San Lorenzo River: Levee Evaluation using Uncertainty Analysis
Nearing the completion of a 15-year planning effort and construction of the San Lorenzo River Flood Control Project Levee upgrades, the California coastal City of Santa Cruz faced changing standards for the U.S. Army Corps of Engineers (USACE) certification of the levee improvement project.
ESA worked with the City of Santa Cruz to evaluate the ability of San Lorenzo Flood Control Project levees to protect against a 100-year flood event under the USACE's draft modified certification standards, using a risk and uncertainty approach. Flood stage uncertainty in the San Lorenzo River is driven by sediment transport impacts to hydrology, hydraulics, and geometry changes. ESA analyzed selected aspects of sediment transport- roughness, discharge probability, starting or antecedent bed conditions, and tidal boundary conditions-without modifying the underlying sediment transport modeling assumptions used by the USACE in developing the design. Our uncertainty analysis found that current levees do not appear to meet certification criteria in at least one reach of the project, though most reaches appear sufficient.
ESA worked with the City of Santa Cruz to understand the implications of the USACE's changing certification standards for levee improvements and whether the current San Lorenzo Flood Control Project levees met the new standards.