QUANTIFYING SEDIMENT LOADINGS FROM STREAMBANK EROSION IN SELECTED AGRICULTURAL WATERSHEDS DRAINING TO LAKE CHAMPLAIN
Watershed Physical Processes Research Unit
2011 Annual Report
1a.Objectives (from AD-416)
The primary objectives of the proposed work are to determine rates and loadings of sediment from streambank erosion along main stem and selected tributaries of a large agricultural watershed draining to Lake Champlain.
1b.Approach (from AD-416)
The scope of the project is the main stem and four tributaries (Hereford Brook, Trout River, Tyler Branch and Black Creek) of the Missisquoi River, VT. Tests of the geotechnical and hydraulic erosion resistance of bank materials will be conducted at each site that is selected for detailed investigation. Surveys of bank geometry and vegetation characteristics (species, age and density) will also be conducted at the sites. These data will be used to determine appropriate input parameters for each bank layer at the selected sites for bank-stability modeling. The major controlling processes responsible for bank erosion will be modeled iteratively using the Bank-Stability and Toe-Erosion Model (BSTEM) developed by the ARS, National Sedimentation Laboratory that has been successfully used previously for these purposes in the Mid South and other regions. Simulations for existing bank conditions along the main stem and tributaries will be conducted for each site over a range of annual hydrographs representing the 99th, 95th, 90th, 75th, 50th, and 25th percentile flow year. Discharge data from U.S. Geological Survey (USGS) gauging stations will be converted to flow depths for each significant storm event for input into the toe-erosion sub-model. Combined toe-erosion and mass failure will then be simulated for each event at each site in an iterative fashion. Results will then be extrapolated to the remainder of the channel lengths based on field and aerial reconnaissance of the extent of streambank failures.
The research approach centers on quantifying the hydraulic and geotechnical resistance of streambank sediments for the purpose of simulating streambank erosion rates using the Bank-Stability and Toe-Erosion Model (BSTEM). Field-data collection and BSTEM modeling of existing conditions has been completed at 30 sites in the Missisquoi River Basin. Bank-stability modeling is currently being conducted at the 30 sites under three sets of alternative mitigation strategies to determine the potential reduction in streambank loadings. Analysis of a range of alternatives will be expressed in terms of potential sediment-load reductions. A cost-basis analysis of these potential measures will also be included based on BSTEM results and cost information obtained from local contractors. Preliminary modeling results were presented to the cooperator in early 2011 at a meeting in Burlington, VT. Project monitoring is conducted by conference calls and by meetings in the field area. A draft, final report is expected to be delivered to the cooperator in September 2011.