| Abstract/Description or Keywords |
sediment, landslide, mass movement, forest harvest, erosion, channel, salmon habitat; Sediment budgets, averaged over one or more decades, have been estimated for four small (3.9 to l2.6 km2) drainage basins in the Queen Charlotte Islands for periods before and after clear-cut logging of 10 to 20% of the area, including stream banks. Data were obtained by field and photogrammetric measurements of sediment deposits supplemented by regional rate estimates for minor erosional processes. Landslides, riparian erosion, and soil creep are important sediment sources before logging, the former two dominating. Sediment production on hillslopes and delivery to stream channels may increase following logging, but not invariably. In each of the study basins, significant stream bank erosion following logging resulted in the accumulation of a substantial "wedge" of coarse sediment in the stream channel. Sediment transport through the channels has increased by up to 10 times; however, the residence time for the greatly increased volume of in-channel sediment has increased by up to 100 times. The in-stream sediment wedges are areas of persistently poor aquatic habitat. Their development was associated with obsolescent logging practices and they remain atypical. |
