Laboratory experiments and smooth particle hydrodynamics simulations of monochromatic wave transformation over a fringing reef profile with excavation pit

The sand dredging activities on the reef flat to meet the material requirement of engineering construction are prevalent around some Asia-Pacific reef islands, and its potential impact on the coastal hazard mitigation raises growing attention in the community of coastal research. In contrast to the extensively studied spectral wave processes with reef-flat excavation pit over fringing reefs, limited investigations have focused on the wave transformation possesses over such an artificially modified reef profile under monochromatic waves. To remedy current research deficiency, a new set of physical experiments is conducted to investigate the propagation and runup of monochromatic waves over fringing reefs with a reef-flat excavation pit. A series of incident waves are tested in a wave tank, and the influences of the pit's width and location are examined. An empirical formula is also proposed for predicting the measured wave runups. Meanwhile, a Smooth Particle Hydrodynamics model is innovatively introduced in this study. The adopted model is first validated by the present experimental data in view of cross-shore variations of wave and current on the reef flat as well as wave runup on the back-reef slope. Subsequently, the adopted model is used to examine the impacts of such pit characteristics as pit side slope, pit depth, and pit number on the wave processes that are not addressed by present laboratory experiments.