Summary

The objective of this study was to provide watershed sedimentation information to decision makers to inform management decisions related to soil surface erosion, water quality, and reservoir capacity. An HEC-HMS model of the UNBRW was created with representation of physical basin characteristics based on watershed soil, terrain, land use, and precipitation data. The HEC-HMS model was calibrated and validated based on observed data collected within the watershed. Model results produced valuable sedimentation information including the following:

  • The sediment yield rate for each subbasin giving indication of the most erodible regions in the watershed.
  • Sediment time series (sedigraph) for each grain class to provide boundary conditions to hydraulic sediment models such as HEC-RAS.
  • Long-term aggradation and degradation trends for each reach to indicate reaches with higher erosion rates. This information could be used to assist in formulating possible corrective measures to enhance fish and wildlife habitat, water quality, flood control, and bank stability.
  • Average trap efficiency rate for each reservoir to calculate the reasonable life expectancy of each reservoir.

This information can be used to assist management officials in determining non-point source contributors in the watershed and TSS loading within the watershed, as well as establishing TMDLs to achieve water quality standards.