The Influence of Groundwater on Profile Evolution of Fine and Coarse Sand Beaches

This paper reports on laboratory experiments carried out on fine and coarse sand beaches under raised and lowered back beach groundwater levels. Onshore sediment transport was enhanced when the groundwater level was lowered under both accretionary and erosive conditions, whereas higher groundwater level promoted offshore sediment transport. Under swell conditions, the coarse beach showed accretion at all groundwater levels. In contrast, on the fine sand beach, lowering the groundwater level was able to induce accretion on a previously erosive profile. The groundwater level had less effect on beach profile evolution under storm conditions, suggesting that artificially lowering groundwater levels would not help much in the control of storm erosion, but could promote post-storm accretion on permeable beaches. Agreement between measured and modelled head levels was better on the coarse beach than on the fine beach, and better in the swash zone and within the beach than in the surf zone.