The effect of sequential storms on the performance of homogeneous berm breakwaters

Abstract

Reshaping of homogeneous berm breakwaters have been experimentally investigated using 2D physical tests. Berm recession depends on storm duration in addition to breakwater geometry and other storm parameters such as significant wave height and peak period. Furthermore, a berm breakwater may experience some recessions prior to exposing to a design storm for which the breakwater is designed. In this study, 109 tests have been conducted totally to investigate the enhancement of berm recession during design storms and also to study the effect of sequential storms on the ultimate berm recession during the life span of berm breakwaters. The measured cumulative recessions have been compared with direct recessions obtained from a breakwater with no initial reshaping. According to the results, the effect of earlier sea states on final berm recession depends on the design stability index and it can be neglected only if the design storm is too weak ( H 0 T 0 < 40 ) or it is too strong ( H 0 T 0 > 80 ). For weak design storms, earlier reshaping is negligible, while for strong design storm, the final reshaped profile will be governed only by such design storms regardless of earlier sea states. The results show that the predicted berm recession against design storms can be maximum 10% less than the actual recession in the case of missing the effect of earlier sea states. Since this conclusion is valid for both statically and dynamically stable berm breakwaters (the maximum value occurs around H 0 T 0 = 70 ), it is suggested finally that designers consider 10% more recession than the predicted values by existing design formulae to be sure about the endurance of berm width against the cumulative berm recessions during design life of reshaping berm breakwaters. The observations showed also that this width can efficiently dissipate the wave energy and protect underneath layers. • Homogenous reshaping berm breakwaters are studied using 109 physical tests. • A new formula is proposed to calculate berm recession during storms as a function of modified stability index. • Cumulative recession during design life of berm breakwater is investigated and an applicable suggestion is provided. • A modified stability index is proposed for measuring the influence of design storms.