Sediment Budget: Mississippi Sound Barrier Islands

Abstract

Historical shoreline and bathymetric survey data were compiled for the barrier islands and passes fronting Mississippi Sound to develop a regional sediment budget spanning a 90-year period. Net littoral sand transport along the islands and passes is primarily unidirectional (east-to-west). Beach erosion along the east side of each island and sand spit deposition to the west result in an average sand flux of about 430,000 cy/yr throughout the barrier island system. Dog Keys Pass, located updrift of East Ship Island, is the only inlet that is a net sediment sink. It also is the widest pass in the system and has two active channels and ebb shoals. As such, a deficit of sand exists along East Ship Island. Littoral sand transport decreases rapidly on West Ship Island, where exchange of sand between islands terminates because of wave sheltering from shoals and islands of the old St. Bernard delta complex, Louisiana.Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it Historical shoreline and bathymetric survey data were compiled for the barrier islands and passes fronting Mississippi Sound to develop a regional sediment budget spanning a 90-year period. Net littoral sand transport along the islands and passes is primarily unidirectional (east-to-west). Beach erosion along the east side of each island and sand spit deposition to the west result in an average sand flux of about 430,000 cy/yr throughout the barrier island system. Dog Keys Pass, located updrift of East Ship Island, is the only inlet that is a net sediment sink. It also is the widest pass in the system and has two active channels and ebb shoals. As such, a deficit of sand exists along East Ship Island. Littoral sand transport decreases rapidly on West Ship Island, where exchange of sand between islands terminates because of wave sheltering from shoals and islands of the old St. Bernard delta complex, Louisiana.

A Comprehensive Sediment Budget for the Mississippi Barrier Islands

“…To be consistent with Byrnes et al (2012) who studied the Mississippi coastal system based on observed island changes for the period from 1917 to 2010, the hurricane hindcast encompasses the same period. By considering all categories 4 and 5 hurricanes that have occurred in the Gulf of Mexico and the hurricanes and tropical storms with wind speeds exceeding 39 mph which made landfall within 500 km of Ship Island 208 hurricanes remain.…”

“…In the present study, the previous work (Byrnes et al, 2012;Rosati et al, 2009) in which this morphological cell is bounded in the East by the Fort Morgan Peninsula and in the West by Cat island is followed (here referred to as the Mississippi Coastal Cell or MCC).…”

“…The scale of the restoration is based on adding approximately the same volume of sand to the system that has been removed over the past decades (upwards of approximately 22 Mcy, see USACE, 2009a,b) due to (maintenance) dredging. More recent MsCIP studies by Byrnes et al (2012), which considered both the volume of sediment removed from maintenance dredging and associated placement of dredged sediment within the system indicates that approximately 13.1 Mcy has been removed from the littoral system of the barrier islands. Restoring the Mississippi barrier islands to a condition similar to the natural system that functioned before human intervention (generally defined as the pre-Camille conditions) offers the best opportunity to ensure the long-term viability of these islands.…”

“…First, the sediment budget study of Byrnes et al (2012) is considered. In this study, which is based on historical shoreline and bathymetric survey data over a period of about 90 years between 1917 and 2010 sediment transports were derived from observed volume changes (corrected for dredging) between consecutive surveys.…”

“…In this study, which is based on historical shoreline and bathymetric survey data over a period of about 90 years between 1917 and 2010 sediment transports were derived from observed volume changes (corrected for dredging) between consecutive surveys. In Figure 9, the MCC-model results are compared with the macro-scale sediment budget of Byrnes et al (2012). Byrnes considers 5 boxes for which the sediment exchange with the surrounding area including the Gulf and sound side of the islands and offshore was determined.…”