SEDIMENTARY IMPACT OF HURRICANES DENNIS AND KATRINA ON WEEKS BAY, ALABAMA

The 2005 hurricane season will long be remembered for the number and intensity of storms that affected the United States Gulf Coast. In a six week time span, Hurricanes Dennis (July 10, 2005) and Katrina (August 29, 2005) made landfall as strong category 3 storms between Navarre Beach, FL and the Mississippi-Louisiana border. Midway between these two points of landfall lies Weeks Bay, a small estuary (7 square km) located on the eastern shore of Mobile Bay, in south-western Alabama. For the past eight years, this estuary has been the subject area for sedimentary analysis by undergraduate students at the University of South Alabama. Using baseline data from the 2005 study (post-Hurricane Ivan), we have been able to assess the combined sedimentary effects of Hurricanes Dennis and Katrina on Weeks Bay bottom sediment. In this study cycle, we collected over 600 bottom samples using a Ponar grab sampler deployed from a small boat. Grain size analysis was done on these samples to produce a series of sediment distribution maps. Hurricane Dennis produced a 0.9 m (above mean sea level) storm surge near the mouth of Weeks Bay. The storm surge induced by Hurricane Katrina was the highest ever recorded in the bay (2.2 m above mean sea level), yet neither storm drastically changed grain size distribution or generated a prominent storm bed as did previous hurricanes (e.g., Georges in 1998 or Ivan in 2004). Our preliminary results suggest that storm surge alone may not dictate sediment re-distribution during hurricanes.