Impact of Sea Embankment Works in Cat Hai Island District (Hai Phong City, Vietnam) on Hydrodynamic Fields and Sediment Transport

Coastal construction works have a specific impact on hydrodynamic fields. The MIKE 21/3 model is used to simulate the scenarios before and after the construction work (area of 752 ha in Cat Hai district, Hai Phong city). The simulation results show that: after the construction, there is no impact leading to the change of the water level regime in the study area; the flow direction changes quite a lot after construction, especially in the east of the calculating area. Due to the narrowing of the water area outside the Lach Huyen estuary, the flow in both spring and ebb tides is markedly increased in magnitude and spatial. Amongst the three modelled rivers—Lach Huyen, Cam, and Lach Tray rivers—the sediment from Lach Huyen and Cam rivers is the most direct and robustly influenced. In the case of construction, there is not much difference between the dry and the rainy season scenarios. However, it is necessary to pay attention to reinforcing the cape area with embankments, underground breakwaters, etc., to ensure the area’s stability under the impact of extreme conditions such as storms and intense monsoons.