Depth of closure over large regions using airborne bathymetric lidar

Abstract

The depth at which significant bathymetric change can be expected is an important morphological factor for science and engineering on sandy coastlines. Although most depth of closure studies have been conducted on a limited number of sites, the great quantity of airborne lidar bathymetry data collected over the past decade allows for a much wider study region. Here, we present depth of closure analysis over 600km of sandy coastline using the Joint Airborne Lidar Bathymetry Technical Center of Expertise (JALBTCX) dataset. Improved closure predictions resulted when both extreme waves (as represented by the 12hour exceedance significant wave height over a given time interval), and more typical storm waves (as represented by the 99% significant wave height) were jointly considered. In contrast to some other studies, wave steepness terms were found to be negligible. Consideration of error terms in least-squares closure predictions was used to develop relations with different degrees of conservatism: e.g. to provide closure depth exceeded by only 10% of observations. Results are presented for four closure criteria: root-mean-square depth changes Δhclose=[20,30]cm, and relative depth changes Δhclose/h=[0.02,0.04]. Further improvements in accuracy may occur once decadal wave hindcasts include storm surge variations in water levels, and have increased nearshore resolution.