Storm impact and recovery on pebble beaches

Abstract

This study examines the impact of individual storm events, the recovery, and the effect of successive events on pebble beaches. As a first step, storm events in the Normandy region (France) were identified and classified according to their energy content using a 42-year wave height time series. Of the total number of identified storms, 187 were classified as Weak. 74 storms fell under the Moderate category, 25 storms were classified as Significant, 9 storms were labeled as Severe, and 2 storms were characterized as Extreme. A close examination of storm characteristics was done for the 2018-2019 and 2019-2020 winter seasons, where two Severe storms took place in each season. During these periods, the response of the beach was characterized through i) an evaluation of the intertidal beach volume using Digital Elevation Models (DEMs) generated through a video camera platform, and ii) an examination of shoreline change using Sentinel-2 satellite imagery. The analysis revealed distinctive differences between the two winter seasons. The 2018-2019 contained half the storm energy content compared to the 2019-2020 season. During the first winter season, the Severe storm took place by the end of the winter period and encountered an eroded beach. Subsequently, there was a slight volume increase during the summer season which did not fully recover the pre-winter beach volume. As the 2019-2020 winter season commenced, there was further erosion, notably following the impact of the Severe storm (Ciara), which stood out as the most energetic storm during the study period. This event caused the beach to reach its minimum volume in the study, the posterior series of moderate and weak storms arriving at the beach assisted to the partial recovery of the beach volume. By July 2020, the beach volume had reached the pre-winter 2018-2019 values. The assessment of shoreline change using satellite images was used to complement the partial beach coverage of the cameras. Although, this approach was limited by the resolution of satellite images, evidence of shoreline retreat and beach rotation developments were associated to certain storm events, assisting in the evaluation of the beach response to storms.