Forest practices and streamflow in western Oregon: Issue 49

Robert Dennis Harr

ene 1976 · U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station

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Forest management activities, including roadbuilding, clearcut logging, and broadcast burning, can change certain portions of the forest hydrologic cycle. Watershed studies and other hydrologic research in the Coast and western Cascade Ranges of Oregon have shown that these changes may increase annual water yield up to 62 centimeters, double minimum flows in summer, and increase fall peak flows up to 200 percent and small winter peak flows up to 45 percent in small watersheds. Changes in streamflow resulting from clearcut logging had little effect on either onsite damage to stream channels and hydraulic structures or downstream flooding when yarding caused only light disturbance of soil. By increasing the size of larger peak flows, roadbuilding and soil compaction may cause onsite damage in small, headwater basins. Increases in annual yield and minimum flows may be substantial on small watersheds that are clearcut; under sustained yield forest management, such increases are masked in large, parent watersheds by unaltered streamflow from unlogged watersheds.