Numerical prediction of medium-term tidal flat evolution in the Yangtze Estuary: impacts of the Three Gorges project

A two-dimensional (2-D) numerical model and a three-dimensional (3-D) numerical model of the Yangtze Estuary, including tidal flow, suspended sediment transport and bed evolution, were established based on the Delft3D-FLOW model respectively. The models were calibrated with the field data. The calibrated models were employed to predict the morphological evolution process of the Yangtze Estuary for the next 20 years, with the predicted area covering the Chongming Eastern Beach and the Nanhui Tidal Flat. According to the simulated results in the medium term, due to the progress of the Three Gorges, erosion will happen in the southeast and south region and deposition will happen in the northeast and north region of the Chongming Eastern Beach, while a deep channel will be formed gradually in the middle part. The Nanhui Tidal Flat will develop southeastwards. Five scenarios of different river discharges and sediment loads are obtained from an exponential regression equation between flow rate and suspended sediment concentration deduced from the monthly averaged flow rate and suspended sediment concentration during 2003–2009. These five scenarios were used for investigating the topographic responses of the Chongming Eastern Beach and the Nanhui Tidal Flat to different river discharge and sediment supply conditions. The predictions show that the erosion rate will decrease and the deposition rate will increase with the increase of sediment supply, i.e., less the sediment supply leads to more recession.