A framework for water supply regulation in coastal areas by avoiding saltwater withdrawal considering upstream streamflow distribution.

Freshwater availability in coastal areas depends on the withdrawal from tidal rivers. It is severely threatened by saltwater intrusion, especially in the dry season. Freshwater availability is associated closely with natural factors and human activities. Limited research has investigated how freshwater availability is influenced by saltwater intrusion, streamflow, projects, etc., and how the water supply security downstream is affected by the abovementioned factors. To fill these gaps, this paper presents a new framework, i.e., water supply regulation by avoiding saltwater withdrawal (RASW). The framework is based on data on streamflow, tide, wind, the salinity of withdrawal stations, capacities of withdrawal projects and reservoirs, and water demand, which holistically develops relationships among saltwater intrusion, upstream streamflow, and water supply. The RASW contains three phases, i.e., estuary salinity-exceedance simulation, upstream streamflow distribution design, and local water supply security analysis. The proposed intellectual framework and methodology have been tested on the water supply for Zhuhai-Macao of the Guangdong-Hong Kong-Macao Great Bay Area, South China. Results demonstrated that the meta-Gaussian copula efficiently simulated the six-dimensional monthly streamflow distribution and was appropriate for streamflow distribution scenario design. Water supply security benefited greatly from the joint river-reservoir regulation mode. Nevertheless, the water supply security was threatened in the extreme scenarios when the extremely low streamflow distribution happened in the late period or lasted for an extended period. The proposed framework facilitates integrated decision-making for water supply security in coastal areas. Utilizing the streamflow distribution as a management tool and controlling them to avoid extremely low streamflow and adjust their occurrence time can alleviate water supply pressure. Moreover, the capacities of local regulating facilities should be designed with full consideration.