The Pattern of Saltwater Intruding into the Changjiang Estuary and the Utilization of Freshwater Resources

The geomorphic features of the Changjiang estuary are characterized by the multi order branching. The saltwater intrusion has the following four distinct forms:direct intrusion from the outer sea;saltwater exchange by shoal passages;saltwater downstream from other waterways;saltwater intrusion by tidal flooding. Temportal changes in the salinity of the Changjiang estuary have daily, semimonthly, seasonal and yearly variation. There exists the sharp three demarcation lines of salinity gradient along the South Branch-South Channel. Two main problems had to be solved before building reservoirs of avoide saltwater and store freshwater in the Changjiang estuary. One is to calculate the longest duration that the chlorinity exceeds 250×10 6 in the water resources area, which is the criterion value for determining the storage capacity of reservoirs. Mathematical methods including the cybernetics, the frequecncy spected analysis and mathematical modelling are adopted here to get more correct times when the chlorinity exceeds 250×10 6 . And the other is to determine reasonably site of the pumping station and the height of water intake of water pumps from the river bed. The above problems can be solved after understanding the pattern of temporal and spatial variation of the saltwater intrusion in the Changjiang estuary. The above conclusions have played an important role in forming the reservoir scheme of the Baoshan lron and Steel Plant, and supplied basic data for selection of the postion and storage capacity for the Chenhang reservoir.