1 DAMAGE VARIATIONS ON LOW-CRESTED BREAKWATERS Rolando Garcia 1 and Nobuhisa Kobayashi 2 The cross-shore numerical model CSHORE extended to oblique waves is used to predict the spatial variation of damage on different sections of the trunk and head of a low-crested breakwater. The agreement is mostly within a factor of 2 but the model overpredicts damage on the back head of a submerged structure. An experiment was conducted in a wave flume for a low-crested stone structure located inside the surf zone on a sand beach. The model is shown to reproduce the measured cross-shore wave transformation on the beach without and with the structure as well as the measured small damage on the structure. Keywords: low-crested breakwater; rubble mound; damage; trunk; head INTRODUCTION Low-crested stone structures (LCS) are constructed to provide sheltered areas with some wave transmission. Damage on LCS depends on its crest height above the still water level (SWL) and varies spatially on the trunk and head of the breakwater. The cross-shore numerical model CSHORE was developed to predict irregular wave breaking and transmission over and through a submerged porous structure (Kobayashi, et al., 2007) and was extended to predict damage progression on a conventional stone breakwater with little wave overtopping (Kobayashi, et al., 2010) and deformation of a reef breakwater with wave transmission (Kobayashi, et al., 2013). In this study, CSHORE is extended to obliquely incident waves and compared with available data on wave transmission and damage on different trunk and head sections of a LCS. Comparisons of wave transmission prediction against available data for obliquely incident waves are presented in Garcia and Kobayashi (2014). The damage on the front and back sections of the round head is predicted assuming similarity of head and trunk damage for LCS. An experiment was conducted for a LCS located inside the surf zone on a sand beach during a storm in order to assess the utility of CSHORE for a typical field application. NUMERICAL MODEL Figure 1 depicts a LCS with its crest below the SWL. The cross-shore coordinate x is positive onshore with x = 0 at the seaward location of the incident irregular wave measurement. The irregular waves are represented by the spectral significant wave height H m0 and spectral peak period T p . CSHORE assumes alongshore uniformity with the alongshore coordinate y parallel to the straight trunk. The vertical coordinate z is positive upwards with z = 0 at the SWL. The upper and lower boundaries of the breakwater are located at z = z b and z p , respectively, where the lower boundary is assumed to be fixed and impermeable. Figure 1. Onshore (x), alongshore (y), and vertical (z) coordinates of numerical model. 1 PRDW-AV Consulting Port and Coastal Engineers, Chile, rgarcia@prdw.com, rgarcia@udel.edu 2 Center for Applied Coastal Research, University of Delaware, nk@udel.edu z 0 x SWL z b = z p z p z b = z p x SWL x S z b Impermeable Bottom F Cross Section Plan View x y Waves θ Trunk Head 0