The Condit Dam breach on the White Salmon River (WSR) in Washington provided a unique opportunity to study how a bedrock-confined, gravel-bed river responds to a large influx of fine reservoir sediment. On October 26, 2011, a dynamite explosion breached a hole in the base of the 38 m tall dam, causing rapid reservoir erosion and downstream transport of fine sediment through the 5,300 m of channel separating the reservoir from the mouth of the WSR, where it flows into the Columbia River. In my research, I combined field data, aerial photographs, and LiDAR surveys to measure pre-breach and post-breach geomorphic conditions, up to 9 months after the breach, to assess downstream geomorphic response through a confined reach (reach 1) with forced pool-riffle morphology and a less-confined reach (reach 2) near the rivers mouth. I found that the magnitude and duration of geomorphic adjustment was smaller over riffles than pools and over reach 1 than reach 2. By 3 weeks after the dam breach, pools stored about twice as much of the reservoir-derived sediment (~95,000 cubic m) as riffles (~50,000 cubic m). By 9 months post-breach, nearly all (90%) of the sediment had been evacuated from riffles (~5,000 cubic m remained), whereas about half of the sediment initially stored in pools had been evacuated (~50,000 cubic m remained). Reach 1 stored ~145,000 cubic m within the 3 weeks after the dam breach compared to the 650,000 cubic m stored in reach 2. By 9 months post-breach, the volume of sediment stored in reach 1 (~40,000 cubic m) decreased by 72% and the volume in reach 2 (~490,000 cubic m) decreased by only 25%. I also found significant storage behind large wood deposits and throughout the transition between reach 1 and reach 2. My findings suggest a conceptual model by which reductions in grain and bedform roughness caused by initial sediment deposition in reach 1 contribute to sediment transport and deposition in reach 2. Findings from the WSR can help inform recovery from other sediment disturbances and dam removals.
| Identifer | oai:union.ndltd.org:MONTANA/oai:etd.lib.umt.edu:etd-09042014-120843 |
| Date | 24 October 2014 |
| Creators | Colaiacomo, Erika J. |
| Contributors | Dr. Andrew Wilcox, Dr. Johnnie Moore, Dr. Lisa Eby |
| Publisher | The University of Montana |
| Source Sets | University of Montana Missoula |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.umt.edu/theses/available/etd-09042014-120843/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Montana or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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