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Title: A physically-based channel-modeling framework integrating HEC-RAS sediment transport capabilities and the USDA-ARS bank-stability and toe-erosion model (BSTEM)

item GIBSON, STANFORD - Us Army Corp Of Engineers (USACE)
item SIMON, ANDREW - Cardno Entrix
item Langendoen, Eddy
item BANKHEAD, NATASHA - Cardno Entrix
item SHELLEY, JOHN - Us Army Corp Of Engineers (USACE)

Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: 9/25/2015
Publication Date: 9/25/2015
Citation: Gibson, S., Simon, A., Langendoen, E.J., Bankhead, N., Shelley, J. 2015. A physically-based channel-modeling framework integrating HEC-RAS sediment transport capabilities and the USDA-ARS bank-stability and toe-erosion model (BSTEM). In: Proc. 3rd Joint Federal Interagency Sedimentation and Hydrologic Modeling Conference, April 19-23, 2015, Reno, NV. 12 pp.

Interpretive Summary: The current version of the widely-used River Analysis System software HEC-RAS developed by the U.S. Army Corps of Engineers, Hydrologic Engineering Center (HEC) is unable to simulate channel width adjustment. Scientists at the USDA, ARS, National Sedimentation Laboratory (NSL) in collaboration with researchers from HEC have integrated the physically-based bank erosion modules from the ARS channel evolution computer model CONCEPTS and the ARS bank stability and toe erosion model BSTEM. The new features were validated against the comprehensive streambank erosion dataset collected by NSL between 1996 and 2007 on the Goodwin Creek, Mississippi. The improved HEC-RAS model will be used by various districts of the Corps of Engineers to manage flow and sediment releases from impoundments on the Missouri River and its tributaries.

Technical Abstract: Classical, one-dimensional, mobile bed, sediment-transport models simulate vertical channel adjustment, raising or lowering cross-section node elevations to simulate erosion or deposition. This approach does not account for bank erosion processes including toe scour and mass failure. In many systems lateral channel adjustments can be as important – or more important – than vertical bed changes. There are also important feedbacks between incision, deposition, toe scour, and bank-failure processes. Each process can depend on the others. Additionally, bank-derived sediments can affect downstream processes and impact downstream projects, depositing in flood damage reduction channels, silting natural or engineered spawning substrates, or filling downstream reservoirs. Therefore, to account for these processes and the feedbacks between them, the USDA-ARS Bank Stability and Toe Erosion Model (BSTEM) has been integrated with the sediment transport methods in HEC-RAS 5.0. BSTEM is a physically based bank-erosion model that accounts for hydraulic, toe erosion and bank- failure processes in homogeneous or layered banks. It computes toe-erosion by subdividing flow segments in the near bank zone to compute a vertical distribution of boundary shear stresses and calculates a critical failure plane through layered bank sediments, failing the bank and adjusting the cross section when driving forces exceed resisting forces. Because of their complementary features, river modelers often run HEC-RAS and BSTEM iteratively, in tandem, simulating toe scour and bank failure with BSTEM and computing water surface elevations, simulating bed change and routing bed and bank-derived sediment with HEC-RAS. To provide a more efficient, integrated modeling framework and continuous simulation of potential bed and bank-erosion loadings, HEC-RAS and BSTEM have been coupled, automating the feedbacks between hydraulic, bed, toe, and bank processes. BSTEM uses HEC-RAS hydraulics to determine water surface elevations and to compute the vertical distribution of shear stresses along the bank surface, and evaluates if cross section deposition or erosion simulated by HEC-RAS sediment transport exacerbates or improves bank stability. If BSTEM computes failure, HEC-RAS updates the cross section to reflect the new bank geometry and adds the sediment mass of the failed layers (by particle-size class) to the transport model, routing it downstream. This paper will describe the model integration, and present an example, verification, application.