Beach Changes on Coasts with Different Wave Climates

Abstract

Seasonal and longer-term beach variability is quantified for seven U.S. beaches exposed to widely varying wave climates. One U.S. west coast location (southern California) and six U.S. east coast locations (from North Carolina to Massachusetts) form the basis of this study. Wave exposure varies from complete exposure to open ocean waves, to partly sheltered locations, and finally to nearly complete sheltering where locally-generated waves dominate. Beach response was documented with beach profiles distributed along each of the seven coastal locations, spanning a minimum of five years of observation. Frequency of measurement was at least once per month, with periods of more intense weekly sampling lasting for up to two years (southern California location). Wave climate was either measured directly or estimated from hindcast and/or compilations of ship observations. Consequently, wave information varies in detail from joint statistics of wave height, frequency, and direction, to compilations of local storm history (and hence inferred wave behaviour). Magnitude of annual beach variability ranged from 3.3 m3 per metre of beach to 0.2 m3 per metre of beach, with the greatest variability in regions exposed to open ocean waves (most severe wave climate) and the lowest variability along protected coasts (least severe wave climate). All open coast locations studied had a seasonal variability which accounted for at least 50% of the beach variability. Protected coastal locations had less pronounced seasonal signatures. These seasonal and aseasonal beach responses mirror corresponding seasonality (or lack thereof) in wave and storm climates. The study re-emphasizes the need for careful measurement or estimation of coastal wave climate to enable predictive modelling of shoreline behaviour, and discusses different analysis techniques for analyzing changes in beach profiles through time.