Hydrodynamic response study for the berm breakwater under long crested random waves

The berm breakwater or reshaping breakwater is a special type of breakwater. The main advantage of this type of breakwater is the requirement of relatively smaller sized armour stones which accelerate the construction speed and reduce the cost of the construction. The stability of berm breakwater is strongly influenced by the weight of units used in primary layer, interlocking properties of the armour units, geometry (width and elevation) of the berm, down slope and the toe berm characteristics. In the present study, the experiments are carried out to study the structural and hydrodynamic response of trunk section in 13m water depth for the berm breakwater proposed at Gopalpur port, Orissa, India. The studies are pertaining that simulating the cyclonic wave condition of Phailin cyclone (October 12, 2013) which has crossed Gopalpur, partly damaging the berm breakwater under construction. The breakwater is designed as a non-overtopping structure with the crest level of (+) 11m CD. The berm width of 15m and the berm level of (+) 6.7m CD is adopted considering the constructional feasibility. The down slope of 1V:1.5H is considered. The armour stone gradation is 3T to 5T, 5T to 7T and 9T-12T has been adopted. For the present experiments, 1:35 scale model has been chosen and tested under long crested random waves. The stability of the structure is compared to the tests under design water level at Mean High Water Spring (MHWS) + storm surge and at MHWS. Swell and Sea wave parameters are considered for the MHWS + storm surge and MHWS respectively. The recession of the primary armour layer has been measured and which is compared with the stability and failure criteria reported in the literature and the design guidelines for berm width. It is found that recession is 2 to 3 times of the diameter of stone. The wave run-up and overtopping discharge also presented in this paper.