Peak flow responses to clear-cutting and roads in small and large basins, western Cascades, Oregon: A second opinion

In this paper, we conduct a reanalysis of methods and data used by Jones an d Grant [1996]. Data from three small watersheds (60-101 ha) and three pair s of large basins (60-600 km(2)) in Oregon's western Cascades were used to evaluate effects of timber harvest and road construction on peak flows. We could not detect any effect of cutting on peak flows in one of the large ba sin pairs, and results were inconclusive in the other two large basin pairs . One small watershed was 100% clear-cut, a second was 31% patch-cut with 6 % of the area affected by road construction, and a third was held as a long -term control. Peak flows were increased up to 90% for the smallest peak ev ents on the dear-cut watershed and up to 40% for the smallest peak flows on the patch-cut and roaded watershed. Percentage treatment effects decreased as flow event size increased and were not detectable for flows with 2-year return intervals or greater on either treated watershed. Treatment effects decreased over time but were still found after 20 years on the dear-cut wa tershed but for only 10 years on the patch-cut and roaded watershed.