There are an estimated two million low-head dams fragmenting rivers throughout the U.S. Low-head dams, historically installed to power mills and factories and now typically used to provide water storage for irrigation, interrupt the natural transfer of sediment downstream by creating pools upstream that widen the river and allow finer sediment to deposit in the river bed. By 2030, over 70% of the low-head dams in the U.S. will be considered past their design life expectancy. These factors have led to an increase in dam removals, including Hofmann Dam in northern Illinois. Constructed in 1950 on the Des Plaines River in Lyons, IL, the dam was removed in 2012 to improve the aquatic health of the river and for safety reasons. Utilizing topographical cross section data collected by IDNR one year prior and three years post removal, as well as collecting additional topographic surveys and gravel data in fall 2017, I analyzed channel characteristics using ArcMap and HEC-RAS to determine how the river has responded to the removal. Upstream of the dam within the impoundment, erosion occurred immediately after dam removal and is still occurring five years later resulting in an increase in the thalweg depth and a decrease in channel width. Downstream of the dam, the eroded sediment was deposited one-year after removal but this decreased with increasing downstream distance from the dam. Five years after removal, the deposited sediment has begun to erode and will continue until bedrock is reached. Finally, according to preliminary modeling, the removal of Hofmann Dam and the erosion and deposition near the dam has resulted in the increase in average water velocity during flood conditions and the creation of riffles and runs.
|Commitee:||Benjankar, Rohan, Grossman, Michael|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 58/01M(E), Masters Abstracts International|
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