The Bragg reflections of oblique water waves by periodic surface-piercing structures over periodic bottoms are investigated using the eigenfunction matching method (EMM). Based on the assumption of small wave amplitude, the linear wave theory is employed in the solution procedure. In the step approximation, the surface-piercing structures and the bottom profiles are sliced into shelves separated by abrupt steps. For each shelf, the solution is composed of eigenfunctions with unknown coefficients representing the wave amplitudes. Upon applying the conservations of mass and momentum, a system of linear equations is obtained and is then solved by a sparse-matrix solver. The proposed EMM is validated by several examples in the literature. Then, the method is applied to solve Bragg reflections of oblique water waves by various surface-piercing structures over periodic bottoms. From the numerical experiments, Bragg’s law of oblique waves was used to predict the occurrences of Bragg resonance.

According to a field survey in 2012, the bathymetry near Mailiao Port, located in central Taiwan’s west coast, has a scouring hole that extends approximately 500 m × 100 m with a maximum scour depth of 26 m (eroded from its design depth −22 m to −48 m). To investigate the scour mechanism near the breakwater head and prevent the breakwater from collapsing, this study conducts comprehensive analysis by analyzing field observed data, performing hydraulic model tests, and conducting numerical modeling for the area near the Mailiao Port. The results show that the current plays an important role in the scour process. The physical model tests and numerical simulations both can reproduce the scour phenomenon of the study site. By analyzing field observed data we validated through physical and numerical models. This study concludes that the current caused by the ebb and flood tide, as well as the steep and shallow seabed topography, together comprise the seabed scour mechanism near the Mailiao Port breakwater head.

Pengpeng Beach, near Niaoyu Fishing Harbor, is an offshore sandbar that formed on the west side of Niaoyu Island in Penghu County, Taiwan, in 1995. Due to siltation, Pengpeng Beach also forms a sandbar tail that stretches toward the Niaoyu Fishing Harbor, meaning the Niaoyu Fishing Harbor and its navigation channel are facing serious siltation problems. This study aimed to find a solution for the siltation problem of the area by utilizing geotextile tubes, which are an economical material in terms of their material and construction cost, as well as being ecologically friendly in terms of their carbon emissions during production and transportation. Based on numerical simulations, location candidates for placing silt trap facilities were tested, selected, and modified to develop alternative mitigation plans. Evaluation of the mitigation plans was based on (1) the silt mitigation effect; (2) engineering cost; (3) public acceptance; and (4) impact on the surrounding landscape. The results showed that the proposed silt mitigation plan would be effective, and the plan was accepted by the local residents and government.