Numerical study on hydrodynamic impacts of 3D excavation pit on tsunami-like wave at fringing reef

In recent years, dredging reef sand and aggregate as building materials for infrastructures has become a common practice in many atoll islands, which can significantly reshape the wave hydrodynamic environment at the fringing reef. Hence, it becomes necessary to evaluate the hydrodynamic impacts of excavation pits at fringing reef. However, previous research adopted a simplified two-dimensional (2D) excavation pit model, which ignores the influences of 3D geometric characteristics of excavation pit. This study performs a three-dimensional (3D) numerical study on the hydrodynamic impacts of 3D excavation pit on tsunami-like wave at fringing reef by using a nonhydrostatic wave model (NHWAVE). Impacts of several main factors, such as water depth, wave height, pit location, geometric dimensions of pit, the spacing between two serially connected pits and the spacing between two parallel connected pits are carefully discussed. Research results reveal that 3D excavation pit can significantly reshape the wave hydrodynamic environment at the fringing reef, especially the local wave height at the pit. In addition to wave breaking at the reef edge, the 3D excavation pit can further damp out a portion of energy of the breaking surge bore, which can reduce the maximum value of wave runup height at centerline of computational domain. However, maximum value of wave runup height near the two sides of pit are slightly increased to some extent.