The Optimal Porosity of Stream-Wise Groins for Wave Attenuation Under Different Cross Slope Conditions

Abstract

To control river regime from ship wave attacks, porous structure have been built along the riverbank. The results are not as good as expected at all locations even though same structures are applied. This study firstly investigated the interaction between porous structure and waves under different volumetric porosity of structure (θ) by conducting physical experiments. Based on that, relationship between θ and drag coefficient was established by using a 1-D model. The optimal θ to mitigate wave attacks was then determined by a 2-D model taking into consideration not only cross slope behind groins (i) but also the gap between two neighboring groins (G). In cases of i =1/100, the combination of  = 0.4 and L/G = 5 (L is the stream-wise length of a groin) could bring out the best wave energy reduction. It is necessary to consider both of i and G for designing stream-wise groins.