Peak streamflows from the transient snow zone, western Cascades, Oregon

Streamflow records for six watersheds in Oregon's Willamette National Forest indicate hydrologic conditions of the watersheds have changed over the past 4-5 decades. Increased size of the peak flows appears related to cumulative effects of timber harvest activities, primarily clearcut logging in the transient snow zone. There is a strong possibility that higher windspeed and turbulence following clearcutting has increased the rate of melt of warm snowpacks during rainfall. More rapid delivery of water to soil and to streams increases the probability of landslides and stream channel erosion in headwater areas as well as channel erosion processes downstream. Timber harvesting scheduling should take into account both the possibility for changes in snow accumulation and melt resulting from logging in the transient snow zone and the time required for hydrologic recovery.