Effects of logging and road building on hillslope erosion, stream discharge, and water qualityEPA Grant Number: U915362
Title: Effects of logging and road building on hillslope erosion, stream discharge, and water quality
Investigators: Robinson Ambers, Rebecca Kelly
Institution: University of Oregon
EPA Project Officer: Boddie, Georgette
Project Period: September 28, 1998 through January 1, 2000
Project Amount: $63,436
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Fellowship - Geology , Ecological Indicators/Assessment/Restoration , Academic Fellowships
In recent years, the Pacific Northwest has been the focus of substantial research and controversy over the effects of logging and road building on hillslope erosion, stream discharge, and water quality. Concerns range from possible increases in the frequency of debris flows to habitat deterioration for salmonid fishes and other aquatic life. This study addresses certain sediment-related aspects of the problem by examining the effects of land use, particularly timber harvesting, on sediment production and yield through time in a watershed-reservoir system in the west-central Cascades of Oregon. The goals of the study are to determine (1) what aspects of sedimentation in the reservoir reflect the land use history of the drainage basin and (2) how different land management practices have affected sediment yield through time and space.
The study area is a medium-sized (685 sq. km) watershed which drains into Dorena Reservoir a few miles east of the town of Cottage Grove, Oregon, in the Western Cascade Mountains. Rocks in the drainage basin range in composition from basalt to andesite with distinct components of granodiorite and rhyolite, and soil types vary accordingly. Local land use activities are largely related to timber harvesting and consequent road building; but livestock grazing, small-scale placer mining, and underground mining also occur in certain areas of the basin. A number of different techniques will be used to decipher the Dorena watershed story. An important component of the study is a sediment budget analysis of the watershed and corresponding sedimentation survey of the nearly fifty-year-old Dorena Reservoir. Within the reservoir, lake-bottom sediment cores will be characterized in terms of stratigraphy, age, organic content, and mineralogy. An attempt will be made to correlate stratigraphic layering with stream hydrographs and lake elevation records, and Cs-137 dating will be used to test the correlations. The mineralogy of the sediments will be analyzed in order to determine provenance within the watershed. In the wet, temperate climate of western Oregon, various igneous and sedimentary rock types and compositions weather into distinct soil profiles whose mineralogy differs from place to place and down profile. A comparison of the mineralogies of the watershed's major soil types and the reservoir sediments should show a connection between sedimentation events and naturally- or artificially-induced erosion events in the source area. The stratigraphy and provenance of the reservoir sediments, in combination with hydrographic data and a sediment budget of the watershed-reservoir system, may thus provide a record of the effects of land use through time.