United States Department of Agriculture Post-Fire Treatment Forest Service Rocky Mountain Effectiveness for Research Station General Technical Hillslope Stabilization Report RMRS-GTR-240 August 2010 Peter R. Robichaud, Louise E. Ashmun, and Bruce D. Sims A SUMMARY OF KNOWLEDGE FROM THE Robichaud, Peter R.; Ashmun, Louise E.; Sims, Bruce D. 2010. Post-fire treatment effectiveness for hill- slope stabilization. Gen. Tech. Rep. RMRS-GTR-240. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 62 p. Abstract This synthesis of post-fire treatment effectiveness reviews the past decade of research, monitoring, and product development related to post-fire hillslope emergency stabilization treatments, including erosion barri- ers, mulching, chemical soil treatments, and combinations of these treatments. In the past ten years, erosion barrier treatments (contour-felled logs and straw wattles) have declined in use and are now rarely applied as a post-fire hillslope treatment. In contrast, dry mulch treatments (agricultural straw, wood strands, wood shreds, etc.) have quickly gained acceptance as effective, though somewhat expensive, post-fire hillslope stabilization treatments and are frequently recommended when values-at-risk warrant protection. This change has been motivated by research that shows the proportion of exposed mineral soil (or conversely, the propor- tion of ground cover) to be the primary treatment factor controlling post-fire hillslope erosion. Erosion barrier treatments provide little ground cover and have been shown to be less effective than mulch, especially during short-duration, high intensity rainfall events. In addition, innovative options for producing and applying mulch materials have adapted these materials for use on large burned areas that are inaccessible by road. Although longer-term studies on mulch treatment effectiveness are on-going, early results and short-term studies have shown that dry mulches can be highly effective in reducing post-fire runoff and erosion. Hydromulches have been used after some fires, but they have been less effective than dry mulches in stabilizing burned hillslopes and generally decompose or degrade within a year. Keywords: BAER, contour-felled logs, hydromulch, LEB, straw mulch, PAM, wood shreds, wood strands Authors Acknowledgments Peter R. Robichaud is a Research Engineer with the Air, Wa- This synthesis project (Project Number 08-2-1-10) was tershed, and Aquatics Science Program at the Rocky Mountain funded by the Joint Fire Sciences Program, a collaborative Research Station’s Forestry Sciences Laboratory in Moscow, between the U.S. Department of Interior and U.S. Department Idaho. He develops and implements research protocols for of Agriculture, Forest Service that supports fire research. Much measuring and predicting post-fire runoff and erosion and of the research reported herein was funded wholly or in part post-fire treatment effectiveness. by the Joint Fire Sciences Program. We are indebted to our reviewers: Jeff Bruggink, Chris Holbeck, Carolyn Napper, and Louise E. Ashmun is a Civil Engineer with the Air, Watershed, Wayne Robbie. They all have wide-ranging experience on and Aquatics Science Program at the Rocky Mountain Research post-fire assessment teams, and their comments significantly Station’s Forestry Sciences Laboratory in Moscow, Idaho. She improved this document and the companion web page (http:// provides technical support for research and technology transfer forest.moscowfsl.wsu.edu/BAERTOOLS/HillslopeTrt). We on grant-funded projects. specifically recognize and thank John Moody, who provided a thorough review of the draft document and made suggestions Bruce D. Sims is the Regional Hydrologist for the Northern that greatly enhanced the focus, content, and organization of Region of the USDA Forest Service in Missoula, Montana. this synthesis. His duties include oversight of the Burned Area Emergency Response (BAER) program for the Region. You may order additional copies of this publication by sending your mailing information in label form through one of the following media. 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Publishing Services Telephone (970) 498-1392 FAX (970) 498-1122 E-mail [email protected] Web site http://www.fs.fed.us/rmrs Mailing Address Publications Distribution Rocky Mountain Research Station 240 West Prospect Road Fort Collins, CO 80526 Contents Preface ............................................................................................................. ii Scope of Post-Fire Treatment Effectiveness for Hillslope Stabilization ................................................................... ii Introduction .....................................................................................................1 Post-Fire Treatment Types ...................................................................1 Post-Fire Treatment Effectiveness and Treatment Performance ..........2 Post-Fire Hydrology and Erosion ....................................................................2 Factors That Impact Post-Fire Watershed Response and Treatment Effectiveness .................................................................4 Post-Fire Erosion by Wind and Gravity ...............................................8 Comparing Results and Scale of Measurements ..................................8 Erosion Barrier Treatments ............................................................................10 Erosion Barrier Performance Characteristics .....................................12 Erosion Barrier Treatment Effectiveness ...........................................14 Mulch Treatments ..........................................................................................15 Dry Mulches .......................................................................................16 Hydromulches ....................................................................................17 Performance Characteristics of Mulches ...........................................18 Mulch Treatment Effectiveness .........................................................24 Chemical Soil Surface Treatments .................................................................27 Performance Characteristics of PAM and Other Polymers ................28 Effectiveness of PAM and Other Polymers .......................................29 Treatment Combination .................................................................................29 Management Implications ..............................................................................30 Longer-Term Treatment Effectiveness ...............................................30 Choosing Treatments .........................................................................30 Monitoring Post-Fire Treatment Effectiveness ..................................33 Using the “Best Available” Treatments ..............................................33 References ......................................................................................................33 Appendix A: Hillslope Treatment Effectiveness and Performance Characteristics Summary Table .............................................................38 Appendix B: Erosion Barrier Treatment Effectiveness Studies (2000 to the present) ..............................................................................39 Appendix C: Mulch Treatment Effectiveness Studies (2000 to the present) ..............................................................................48 Appendix D: Polyacrylamide (PAM) Treatment Effectiveness Studies (2000 to the present) ..............................................................................59 Appendix E: Combination Treatments Effectiveness Studies (2000 to present) ....................................................................................61 i Preface Scope of Post-Fire Treatment Effectiveness for Hillslope Stabilization This report is a synthesis of post-fire emergency hill- slope stabilization treatment effectiveness information that This synthesis focuses on post-fire hillslope emergency was written to provide guidance for future post-fire treat- stabilization treatments, including erosion barriers, mulch- ment selection and use. It builds on an earlier synthesis, ing, chemical soil treatments, and combinations of these Evaluating the Effectiveness of Postfire Rehabilitation treatments. This is a narrow focus given the range of post- Treatments (Robichaud and others 2000) (fig. 1). Since fire emergency responses typically implemented by BAER that publication, the effectiveness of emergency post- teams (see Napper 2006 for a comprehensive review of fire hillslope treatments have been evaluated in several post-fire treatments). However, these hillslope treatments scientific studies and treatment monitoring reports pre- are usually the most expensive post-fire treatments used, pared by Burned Area Emergency Response (BAER) which makes cost effectiveness an important factor in and Emergency Stabilization and Rehabilitation (ESR) their selection. In addition, recent reports synthesize the teams. In addition, our knowledge of how environmental current information for other post-fire emergency treat- factors impact treatment effectiveness and the develop- ments. For example, a synthesis of broadcast seeding, ment of new post-fire hillslope treatment products and one of the first and most extensively used post-fire hillslope application techniques has grown. The objective of this treatments