Francesco Aristodemo

Large-scale morphodynamic experiments on a beach drainage system

This research describes a unique set of experiments undertaken at the Large Wave Channel (Hannover) aimed to study the morphodynamic behaviour of a beach face containing a buried drainage system. The advantage of using a large wave flume is that scale effects that affected previous laboratory experiments are minimized. This compares the response of the undrained beach under controlled wave forcing with the response of the drained one with the same wave action. Low, medium and high levels of wave energy were used for the experiments, with significant wave heights of 0.39–0.83 m and wave steepnesses between 0.004 and 0.013. Any positive effect of the drains on the beach face was confined by the position of the cone of depression in the aquifer surface. The best performance of the system was observed with two drains operating at the same time under low to moderate wave energy.

Full-scale experiments on a beach drainage system: hydrodynamic effects inside beach

An extensive full-scale laboratory investigation on a two-dimensional physical model of a beach drainage system (BDS) was performed at “Grosser Wellen-Kanal” of Hannover, Germany. This research deals with the hydrodynamic aspects of a beach equipped with a BDS, while the morphodynamic aspects of the study are discussed in a companion paper. Knowledge of both the hydrodynamic and the morphodynamic behaviours of a drained beach allows the definition of the main design criteria. The adopted BDS was constituted by four corrugated pipes. Several drain configurations in static and dynamic conditions were considered, paying attention to water table oscillations, drains and groundwater regime and drainage discharge induced by the system start-up. The main results indicate a rise in the unsaturated beach and the presence of a hydraulic disconnection in the groundwater–drain system. The analyses yield useful hydrodynamic information influencing the general system efficiency.

Beach sediment mixing under drained and undrained conditions

ABSTRACT Ciavola, P., Contestabile, P., Aristodemo, F., and Vicinanza, D., 2013. Beach sediment mixing under drained and undrained conditions. The paper describes a set of experiments undertaken at the Grosser Wellen Kanal (GWK) in Hannover on sediment mixing on a beachface exposed to the action of a buried drainage system. Experiments were performed using a set of drains (up to three working simultaneously), located at variable distance from the shoreline. Wave energy during the tests ranged from medium (0.59 m < Hs < 0.61 m) to high (0.76 m < Hs < 0.83 m). Beach profiles were measured at the end of each test. Further validation came from measurements using a grid of rods that were monitored at the same time as the beach profiles were surveyed. While some beach stabilization was observed for low energy conditions, for medium and high energy conditions the benefit of having the drains operative was not so clear. The comparison between beach profiler and rods showed good agreement regarding relative vertical accretion and erosion events. In any case, it was evident that the sedimentary effect on the beachface was confined to a narrow area above the drains. The drained area showed slightly lower values of sediment mixing under drained conditions, but evidently this factor was not important enough to trigger a widespread beach stabilization. Values of sediment mixing averaged across the whole beachface ranged between 2–4 % and 4–6 % of the breaking wave height respectively for high and medium energy wave conditions. Grain size, beach slope and drain configurations used here are fully comparable to field installations present in the literature.