Persistence of effects of high sediment loading in a salmon-bearing river, northern California
Mary Ann Madej, Vicki Ozaki, 2009. "Persistence of effects of high sediment loading in a salmon-bearing river, northern California", Management and Restoration of Fluvial Systems with Broad Historical Changes and Human Impacts, L. Allan James, Sara L. Rathburn, G. Richard Whittecar
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Regional high-magnitude rainstorms have produced several large floods in north coastal California during the last century, which resulted in extensive mass-movement activity and channel aggradation. Channel monitoring in Redwood Creek, through the use of cross-sectional surveys, thalweg profiles, and pebble counts, has documented the persistence and routing of channel-stored sediment following these large floods in the 1960s and 1970s. Channel response varied on the basis of timing of peak aggradation. Channel-stored sediment was evacuated rapidly from the upstream third of the Redwood Creek channel, and the channel bed stabilized by 1985 as the bed coarsened. Currently only narrow remnants of flood deposits remain and are well vegetated. In the downstream reach, channel aggradation peaked in the 1990s, and the channel is still incising. Channel-bed elevations throughout the watershed showed an approximate exponential decrease with time, but decay rates were highest in areas with the thickest flood deposits. Pool frequencies and depths generally increased from 1977 to 1995, as did median residual water depths, but a 10 yr flood in 1997 resulted in a moderate reversal of this trend. Channel aggradation generated during 25 yr return interval floods has persisted in Redwood Creek for more than 30 yr and has impacted many life cycles of salmon. Watershed restoration work is currently focused on correcting erosion problems on hillslopes to reduce future sediment supply to Redwood Creek instead of attempting in-channel manipulations.