The Flushing of Louisiana's Coastal Bays under Hurricane Conditions

Abstract

Hurricane storm surges cause coastal inundations and saltwater intrusions into land and wetland areas where freshwater dominates at normal times. The extent of the salty ocean water intrusion in time and space, over the normally low-salinity regimes, determines how much damage the surge does to the coastal ecosystem. With few exceptions, little effort has been made to understand the dynamics of the surge flushing out of hurricane-flooded coastal bays, particularly those in the northern Gulf of Mexico, known for its broad continental shelf and mild-slope near-shore region. This study focuses on the process during which the flood water is flushed out through both inundated land and tidal passages. For this purpose, an investigation of storm surge impact to the coast of Louisiana is conducted using the state-of-the-art finite-volume coastal ocean model FVCOM (Chen et al., 2003). We apply FVCOM to storm surges caused by Hurricane Rita of September 2005 and Hurricane Ike of September 2008 and analyze their inundation of coastal areas. Data from existing platforms along the coast are used in the validation of the model. These model results of storm surges allow an analysis of the effects of (1) the geometry of the water body affected, (2) the specific hurricane characteristics, and (3) the trajectory of the hurricane relative to the bay. Our case-studies in Sabine Lake. Calcasieu Lake and Vermilion Bay in southwest Louisiana demonstrate how the relative geometry of the bay/track is crucial in determining a storm's impact, and how the different dynamics of surge build-up versus receding stages produce distinct asymmetric in-and-out flushing patterns. Flushing rates are calculated and compared with the normal tidal conditions.