HURRICANE-INDUCED TRANSPORT OF SAND IN A NORTHERN GULF COAST ESTUARY

Weeks Bay is a small estuary (approximately 7 km²) located in Baldwin County in south western Alabama. Since 1997 when undergraduate geology students at the University of South Alabama first began to monitor sediment distribution in the estuary, Weeks Bay has been impacted by 5 hurricanes. Danny in 1997, Ivan in 2004 and Dennis in 2005 were essentially direct hits on Weeks Bay. Georges in 1998 and Katrina in 2005 made landfall elsewhere along the northern Gulf Coast, but still strongly influenced sediment transport and sedimentation into and within the bay. Following most of the named storms, sediment distribution maps based upon comprehensive grain size analysis of grab samples were made across Weeks Bay. Comparison of these maps demonstrates that hurricanes are the major transport mechanism of sand-sized sediment from the mouth of Weeks Bay northward into its interior. Hurricanes Georges and Ivan both produced characteristic storm beds near the mouth of Weeks Bay, but Hurricane Katrina, which generated the highest storm surge ever recorded in the estuary, surprisingly did not. Fair weather processes are responsible for sand transport along much of the shoreline of Weeks Bay and silty clay deposition throughout much of the bay’s interior. Flood events generated from rivers that flow into Weeks Bay, like those produced following the landfall of Hurricane Danny in 1997, are capable of transporting sand across the estuary southward toward the mouth; however, their preservation in the sediment record is tenuous given the intensity of bioturbation in the bay.