Investigation of proposed countermeasures against coastal erosion and sediment invasion around half-buried floodway

Abstract

ABSTRACTCountermeasures are investigated against coastal erosion and sediment invasion around a half-buried floodway through a series of small-scale physical model experimentations. Further, countermeasures are proposed to shorten the protruded length of the floodway across the shoreline to prevent interruption of longshore sediment transport and to excavate downdrift sediments at the mouth of the floodway to minimize the downdrift erosion as well as the sedimentation inside the floodway. Results of the study show that the shortened floodway is successful in mitigating downdrift erosion, while continuous downdrift excavation is proven to be significantly effective in reducing sedimentation inside the floodway when excavation is implemented with the same order-of-magnitude of the longshore sand transport rate. Attention must be paid, however, on the effect of wave randomness and floodway discharge during stormy waves as they further increase sedimentation inside the floodway apparently owing to onshore sediment movement enhanced by asymmetric horizontal acceleration and to a large skewness in the water particle velocity at the mouth of the floodway.