Case Study Evaluating The New Reservoir Volume Reduction Tool In Hec-Hms

Dams and reservoirs disrupt the natural transport of sediment in streams by creating large backwater areas with low velocities, allowing sediment to settle to the bottom of the reservoir. Over time, sediment deposition reduces the storage volume and surface area of the reservoir, which can have a detrimental effect on authorized purposes such as water supply, flood control, and recreation. Accurately predicting sediment deposition is necessary for determining sedimentation impacts and planning future resources. Sediment deposition can be predicted by estimating the incoming sediment load and the trapping efficiency of the reservoir, along with other parameters. Past studies have calculated volume change using tools such as Microsoft Excel and ArcGIS. However, these tools can be labor intensive and require the use of large, cumbersome datasets. HEC-HMS versions 4.9 and 4.10 added a new reservoir volume reduction tool, which allows for the efficient calculation of reservoir volume change. The new features were tested at three reservoirs in the state of Kansas (Tuttle Creek, Kanopolis, and Perry), which have experienced significant sediment deposition since project construction. Bathymetric surveys show that Kanopolis has lost approximately 36% of its multipurpose pool volume, Tuttle Creek 39%, and Perry 18%. Simple HEC-HMS models were created for all three reservoirs to evaluate the effectiveness of the new HEC-HMS tool in estimating long-term volume change from sediment deposition. A comparison of the model results to surveyed volume change shows that HMS can efficiently and accurately predict the volume reduction due to sedimentation.