Simulated Wave-Induced Erosion of the Mississippi River–Gulf Outlet Levees during Hurricane Katrina

Abstract

This case study on the Mississippi River Gulf Outlet earthen berm/spoil bank (EBSB) illustrates a method to quantitatively analyze wave-induced lateral erosion and breaching through the flood side of coastal flood protection levees with grass armor prior to overtopping. Lateral wave-induced erosion was evaluated based on a three-step process: (1) velocity profiles were generated using a general purpose transient dynamic finite element program; (2) resistance to wave-induced erosion as a result of grass cover (turf) on the flood face of the EBSB was estimated and no wave-induced erosion was applied until the grass cover protection failed; and (3) estimated soil erodibility characteristics were used, in combination with the estimated wave-induced flood face velocities, to estimate the magnitude of lateral erosion. This case study identified that soil erodibility characteristics directly impact coastal flood protection levee performance, grass/turf armoring provides erosion protection for a limited duration, and identification and evaluation of pre-overtopping wave-induced erosion is an important failure mode to be considered in order to ensure reliable coastal flood protection.