Submarine pipelines are the lifelines of the national economy. Under the influence of typhoons, high-speed currents and waves continuously erode the seabed, leading to suspension or even rupture of pipelines. Therefore, it is of great importance to study the sediment transport under the action of waves and currents. A numerical model of sediment scouring and deposition combining wave and currents is established, which considered tidal current, storm surges, wind waves, and sediments in the East China Sea. Combining with the monitoring of the actual laying condition of pipelines, it is found that the area with the most serious scouring is around KP300. It is shown that the typhoon weather with high intensity and density will lead to the suspension of pipelines, which is noteworthy in the construction of marine engineering.

Sanmen Bay is located in the middle of Zhejiang coastal area. It is a semi-enclosed bay with many silty tongue-like shoals. There are also harbors with good water depth. This form of shoals and branches constitutes a unique muddy coastal landform on the Zhejiang-Fujian coast. Large areas of tidal flats provide conditions for reclamation. Since the beginning of the new millennium, the speed of reclamation in Sanmen Bay has accelerated, and its cumulative impact on the environment has gradually increased. Based on the high-resolution water depth and coastline data of 2003 and 2013, this paper establishes a numerical model based on Delft3D to study the cumulative response of hydrodynamics, tidal prism, and water exchange capacity to the reclamation project in a decade. The calculation results show that within ten years, the reclamation of the sea has reduced the area of the shoal in Sanmen Bay. The trend of the ebb current in the bay has been weakened, and the tidal prism has been reduced by nearly 7%. Also, the reclamation projects have weakened the overall water exchange capacity of Sanmen Bay with the outside world. Due to the topographical features of Sanmen Bay, the degree of influence varies from region to region.