In order to reduce the siltation downstream of tide gates constructed in a seaward channel that has a significant impact on the efficiency of the drainage culvert and navigation capability of the seaward channel, the CST module in the MIKE11 model was used to study the water requirement for silt scouring in the seaward channel at the Xinyang Port in Yancheng City. The CST module was developed by coupling a hydrodynamic model and sediment transport model, with the model parameters calibrated using the measured data of water level, flow rate, and siltation height at three sections, located, respectively, 60 m, 970 m and 3 030 m downstream of the gate. The calculated ecological flow rate for silt scouring and port protection with the MIKE11 CST model was 80 m³/s under a siltation height of no more than 0. 1 m. This value was close to the flow rate of 85 m³/s obtained from experiments on silt scouring by water diversion from the Yangtze River at the Xinyang Port in December 2006, under the conditions of no silting and no scouring.