Storm-Driven Shoreface Morphodynamics on a Low-Wave Energy Delta: The Role of Nearshore Topography and Shoreline Orientation

An analysis of storm-driven sedimentary changes on the shoreface of a low-wave-energy cuspate delta on the southern coast of Spain is examined. Bathymetric surveys, ranging from 1- to 40-m depth, were collected 2 days before and 9 days after a high-magnitude Levante storm. The storm lasted only 36 hours, with peak wind gusts of 100 km/h (28 m/s) and maximum wave heights of 7.4 m. Storms of similar magnitude have only been recorded four times in the last 20 years along this coast. The deltaic nearshore and shoreface was divided into three main morphologic and morphodynamic zones based on process-response mechanisms following the storm event. The eastern section, characterised by a steep and concave shoreface, only had minor erosion and deposition as a result of the storm. The area seaward of the river mouth, an intermediate zone where the coastline changes orientation, is characterised by a widening surf zone and an irregular shoreface out to 10-m depth before dipping steeply to 40-m depth. Poststorm changes along this transitional area resulted in the deposition of a thin veneer of sediment over a 3 km(2) area from 10- to 40-m depth. The western section, a shallow and wide delta front with a double-bar, a trough, and shore-oblique topography, was modified the most by the storm, with significant upper shoreface erosion and shore-oblique erosional scars in 5-7-m depth. Results of spectral wave modelling of wave-induced force match well with observed morphological change; force is minimal along the east coast, more pronounced along the steep shoreface opposite the river mouth, and at a maximum along the west coast. It is suggested that coastal orientation, shoreface morphology (topography, gradients), and storm parameters (wave and wind direction) generated contrasting wind and wave-induced currents on the delta shoreface, resulting in spatial differences in storm response.