A Note on Transient Beach Evolution with Artificial Seepage in the Swash Zone

Abstract

In this study, the effect of seepage flow in the swash zone on beach profile evolution under erosive waves was examined experimentally. The seepage flow was induced artificially by a porous drain pipe buried at various locations beneath the swash zone. Transient beach profiles with and without seepage were recorded at different time intervals from the start of the wave attack. The results show that the drain pipe placed beneath the middle of the swash zone generally promotes the fastest accretion in the beginning. The presence of the seepage also induces a steeper upper beach slope. Continuous monitoring of beach profile evolution over a period of 36 hours shows, however, that over time the drain system has no significant impact on the shore profile under erosive wave attack except on the upper beach portion. Despite the fact that the long-term effect appears small, the induced seepage does generally retard erosion in the swash zone in the first few hours of the experiment, and the transient protection may be useful in a coastal drain design.