Abstract
A method to continuously measure bed and water levels along a cross-shore transect of vertical poles is evaluated. This remote sensing based method uses video imagery of swash flows propagating past an array of vertical poles buried on the beach face. Using datasets collected at two beaches in Chile, the method is compared against measurements obtained with conventional co-localized instruments: LiDAR and ultrasonic distance meters. The present video swash pole technique shows good skill in retrieving swash zone bed level and water levels, while providing the possibility to measure morphological variations at time scales varying from wave groups (tens of seconds) to hours. Discrepancies between video and ultrasonic distance meters are found when short time scales are used, for both depositional and erosion events, but longer duration trends are captured well. Water surface elevations at the wave-by-wave scale proved to be accurate for the backwash phase (root-mean-sqaure-error, RMSE down to 0.028 m, R 2 up to 0.89), when compared against LiDAR. However, discrepancies have been found during the uprush phase (RMSE up to 0.062 m, R 2 down to 0.71), when the influence of the pole on the swash flow generates an overestimation of the water surface. Overall, owing to its simplicity of deployment, low cost and reasonable accuracy, the technique is considered suitable for swash studies.
Highlights
The swash zone is the nearshore region that defines the transition between land and sea.Incoming bores from the inner surf zone collapse and transform into a thin water lens, leading to a zone of alternately dry and submerged states
Raw LiDAR measurements were de-spiked to reduce outliers, and random noise was reduced using a filter with a moving time-average with a window of 0.2 s (e.g., [20])
This work assesses the performance of a video-based technique for monitoring bed and water surface levels of the swash zone at the scale of individual waves
Summary
The swash zone is the nearshore region that defines the transition between land and sea.Incoming bores from the inner surf zone collapse and transform into a thin water lens, leading to a zone of alternately dry and submerged states. The swash zone is the nearshore region that defines the transition between land and sea. The swash zone is highly dynamic, with processes. 2018, 10, 49 acting at multiple time scales, from the order of seconds (waves) to hours (tides) and days (storms). The majority of research efforts focusing on the swash zone have been devoted to linking time-averaged bulk characteristics of inner surf and swash hydrodynamics with morphological evolution at time scales ranging from hours to days (e.g., [1,2,3]), with less focus on shorter time scales. Individual swash events at the wave-by-wave scale. There is consensus in that understanding swash zone processes at these short scales is crucial for understanding the overall morphodynamic response of the swash zone [4]
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