Humboldt State University



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dc.contributor.advisor Stubblefield, Andrew en Reid, Kelley en 2012-02-13T15:51:38Z en 2012-02-13T15:51:38Z en 2011-12 en
dc.identifier.uri en
dc.description This is a study of the relative abundance of fines on the gravel bar before gravel extraction, after extraction, after the first rains of fall, and after the first inundation. en
dc.description Thesis (M.S.)--Humboldt State University, Natural Resourcs: Watershed Management, 2011 en
dc.description.abstract The economy of Humboldt County, California, is dependent on substantial amounts of aggregate skimmed from the local gravel bars, but National Marine Fisheries states that the extraction produces excessive fine sediments, which disrupt salmon behavior, and possibly fill interstitial spaces in the riverbed, and reduce salmon egg viability. The objective of my study is to determine whether sand and gravel extraction from gravel bars is an adverse source of fine materials for spawning salmon before the rivers become opaque with turbid runoff from various other sources. Either a rainstorm or high flows that overtop the extraction surface could wash the fines off the extraction surface and fill interstitial spaces between spawning gravels or produce sediment plumes that disrupt the behavior of adult salmon. I used three tests to determine whether fine sediments are washed off the gravel bar before the extraction surface is inundated by high flows. The tests included direct observation of sediment plumes, particle size analysis, and fluorescent-dyed sand tracers. A comparison of samples from gravel bar surfaces before and after extraction, after the first rains of fall, and after inundation, revealed that there were significantly more coarse sands after extraction and after inundation than on the pre-extraction surface. The percentage of the finest sediments (less than ⅛ mm) was greater on the pre-extraction surface than on the post-extraction surface. The percentage of fines was not significantly different between post-extraction or after rains, or between the post-extraction and after- inundation samples. Fines from these gravel extraction surfaces were not directly a source of fine sediments in the first autumnal rains. In subsurface comparisons, there was a slightly higher percentage of coarse sands in the post-extraction sediments compared with after-rains sample. The use of stained particle tracers did not contribute to the understanding of sediment movement on gravel bars in this study. Stained particles settled when exposed to rain. I observed two sediment plumes from gravel bars in the course of this investigation. In one, the river was already turbid from a variety of sources as the river flowed across the extraction surface. However, the downstream edge of the O’Neill gravel bar contained streamers of clear looking water and sediment plumes. The second sediment plume seemed to be from hyporheic flow at the edge between a haul road and a trench. Neither case fully supported the argument that fine sediments wash off the gravel bars. en
dc.description.sponsorship U.S. Army Corps of Engineers en
dc.language.iso en_US en
dc.publisher Humboldt State University en
dc.subject Gravel en
dc.subject Sediment en
dc.subject Extraction en
dc.subject Texture en
dc.subject Gravel bar en
dc.subject Gravel extraction en
dc.subject Bar texture en
dc.subject Fines en
dc.title An assessment of gravel bar texture and composition following in-channel mining in the Mad River, California en
dc.type Masters Thesis en
dc.description.program Natural Resources en

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