HR: 0830h
AN: H51D-1095    [PDF]
TI: Landslide Sediment Production in the Middle Fork Eel River: 1940-2002
AU: * de la Fuente, J A
EM: jdelafuente@fs.fed.us
AF: Klamath National Forest, 1312 Fairlane Road, Yreka, CA 96097 United States
AU: Snavely, W P
EM: wsnavely@fs.fed.us
AF: Klamath National Forest, 1312 Fairlane Road, Yreka, CA 96097 United States
AU: Miller, A R
EM: alishamiller@fs.fed.us
AF: Shasta Trinity National Forest, 2400 Washington Avenue, Redding, CA 96001 United States
AU: Elder, D
EM: delder@fs.fed.us
AF: Klamath National Forest, 1312 Fairlane Road, Yreka, CA 96097 United States
AB: A sequential air photo analysis was conducted by the U.S. Forest Service (USFS) and North State Resources in the 753 square mile Middle Fork Eel River basin, under contract to US Environmental Protection Agency as part of a Total Maximum Daily Load (TMDL) assessment. All landslides visible on air photos which appeared to deliver sediment to the stream system were mapped, and the delivered volume estimated. Landslides on undisturbed hillslopes were classified as natural, those within recently burned areas as fire-related, those in harvest units as harvest-related, and those adjacent to roads as road-related. About 5% of the landslides were field verified. Data were then summed for three air photo intervals, spanning the period 1940-2002. A total of 4,122 landslides were inventoried, delivering a total of 24,969,836 cubic yards of sediment to the stream system, and occupying 13,526 acres. The photo interval 1940-1969 accounted for 79% of the delivered volume, 1970-1984 for 8%, and 1985-2002 for 13%. This pattern is similar to that observed in many NW California watersheds where the storms of 1955 and 1964 generated large volumes of landslide sediment. Landslide volume per unit area delivered to streams from 1940-2002 averaged 0.84 cubic yards/acre/year for the Middle Fork Eel, and was highest in the Black Butte River, and Williams-Thatcher subwatersheds which exhibited rates of 1.55 and 1.31 cubic yards/acre/year respectively. The lowest delivery rates were in Upper Middle Fork (0.29), and Round Valley (0.44). Natural landslides accounted for 89.9% of the total, fire-related for 1.9%, harvest-related for 0.4%, road-related for 3.4%, and undetermined 4.4%. A large proportion of the total delivered sediment originated from the toes of large deep seated landslides adjacent to streams. Many of these landslides exhibited multiple years of activity, shedding debris slides of varying sizes at different times. The mapped active landslides are concentrated near streams, but do not display any obvious affinity with specific bedrock units. The landslide sediment delivery rate in the Middle Fork Eel basin determined by this study (0.84 cuyd/ac/yr) compares to published values for other parts of the Eel basin as follows: North Fork Eel 0.16 (USFS, 2003); Middle Fork Eel 5.93 (USGS, 1986, total sediment); South Fork Eel 2.26 (Tetra Tech, 1998). Different techniques were used in each study, making direct comparison problematic. A model employed by the USFS in 2001 predicted landslide rates (cubic yards/acre/year) very similar to those measured by this study: Black Butte River 1.55 measured versus 1.33 predicted; Elk/Dos Rios 0.45 vs 0.96; Upper Middle Fork 0.29 versus 0.62; Williams Thatcher 1.31 vs 1.17.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
DE: 1869 Stochastic processes
SC: Hydrology [H]
MN: 2003 Fall Meeting