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Sea Level Rise Shoreline Model Reconstructs Past to Predict Future

Published on: 10/15/2015
Research Area(s): Coastal Change
Primary Contact(s): david.kidwell@noaa.gov

A unique NCCOS sponsored study, recently published in Continental Shelf Research, examined the influence of sea level rise (SLR) on historic mainland and barrier island beaches and salt marshes of Mississippi's Grand Bay in Mississippi Sound. The research used historical data to investigate how excess erosion in Grand Bay and SLR will affect any future changes to the morphology of the Sound, such as rebuilding Grand Batture Island or modifications to shipping channels.

Over the past century, the marine-dominant Grand Bay estuary, home of NOAA's Grand Bay National Estuarine Research Reserve and a NOAA Sentinel Site, underwent natural and anthropogenic induced landscape changes due to erosion from changing tidal and wave forces, hurricanes and highway construction. This led to diversion of the estuary's sediment source and the erosion of Grand Batture, its protective barrier island. The modelling study, part of the NCCOS Ecological Effects of Sea Level Rise project in the northern Gulf of Mexico, evaluated the combined effects of historic sea level rise (SLR) with barrier island and beach morphology on tidal hydrodynamics in the estuary. Researchers used a high resolution large-domain hydrodynamic model to simulate present (circa 2005) and past (circa 1848, 1917, and 1960) conditions with unique sea levels, bathymetry, topography and shorelines representing conditions at those times.

Difference in maximum tidal velocities in Mississippi Sound, 2005 versus 1848 due to sea level rise and coastal morphology changes. Credit D. Passeri, University of Central Florida

Difference in maximum tidal velocities in Mississippi Sound, 2005 versus 1848 due to sea level rise and coastal morphology changes. Credit D. Passeri, University of Central Florida

The model showed that the westward migration of Petit Bois Island allowed stronger tidal velocities centered on the Grand Batture Island. Maximum tidal velocities within the Grand Bay estuary tested 5 cm/second faster historically, and reversed from being flood dominant in 1848 to ebb dominant in 2005. Higher saline waters from the Sound altered marine life and significantly reduced the oyster population over the past century.

Comparison of past and present conditions illustrates the system's tidal response to SLR and the changing landscape. Better understanding of past coastal morphology and the role of SLR on tidal hydrodynamics provides insight into potential future changes.

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