Seasonal Shoreline Variability Induced by Subtidal Water Level Fluctuations at Reef-Fringed Beaches

作者：Segura, L. E.^*; Hansen, J. E.; Lowe, R. J.

来源：JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE, 2018, 123(3): 433-447.

DOI：10.1002/2017JF004385

• beach morphodynamics
• fringing reefs
• Leeuwin Current
• sea level

The comparative role of subtidal water level and wave height variations on seasonal shoreline changes was investigated at a reef-fringed beach in southwestern Australia. The data set consisted of continuous sea level and wave records, monthly topographic beach surveys over a 2year period, and bimonthly high-resolution aerial images over a 7year period. Shorelines were extracted from images and topographic surveys, and then an empirical orthogonal EOF) analysis was applied to both data sets. The temporal amplitudes of the first EOF mode of the image-derived shoreline data set (approximate to 60% of the variance) were most correlated with 30day averages of the subtidal water level (variations up to 0.2m) driven by geostrophic adjustment of the Leeuwin Current. The geostrophic response of the Leeuwin Current was found to be further correlated with the phasing of the El Nino-Southern Oscillation, leading to higher water levels during La Nina and lower levels during El Nino, which as a consequence resulted in interannual variations in the shoreline behavior reflected in the first EOF mode. The temporal amplitudes of the second EOF mode (approximate to 20% of the variance) were most correlated with 50day averages in offshore wave height. Our results indicate that the seasonal beach response was primarily influenced by seasonal variations in offshore water level rather than by wave heights as has been generally observed in exposed beaches. A simple EOF-based model is presented, which reproduces the alongshore-variable shoreline response and its seasonal and interannual modulation due to El Nino-Southern Oscillation events over the study period.

• 出版日期2018-3