Prediction on Changes of Seabed due to Sluice Built on entrance of Haiyou Branch in Sanmen Bay

Abstract Haiyou branch is the main branch of Sanmen Bay, it is an optional plan to construct sluice at the entrance of Haiyou branch to store fresh water for the utilization of freshwater resources in the Sanmen Bay basin. Basing on the verification of historical tidal currents and seabed erosion and deposition, numerical and physical models are established. Numerical calculations and physical model test show that the impact on hydrodynamic and seabed environment after the construction of sluice will be limited to the local sea area outside the sluice, where the downstream area of sluice, Shepan waterway and Maotou waterway are located, and the siltation strength decreases from the sluice towards Maotou waterway. After the construction of the sluice, the tidal inflow volume of Shepan section will decrease by 11.3% to 17.1%, the tidal volume of Maotou section decrease by 1.7% to 4.3%, and the tidal volume of Qinshan section and Qimen section remain basically unchanged. Within one year, the downstream area of sluice will be deposited with 0.5m∼0.7m, Maotou waterway with about 0.15m, and there is also little siltation at Qimen waterway and other waterway. Due to the impact of the sluice construction of Haiyou branch, after a long time, the deposition of deep pool in Maotou waterway is 2.0m∼2.5m. A once-in-50-year flood from the upper reaches will not cause significant seabed changes in the deep pool of Maotou waterway.