Long-term patterns of sediment transport following timber harvest, western Cascade Mountains, Oregon

The objective of this study was to quantify the long-term effectsof two intensities of timber harvest on sediment delivery at seasonaland yearly time scales. Differences in total sediment flux over a 30-year period were compared for three small forested watersheds (WS1, 2, and 3) located in the H. J. Andrews Experimental Forest in theWestern Cascade range of Oregon. The landscape is steeply dis-sected, underlain by mixed volcanic rocks, and vegetated with 400-to 500-year old stands of Douglas-fir and hemlock. Sampling ofsuspended and bedload sediment was initiated in 1957 and contin-ued through 1988 on all three watersheds which have drainage areasof 96, 60, and 101 ha, respectively. Three different treatments werecompared: a 100% clearcut watershed without roads completed in 1966 (WS 1), a 25% harvested patch-cut watershed with 6% of areain roads completed in 1963 (WS 3), and a forested control (WS 2),which was not harvested. Suspended sediment was sampled duringand between storms. Bedload was measured annually in a stilling
reservoir.