Large-Scale Patterns in Hurricane-Driven Shoreline Change

Abstract

The effects of storm events on cross-shore beach profiles have been the subject of concerted examination by nearshore researchers for decades. Because these investigations typically span relatively short (less than a kilometer) shoreline reaches, alongshore patterns of storm-driven shoreline change at multikilometer scales remain poorly understood. Here we measure shoreline position from seven airborne lidar surveys of coastal topography, spanning 12 years (1996–2008), along a continuous ∼80 km stretch of the northern North Carolina Outer Banks, United States. Two of the lidar surveys were flown in the wakes of Hurricane Bonnie (1998) and Hurricane Floyd (1999), allowing a rare window into storm-related alongshore coastline changes at large scales. In power spectra of shoreline change variance and in calculations of plan view shoreline curvature, we find evidence of transient behaviors at relatively small alongshore scales (less than a kilometer) and an interesting combination of both transient and cumulative shoreline change patterns at larger scales (1–10 km). Large-scale plan view shoreline undulations grow in amplitude during the storm intervals we examined, possibly forced by a large-scale morphodynamic instability. Long-term (decadal) shoreline adjustments, however, trend in the opposite direction, with an overall diffusion or smoothing of shoreline shape at multiple-kilometer scales, probably due to gradients in alongshore sediment transport. Although storms can significantly reshape the coastline across a wide range of scales, those changes do not necessarily accumulate to patterns of long-term change.