Reflection of regular waves from caisson-type porous seawalls

In this paper, the reflection characteristics of vertical rigid, semi-porous and porous seawalls is investigated under regular waves by use of physical models. Several experiments were carried out for a wide range of wave heights and periods and for different water depths in the Soil Conservation and Watershed Management Research Institute flume. Based on these experiments, it was concluded that the porous seawall has better performance than rigid and semi-porous seawall in reducing the wave reflection. The reflection coefficient (Kr) due to regular waves for the porous seawall ranges from 0.57–0.89 and for semi-porous wall it is 0.70–0.94, whereas for the vertical rigid wall, it is found to be more than 0.9. It was also found that the reflection coefficient decreases with the increase of the wave steepness (Hi/L), the relative water depth (d/L), and the seawall porosity (n). A comparison of the results for identical input condition shows that an average the reduction in Kr for semi-porous and porous seawall as compared to the rigid wall is about 18% and 32%, respectively. Based on the measured data, dimensional analysis and multiple regression analysis, new empirical relations have been proposed to predict the wave reflection coefficient. Verifying the predictive formulae with the other experimental results revealed that the equations could be used for practical purposes.