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 and is severely threatened by saltwater intrusion, especially in the dry season. Freshwater availability is associated with natural factors and human activities. Although analyses of freshwater availability under saltwater intrusion is problematic, it has received limited attention in the literature. We propose a new framework, i.e. regulation by avoiding saltwater withdrawal (RASW), where the relationships among saltwater intrusion, upstream streamflow, and water supply are established, using hybrid data-driven method coupling wavelet transform and random forest, and considering data on streamflow, tide, wind, salinity of withdrawal stations, capacities of withdrawal projects and reservoirs, and water demand. RASW contains three phases, i.e. estuary salinity-exceedance simulation, upstream streamflow distribution design, and local water supply security analysis. The method is tested on the water supply for Zhuhai-Macao of the Guangdong-Hong Kong-Macao Great Bay Area, South China. Results demonstrate that the salinity-exceedance simulation model using a hybrid data-driven method is quite accurate. The meta-Gaussian copula efficiently simulates the six-dimensional distribution of upstream monthly streamflow and is appropriate for streamflow distribution scenario design. Water supply security benefits greatly from the joint river-reservoir regulation mode. But for a given exceedance frequency of average streamflow, the modes and security situations are diverse, due to various streamflow distributions, i.e. extremely low streamflow and its occurrence time. The proposed framework facilitates integrated decision-making for water supply security in coastal areas. Moreover, the capacities of facilities should be carefully considered according to local conditions, and streamflow distribution design can be utilized as a management tool to regulate water supply system.