Impacts of land reclamation projects on hydrodynamics and morphodynamics in the highly altered North Branch of the Changjiang Estuary

The estuary is highly dynamic and sensitive to external and internal forcing. We examine a chain reaction of hydrodynamic and morphodynamic responses to a series of land reclamation projects during the period 1997 to 2017 in the North Branch of the Changjiang Estuary through the Digital Elevation Model (DEM) comparison and the numerical simulation by the Finite Volume Community Ocean Model (FVCOM). The results show that tidal amplification was further strengthened by the artificially reduced channel volume in the middle and upper segments of the North Branch due to the implementation of several large-scale land-reclamation projects in the first stage (1997–2007), and the channel siltation in the middle and upper segments was in turn further promoted by the increased tidal flows with flood dominance. In the second stage (2007–2017), tidal amplification was relaxed by the channel narrowing project at the lower segment and the waterway improvement project through channel dredging works at the middle and upper segments. Contemporary erosion volume was almost balanced by the accretion volume in the North Branch because of the weakening dominance of flood over ebb flows. Spatiotemporal variation in channel accretion and erosion patterns in response to estuarine engineering projects was vividly mirrored by the change of simulated bed shear stress in that the areas with increased (decreased) bed shear stress underwent severe erosion (accretion). These findings highlight again the dynamic feature of tide-dominated estuaries and the importance of simulation tools to the estuarine management.