United States Department of Agriculture Proceedings of a Workshop Forest Service on Slope Stability: Pacific Northwest Forest andRange Experiment Station Problems and Solutions General Technical Report PNW-1 80 in Forest Management April 1985 This file was created by scanning the printed publication. Mis-scans identified by the software have been corrected; however, some errors may remain. Papers were prepared in camera-ready form for print- ing by the authors, who are therefore responsible for the content and accuracy. Opinions expressed may not necessarily reflect the position of the U.S. Department of Agriculture. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the 1J.S. Depart- ment of Agriculture of any product or service to the exclusion of others that may be suitable. Proceedings of a Workshop on Slope Stability: Problems and Solutions in Forest Management Seattle, Washington February 6-8, 1984 Doug Swanston Technical Editor Sponsored by: USDA Forest Service U niversity of Washington, College of Forest Resources Oregon State University, College of Forestry Published by: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, Oregon General Technical Report PNW-180' April 1985 CONTENTS Page FOREWORD -- Douglas N. Swanston ............................. iv KEYNOTE ADDRESS Landslides on Steep Forested Terrain: The Problem and Resource Management Implications .............................. F. Dale Robertson EXTENT OF PROBLEM Survey of Slope Stability Problems on Forest Lands in the West . 51 Edward R . Burroughs, Jr . Factors Influencing the Stability of Slopes .................... 17 R. C. Sidle Landslide Damage to the Forest Environment ..................... 26 George W. Brown CURRENT TECHNIQUES FOR PROBLEM SOLVING Pitfalls in the Strict Reliance on Expert Opinion in Assessing Stability Hazard . 30 James A. McNutt and Dale McGreer Subjective Techniques for Identification and Hazard Assessment of Unstable Terrain . 36 Dale Wilson The Engineering Approach to Landslide Risk Analysis ................. 43 W. L. Schroeder Computer-based Landslide Delineation and Risk Assessment Procedures for Management Planning .............................. 51 Tim J. Ward PRACTICAL FIELD APPLICATION OF AVAILABLE METHODOLOGIES , A Serendipitous Integration of Research with Management Needs--The British Columbia Fish/Forestry Interaction Program ......................... 58 V. A. Poulin Harvest Planning and Layout on Steep Terrain--The Siuslaw Model .......... 64 George Bush Use of Soils and Geomorphic Information for Road Location and Timber Management in the Oregon Coast Ranges ....................... 68 Byron R. Thomas Road Location in Sensitive Watersheds: An Industry Perspective .......... 78 S. H. Duncan Landslide disaster Assessment in the Wasatch Range ................ 81 Paul Winkelaar Applications of Geotechnical Data to Forest Management ............... 87 Tom Reilly and Bill Powell A Complete Three-level Approach for Analyzing Landslides on Forest Lands . , . 94 Rodney W, Prellwitz Page PANEL DISCUSSIONS: NEEDS AND LIMITATIONS FOR EFFECTIVE LAND MANAGEMENT RISK ASSESSMENT OF POTENTIALLY UNSTABLE TERRAIN Opening address: Decisionmaking in the Presence of Risk .............. 99 Stefan D. Bloomfield Panel 1--Comments by Practicing Land Managers on the Question: Mat Levels of Political/Social Influence on Risk are Appropriate in Forest Land Management Decisionmaking? DanBigger .................................. 105 Paul Swateck ................................. 106 .. R. T.Bail.ey ..................................... 107 JohnT.Drake ................................... 109 NeilSkill ................................... 109 Panel 2--Comments by Practicing Land Managers on the Question: How Do the Concepts of Risk Influence Field Decisions? Soteco Muniz ................................. 110 Leo W. Wilson. ................................ 111 MelvinL. Kessel ............................... 112 JosephH.Harn ................................ 112 Kenneth D. Weyers ............................... 113 Panel 3--Coments by Practicing Land Managers on the Question: Given the Social-Political Constraints Imposed on the Land Manager and Levels of Risk Currently Acceptable, What Information and Levels of Application are Needed for Improved. Land Management Decisionmaking? -.M..L..:W;... Bourgeois ...........................................................................114 Dick--.Olsen- ........-..--. ..... -. ................. ..& .-i.,. ........................:-. *.. ....................... 1'16 .Da>e.J,..;.7MeGreer: *... ...................................r*.i. .... *...-. ,!..-.... , .... ................-,.L 1.17 Wchael -J... Cook ..... ........................................................................ ,118 Ted, StubbZefi-eEd .....................................-....... .118. WORKSHOP SUMMARY Status of Enowledge--Reliability of Techniques--Direction for Improved Decisionmaking Jeff Skmn ......................................... 1.20 '+W-C...Et$jWm................................................... r2-2 FOREWORD Forest and related resource management in February 1984 a workshop on "Slope stability: mountainous areas of the western United States, problems and solutions in forest mnagernent" was Canada, and Alaska is severely restricted by held at the Univeristy of Washington, Seattle, unstable'terrain that is susceptible to soil and was designed to give high-level movement varying from surface creep to administrators, decisionmakers, and planners a catastrophic landslides. Management practices current perspective on the status of these that might trigger or increase such disturbance research and administrative studies, key are increasingly subject to public scrutiny. findings, and how new information is being applied. Land managmnt-planning as required by the Resources Planning Act (RPA) (PL93-378 1, the Publication of the proceedings of this workshop National Forest Management Act (NFMA) (PL94-588) , accomplishes two primary purposes. The first is the Resource Conservation Act (RCA) (PL95-192) to bringing together in coherent form, and from and other Federal and State laws requires that as wide a range of experience as possible, soil stability receive strong consideration in information on resources and,techniques usefhl to long-range-plans. Accordingly,.planners have a the land manager who must identify, assess, and critical need for the best possible information mitigate the risk of soil mass movements from on soil stability and risk of landslides, and steep, forested terrain. The second is to define potential impacts on other resources. managerial risk and provide a forum for the expression by land managers of views on the Much research and development work has been done concepts of risk in forest land management in the West by public agencies, industry, and decisionmaking. Foremost among these views are universities on the causes, effects, prevention, the perceived needs, in terms of data and and impacts of soil movement. The largest techniques, for effective risk assessment given project of this nature has been the USDA Forest current social and political constraints. Service's Interstation Soil Mass Movement Research Program which was begun in 1972. This The concepts, techniques, and applications effort is being conducted by threewestern Forest presented constitute some of the best and most Service Experiment Stations (Pacific Southwest, successful approaches currently being applied by Pacific Northwest, and Intermountain Forest and specialists and land management decisionmakers. Range Experiment Stations) working in close They are, by no means, the only viable approac,hes cooperation with the western Regionsof the to assessment and management of this difficult Forest Service, the Bureau of Land Management, terrain. After all, there is no single "best western States, universities, and others approach" applicable under all conditions. Laird concerned with slope stability problems. Since managers are encouraged to consult soils, the program began, more than 100 technical hydrology, and geotechnical specialists with reports have been produced, and land managers and specific local knowledge and experience for researchers have made significant progress in guidance in applying these or similar approaches. applying the information in the field. In KEYNOTE ADDRESS LANDSLIDES ON STEEP FORESTED TERRAIN: THE PROBLEM AND RESOURCE MANAGEMENT IMPLICATIONS F. Dale Robertson INTRODUCTION By winter 1973, the controversy over timber I always look forward to escaping the Washington, harvesting and road building practices had built D.C., environment and appreciate the opportunity up to the point where the Oregon Wildlife to return to the Pacific Northwest where the real Commission and the fisheries interests were no action in forestry is. longer willing to let existing management practices continue unchallenged. In analyzing It was a little over 10 years ago, when I was a the situation, the Siuslaw National Forest. staff brand new Forest Supervisor at the Siuslaw basically agreed with many of the concerns National Forest, that I first faced the challenge expressed by the Oregon Wildlife Commission and of trying to practice forestry on unstable decided that some change in management practices terrain. I remember arriving in November 1973, was in order. The