Shirlal, K.G.Rao, S.Manu, M.2026-02-052007ISH Journal of Hydraulic Engineering, 2007, 13, 1, pp. 18-319715010https://doi.org/10.1080/09715010.2007.10514855https://idr.nitk.ac.in/handle/123456789/27829Breakwater's vulnerability to extreme events such as storms is a reality. To avert the failure of the breakwater, one of the things engineers can do is to design a seaward reef which breaks steep waves and attenuates them. The stability of such a reef, a conventional rubble mound breakwater and a breakwater protected by a seaward submerged reef is investigated through physical model study using regular waves. Tests are carried out for different relative spacings between two rubble mound structures (X/d = 2.5 to 13.33) and for different relative heights (h/d = 0.625 to 0.833) while keeping reef crest width B constant at 0.1m (i.e. the relative crest width B/d = 0.25 to 0.33). The submerged reef of crest width 0.1m located at a seaward distance X of 1 m, 2.5 m and 4.0 m reduces the breakwater damages by a range of 4 to 41 %, 40 to 66% and 63 to 80% respectively. The stability equations for reef and defenced breakwater are derived from curve fitting through the experimental data. © 2007 Taylor & Francis Group, LLC.Conventional BreakwaterCrest height reductionDefenced breakwaterReefRegular wavesStabilityWave breaking