Abstract
This study provides laboratory observations of the nearshore hydrodynamics and detailed topographic surveys associated with the morphological response of a beach-dune system to oblique waves during a storm event. A physical model consisting of a 20 m long sandy steep beach constructed in a wave basin, and a wave paddle oriented obliquely to the beach shoreline is used to generate irregular waves at the offshore boundary. In the experiment, the wave height is varied over time in five segments to simulate the change in the energy from a passing storm and is varied alongshore to initiate an alongshore gradient in waves and wave-driven currents. To simulate a constant storm surge, a high mean water level relative to the dune is used, enabling waves to reach the dune toe. The results indicate the formation and evolution of a beach scarp. The retreat of the scarp initially corresponds to time-varying wave energy, but becomes controlled by the changing nearshore beach slope over time. The alongshore current magnitude is governed by the spatio-temporal variability in wave energy and is the main driver of sediment flux. The sand that is eroded from the dune initially deposits at the dune toe when nearshore circulation is weak. However, as the wave energy increases sediment is transported along the beach and is deposited, increasing the surf zone width. The experimental results indicate that small waves at high water levels relative to the dune can drive the formation of a beach scarp. In addition, different levels of incident wave energy drive different rates of sediment transport and morphological evolution with high alongshore variability throughout a storm event.
Published Version
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