University of California Water Resources Center

This research on effects of large organic debris on stream channel form and process relevant to anadromous fish habitat was along three lines of inquiry. First, new ways to evaluate discrete hydrologic environments, such as pools, riffles and debris accumulations were developed. Experiments completed provided basic data to test a model useful for predicting hydraulic geometry of pools and riffles. These experiments will help managers develop design criteria for construction or improvement of fish habitat in channel restoration projects. Similar hydrologic experiments in Redwood National Park, have been completed to evaluate the stream power associated with organic steps and defines a sediment buffer system that modulates the movement of bedload through the fluvial system.

A second line of inquiry involved in debris removal experiments in Redwood National Park. Significant hydrologic and morphologic changes occurred as a result of the debris removal. Results of the debris pulling experiment suggest that the stream is now more sluggish and has less hydrologic variability than prior to the debris removal.

The third line if inquiry was a comparative study between undisturbed streams flowing through old growth redwood forest with those impacted by timber harvesting. Large organic debris (greater than 10cm in diameter) is equally effective on controlling gross channel form in both undisturbed and disturbed channels, but there is a difference in the size and quantity of debris, channel morphology, and thus anadromous fish habitat. There is a higher percentage of unstable stored sediment in disturbed basins and sediment storage sites tend to be filled more often. Once storage sites are full, sediment may be transported more directly through the channel to downstream sites, producing a sediment pollution problem.