Correlation between shoreline change and planform curvature on wave‐dominated, sandy coasts

Low-lying, wave-dominated, sandy coastlines can exhibit high rates of shoreline change that may impact coastal infrastructure, habitation, recreation, and economy. Efforts to understand and quantify controls on shoreline change typically examine factors such as sea-level rise; anthropogenic modifications; geologic substrate, nearshore bathymetry, and regional geography; and sediment grain size. The role of shoreline planform curvature, however, tends to be overlooked. Theoretical and numerical model considerations indicate that incident offshore waves interacting with even subtle shoreline curvature can drive gradients in net alongshore sediment flux that can cause significant erosion or accretion. However, these predictions or assumptions have not often been tested against observations, especially over large spatial and temporal scales. Here, we examined the correlation between shoreline curvature and shoreline change rates for spatially extended segments of the U.S. Atlantic and Gulf Coasts (similar to 1,700 km total). Where shoreline stabilization (nourishment or hard structures) does not dominate the shoreline change signal, we find a significant negative correlation between shoreline curvature and shoreline change rates (i.e., convex-seaward curvature [promontories] is associated with shoreline erosion, and concave-seaward curvature [embayments] with accretion) at spatial scales of 1-5 km alongshore and timescales of decades to centuries. This indicates that shoreline changes observed in these reaches can be explained in part by gradients in alongshore sediment flux acting to smooth spatial variations in shoreline curvature. Our results suggest that shoreline curvature should be included as a key variable in modeling and risk assessment of coastal change on wave-dominated, sandy coastlines.