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Abstract

Theory is reviewed which relates infiltration into a permeable beach with the net onshore or offshore transport of sediment by wave action. This theory is tested experimentally by using sands of different permeability and by using underdrains in the beach and a pump to increase the infiltration capacity. Previous studies are reviewed, although these earlier studies have had different purposes. Some prior investigations have studied wave propagation over a permeable slope or have determined wave damping and energy dissipation due to percolation into a porous bed. Other studies have investigated wave interactions with permeable structures such as rubblemound breakwaters and have shown that the exchange of fluid between the external and internal flow regions markedly affects wave uprush, backrush and set-up in the surf zone. A limited number of previous studies have considered the flow of fluid into a permeable beach and its role in beach stabilization and erosion control. The present tests were performed in the wave flume of the Hydraulics Laboratory of the Department of Civil Engineering at the University of British Columbia. Intermediate and equilibrium beach profiles are presented and compared. The findings of this study indicate substantial differences between impermeable and porous material. Experimental results show more permeable beaches form steeper profiles, while less permeable beaches form shallower profiles. Moreover, increasing infiltration by pumping initiates immediate onshore sediment motion and considerable steepening of the cross-sectional profile. To a large extent this steepening process was reversible when pumping was stopped. The results of this study confirm the predictions of the theory that infiltration contributes directly to a net onshore stress and onshore sediment transport.