REGIONAL ANALYSIS OF SUSPENDED-SEDIMENT TRANSPORT RATES
Watershed Physical Processes Research Unit
2008 Annual Report
1a.Objectives (from AD-416)
(1) Regional analysis of sediment-transport rates for Level III ecoregions of the Southeastern United States. For all sites determine: suspended-sediment transport ratings (dimensional and dimensionless) and annual suspended-sediment loads and yields. For selected sites in each ecoregion, determine magnitude, frequency, duration relations for suspended-sediment transport. (2) Technology transfer of bank-stability model and provide training on model use and data collection to support model. (3) Develop protocol for linking sediment and stream biology.
1b.Approach (from AD-416)
Historical flow and sediment-transport data from sites across Mississippi, the Mid South and the Southeastern United States will be used to develop sediment-transport rating relations and substrate-composition parameters each site. Annual suspended-sediment loads will be calculated for all sites in EPA Region IV and sorted by Level III ecoregion to determine regional trends for stable and unstable sites. Trends of bed-material composition will similarly be identified. Rapid geomorphic assessments conducted during previous studies will be used to determine the relative stability of the stream and used to sort sited into stable and unstable groupings. Statistical analysis of sediment-transport rating relations will be used to determine if characteristic relations can be developed for streams of given stability and bed-material characteristics. These data will be used to investigate the possibility of establishing empirical, dimensionless sediment ratings for un-gauged streams. The relative stability of streambeds and the likelihood that rates of bed erosion or deposition exceed background rates will be estimated at gaged sites using an excess shear-stress approach. Potential links between sediment-transport rates, bed-material conditions and aquatic indices in the Southeastern Plains Ecoregion (Ecoregion 65) will be investigated using both (1) an empirical-statistical approach using historical data from throughout the region where data are available, and (2) by making simultaneous measurements and sampling of flow, sediment transport conditions and aquatic-community structure at two stable and unstable sites in Mississippi and Georgia as case studies. These data will be compared with existing ecological data to provide a means of differentiating impacted from non-disturbed systems. A spreadsheet model to evaluate bank stability will be developed and workshops will be provided on model use and required data collection to support its use.
Analysis of historical flow and sediment data in combination with field evaluations of channel stability resulted in improved estimates of “reference” or target values for sediment for ecoregions throughout the southeastern United States. This analysis was extended to include the magnitude, frequency, and duration of a range of concentrations for stable and unstable streams to be used by biologists to investigate threshold conditions for aquatic health. These results are highly valued by state and federal agencies that are charged with using scientifically-defensible methodologies to develop Total Maximum Daily Loads for sediment. A peer-reviewed journal article providing the first regionally-based evaluation of sediment frequency and duration for stable, “reference” streams has been accepted and is “in press”. Preliminary results of an investigation of the possibility of estimating suspended-sediment concentration from measurements of turbidity has shown that relations between the two variables are consistent within the Yazoo River Basin. Additional sites and sampling are planned for FY 09. The Bank-Stability and Toe-Erosion Model has been enhanced to include a variably saturated groundwater flow model. This new sub-model is currently being tested and validated. Results of this research are critical to action agencies to determine potential impacts of sediment, particularly from streambank erosion on designated uses of Mid South water bodies. Monitoring of project progress is accomplished by at least annual meetings with the cooperator and by more frequent conference calls and e-mail communications.