Williams, H., 2018. Assessing the effectiveness of coastal foredune barriers in reducing hurricane washover sedimentation.
This study tests the effectiveness of physical barriers in blocking or reducing washover sedimentation in coastal marshes. It is widely assumed that natural and artificial physical barriers, such as foredunes and roads, block or reduce storm overwash. However, there appears to be little documented assessment of this effect. This topic has gained significance recently because of concerns over sea-level rise induced by global warming creating a larger potential threat from storm overwash. Nearshore physical barriers act to protect populations and infrastructure farther inland from storm surge, but they may also reduce sediment delivery to coastal marshlands, slowing their vertical accretion and contributing to their submergence by rising sea level. Consequently, there is a critical need for more information on the effect of physical barriers on marsh sedimentation. Washover sediment beds were examined along two transects across marshes in McFaddin National Wildlife Refuge in southeastern Texas, one in the lee of a higher and wider foredune barrier and one where foredunes are lower and narrower. Washover sediment beds deposited by Hurricanes Rita (2005) and Ike (2008) were found on both transects. Comparison of washover sedimentation along the two transects showed an average 40% reduction in sediment volume and an average reduction in inland extent of deposits of 505 m in the lee of the higher and wider barrier. These results show that even relatively subtle increases in barrier dimensions can cause substantial reductions in the magnitude of washover sedimentation in marshes. These findings have implications for paleotempestology studies that use the magnitude of washover sedimentation in the lee of dynamic coastal barriers as geologic proxies of storm intensity. Coastal management agencies contemplating the use of physical barriers to block storm surge should take into consideration the impact of such barriers on the sustainability of coastal marshes faced with rising sea level.