Analysis of the influence of Deep Waterway Project on morphological evolution in the North Passage of the Changjiang Estuary, China

Based on the difference of flow field, suspended sediment concentration and transportation in the North Passage between in Jan. 1998 and in Feb. 2008 using Delft3D model, the dynamical mechanisms of the morphological change in the North Passage are discussed in this paper. The results are summarized as follows: 1) the water depth in the North Passage has increased due to the enhanced resistance produced by the groins of the Deep Waterway Project. The ebb tide current is significantly blocked by these dikes and groynes. 2) The flow field also has been changed by the increased water depth, including that the flow velocity has decreased in the entrance region and the dikes-groins region and decreased in the upper and middle regions of the main channel, and increased in the lower and partial of upper region. The location of maximum velocity has moved downstream from the middle to lower region of the main channel, the maximum velocity is 0.2m/s larger in Feb. 2008 than that in Jan. 1998, and the velocity amplitude in dikes-groins region has about 1.0 m/s decreasing in Feb. 2008 compared with that in Jan. 1998. 3) The locations of weakened and increasing velocity are identical with the regions of significant sediment deposition and erosion respectively. 4) The construction has blocked the cross-dike transportation of high-concentration suspended sediment from Jiuduansha Shoal into the North Passage. 5) In the future, the region of entrance and dikes-groins might have potential trend of siltation process, especially the dikes-groins region built during 2^nd phase.