Levee Failures and Social Vulnerability in the Sacramento-San Joaquin Delta Area, California

This paper examines the spatial variability in the social vulnerability of residents to potential levee failures in the Sacramento Delta region. To determine the likely flood exposure, levees of concern to the U.S. Army Corps of Engineers and California’s Department of Water Resources were mapped. The HAZUS-MH loss estimation software and 100-year protection standard were used to hypothetically breach levees to determine a coarse approximation of the level and spatial extent of inundation. To assess the differential social consequences of such an event, a social vulnerability index was computed at the census tract level for San Joaquin, Sacramento, and Yolo counties following the vulnerability metrics developed by Cutter et al. in 2003. When integrated with the flood exposure data, there is a clustering of high social vulnerability zones within high risk flood areas. While the spatial pattern is not uniform throughout the tricounty area, these pockets of high vulnerability (largely driven by social factors) warrant management concern about the disproportionate impact of catastrophic levee failures on these populations and the level of local, state, and federal preparedness to cope with such an event.