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United States Department of Agriculture

Agricultural Research Service

Research Project: REGIONAL ANALYSIS OF SUSPENDED-SEDIMENT TRANSPORT RATES

Location: Watershed Physical Processes Research Unit

2007 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.


3.Progress Report
This report serves to document research conducted under a Reimbursable Cooperative Agreement between ARS and the U.S. Environmental Protection Agency (EPA) Region IV. 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." 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 Mid South. 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. The biological part of this research is being conducted by the University of Tennessee for the two ecoregions that comprise the Yazoo River Basin. A National Sedimentation Laboratory (NSL) research report was delivered to the cooperator with an abridged report submitted to a peer-reviewed journal providing the first regionally-based evaluation of sediment frequency and duration for stable, "reference" streams. Relations between suspended-sediment concentration and turbidity are being studied at five sites in the Yazoo River Basin to investigate whether a general relation can be established for the region. Version 4.2 of the in house bank-stability and toe-erosion model has been enhanced to include (1) a search routine for the most critical failure-plane angle, (2) an improved mechanism to quantify the effect of roots on bank reinforcement, and more accurate depiction of bank-steeppening by hydraulic erosion at the bank toe. 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. These results are highly valued by state and federal agencies that are charged with using scientifically-defensible methodologies to develop Total Maxium Daily Load (TMDLs) for sediment. In addition, results from this study will be combined with previous and ongoing studies to produce a national view of "background" sediment transport rates to better understand the production and delivery of sediment in divergent regions of the United States.


Last Modified: 4/24/2014
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