HR: 0830h
AN: H51D-1097    [PDF]
TI: Landslide Rates in the Eastern Cascade Mountain Range
AU: Bergen, K J
EM: kbergen@fas.harvard.edu
AF: Harvard College, University Hall, Cambridge, MA 02138 United States
AU: * Doten, C O
EM: colleen@hydro.washington.edu
AF: University of Washington, Department of Civil and Environmental Engineering, Box 352700, Seattle, WA 98195 United States
AU: Lettenmaier, D P
EM: dennisl@u.washington.edu
AF: University of Washington, Department of Civil and Environmental Engineering, Box 352700, Seattle, WA 98195 United States
AB: Assessing landslide rates is an important factor in quantifying sediment generation in mountainous watersheds. Prediction of the role of land cover change, especially forest harvest and fires, on sediment generation is currently a problem of particular interest to forest management agencies. Traditional aerial photograph interpretation techniques have long been used for estimation of failure rates, however to date such data has rarely been used in a predictive modeling context. Furthermore, relatively little quantitative data exist that are applicable to the east slopes of the Cascade Mountains, where recent fires have created an interest in improved prediction techniques that might help better understand the implications of post-fire sediment generation for the health of streams. Using aerial stereo photographs from the years 1970, 1975, 1979, 1985, and 1992, provided by the U.S. Forest Service, landslides were mapped in the Rainy Creek tributary of the Little Wenatchee basin of the northeastern Washington Cascades. The slides were mapped onto digital orthophotos and were categorized by a confidence scheme based on the visible features of a landslide. Slides were further categorized by the land type (forested, harvested, unforested, burned, and road-related) they occurred in, and stream and forest road intersections were also noted. Landslide rates and slide densities were calculated based on the photo record intervals. The volume of removed sediment was also estimated. These rates were compared to precipitation records over the same time period to evaluate the effect of large storms on mass wasting in this region. Estimated slide number and area densities are compared with similar studies elsewhere in the western U.S. Also, predicted and estimated number and area of slides from a numerical model described in a companion paper (Doten et al) are compared with the orthophoto estimates for the 22-years period 1970-92.
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2003 Fall Meeting