Modeling morphological change in anthropogenically controlled estuaries

Sluice gates are a type of tidal barrage that are built across estuaries to control saline water intrusion and river flooding. Around 300 sluice gates have been installed in the estuaries along the coastline of China, with more than a third being constructed on the coastal plain of the southern Yellow Sea. These structures induce significant, but as yet unquantified, anthropogenic impacts on estuarine environments; e.g., hydrological and sedimentary changes. This study used the Delft3D process-based model to quantify the impact of a sluice gate on an estuarine system that has been extensively modified by human activity. Both observed data and model results show that the sedimentation rate increased remarkably in response to tidal wave deformation when the gate remained closed. This increased sedimentation was particularly apparent in the downstream area near the gate, as well as in the middle section of the downstream channel. In this case, the sediment-carrying capacity of the flood tide was enhanced, whereas that of the ebb tide was reduced. Consequently, sediment tended to become trapped in the river channel and eventually settled to the bed. Numerical simulations indicate that gate location plays a key role in controlling siltation patterns. Long channels cause intense siltation, whereas short channels tend to favor undisturbed sediment transport patterns and are not as conducive to increased siltation as long channels. Model results suggest that to reduce siltation, it is important to choose an appropriate sluice gate location and to optimize the timing and duration of upstream water release. These findings reveal the mechanisms that drive the morphological evolution of tidal estuaries containing sluice gates, and provide a typical example of anthropogenically controlled geomorphological processes.