric features impacting conveyance while also minimizing model inefficiencies and increased computational time. Upstream and downstream model extents were set to be far enough upstream and downstream to fully depict any impacts caused by the project. Initially, a coarse mesh was developed using larger elements and used in a simulation.

The model results informed the insertion of additional resolution throughout the domain. This iterative refinement process continued until changes in simulation solutions were minimal.

Figure 3: Mesh Elements

Figure 4: ARR Mesh Quality Plot

5.4. Roughness Assignments

A Manning’s roughness of 0.035 was used for the channel, 0.023 was used for the gravel road, 0.015 was used for overbank areas with open grass, and 0.1 was used for forested overbank areas. These values were estimated based upon available site photos. The proposed CMP was assigned an n-value of 0.012 and the downstream riprap was assigned a value of 0.055.

5.5. Boundary Conditions

Peak discharges, determined using StreamStats, were used as Inlet Q boundary conditions in the SRH-2D simulations. The SMS “Channel Calculator” tool was used to compute and assign a normal depth for the outflow boundary condition for all simulations.

Figure 5: Annotated Plot Showing all Boundary Conditions

5.6. Modeling of Proposed Structure

The recommended method to model culverts in SMS is through use of the 3D Structure coverage tool. This tool generates a 3D UGrid to visualize culverts in the graphics window and generate a new mesh to reflect the culvert elevations, and a ceiling elevation dataset to represent the culvert pressure zones. The terrain file used in the proposed conditions SMS simulations was modified to incorporate the proposed roadway profile at the crossing.

Figure 6: 3D UGrid Proposed RCP 60-inch Culvert

5.7. Model Run Control Parameters

All SRH-2D model controls were set to a 0.5-second timestep. All simulations were set to an automatic initial condition, and the total period that the simulation run analyzed was set to 4-hours. This was a long enough period to allow the model to reach a steady state solution for all simulation runs. Output frequency was set to simulation end. The default parabolic turbulence parameter option was selected and set to the default value of 0.7. Each simulation required less than 10 minutes of total run time.

6. Results Table 5: Proposed Conditions Hydraulic Results (Design Flood Event – 25-Year)

Roadway Elevation at Crossing (ft)

Bottom of Aggregate Base

Layer (ft)

Headwater Water Surface Elevation (ft)

WSEL ≤ Bottom of Aggregate Base

Layer?

Proposed RCP 2955 2954.17 2921.64 YES

Headwater elevation from SMS WSE observation profile

Table 6: Proposed Conditions HW/D Results (Design Flood Event - 25-Year)

Headwater Depth (ft) Culvert Diameter (ft) HW/D Proposed RCP 1.79 5.0 0.4

7. Riprap Analysis – Culvert Outlet Protection The Federal Highway Administration (FHWA) Hydraulic Toolbox was used to compute riprap size for culvert outlet protection. The toolbox adopts the FHWA Hec-14 Chapter 10 Equation 10.4 for culvert outlet riprap apron design.

𝐷50 = 0.2𝐷( 𝑄

ඥ𝑔𝐷2.5 )4 3ൗ ൬

𝐷

𝑇𝑊

൰

Figure 7: HEC-14 Equation 10.4

Where:

D50 = Riprap Size (ft) Q = Design Discharge (ft3/s) D = Culvert Diameter (circular) (ft) TW = Tailwater Depth (ft) g = Acceleration due to gravity (32.2 ft/s2)

As stated in HEC-14, whenever the flow is supercritical in the culvert, the culvert diameter is adjusted as follows:

𝐷′ = 𝐷 + 𝑦𝑛

Figure 8: HEC-14 Equation 10.5

Where:

D’ = Adjusted culvert rise(ft)

Yn = normal (supercritical) depth in the culvert (ft)

Inputs to these equations were taken directly from the SMS 100-year simulation results.

Table 7: Outlet Protection Analysis Inputs and Results

100-Year Discharge (ft3/s) 82.0 Diameter (ft) 5.0

Tailwater Depth (ft) 1 Normal Depth in Culvert (ft) 1.7

Flow Type Supercritical D50 (ft) 1.4 D50 (in) 16.9

A Class IV riprap gradation is recommended.

Figure 9: HEC-14 Table 10.1

In accordance with HEC-14, the recommended apron length and depth are outlined below:

Apron Length:

6 x D

6 x 5 = 30 feet

Apron Depth:

2.2 x D50

2.2 x 14 inches = 30.8 inches (2.6 feet)

ATTACHMENT A

EXHIBITS AND CALCULATIONS

1. SMS SRH-2D Water Surface Profiles

SMS SRH-2D WATER SURFACE PROFILES

FSR 13 – MP 10.5

DSR 2019-1.11

STA 11+41.00

Hydraulics Report FSR 13 – MP 10.5

WV ERFO FS MNGAH921 2018-1(1) DSR 2019-1.11 – STA 11+41

TABLE OF CONTENTS

1. Purpose

2. Existing Structure

2.1. Location

2.2. Existing Geometry

3. Proposed Geometry

4. Hydrology

5. Hydraulic Analysis

5.1. Modeling Method and Program Used

5.2. Topographic and Bathymetric Data

5.3. Model Geometry

5.4. Roughness Assignments

5.5. Boundary Conditions

5.6. Modeling of Proposed Structure

5.7. Model Run Control Parameters

6. Results

7. Riprap Analysis – Culvert Outlet Protection

LIST OF FIGURES

Figure 1: Project Location Map Figure 2: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours Figure 3: Mesh Elements Figure 4: ARR Mesh Quality Plot Figure 5: Boundary Conditions Figure 6: 3D UGrid Proposed Bridge (Approximating the RCBC) Figure 7: HEC-14 Equation 10.4 Figure 7: HEC-14 Equation 10.5

LIST OF TABLES

Table 1: Stacked Culvert Survey Data Table 2: Proposed Geometry Table 3: StreamStats Peak Discharge Data Table 4: Capacity Design, Scour Design, and Countermeasure Design Standards Table 5: Proposed Conditions Hydraulic Results (Design Flood Event – 25-Year) Table 6: Proposed Conditions HW/D Results (Design Flood Event - 25-Year) Table 7: Outlet Protection Analysis Inputs and Results

1. Purpose The purpose of this report is to assess the proposed hydraulic conditions at DSR 2019-1.11 – FSR 13 which conveys flows of Laurel Run through Canaan Loop Road.

2. Existing Structure

2.1. Location

Figure 1: Project Location Map

2.2. Existing Geometry

Stacked culverts of the following parameters:

Table 1: Stacked Culvert Survey Data Name - From Survey Data

Diameter

(ft) Material

Upstream Invert

(NAVD 88)

Downstream Invert

(NAVD 88)

Length (ft)

635 2 1.80 Ductile Iron Pipe 3239.60 3239.61 29.22 635 1.80 Ductile Iron Pipe 3241.15 3241.41 31.37

635 3 1.80 Ductile Iron Pipe 3239.46 3239.71 29.93 635 1 1.80 Ductile Iron Pipe 3241.49 3241.20 30.09 635 4 1.80 Ductile Iron Pipe 3239.83 3239.41 29.32

Project Location:

13 Canaan Mtn 9

LAT: 39.0756690

LONG: -79.5744200

3. Proposed Geometry The roadway will be reconstructed at new elevations and a 5’ x 8’ reinforced concrete box culvert (RCBC) will be installed at the crossing with 1-foot of streambed embedment. The culvert will be embedded 1-foot with a final opening dimension of 4’ x 8’.

Table 2: Proposed Geometry

Material Span (ft) Rise (ft) Upstream Invert (ft)

Downstream Invert (ft)

Embedment Depth (ft)

Reinforced Concrete Box Culvert 8 5 3239.57 3238.82 1

4. Hydrology Laurel Run is an unregulated and ungaged stream. Peak discharges were estimated using USGS Stream Stats. The drainage area delineated using StreamStats was found to be 0.92 mi2. The resulting peak discharge data produced using StreamStats is presented below:

Table 3: StreamStats Peak Discharge Data

Frequency Flow Rate (ft3/s)

2-YR 64.5

10-YR 143

25-YR 192

50-YR 234

100-YR 278

200-YR 325

500-YR 393

Canaan Loop Road is considered a Low-Standard Road. Design flood standards for this type of roadway are presented in Table 4:

Table 4: Capacity Design, Scour Design, and Countermeasure Design Standards

Capacity Design Flood Frequency

Scour Design Flood Frequency

Scour Check Flood Frequency

Countermeasure Design Flood Frequency

Q25 Q50 Q100 Q100

5. Hydraulic Analysis

5.1. Modeling Method and Program Used

WSP developed a two-dimensional model of the 2019-1.11 crossing using the Sedimentation and River Hydraulics model (SRH-2D) within the Surface-water Modeling System (SMS Version 13.3.9) graphical user interface. SRH-2D was developed by the US Bureau of Reclamation (USBR), with cooperating technical development from the Federal Highway Administration (FHWA). SRH-2D is the preferred river modeling approach by FHWA for river crossing structures.

SRH-2D is a depth-averaged two-dimensional hydraulic model that uses a flexible mesh based finite element analysis of hydraulic systems. The model provides robust analysis of 2D dominated flow fields such as flows with in-stream structures, through bends, perched rivers, side channel and agricultural returns, and braided channel systems.

The design objective of the 2-D hydraulic modeling in this study was to develop depth and velocity inputs for analysis of scour potential at the proposed bridge crossing. Modeling details and results are summarized in the following sections.

5.2. Topographic and Bathymetric Data

Field topographic and bathymetric survey data was collected by JMT in 2022. This survey data extended approximately 100-feet upstream and 100-feet downstream of the roadway crossing. Due to the area required for the floodplain model, WSP utilized secondary data from the Randolph County FEMA 2018- 2019 dataset, available through West Virginia University, for areas outside the surveyed area. These datasets were merged to create a complete terrain within the SMS software. The vertical datum for all sources is NAVD 88, the horizontal datum for all sources is NAD 83. Projection was set to State Plane Coordinate System, Zone: West Virginia North (FIPS 4701).

Figure 2: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours

5.3. Model Geometry

The modeling mesh is a collection of vertices, edges, and faces defining the three-dimensional spatial information of the ground surface. SRH-2D uses a finite element mesh to define the geometric surface and set the modeling limits. The SRH-2D modeling site extends from approximately 450 feet upstream of the crossing to approximately 300 feet downstream. The model domain width was sized to extend a conservative distance to capture the anticipated flood boundaries.

Both the patch and paving mesh type were utilized to create the model mesh. Triangular paving was primarily used in the overbank regions while rectangular patching was used throughout the channel and the crossing. The mesh contains roughly 21,000 elements.

The mesh extents and total number of elements was developed to best capture geometric features impacting conveyance while also minimizing model inefficiencies and increased computational time. Upstream and downstream model extents were set to be far enough upstream and downstream to fully depict any impacts caused by the project. Initially, a coarse mesh was developed using larger elements and used in a simulation.

The model results informed the insertion of additional resolution throughout the domain. This iterative

Figure 3: Mesh Elements

Figure 4: ARR Mesh Quality Plot

5.4. Roughness Assignments

A Manning’s roughness of 0.035 was used for the channel, 0.1 was used for overbank areas, 0.023 was used for the roadway and 0.05 was used for riprap countermeasure extents upstream and downstream of the proposed culvert.

5.5. Boundary Conditions

Peak discharges, determined using StreamStats, were used as Inlet Q boundary conditions in the SRH-2D simulations. The SMS “Channel Calculator” tool was used to compute and assign a normal depth for the outflow boundary condition for all simulations.

Figure 5: Boundary Conditions

5.6. Modeling of Proposed Structure

The recommended method to model culverts in SMS is through use of the 3D Structure coverage tool. This tool automatically generates an optimized mesh through the structure footprint, a ceiling elevation dataset to represent the culvert pressure zones, and a 3D UGrid to visualize culverts in the graphics window. The terrain file used in the proposed conditions SMS simulations was modified to incorporate the proposed roadway profile at the crossing.

Figure 6: 3D UGrid Proposed Reinforced Concrete Box Culvert

5.7. Model Run Control Parameters

All SRH-2D model controls were set to a 0.75-second timestep. A time step less than 1-second was found to be necessary to maintain hydraulic computational stability during the model run for all mesh options. All simulations were set to a dry initial condition, and the total period that the simulation run analyzed was set to 4-hours. This was a long enough period to allow the model to reach a steady state solution for all simulation runs. Output frequency was set to 15-minute intervals. The default parabolic turbulence parameter option was selected and set to the default value of 0.7. Each simulation required less than 10 minutes of total run time.

6. Results Table 5: Proposed Conditions Hydraulic Results (Design Flood Event – 25-Year)

Roadway Elevation at Crossing (ft)

Bottom of Aggregate Base

Layer (ft)

Headwater Water Surface Elevation (ft)

WSEL ≤ Bottom of Aggregate Base

Layer?

Proposed RCBC 3245 3244.17 3243.00 YES

Headwater elevation from SMS WSE observation profile

Table 6: Proposed Conditions HW/D Results (Design Flood Event - 25-Year)

Average Headwater

Depth (ft) Box Culvert Interior Height (ft) HW/D Proposed RCBC 3.93 4.0 1.0

Interior Height as 4 ft x 8 ft due to 1 foot of embedment in the 5 ft x 8 ft RCBC

7. Riprap Analysis – Culvert Outlet Protection The Federal Highway Administration (FHWA) Hydraulic Toolbox was used to compute riprap size for culvert outlet protection. The toolbox adopts the FHWA Hec-14 Chapter 10 Equation 10.4 for culvert outlet riprap apron design.

𝐷𝐷50 = 0.2𝐷𝐷(

𝑄𝑄

�𝑔𝑔𝐷𝐷2.5

)4 3� �

𝐷𝐷

𝑇𝑇𝑇𝑇

Figure 7: HEC-14 Equation 10.4

Where:

D50 = Riprap Size (ft) Q = Design Discharge (ft3/s) D = Culvert Diameter (circular) (ft) TW = Tailwater Depth (ft) g = Acceleration due to gravity (32.2 ft/s2)

As stated in HEC-14, whenever the flow is supercritical in the culvert, the culvert diameter is adjusted as follows:

𝐷𝐷′ =

𝐷𝐷 + 𝑦𝑦𝑛𝑛

Figure 8: HEC-14 Equation 10.5

Where:

D’ = Adjusted culvert rise(ft) Yn = normal (supercritical) depth in the culvert (ft)

As the culvert effectively has dimensions of 3’ x 8’ (due to the 1-foot embedment), an equivalent circular diameter is computed as 5.5-feet. Froude values extracted from the 100-year simulation indicate subcritical conditions through the culvert.

Inputs to these equations were taken directly from the SMS 100-year simulation results.

Table 7: Outlet Protection Analysis Inputs and Results

100-Year Discharge (ft3/s) 278 Equivalent Circular Diameter (ft) 6.4

Tailwater Depth (ft) 4.08 Normal Depth in Culvert (ft) 3.9

Flow Type Subcritical D50 (ft) 0.7 D50 (in) 8.9

A Class IV riprap gradation is recommended.

In accordance with HEC-14, the recommended apron length and depth are outlined below:

Apron Length:

6 x 3

6 x 3 = 18 feet

Apron Depth:

2.2 x D50

2.2 x 14 inches = 30.8 inches (2.6 feet)

1. SMS SRH-2D Water Surface Profiles

SMS SRH-2D WATER SURFACE PROFILES

TR 115A – MP 0.6

DSR 2019-1.18

STA 182+59.91

Hydraulics Report TR 115A – MP 0.6

WV ERFO FS MNGAH921 2018-1(1) DSR 2019-1.18 – STA 182+59.91

TABLE OF CONTENTS

1. Purpose

2. Existing Structure

2.1. Location

2.2. Existing Geometry

3. Proposed Geometry

4. FEMA Regulatory Status

5. Hydrology

6. Hydraulic Analysis

6.1. Modeling Method and Program Used

6.2. Topographic and Bathymetric Data

6.3. Model Geometry

6.4. Roughness Assignments

6.5. Boundary Conditions

6.6. Modeling of Proposed Structure

6.7. Model Run Control Parameters

6.8. Results

7. Outlet Protection

8. Estimating Wing Wall Depth Requirements

LIST OF FIGURES

Figure 1: Project Location Map Figure 2: Existing Box Culvert Figure 3: Existing Arch Bridge Figure 4: Site Map Figure 5: Excerpt of FIRM Panel 54093C0144E Figure 6: FEMA FIS Flood Profile 22P With Annotations Figure 7: Logarithmic Interpolation – Upstream of Snyder Run Figure 8: Logarithmic Interpolation – Downstream of Snyder Run Figure 9: Logarithmic Interpolation – Water Surface Elevations Figure 10: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours Figure 11: Mesh Elements Figure 12: ARR Mesh Quality Plot Figure 13: Boundary Conditions Figure 14: 3D UGrid Culverts and Bridge Figure 15: 500-Year Water Surface Extents

LIST OF TABLES

Table 1: Hydraulic Structure Parameters Table 2: Relief Pipe Proposed Geometry Table 3: Summary of Peak Discharges (FEMA FIS 54093CV000A) Table 4: Resulting Peak Discharges Table 5: Capacity Design, Scour Design, and Countermeasure Design Standards Table 6: Final Flow Rates and Water Surface Elevations

1. Purpose The purpose of this report is to assess the proposed hydraulic conditions at DSR 2019-1.18 – Trail which conveys flows of Snyder Run through Thomas Rail Trail and Blackwater Canyon Trail.

2. Existing Structure

2.1. Location

Figure 1: Project Location Map

2.2. Existing Geometry

The existing hydraulic structure elevations and sizes were obtained from topographic survey.

Project Location:

Blackwater Canyon Trail

LAT: 39.1414075

LONG: -79.5114622

Project Location:

Thomas Rail Trail

LAT: 39.141281

LONG: -79.511838

Table 1: Hydraulic Structure Parameters

Culvert Material Opening

Height (ft) Opening

Width (ft) Length

(ft) Upstream Invert

(NAVD 88)

Downstream Invert

(NAVD 88)

Thomas Rail

Trail Concrete Box

Culvert 9.5 10.0 45 2876.60 2875.45

Blackwater Canyon Trail

Concrete Arch Bridge 16.0 11.0 35 2871.10 2871.36

Figure 2: Existing Box Culvert

Figure 3: Existing Arch Bridge

3. Proposed Geometry The roadway will be reconstructed at new elevations and a wing wall will be reconstructed upstream of the concrete arch bridge. No changes to the dimensions of either hydraulic structure is proposed.

An additional 30” HDPE relief pipe will be installed approximately 90-feet Northeast of the concrete arch bridge.

Table 2: Relief Pipe Proposed Geometry

Material Diameter (ft)

Upstream Invert (ft)

Downstream Invert (ft) Length (ft)

HDPE Pipe 2.5 2882.10 2879.37 33

Figure 4: Site Map

4. FEMA Regulatory Status Snyder Run conveys flow to the North Fork Blackwater River, a FEMA Flood Zone AE and FEMA designated Floodway. The floodplain administration jurisdiction is Tucker County, West Virginia (and Incorporated Areas).

Box Culvert

Arch Bridge

Proposed 30” HDPE Pipe

North Fork Blackwater River

(FEMA Regulated) Snyder Run

Wing Wall for Repair

Figure 5: Excerpt of FIRM Panel 54093C0144E

The proposed work involving wing wall reconstruction of the concrete arch bridge and installation of a 30” HDPE relief pipe is anticipated to be outside of the FEMA Flood Hazard Area extents, and thus will not require coordination with local floodplain administrators.

5. Hydrology The current effective FEMA FIS (54093CV000A) for Tucket County, West Virginia (And Incorporated Areas) is dated July 6, 2010. The FEMA FIS includes a summary of discharges for the North Fork Blackwater River upstream and downstream of Snyder Run.

Table 3: Summary of Peak Discharges (FEMA FIS 54093CV000A)

Recurrence Interval

Upstream of Snyder Run

Downstream of Snyder Run

Flow Rate (cfs) Flow Rate (cfs) 10-Year 1,340 1,810 50-Year 2,150 2,850 100-Year 2,570 3,370 500-Year 3,710 4,780

The difference between the two discharge rates is assumed to be the contributing flow from Snyder Run.

The resulting discharges are as follows:

Table 4: Resulting Peak Discharges

Recurrence Interval

North Fork Blackwater River Snyder Run

Flow Rate (cfs) Flow Rate (cfs) 10-Year 1,340 470 50-Year 2,150 700 100-Year 2,570 800 500-Year 3,710 1070

The FEMA FIS Flood Profile 22P includes computed water surface elevations along the North Fork Blackwater River, including at the downstream limits of the SMS model.

Figure 6: FEMA FIS Flood Profile 22P With Annotations

This flood profile was used to develop the following downstream water surface elevations along the North Fork Blackwater River:

Recurrence Interval Water Surface Elevation (ft)

10-Year 2865 50-Year 2865.9 100-Year 2866 500-Year 2868

The Thomas Rail Trail and the Blackwater Canyon Trail are each considered as Low-Standard Roads.

Design flood standards for this type of roadway are presented in Table 5:

Table 5: Capacity Design, Scour Design, and Countermeasure Design Standards

Capacity Design Flood Frequency

Scour Design Flood Frequency

Scour Check Flood Frequency

Countermeasure Design Flood Frequency

Q25 Q50 Q100 Q100

To Develop a 25-yr discharge value, a logarithmic trendline was applied to a plot of annual exceedance probability vs discharge as shown below:

Figure 7: Logarithmic Interpolation – Upstream of Snyder Run

Figure 8: Logarithmic Interpolation – Downstream of Snyder Run

This resulted in a computed 25-year flow rate of 1814.1 cfs upstream, and 2413.4 cfs downstream for a contributing Snyder Run discharge of 599.4 cfs.

Logarithmic interpolation was also used to develop a 25-year water surface elevation at the downstream model limits. Similar steps were taken to develop data for the 2-year, and 200-year events.

Figure 9: Logarithmic Interpolation – Water Surface Elevations

The resulting upstream boundary condition steady flow discharges and downstream constant water surface elevations are as follows:

Table 6: Final Flow Rates and Water Surface Elevations

Recurrence Interval

North Fork Blackwater River Snyder Run North Fork

Blackwater River Flow Rate (cfs) Flow Rate (cfs) Downstream WSE (ft)

2-Year 287.3 209.4 2863.57 10-Year 1,340 470 2865 25-Year 1,814.1 599.4 2865.46 50-Year 2,150 700 2865.9 100-Year 2,570 800 2866 200-Year 3071.3 920.2 2867.02 500-Year 3,710 1070 2868

2-year, 25-Year and 200-Year data obtained through logarithmic interpolation of FEMA FIS values.

6. Hydraulic Analysis

6.1. Modeling Method and Program Used

WSP developed a two-dimensional model of the 2019-1.18 crossings using the Sedimentation and River Hydraulics model (SRH-2D) within the Surface-water Modeling System (SMS Version 13.3.10) graphical user interface. SRH-2D was developed by the US Bureau of Reclamation (USBR), with cooperating technical development from the Federal Highway Administration (FHWA). SRH-2D is the preferred river modeling approach by FHWA for river crossing structures.

SRH-2D is a depth-averaged two-dimensional hydraulic model that uses a flexible mesh based finite element analysis of hydraulic systems. The model provides robust analysis of 2D dominated flow fields such as flows with in-stream structures, through bends, perched rivers, side channel and agricultural returns, and braided channel systems.

The design objective of the 2-D hydraulic modeling in this study was to develop depth and velocity inputs for analysis of scour potential at the proposed bridge crossing. Modeling details and results are summarized in the following sections.

6.2. Topographic and Bathymetric Data

Field topographic and bathymetric survey data was collected by JMT in 2022 This survey data extended approximately 50-feet upstream of the box culvert and 60-feet downstream of the arch bridge crossing. Due to the area required for the floodplain model, WSP utilized secondary data from the Randolph County FEMA 2018-2019 dataset, available through West Virginia University, for areas outside the surveyed area.

These datasets were merged to create a complete terrain within the SMS software. The vertical datum for all sources is NAVD 88, the horizontal datum for all sources is NAD 83. Projection was set to State Plane Coordinate System, Zone: West Virginia North (FIPS 4701).

Figure 10: 3D-Rotated View of SMS Generated Mesh Displaying 1-Foot Contours

6.3. Model Geometry

The modeling mesh is a collection of vertices, edges, and faces defining the three-dimensional spatial information of the ground surface. SRH-2D uses a finite element mesh to define the geometric surface and set the modeling limits. The SRH-2D modeling site extends from approximately 650 feet upstream and 650 downstream of the North Fork of the Blackwater River. The mesh also extends approximately 1,130 feet along Snyder Run.

Both the patch and paving mesh type were utilized to create the model mesh. Triangular paving was primarily used in the overbank regions while rectangular patching was used throughout the channels and the crossings. The mesh contains roughly 20,000 elements.

The mesh extents and total number of elements was developed to best capture geometric features impacting conveyance while also minimizing model inefficiencies and increased computational time. Upstream and downstream model extents were set to be far enough upstream and downstream to fully depict any impacts caused by the project. Initially, a coarse mesh was developed using larger elements and used in a simulation.

The model results informed the insertion of additional resolution throughout the domain. This iterative

Figure 11: Mesh Elements

Figure 12: ARR Mesh Quality Plot

6.4. Roughness Assignments

A Manning’s roughness of 0.04 was used for the channel, 0.09 was used for forested overbank areas, 0.05 was used for grassy overbank areas, 0.013 was used for the roadway, and 0.012 was used for the concrete box culvert and the HDPE pipe.

6.5. Boundary Conditions

Peak discharges were used as Inlet Q boundary conditions in the SRH-2D simulations. Known water surface elevations are used as Exit boundary conditions along the North Fork of the Blackwater River. A discussion regarding how these values were extracted from the FEMA FIS are included in Section 5.

Figure 13: Boundary Conditions

6.6. Modeling of Proposed Structure

The recommended method to model culverts in SMS is through use of the 3D Structure coverage tool. This tool generates a 3D UGrid to visualize culverts in the graphics window and generate a ceiling elevation dataset to represent the culvert pressure zones. The terrain file used in the proposed conditions SMS simulations was modified to incorporate the proposed roadway profile at the crossing.

Figure 14: 3D UGrid Culverts and Bridge

6.7. Model Run Control Parameters

All SRH-2D model controls were set to a 0.75-second timestep. A time step less than 1-second was found to be necessary to maintain hydraulic computational stability during the model run for all mesh options. All simulations were set to a dry initial condition, and the total period that the simulation run analyzed was set to 4-hours. This was a long enough period to allow the model to reach a steady state solution for all simulation runs. Output frequency was set to 10-minute intervals. The default parabolic turbulence parameter option was selected and set to the default value of 0.7. Each simulation required less than 10 minutes of total run time.

6.8. Results

Simulations were run for the 2-year, 25-year, 50-year, 100-year, 200-year, and 500-year events. Only the 500-year event results in flow from Snyder Run reaching the proposed 30” HDPE relief pipe. As there is no flow for events less than the 500-year, the 30” HDPE pipe meets low standard road capacity design requirements.

Figure 15: 500-Year Water Surface Extents

7. Outlet Protection Riprap should be placed at the HDPE relief pipe outlet in accordance with EFLHD detail E251-01 with slope set to match the existing grade.

8. Estimating Wing Wall Depth Requirements To determine the depth of the proposed wingwall upstream of the existing arch bridge, potential scour depths downstream of the existing box culvert were evaluated with a standalone HY-8 file. This HY-8 model was used to estimate the scour hole geometry following HEC-14 Chapter 5 guidance.

The computations result in an estimated scour hole depth of 10.9-feet for the 100-year event. HY-8 outputs are included in Attachment A.

1. HY-8 Box Culvert Scour Hole Estimate (For Wing Wall Replacement Depth)

2. SMS SRH-2D Water Surface Extents

HY-8 BOX CULVERT SCOUR HOLE ESTIMATE

(FOR WING WALL REPLACEMENT DEPTH)

HY-8 Energy Dissipation Results

Scour Hole Geometry Parameter Value Units Select Culvert and Flow Crossing 2019-1.18 - Scour Hole

Estimate

Culvert Culvert 1 Flow 800.00 cfs Culvert Data Culvert Width (including multiple barrels)

10.0 ft

Culvert Height 9.5 ft Outlet Depth 4.32 ft Outlet Velocity 18.51 ft/s Froude Number 1.57 Tailwater Depth 4.14 ft Tailwater Velocity 12.86 ft/s Tailwater Slope (SO) 0.0256 Scour Data Time to Peak Note: if Time to Peak is unknown, enter 30 min

Time to Peak 30.00 min Cohesion Noncohesive D16 Value 20.00 mm D84 Value 88.00 mm Tailwater Flow Depth after Culvert Outlet

Normal Depth

Results Assumptions Soil Sigma 2.10 Scour Hole Dimensions Length 131.007 ft Width 84.601 ft Depth 10.870 ft Volume 39860.044 ft^3 DS at .4(LS) 52.403 ft Tailwater Depth (TW) 4.143 ft Velocity with TW and WS 1.739 ft/s

SMS SRH-2D WATER SURFACE EXTENTS

2-Year

25-Year

50-Year

100-Year

200-Year

500-Year