EFFECTS ON BEDLOAD TRANSPORT OF EXPERIMENTAL REMOVAL OF WOODY DEBRIS FROM A FOREST GRAVEL-BED STREAM

Experimental removal of woody debris from a small, gravel-bed stream i n a forested area resulted in a four-fold increase in bedload transpor t at bankfull discharge. This was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low- energy hydraulic environments related to debris. Bank erosion delivere d additional sediment to the channel, and transport energy was increas ed by an inferred increase in the component of total boundary shear st ress affecting grains on the bed. Increased transport following debris removal in May 1987 continued throughout the entire autumn storm seas on through late November 1987, indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as larg e as bankfull. Stream bed adjustments included development of a semi-r egular sequence of alternate bars and pools, many of which were spaced independently of former pool locations.