Overtopping wave reduction capability of Rakuna IV armor block used for rubblemound breakwater

Abstract

Run up, overtopping are the main reasons that damage and unstabilize the coastal and basin protective structures. So, overtopping wave is an inevitable load during coastal structures designing process, particularly at present very complicated real situation of global sea level rise and climate change. Based on the early researches, allowable mean overtopping wave discharges play an important roll in determining breakwaters' dimension such as top elevation, slope protective alternatives in the port side and so on. The more permissible average overtopping wave discharges, the lower breakwater top elevation needed. Moreover, the weight of armor blocks used on a seaside slope can be reduced. However, the port side slope needs to be properly protected against the impact of overtopping wave. Thus, researching the application of new armored unit blocks with high overtopping wave reduction capability that is corresponsive to typhoon-generated wave conditions is totally in need. Rakuna IV is one of the newly developed wavedissipating blocks invented by Nikken Kogaku (Japan) in 2007, and the stability of this block for rubble mound breakwaters has been investigated under non-wave overtopping conditions by many researchers in Japan, Korea, China, and Vietnam. To be more exhaustive in the design of breakwaters with this kind of block, this study carried out experimental research on wave overtopping performance of RAKUNA-IV (overtopping reduction by roughness factor γr) in wave flume at Ha Noi Water Resources University. Based on the physical model tests' results, the author has determined the overtopping wave reduction coefficient ξr of Rakuna IV block and its relationship with Irribaren number ξm-1,0.