Reservoir sedimentation rates in the Little Washita River experimental watershed, Oklahoma: measurement and controlling factors

Authors: Moriasi, Daniel; Steiner, Jean; Duke, Sara; Starks, Patrick; Verser, Jerry - Alan

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2018
Publication Date: 6/13/2018
Citation: Moriasi, D.N., Steiner, J.L., Duke, S.E., Starks, P.J., Verser, J.A. 2018. Reservoir sedimentation rates in the Little Washita River experimental watershed, Oklahoma: measurement and controlling factors. Journal of the American Water Resources Association. 1-13. https://doi.org/10.1111/1752-1688.12658.
DOI: https://doi.org/10.1111/1752-1688.12658

Interpretive Summary: In the 1930s, severe drought and lack of proper farming methods resulted in lack of vegetation, which combined with subsequent periods of intense rainfall caused increased erosion and flooding. As a result of the Flood Control Act of 1936, $85 billion were appropriated to construct flood control reservoirs around the country. A total of 45 reservoirs were installed between 1969 and 1982 in the Little Washita River Experimental Watershed (LWREW), one of the nationwide Conservation Effects Assessment Project (CEAP) watersheds located in central Oklahoma. Over time, these reservoirs have lost water storage capacity (WSC) due to sedimentation whose rates depend on land use changes and climate variability. However, the current status of the reservoir WSCs is unknown. Therefore, the goals of this study were to: determine current WSC, reservoir sedimentation rate, projected lifespan, and possible factors affecting observed sedimentation rates using statistical analysis methods. Twelve representative reservoirs were selected, bathymetric survey was carried out using a state-of-the-art acoustic profiling system, and the data was processed using a Geographic Information System software. The current WSCs ranged from 14,920 m3 to 217,263 m3, which were 29% and 41% of respective reservoir design WSC, respectively. Average annual reservoir WSC losses varied from 0.84%/year to 2.20%/year, with projected lifespans ranging from 45 to 118 years. Some climate, soils, and topographic variables were determined to affect sedimentation rates and they can be used to estimate current WSC. The ability to estimate the WSC and projected lifespan for various reservoirs using these variables, provides a reasonable cost-effective approach to estimate WSs and is transferrable to other areas with reservoir sedimentation challenges. Current reservoir WSC and projected lifespan information can help water resource managers with planning and decision making to determine causes of action, whether to decommission or dredge the reservoir, and where needed determine management practices to reduce sedimentation rates. Evaluation of these reservoirs fits into the goal of the CEAP to quantify the environmental benefits of conservation practices.

Technical Abstract: Forty-five flood control reservoirs, authorized in the United States Flood Control Act of 1936, were installed between 1969 and 1982 in the Little Washita River Experimental Watershed (LWREW), located in central Oklahoma. Over time, these reservoirs have lost water storage capacity due to sedimentation, with rates dependent on upstream land use and climate variability. In this study, sedimentation rates for 12 reservoirs representing three major landuse categories within LWREW were measured based on bathymetric surveys carried out using an acoustic profiling system. Physiographic and climate attributes of drainage area corresponding to the survey reservoirs were extracted from publicly available data sources including topographic maps, digital elevation models, NRCS soils, and weather stations databases. Correlation, regression tree modeling, and stepwise regression were utilized to analyze the relationship between normalized reservoir sedimentation rates (ReSRa) and the drainage area characteristics to determine the major variables controlling sedimentation within the LWREW. Percent of drainage area with extreme slopes, saturated hydraulic conductivity, and maximum daily rainfall event recorded in spring explained most of the variability in ReSRa. It was also found that percent reduction in reservoir surface area, determined from readily available data, can be used as a surrogate for estimating ReSRa. The implications of the results are also discussed.