The increasing acuteness of water scarcity problems, worldwide, requires the adoption of a double approach of water supply management and water demand management. Governments tend to consider river basins as water resources management units and as a spatial basis for the formulation of water management strategies integrating all cross-sectoral issues such as water resources conservation, environment, water resources allocation, water demand management, etc. This is well justified, and is increasingly becoming common practice. The conjunctive management of surface and groundwater is one of the strategies of water supply management best suited to optimize the water resources development, management and conservation within a basin.
Conjunctive Water Management is intended as the efficient utilization of all freshwater resources existing in a specific basin – surface waters, groundwater shallow and deep, but also rainfall, treated wastewaters and other non-conventional sources – according to an overall strategy aimed at improving water availability and reliability. It is crucial for integrated water resources management and helpful to reduce vulnerabilities of water supply systems and mitigate the water supply stress in responding to climate change.
Conjunctive management means using resources in harmony to maximize and stabilize long-term supplies. It does not mean maximizing the use of two separate but interrelated resources for unsustainable short-term gains. Conjunctive management includes two main practices: (i) integrating surface water diversions and groundwater withdrawals to maximize efficiency and minimize impacts on other resource users and ecological processes; (ii) capturing surplus or unused surface water and injecting or infiltrating that water into groundwater aquifers in order to increase recharge rates.
Surface water and groundwater are inextricably linked; understanding of their interactions is essential for developing effective conjunctive water resources management strategies, especially for adaptation to growing climate variability and change that can result in significant impacts on regional and global surface water and groundwater resources. Using groundwater as a complementary source of water has provided an effective means to satisfy the ever-increasing water demands and deal with surface water shortages problems due to the robust capability of groundwater in responding to climate change.
Conjunctive management can involve a variety of water management components and different operational approaches that may cross-political or institutional boundaries. There clearly is no “one-size-fits-all” approach to conjunctive water management. It requires balancing recharge with recovery and monitoring to validate the conjunctive water management. Management should occur at the basin level where the unique set of conditions is well understood and where interested water users can participate and remain informed. Institutional constraints, environmental concerns, economic considerations, and the political climate are also important when implementing conjunctive water management.