Effect of submerged breakwater on profile development

Abstract

This study is part of a Human Capital and Mobility Project called 'Dynamics of Beaches'. This project is a co-operation of six European universities which work together in solving some unknown aspects of a submerged breakwater by means of model experiments. Several agreements about the experiments were made between the partners. These agreements consider the layout of the breakwater, the wave conditions and the initial bottom profile. In this report the effect of a submerged breakwater on hydro- and morphodynamics has been investigated. In order to do this, six similar (2DV) tests with and without a scale model of a submerged breakwater and with a movable bed were performed in the Lange Speurwerkgoot (= wave flume) of the Laboratory of Fluid Mechanics at DUT. By means of varying wave height and wave period the influence of these parameters on hydro- and morphodynamics can be investigated. For these purposes wave heights, flow velocities, sediment concentrations and bottom profiles were measured at several locations in place and time. The following topics are discussed in this report: -profile development -wave height development -velocity distributions -sediment concentration distributions -sediment transport rates -comparison with Unibest-TC The experiments show that profile development is less pronounced in case of a breakwater present. However, it does not prevent the sediment to cross the breakwater in a seawards direction. Due to the presence of the breakwater, wave heights are reduced landwards of it. Seawards, the presence of a breakwater leads to an increase of wave heights. The breakwater also decreases the time-average velocities landwards of the breakwater. Furthermore, a comparison between the sediment transport based on measured profiles and the sediment transport based on multiplification of time-average sediment concentrations and time-average velocities shows that the last method leads to an overprediction of the sediment transport. Comparing measured profile development and wave height development with values calculated by a computer program called Unibest-TC shows that this program still has significant shortcomings in modelling the effects of a submerged breakwater.