A numerical investigation of the 2DH wave characteristics across a fringing reef profile with reef-flat excavation pit.

The dredging of reef-flat sand for engineering construction is a common activity on some Asia-Pacific reef islands, which attract increasing concerns in the community of coastal hazard mitigation. Comparing to the well-studied one-dimensional horizontal (1DH) fringing reefs with excavation pit on the reef flat, little is known about such wave characteristics as sea and swell (SS) waves, infragravity (IG) waves, wave-induced setup and wave-driven current in a two-dimensional horizontal (2DH) fringing reef configuration with the reef-flat pit. To remedy this research gap, a 2DH numerical model according to a set of Boussinesq equations is proposed in this study. The 1DH form of used model is firstly verified with a wave flume experiment based on SS wave height, IG wave height and wave setup along the 1DH reef profile with and without the pit, then its 2DH form is verified by a wave basin experiment in view of both wave and mean current processes in a reef-lagoon-channel system. A comparison between 1DH and 2DH reef configurations with pit is also conducted to further validate the 2DH model. Subsequently, the model is adopted to investigate the effect of excavation pit on these wave processes, particularly for the wave-driven current, in the 2DH reef configuration. The present model is finally used to examine the influences of incident wave conditions and pit morphological features on the wave characteristics in the 2DH reef environment. • Wave processes over 2DH fringing reefs with excavation pit are numerically investigated. • Both impacts of wave forcing conditions and pit morphological factors are examined. • The pit causes both less SS wave transmission and IG wave amplification behind the pit. • The pit results in a mean current circulation around the pit on the reef flat. [ABSTRACT FROM AUTHOR]