Investigations on the reflection behaviour of a slotted seawall

Based on the linear wave theory and the eigenfunction expansion method, the interaction between waves and a slotted seawall is studied analytically as well as experimentally. The analytical investigations show that the reflec tion characteristics of a slotted seawall depend mainly on the porosity of the slotted plate and the incident wave height. It is found that the reflec tion coefficient reaches its minimum value as the chamber width is about a quarter of the incident wavelength. The reflection behaviour becomes optima l when the porosity is moderate (about 0.2 in the present study). The immer sed depth has some effect on the reflection coefficient of the seawall stru cture, but the improvement is small when the immersed depth is larger than the half of the water depth. A series of physical model experiments are car ried out to examine the analytical results. Comparisons between the analyti cal and experimental results of reflection coefficients are made for some c omparable cases and show good agreement provided certain parameters of this model are suitably chosen. This demonstrates that the analytical model is able to account adequately for energy dissipation by the slotted plate and can provide instruction for the design of such seawalls. (C) 2001 Elsevier Science B,V. All rights reserved.