Impacts of deep waterway project on morphological changes within the north passage of the changjiang estuary, China

Over the past decade, three phases of the Deep Waterway Project (DWP) have been carried out to deepen the shipping channel of the Changjiang Estuary, where a significant sandbar previously dominated. This project has produced significant hydrodynamic and morphological changes within the North Passage of the Changjiang Estuary. High-resolution and continuous seasonal bathymetric data from 1998 to 2008 provide good insight into sedimentation processes. These data reveal several significant characteristics: (1) During phase I, strong erosion occurred around the upper region, and the entrance, middle, and lower regions are under moderate deposition. The groin-blocked region had strong depositions. (2) The main-channel region shifted to erosion-dominant conditions during phase II. Erosion also occurred in the northern areas of the upper and middle regions. The entrance and southern areas of the upper and middle regions experienced deposition. (3) During phase III, the entrance region reached sedimentation equilibrium, and the northern area of the lower region experienced strong erosion. The southern areas of the middle and lower regions were under deposition. Domain-nesting Delft3D-flow model is applied to understand the mechanisms of the observed morphology and its changes induced by three phases of the DWP, which reveals that hydrodynamics intensify within the main-channel regions and decrease in the groin-blocked regions. These results are consistent with sedimentation patterns found. The simulations also show that dikes effectively keep the high suspended sediment concentration waters of Jiuduansha Shoal from entering the North Passage.