Numerical Simulation and Practical Sand Silting in Waterways of Langya Bay

Dongjiakou Harbor is located at the Langya Bay in the city of Qingdao, Shandong Province. It is a multi-functional harbor of heavy passing capacity under planning in China. The sediment distribution and dispersion in the waterways and harbor basin water areas is of great importance to the construction and operation of the harbor. This article is based on the measurement of waves and currents as well as sediment suspension characteristics on site, and using numerical methods to predict the dispersion and deposition rules in this area. A combined wave-current-sediment model of COHERENS-SED is created through the combination of hydrodynamic model COHERENS and wave model SWAN as well as a sedimentation model SED developed by the authors. Inside COHERENS-SED, SWAN is regarded as a subroutine and it gets time and space varying current velocity and surface elevation from COHERENS. COHERENS gets time and space varying wave relevant parameters calculated by SWAN. Wave-enhanced bottom stress, wave dependent surface drag coefficient and radiation stress are introduced to COHERENS. Then a fully coupled hydrodynamic–sediment model COHERENS-SED accounting for interaction between the waves and currents is obtained and adopted to simulate these hydrodynamic conditions and the sedimentation processes in Langya Bay area. The open boundary of waves and currents is obtained through nesting from running a wider model which includes the Bohai Sea and the North Yellow Sea with coarser solution and contains coastal regions of Shandong Peninsula which includes the whole area of Langya Bay. Generally, the values of time series of current velocities, current directions and water levels as well as sediment concentrations have good agreements with observation data. The study shows the currents in the waterways and harbor basin water areas are relatively weak due to the narrow water width at the port mouth and the current directions parallel to the wharf directions. Also, sediment dispersion scales and strength are predicted according to the computation. The study also estimates the average sediment deposition amount and seabed erosion in this area. Besides, significant wave height and wave period obtained by COHERENS-SWAN shows that simulation result with wave-current interaction is better agreed with the measurement than the case without current.