Effectiveness of Washington Forest Practices at Reducing Landslide Rates and Volumes: A Study Design
Abstract
This study design to evaluate the effectiveness of Washington State Forest Practices at reducing landslide rates and volumes is unique in three respects: 1) Existing landslide and forest management data have been used in an attempt to establish a sample design likely to provide statistically significant landscape-scale comparisons between past and present forest practices; 2) Triggering mechanisms of individual landslides will be field-identified to provide information about individual rules and best management practices at the site-scale; 3)When are large storm somewhere in Washington State triggers a population of new landslides, aerial photography and field work will initiate from existing contracts. Optimizing sample size was critical to developing a practical field sampling protocol within limitations of time and funding. Data from previous regional landslide studies in the forested Pacific Northwest provided guidance for identifying the smallest possible blocks likely to contain a sufficient number of landslides in each of the strata to recognize statistically significant differences in landslide density between them. Sample design includes delineation of 5 harvest strata and 5 road strata. These strata represent different stand ages and types of unstable slope buffering, and different levels of design and maintenance for roads. In the detailed analysis of individual landslides particular focus has been placed on disturbance triggers associated with harvest (e.g., yarding corridors) and on a wide variety of road triggers including inadequate drainage, undersized stream-crossing pipes, poor prism maintenance, and lack of sidecast pullback. The occurrence of these triggers will be compared with new rules and BMPs designed to preclude them. There will be 2 contracts in place, one for acquisition and development of 1:12,000-scale aerial photography of the affected area in the spring following the storm, and one for the delineation of strata per the sample design, followed by the field inventory of landslides and analysis of these data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H13B1379D
- Keywords:
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- 1625 Geomorphology and weathering (0790;
- 1824;
- 1825;
- 1826;
- 1886);
- 1834 Human impacts;
- 4863 Sedimentation (1861)