Efficacy of beach dewatering - Alassio, Italy

The goal of this study is to estimate the efficiency of dewatering operations in Alassio Beach, north Italy by following an integrated approach which included beach volume calculations, daily mapping of the shoreline position, examination of specific beach widening events and daily comparisons of morphodynamic characteristics of the drained beach versus a control section which included wave run-up, bar patterns, rip migration, evolution of the berm and cusp morphology. Alassio beach was documented by a daily time-lapse photography, by repeated DGPS profile measurements and by an hourly wave and sea level monitoring. Following one year of draining the shoreline position and the beach volume of the drained beach and the control section showed little differences; i.e., accumulation of 0.28 m3/m2 and a shoreline advance of 1.1 m on the drained beach, whereas on the control beach the volume change was − 0.03 m3/m2 and the shoreline retreated 1.2 m. Short episodes of beach widening, 1–7 days long, which coincided with onshore bar movement and a relative low sea level, occurred simultaneously on the drained and the control sector. This data indicated the inefficiency of the draining operation. An improved resolution for determining the draining effect was attained by the sequential snap-shot photography which showed many systematic morphological differences between the drained beach and the reference segment. The drained beach developed a berm crest and a linear, often scarped foreshore with a narrow swash zone. No such cumulative morphologies were observed on the non-drained control beach, which commonly displayed cusps that were usually absent on the drained foreshore. The wave data showed recurrent medium wave events of Hs = 1–2 m, which repeatedly interrupted the calms thus “cutting-off” the beach evolution. The draining in Alassio was unable to promote beach accumulation by counteracting the erosive effect of the medium interrupting storms.