Hydraulic Report - 10.0 WV ERFO FS MNGAH921 2018-1(1).pdf

WV ERFO FS MNGAH921 2019-1(1)

Reconstruction of Damaged Roadway and Trail Sections, Bridge Replacement, and

Reconstruction

Hydraulics and Hydrology Report

100% Design

WV ERFO FS MNGAH921 2019-1(1) Hydraulics and Hydrology Report Monongahela National Forest 100% Design i

TABLE OF CONTENTS

1. Introduction and Purpose

2. Design Criteria and Methodology

2.1. Drainage Design Criteria

2.2. Hydrologic Analysis

2.3. Hydraulic Analysis

3. Embankment Slope Analysis

4. References

LIST OF TABLES

Table 2-1: Culvert Hydraulics Design Criteria Table 2-2: Bridge Hydraulics Design Criteria

APPENDICES

Appendix A: Minor Culverts Analysis Appendix B: SMS Major Culverts Analysis Appendix C: SMS Trail Bridges Analysis Appendix D: Embankments Analysis

1. INTRODUCTION AND PURPOSE

This report is a compilation of hydraulic model reports for multiple roadway embankments, bridge and culvert crossings within the Monongahela National Forest in West Virginia. During October 2017, August 2018, and June 2019, a series of heavy rain events caused significant roadway and trail damage within the Monongahela National Forest (the Forest) in West Virginia. The damaged roadways, bridges and trails prevent safe public access into various points of the Forest. These damages were assessed by the Forest in August 2021 in Damage Survey Reports (DSR). Recommended repairs were provided in an initial report submitted in March 2023.

Based on feedback on those recommendations, sites were re-evaluated and modeled to support the repairs of roadway, shoulder, and slope; repairs and replace culverts and trail bridges; and other miscellaneous work. As some sites have multiple repairs, the following reports document the structures that have been hydraulically modeled to support the repair recommendations for the WV ERFO FS MNGAH921 project.

The individual chapters of this report provide the results of hydraulic modeling and discussion for each of the roadway embankments, bridge and culvert crossings.

2. DESIGN CRITERIA AND METHODOLOGY

2.1. DRAINAGE DESIGN CRITERIA

The drainage design criteria for this project is in accordance with the Federal Lands’ Project Development and Drainage Manual (PDDM) Chapter 7. The PDDM design standards for roadway hydraulic structures are based on roadway classification. All roadways evaluated for this project are classified as low-standard.

Low-standard roadway culverts have a design flood equivalent to the 25-year recurrence interval.

Table 2-1: Culvert Hydraulics Design Criteria

Design Value PDDM Standard Used on This Project Culvert Design Flood 25-Year 25-Year

Three flood frequencies are used to design and evaluate the proposed trail bridges and bridge foundations.

These are the hydraulic design flood frequency, the scour design flood frequency and the scour design check flood frequency as presented below.

Table 2-2: Bridge Hydraulics Design Criteria

Hydraulic Design Flood Frequency

Scour Design Flood Frequency Scour Design Check Flood

Frequency Q25 Q50 Q100

2.2. HYDROLOGIC ANALYSIS

Contributing drainage areas to each culvert were estimated using available LiDAR topography. All contributing drainage areas were found to be less than 200 acres. The Rational Method, following procedures described in HDS-2, was used to calculate flow rates for most culverts. For major culverts and trail bridges located along USGS “blue line streams”, StreamStats was used to estimate discharge rates via regression equations.

2.3. HYDRAULIC ANALYSIS

Minor culvert hydraulic analyses were performed for 15 roadway crossings using the FHWA HY-8 computer software utilizing HDS-5 procedures. The 25-year storm event was used for the design of these culverts. Pipe length and inverts were estimated using aerial imagery and LiDAR contour information. As the proposed pipe lengths and invert elevations will be adjusted for field conditions, the estimated information input to HY-8 is used to confirm that the proposed pipe is sized to adequately convey the 25-year discharge. Reports summarizing the analysis and design are included in Appendix A.

Three major culverts and four pedestrian trail bridges were analyzed using the Surface Water Modeling System (SMS) graphical user interface in conjunction with the two-dimensional Sedimentation and River Hydraulics model (SRH-2D) software. Reports summarizing the analysis and design are included in Appendix B and C.

3. EMBANKMENT SLOPE ANALYSIS

Failed embankment sections which were identified in the DSR reports as needing evaluation were analyzed using the FHWA Hydraulic Toolbox. The FHWA Hydraulic toolbox program “Channel Analysis” tool and “Channel Revetment (slopes <2%)” riprap calculator were used to analyze the shear stress and velocity and determine the appropriate riprap armoring in areas adjacent to major streams.

Reports summarizing the embankment slope analysis are included in Appendix D.

4. REFERENCES

Federal Highway Administration (FHWA), 2012d, Evaluating Scour at Bridges HEC-18, Fifth Edition.

Report No. FHWA-HIF-12-003

Federal Highway Administration (FHWA), 2012a, Stream Stability at Highway Structures, HEC-20, Fourth Edition. Report No. FHWA-HIF-12-004

Federal Highway Administration (FHWA), 2009, Bridge Scour and Stream Instability Countermeasures Experience, Selection, and Design Guidance, HEC No. 23, 3rd Edition, Volume 1 & Volume 2, Report No. FHWA- NHI-09-111

Federal Highway Administration (FHWA), 2019, Two-Dimensional Modeling for Highways in the River Environment Tech Brief. Report No. FHWA-HIF-19-061

U.S. Geological Survey (USGS), National Water Information System data available on the World Wide Web (USGS Water Data for the Nation), accessed March 2024, at URL https://waterdata.usgs.gov/nwis/inventory/?site_no=13342500&agency_cd=USGS