THE STRATIGRAPHIC SIGNATURE OF TROPICAL STORM ISIDORE AND HURRICANE LILI ON RACCOON ISLAND

The dual impacts of Tropical Storm Isidore and Hurricane Lili in 2002 provided an opportunity to examine the characteristics of storm deposits within a transgressive depositional system in coastal Louisiana. Tropical Storm Isidore and Hurricane Lili battered the southern Louisiana coast during the hurricane season of 2002. Raccoon Island of the Isles Dernieres barrier island chain underwent land loss of 322 acres as a result of the two storms (Penland, S., et. al. 2003). Raccoon Island is of importance because it is home to the first breakwater project that was impacted by a major storm and home to the Louisiana State Bird, the Brown Pelican. The objectives of this study were to provide coastal scientists with information on the post storm sediment budget, geologic framework, and transgressive storm deposits. In order to study the post storm geologic framework of Raccoon Island, fifteen-pre storm vibracores and twenty-nine post storm vibracores taken around Raccoon Island were analyzed. Mosaicking of aerial photography from 1983-2004 was done in order to visualize the sediment budget of the island prior and post due to major storm events. Pre and post 2002 storm LIDAR data and 1992 post-Hurricane Andrew bathymetric data was used to calculate the depositional changes that took place as a result of the 2002 storms. Sbeach, a coastal engineering based model, was used to simulate beach erosion and the profile of the gulf shoreline. The highest rate of deposition took place on the western backbarrier side of Raccoon Island where an overwash regime is present. The highest rate of erosion took place west of the breakwater structures near the erosional shadow. Post storm stratigraphic analysis concluded that the vibracores consisted of 1.5-2 meters of overwash in the upper unit and 2 meters of prodelta deposits in the bottom unit. Aerial photography from 1983-1996 depicted a pattern of submergence of the western spit of the island resulting from major storm events. 2002 post storm and 2004 aerial photography depicted overwash and inlet formation as a result of the 2002 storms. Sbeach model simulation ran a resulting beach profile of –0.5 meters as a result of wind, wave and reach data from Hurricane Lili and a resulting beach profile of –0.2 meters from Tropical Storm Isidore wind, wave and reach data.