1a.Objectives (from AD-416)
Improve current understanding and characterization of the rates of sediment transport and substrate composition in Mississippi with the purpose of defining "reference"/background and impacted conditions. Utilize a methodology tested successfully in the Mid South to determine "departure" from stable sediment-transport conditions for a diverse range of phyisiographic, and ecological conditions in Mississippi.
1b.Approach (from AD-416)
Historical flow and sediment-transport data from sites across Mississippi and the Mid South will be used to develop sediment-transport rating relations for each site and substrate composition parameters. Effective and annual sediment loads will be sorted by Level III ecoregion, river basin, and sub-basins providing a range of values for each. Rapid geomorphic assessments at each site will determine the relative stability of stream, provide substrate sampling, and bed slope and bank elevation of bankfull stage. These data will be used to study the likelihood that rates of bed erosion or deposition exceed background rates, to differentiate "reference" from impacted sites, and provide an analytic framework for estimating conditions at the bankfull discharge. Where necessary and designated by MDEQ, numerical modeling of upland processes using AnnAGNPS and channel processes using CONCEPTS will be used to determine sediment source areas and test watershed and in-stream BMPs.
This report serves to document research conducted under a Reimbursable Cooperative Agreement between ARS and the Mississippi Department of Environmental Quality (MDEQ). Additional details of research can be found in the report for the in-house project 6408-13000-017-00D, "Integrated Assessment and Analysis of Physical Landscape Processes that Impact the Management Of Agricultural Watersheds." A final report on "reference" sediment-transport conditions for the Big Black and Tombigbee River Basins was delivered to the cooperator. Final analysis of stream-channel and stability conditions as they relate to sediment-transport rates in the Yazoo River Basin is nearing completion. Geomorphic data from about 200 sites where MDEQ has been collected during site visits at locations where biologic information have been compiled in the context of relative channel stability. These data were used to distinguish stable from unstable sites so that sediment loadings from each group could be compared. Regional-ecoregion values of "reference" or "background" rates of sediment transport have been converted to magnitude and frequency relations, and determined for smaller zones within each ecoregion to help MDEQ refine estimates of "target" transport rates for developing TMDLs. Quarterly project reports and conference calls are used to communicate project status.