1a.Objectives (from AD-416):
The two primary objectives of this study are to: (1) characterize the erosion resistance to hydraulic and geotechnical forces of deposits in two reservoirs slated for dam removal (Klamath and Matilija), and (2) determine (predict) magnitudes and styles of channel adjustment through these deposits following removal of the dams. The latter objective will be accomplished by coupling the 2-dimensional flow and sediment transport model SRH-2D developed by the Bureau of Reclamation with National Sedimentation Laboratory (NSL’s) Bank-Stability and Toe-Erosion Model (BSTEM). A subsidiary objective is to determine stable bank geometries for these deposits which can be used by the Bureau for channel design.
1b.Approach (from AD-416):
Sediment cores, spatially distributed throughout the reservoir will be obtained by the Bureau. NSL personnel will accompany Bureau of Reclamation staff during sampling and use a series of instruments for in-situ testing of the hydraulic and geotechnical resistance of the materials to erosion. Data on the critical shear strength and unconfined compressive strength of the deposits will be measured at several depths along the core under saturated conditions. Partial cores will be returned to NSL for further testing under drained conditions and for direct shear tests. Bulk samples will also be returned to NSL and remolded for erosion-resistance testing in soil boxes under various pore-water pressure and applied stress conditions. Data obtained from the in-situ and laboratory testing will be used to populate the Bank-Stability and Toe-Erosion Model (BSTEM) to predict stable-bank geometries under saturated and drained conditions.
Working in concert with scientists from the Bureau of Reclamation and the University of Mississippi, computer codes from the Bureau’s 2-dimensional mobile bed model (SRH-2D) and NSL’s Bank-Stability and Toe-Erosion Model (BSTEM) will be coupled. The resulting model will provide a comprehensive tool to simulate channel-adjustment processes including, degradation, aggradation, bar development, channel widening and lateral migration. Model validation will be accomplished using the detailed data set available from the Goodwin Creek, MS, research bendway. Application of the model to channel adjustment in the reservoir deposits will be conducted by the Bureau.
In FY 2012, collaboratively with the National Center of Computational Hydroscience and Engineering, we completed the conversion of the code of the bank stability and toe erosion model BSTEM from Visual Basic to Fortran. We coupled the Fortran code to the U.S. Bureau of Reclamation’s two-dimensional (2D) river morphology model SRH-2D to improve our predictions of channel adjustment and planform development. We tested both the new standalone BSTEM code and the coupled SRH-2D and BSTEM codes against observed streambank retreat along a section of the Goodwin Creek, Mississippi, between 1996 and 2001. We found that the 2D coupled model represents an improvement over the results previously obtained using the one-dimensional CONCEPTS model. This highlights the further need to couple more accurate multi-dimensional free surface models with bank erosion models.