Modes of Berm and Beachface Recovery Following Storm Reset: Observations Using a Continuously Scanning Lidar

Abstract

AbstractFollowing 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. While the effects of storm erosion have commonly been investigated, detailed studies into poststorm recovery are currently lacking. This study investigates wave‐driven recovery processes of the berm and beachface on a microtidal, swash‐aligned sandy beach. Following complete removal of the berm by a significant storm event, the entire 76‐day rebuilding of a swash berm is analyzed at the timescale of every semidiurnal tidal cycle, utilizing high‐resolution (5 Hz) swash and subaerial beach profile measurements from a continuously scanning fixed lidar. Tide‐by‐tide rates of subaerial volume change during berm recovery were most frequently observed between 1 and 2 m3/m/day, including losses and gains an order of magnitude larger than the more gradual rate of net gain (0.7 m3/m/day) observed for the entire recovery period. Patterns of berm crest formation and vertical growth were found to be primarily governed by the neap‐spring tide variations in total water levels. Tide‐by‐tide beachface and berm volume changes were used to classify four principal behavioral modes of subaerial profile variability during recovery. Using decision tree classification, modes were differentiated according to nearshore dimensionless fall velocity, swash exceedance of the berm crest, and ocean water levels. The findings provide novel behavioral and parametric insight into the tide‐by‐tide rebuilding of the beachface and berm by swash throughout a complete poststorm recovery period.