Determination of optimal rubble mound beach to minimize wave reflection using Analytical and Laboratory methods

As water waves attack marine structures or sloping beaches a part of wave reflects and propagates in the opposite direction of incoming waves. Reflected waves cause increased agitation of the water in front of the structure or they may propagate some distances to become a source of disturbance in a calm area of water. In many laboratory studies it is necessary to separate the measured wave train into components of incident and reflected waves, so that the model response can be related to the parameters of the incident wave field. In a wave flume a complicated multi-reflection system of wave trains is formed as waves are reflected and re-reflected by the model structure, sloping beach and wave paddle. Some methods of analysis have been developed for determination of the reflection coefficient in laboratory wave flumes. A 2D experimental study in the wave flume was carried out to achieve parameters of incident and reflected waves for both regular and irregular waves. The measurement was carried out by a set of two and three probes comparing two different methods. Furthermore, influence of some parameters such as wave heights, beach porosity and its slope was investigated. The impact of incident wave height and frequency, γ coefficient in the JONSWAP spectrum, beach slope and its permeability on reflection were surveyed in detail. Finally optimum beach to cause minimum wave reflection was offered. The results showed that in the short flume, permeable metal beach at an angle of 30 to 45 have the minimum reflection.