1-D movable bed numerical forecast model of salinity of the Qiantang River estuarine reach and its application

The Qiantang River estuary is an alluvial estuary with strong tidal bore, high sediment concentration and easy changeable riverbed. The interaction between tide and fluvial feedback has great effects on saltwater intrusion. In this paper, a 1-D numerical forecast model of salinity has been developed in the light of riverbed deformation, and the process of water flow, sediment transport, river bed deformation and salinity are fully coupled solved. The governing equations of the model are solved by an explicit finite-volume method with good conservation performance. The verification results show that the riverbed deformation has great influence on chlorine, and the chlorine computed by the movable-bed numerical model agrees well with the measured. Therefore, it is necessary to adopt the movable-bed numerical model in long-duration salinity forecast. Finally, the model is used to investigate the response pattern of saltwater intrusion in the Qiantang River estuary to human activities, such as construction of Xin'anjiang-reservoir and the Qiantang River estuary narrowing regulation. And the problem of the water supply guarantee rate of Hangzhou city is also discussed. The results show that Xin'anjiang-reservoir and the Qiantang River estuary regulation engineering have a significant effect on improving the estuarine freshwater resources and ensuring the safety of water supply of Hangzhou city. In order to raise the water supply guarantee rate to 95%, the measures of scheduling release water discharge from the upstream reservoir and building a new backup reservoir should be taken.