Bulk samples of streambed sediment from two reaches of the lower Merced River, California

Bulk samples of streambed sediment were collected from two reaches of the lower Merced River in California's Central Valley to support research intended to evaluate the extent to which large-scale restoration projects provided improved salmon spawning habitat. A related goal of this study was to improve our understanding of the geomorphic factors influencing spawning site selection by salmon. The bulk samples were acquired during the summer of 2016 at the Merced River Ranch and Robinson Reach field sites using a McNeil sampler [McNeil and Ahnell, 1964]. Before collecting each sample, the surface layer was removed to avoid including surface grains as part of the sample. Surface material was scraped off to a depth equal to the diameter of the largest particle found on the surface. The subsurface material was collected to a depth of 0.3 m and grain size distribution data were obtained by running the bulk sample through a series of sieves with screens ranging from 0.063 - 128 mm [Bunte and Abt, 2001]. We used existing bulk sample data of the initial sediment stockpile of the Robinson Reach, which was collected by California Department of Water Resources in 2002 [CADWR, 2005]. Additional bulk sample data were collected during the summer of 2016 at the Merced River Ranch and Robinson Reach field sites. References Bunte, K., and S. R. Abt (2001), Sampling surface and subsurface particle-size distributions in wadable gravel- and cobble-bed streams for analyses in sediment transport, hydraulics, and streambed monitoring, Gen. Tech. Rep. RMRS-GTR-74,113, Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 428 p. CADWR (2005), The Merced River Salmon Habitat Enhancement Project: Robinson Reach Phase III, 159 pp., California Department of Water Resources, San Joaquin District, Fresno, CA. McNeil, W. J., and W. H. Ahnell (1964), Success of pink salmon spawning relative to size of spawning bed materials, U.S. Fish and Wildlife Service, Special Scientific Report – Fisheries 469, Washington, D.C.