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Abstract
Following the rapid and destructive impacts of storm erosion, beach recovery is a key natural process of restoration, returning eroded sediment to the subaerial beach and rebuilding coastal morphology to continue to support the needs of modern-day coastal communities. While more detailed understanding of storm erosion has been developed, this thesis advances insight into wave-driven recovery processes of the subaerial beach following storms on microtidal, wave-dominated sandy beaches.
The onshore return of nearshore sediment back to the shoreline is a primary wave driven process of beach recovery. Shoreline recovery is analysed following 82 individual storms using a 10-year coastal imaging dataset of daily shoreline and sandbar positions. Shoreline recovery rates are quantified, highlighting temporal variability significantly correlated with parameters related to nearshore wave steepness and sandbar morphodynamics. A new conceptual model is presented, describing phases and rates of shoreline recovery through various stages of onshore sandbar migration following storms, from fully detached storm-deposited sandbar morphology through to complete sandbar welding with the shoreline.
After nearshore sediment has returned to the shoreline, swash processes then rework sediment up onto the subaerial beach to rebuild the berm. Following complete removal by a significant storm event, the entire rebuilding of a berm is examined at tide by tide timescales, using high resolution (5 Hz) swash and subaerial beach profile measurements obtained from a continuously scanning Lidar. Tide-by-tide rates of subaerial volume change, berm crest growth and subaerial profile variability are quantified and examined. The findings identify behavioural modes of subaerial profile variability throughout berm recovery, distinguished by swash, nearshore wave and ocean water level conditions.
Finally, alongshore variability in subaerial volume recovery on an embayed coastline is evaluated at distinct spatial scales both within and between four closely-situated embayments following a significant storm event. The range of variability in net rates of subaerial volume recovery within individual embayments was found to be substantially larger (by a factor of 10) than between embayments. This variability was observed between embayment extremities and also locations spaced only a few hundred metres apart, considered to be driven by subaqueous morphodynamics and alongshore gradients in nearshore wave energy.