Effect of submerged breakwaters on a beach profile exposed to regular waves in a wave basin

Effect of submerged breakwaters on a beach profile exposed to regular waves in a wave basin

De Later, J.

D'Angremond, K. (mentor)
van de Graaff, J. (mentor)
Fontijn, H.L. (mentor)
van der Biezen, S. (mentor)

Civil Engineering and Geosciences

1996-08-01

In the framework of a Human Capital and Mobility Project called "Dynamics of Beaches, experiments with the aim of solving unknown aspects of submerged breakwaters have been carried out by six European universities. Agreements were made considering the layout of the breakwater, the wave conditions and the initial bottom profile. This report discusses the effects of a discontinuous breakwater on a profile exposed to regular waves. For this aim, nine experiments with and without a scale model of a breakwater and with a movable bed were carried out in the wave basin of the Laboratory ofFluid Mechanics at DUT. Measurements were carried out with a profile follower, wave probes and fluid velocity meters. By varying the wave heights and the application of two breakwater configurations the results of these measurements contribute (qualitatively) to a better understanding of submerged breakwaters. In this report the following topics are discussed: (1)profile development, (2)sediment distribution over the basin, (3)wave height development, (4)velocity distributions, (5)comparison with results of earlier carried out 2DV experiments. The most striking effect of the submerged breakwater is that, for the applied breakwater and gap lengths, a strong return flow through the gaps between the breakwaters is generated, apparently compensating for the mass flux over the breakwater crests. Compared to the experiments without breakwater, this resulted in relatively large sediment transports seaward through the gap. The sediment distributions showed that sediment was transported from behind the breakwaters towards the gaps between them and further, onto the sea. This is in accordance with the results of the velocity measurements, because the velocity distributions showed strong longshore currents landward ofthe breakwaters. The driving force of these longshore currents, the incoming waves, show a different development depending on the presence of a breakwater in the cross-section. The breakwater results in a reduced wave height landward ofthe breakwater. Compared to the results of comparable 2DV experiments the most striking difference is the offshore sediment transport.

breakwater
offshore reef
wave basin

http://resolver.tudelft.nl/uuid:c33fa96f-6afa-42ca-b8a3-e6da89e722fe

TU Delft, Civil Engineering and Geosciences, Hydraulic Engineering

Student theses

master thesis

(c) 1996 J. de Later