Delta subsidence reversal, levee failure, and aquatic habitat - A cautionary tale

Abstract

Various schemes are often suggested to reverse the subsidence of lands below sea level in California's Sacramento San Joaquin Delta, an area protected by levees (dikes) that have significant probabilities of failure. Elementary modeling is used to estimate the probability distribution of land elevations at time of failure for 36 of these subsided islands, assuming a reasonable potential subsidence rever-sal rate. Given estimated annual probabilities of levee failure, elevation gains at this rate are not expected to exceed 1 to 2 m before flooding, which would be insufficient to restore most subsided islands to mean sea level (msl). However, under some circumstances 1- to 2-m gains are significant. A framework is introduced for evaluating islands as promising candidates for subsidence reversal based on elevation goals other than msl, as dem-onstrated though a hypothetical aquatic habitat example. Here, we recommend relevant subsidence reversal strategies by comparing an elevation goal with each island's anticipated flooded depth, and we prioritize islands for investment based on trade-offs between anticipated outcome and lost agricul-tural revenues. This approach might help integrate subsidence-reversal activities into long-term Delta planning under a range of flooding, land use, and habitat management scenarios.