Erosion countermeasure design in complex flow field: A case study on the American River

Authors: RIVAS, TODD - Us Army Corp Of Engineers (USACE); KEYS, TYLER - Us Army Corp Of Engineers (USACE); LIANG, JOHNSEN - Us Army Corp Of Engineers (USACE); CARMONA, YUNG - Us Army Corp Of Engineers (USACE); AUBUCHON, JONATHAN - Us Army Corp Of Engineers (USACE); Langendoen, Eddy

Submitted to: Joint Federal Interagency Sedimentation and Hydrologic Modeling
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2023
Publication Date: 5/8/2023
Citation: Rivas, T., Keys, T., Liang, J., Carmona, Y., Aubuchon, J., Langendoen, E.J. 2023. Erosion countermeasure design in complex flow field: A case study on the American River. Joint Federal Interagency Sedimentation and Hydrologic Modeling. 14 pp. In Proceedings of SEDHYD 2023, St. Louis, MO, May 8-12, 2023.

Interpretive Summary: A portion of a levee, protecting the City of Sacramento, on the North side of the American River floodplain in the vicinity of multiple bridges was identified to require erosion protection to reduce flood risk. Understanding the erosion risk to the levee, including effects of flow through and around the bridge structures, is needed to minimize environmental impacts and reduce cost while still protecting the large at-risk population living behind the levee. ARS scientists in Oxford, MS, in collaboration with specialists from the US Army Corps of Engineers (USACE), Sacramento District, utilized the USDA-ARS Bank Stability and Toe Erosion Model (BSTEM) to evaluate bank retreat without and with erosion countermeasures. The BSTEM results were used by USACE to inform the performance and risk reduction of the proposed erosion countermeasures. This case study demonstrates the use of BSTEM for risk-informed design of erosion countermeasures for a levee near bridges with complex flow which helped to optimize the design to meet flood risk reduction objectives.

Technical Abstract: The American River Common Features project in Sacramento California identified a portion of a levee on the North side of the floodplain in the vicinity of multiple bridges requiring erosion protection to reduce flood risk. This is needed to protect the levee from high velocities and turbulent flow around the bridge piers and abutments for the design flood event (1/325 Annual Chance Exceedance). The site on the American River includes two highway bridges and one railroad bridge. Some of the columns, posts, and abutments of these bridges are near the levee, increasing turbulence. Understanding the erosion risk to the levee, including effects of flow through and around the bridge structures, is needed to minimize environmental impacts and reduce cost while still protecting the large at-risk population living behind the levee. The risk-informed design at this site utilized the Bank Stability and Toe Erosion Model (BSTEM) developed by USDA-ARS to evaluate bank retreat. A Monte-Carlo simulation was evaluated within BSTEM to provide quantitative bank retreat estimates to inform the existing risk of an erosion related levee breach at the site and for risk-informed design of potential erosion countermeasures. BSTEM model scenarios were developed for the existing conditions to inform the baseline risk assessment. Additional BSTEM models were developed to inform risk assessments of proposed risk reduction measure of placing rock on the levee and along the levee toe. Design consideration was given to potential increased shear stress around the bridge piers and the development of scour around the bridges near the levee toe. The developed design scenarios were meant to bracket the expected condition. The collective BSTEM results were used by the design team to inform the performance and risk reduction of the proposed erosion countermeasures. This case study demonstrates the use of BSTEM for risk-informed design of erosion countermeasures for a levee near bridges with complex flow which helped to optimize the design to meet flood risk reduction objectives.