25 Measuring and Modeling Coastal Morphodynamics: Beaches and Shelves (Posters)

Sunday, 14 March 2010
1:30 PM - 4:15 PM
International ABCDF

COMPARISON OF BEACH EROSION RATES AND SHORELINE ORIENTATION FOLLOWING A BEACH NOURISHMENT PROJECT IN LONG BAY, SC

Paper number: 25-9
Program: Theme Sessions
Time: 1:30 PM – 4:15 PM

Authors

Abstract

In this study, shoreline erosion rates of two recently nourished beaches in Long Bay, SC are compared to document the relative impacts of storms and seasonal beach profile geometry via biannual beach profile and monthly mean high water surveys. Long Bay is a shallow embayment located within a sediment starved passive continental margin. The sites are separated by approximately 20 km with the North Myrtle Beach site located in northern Long Bay with a northeast to southwest orientation and the Garden City/Surfside site is located in central Long Bay with a north to south orientation. The seafloor at each site consists of Quaternary sediments underlain with Late Cretaceous sediments in North Myrtle and Early Tertiary sediments in Garden City/Surfside. Long term erosion rates (1850s-1980) are 0-0.2 m yr-1 at both sites while shorter term erosion rates (1996-2000) are slightly accretional due to beach nourishment.

An estimated 575,000 m3 of sand was placed over 15 km of shoreline in February 2008 and October 2008 at Garden City/Surfside and North Myrtle, respectively. This study analyses two years of monthly mean high water surveys and biannual beach profile surveys that were collected prior to nourishment to present. The resulting data suggests erosion rates are similar at each site and shoreline orientation plays a minor role in erosion of the upper beachface. Most erosion of the upper beachface occurred in fall and winter months, coinciding with the higher wave energy and northeast winds associated with storms. Long term sediment transport is to the southwest and this data set suggests transport of fill material has been to the beachface of adjacent beaches, offshore, and to ebb tidal deltas associated with minor tidal inlets.