Correlation Between Shoreline Change and Planform Curvature on Wave‐Dominated, Sandy Coasts

Abstract

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 (~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.

The Future of Developed Barrier Systems: 2. Alongshore Complexities and Emergent Climate Change Dynamics

“…The interactions described above between different barrier segments depend only on the tendency for gradients in alongshore transport to smooth the coastline (i.e., shoreline “diffusivity”) and are independent of the existence or magnitude of net alongshore sediment transport (Ashton & Murray, 2006; Lauzon et al., 2019; Slott et al., 2008). Nourished barrier segments tend to stabilize shorelines “updrift” as much as “downdrift,” even on coasts with a net alongshore transport, and this stabilization occurs not strictly through spreading of nourishment sediment, but more fundamentally because of gradients in alongshore sediment transport related to shoreline curvatures (Ashton & Murray, 2006; Lauzon et al., 2019; Slott et al., 2008).…”

The Future of Developed Barrier Systems - Part II: Alongshore Complexities and Emergent Climate Change Dynamics

“…The interactions described above between different barrier segments depend only on the tendency for gradients in alongshore transport to smooth the coastline (i.e., shoreline 'diffusivity') and are independent of the existence or magnitude of net alongshore sediment transport Slott et al, 2008;Lauzon et al, 2019). Nourished barrier segments tend to stabilize shorelines 'updrift' as much as 'downdrift', even on coasts with a net alongshore transport, and this stabilization occurs not strictly through spreading of nourishment sediment, but more fundamentally because of gradients in alongshore sediment transport related to shoreline curvatures Slott et al, 2008;Lauzon et al, 2019).…”

Wave‐Climate Asymmetry Influence on Delta Evolution and River Dynamics

“…Shoreline curvature is the second derivative of cross‐shore shoreline position, with respect to the alongshore direction. Under most wave climates, the flux of sediment alongshore tends to converge when the shoreline has a concave‐seaward curvature, causing accretion, and diverge with a convex‐seaward shoreline curvature, causing erosion (A. D. Ashton & Murray, 2006a; Dean & Yoo, 1992; Lauzon et al., 2019). Under such wave climates, alongshore transport tends to smooth the shoreline on the regional scale.…”