United States Department of Agriculture Storm Damage Risk Reduction Guide for Low-Volume Roads EST SERVI FOR CE D E Forest E P R A U RTMENT OF AGRICU L T Service National Technology & Development Program • 7700—Transportation Mgmt • 1277 1814—SDTDC • October 2015 Storm Damage Risk Reduction Guide for Low-Volume Roads By: Gordon Keller, P.E., Geotechnical Engineer Forest Service, Pacific Southwest Region, Plumas National Forest (Retired) Gary Ketcheson, Hydrologist Forest Service, Pacific Northwest Region (Retired) The Forest Service, an agency of the U.S. Department of Agriculture (USDA), has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies. The Forest Service assumes no responsibility for the interpretation or use of this informa- tion by anyone except its own employees. The use of trade, firm, or corporation names is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval of any product or service to the exclusion of others that may be suitable. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activi- ties on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political be- liefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. TABLE OF CONTENTS Acknowledgements .......................................................................................................................... iv 1. Introduction ................................................................................................................................1-1 1.1 Storm Damage Risk Reduction Objectives ..................................................................1-4 1.2 Scope of the Problem ...................................................................................................1-8 Flood History ...........................................................................................................1-8 Emergency Relief for Federally Owned (ERFO) Roads History ...........................1-10 Vulnerable Road Placement .................................................................................1-10 Examples of Storm Damage .................................................................................1-14 Definition of Risk ReductionTreatments ...............................................................1-16 Open Roads ..........................................................................................................1-16 Closed Roads (Roads Placed In Storage) ............................................................1-17 Relative Treatment Costs ......................................................................................1-17 2. Strategic Risk Assessment .........................................................................................................2-1 2.1 Hazard Assessment .....................................................................................................2-1 Landscape-Scale Considerations ...........................................................................2-1 Watershed-Scale Considerations ...........................................................................2-3 Site-Scale Considerations .......................................................................................2-5 Road Location .........................................................................................................2-6 Road Standards ......................................................................................................2-7 Failure Potential ......................................................................................................2-8 2.2 Consequence Assessment ...........................................................................................2-8 Consequences of Failure ........................................................................................2-9 2.3 Overall Risk Assessment ............................................................................................2-10 3. Selection of Appropriate Treatment ............................................................................................3-1 4. Implementation ...........................................................................................................................4-1 4.1 Planning and Preparation and Response .....................................................................4-1 4.2 Best Management Practices as Mitigation ...................................................................4-2 5. Common Storm Damage Risk Reduction Treatments ...............................................................5-1 5.1 Road Maintenance .......................................................................................................5-2 5.2 Road Surface Drainage Improvements ........................................................................5-4 Adding Rolling Dips (Broad-Based Dips) ................................................................5-7 Cross-Drain Culverts (Ditch Relief Culverts) .........................................................5-12 Table of Contents i TABLE OF CONTENTS Waterbars..............................................................................................................5-15 Ditches and Ditch Treatments ...............................................................................5-17 Ditch or Pipe Outlet Armoring ...............................................................................5-21 5.3 Stream Crossing Structure Protection and Improvements .........................................5-23 Culvert and Channel Maintenance ........................................................................5-23 Culvert Diversion Prevention and Overflow Protection .........................................5-23 5.4 Bridge Protection and Improvements .........................................................................5-29 Channel Maintenance and Debris/Sediment Clearing ..........................................5-29 5.5 Erosion Prevention and Erosion Control ....................................................................5-31 Erosion Prevention and Drainage Improvements .................................................5-31 Physical Methods for Erosion Control ...................................................................5-33 Vegetative Methods for Erosion Control ...............................................................5-36 Use of Deep-Rooted, Native Vegetation ...............................................................5-38 Soil Bioengineering and Biotechnical Erosion Control Methods ...........................5-39 Gullies and Gully Prevention .................................................................................5-42 5.6 Fillslope Stabilization Measures .................................................................................5-46 Sidecast Fill Pullback for Slope Stabilization ........................................................5-46 6. Less Common or Higher Cost Storm Damage Risk Reduction (SDRR) Treatments .................6-1 6.1 Less Used Road Surface Drainage Treatments ...........................................................6-1 Converting Inslope Roads to Outslope ...................................................................6-1 Surface Water Diversion Structures ........................................................................6-3 Culvert Cross-Drain Inlet Protection and Drop Inlets ..............................................6-6 6.2 Stream Crossing Structure Protection and Improvements ...........................................6-8 Increasing Culvert Capacity ..................................................................................6-11 Trash Racks ..........................................................................................................6-16 Culvert Reinstallation and Realignment ................................................................6-18 Aquatic Organism Passage Considerations .........................................................6-21 Pipe Inlet/Outlet Protection ...................................................................................6-23 Fords or Low-Water Crossings versus Culverts....................................................6-25 Local Structure, Streambank, and Channel-Stabilization Measures .....................6-30 Local Scour Protection ..........................................................................................6-31 Beaver Plugging Prevention .................................................................................6-40 ii Storm Damage Risk Reduction Guide for Low-Volume Roads TABLE OF CONTENTS 6.3. Bridge Protection and Improvements ........................................................................6-43 Increasing