The effect of sand fencing on the morphology of natural dune systems

Sand fences are a frequently used management tool on developed coastlines because they are inexpensive and easy to install. While the geomorphic effect of sand fences has been investigated before, previous studies have been limited in both temporal and spatial domains. Here, we present the evolution of Bogue Banks, a developed barrier island along the Outer Banks of North Carolina, over a 20-year period from 1997 to 2016 where sand fences were emplaced along parts of the island in 2010. We use LiDAR-derived cross-shore transects (n = 38,454) to measure beach and foredune features along the extent (~40 km) of Bogue Banks for every available year of lidar data as well as the locations of sand fences, which we identify in 39% of the transects following fence construction. First, we found that vertical growth of the natural foredunes along Bogue Banks was slightly positive between 2010 and 2016 despite an increased amount of shoreline erosion. This pattern was coincident with a combination of sand fence installation and beach nourishment efforts, which were most heavily focused on the eastern end of the island. Second, we found that natural foredunes located behind fenced dunes are typically shorter, wider, and smaller in volume than natural foredunes in non-fenced and undeveloped areas. Although this may partly be due to a tendency for fences to be installed in front of more vulnerable dunes, our results suggest that, once emplaced, sand fences prevent growth of the landward foredune behind fenced dunes. These findings suggest that sand fences block sediment supply to landward dunes, leading to a shorter and wider complex foredune than would otherwise naturally occur.