Laboratory study on a beach drainage system

In recent years Beach Drainage Systems (BDS) have been considered as an innovative approach to stabilize the beachface even if it still has to be proven to what extent they are effective in stabilizing the beach or causing accretion. This paper describes tests carried out at the “Grosser WellenKanal” in Hannover aimed at improving the knowledge of the hydrodynamic and morphodynamic behaviour of a beach containing a buried drainage system. Scale effects that affected previous BDS laboratory experiments are minimized by the large scale. The morphodynamic response of the undrained beach compared to a beach drained under the same type of wave action is reported. Experiments were undertaken using a set of multiple drains, up to three working simultaneously, located below the beach and at variable distances from the shoreline. The experimental program was organized in a series of tests with variable wave energy. While a positive effect was observed under low energy conditions, for medium and high energy conditions, the benefit of having the drains operative was not always clear. In any case, it was evident that any positive effect of the drains on the beachface was limited to the position of the cone of depression represented by the lowering of the hydraulic head.

► Behaviour of a beach containing a buried drainage system has been studied. ► Tests were carried out in the large wave flume “Grosser WellenKanal”, Hannover, Germany. ► Drainage system did not have an overall beneficial effect on the beach stabilization under high wave energy conditions. ► A global beach stabilization and an increased accretion were observed for medium and low wave energy conditions. ► The poor performance of the system proves to be dependent on the characteristics of the sand and the drains, as well as their position.