Conjunctive Use

Conjunctive use refers to the integrated and coordinated management of surface water and groundwater resources within a basin or region, leveraging the distinct advantages of each source to optimize overall water supply reliability, efficiency, and sustainability. Surface water is typically more available during wet seasons and precipitation events but subject to seasonal variability, while groundwater provides a more stable, buffered supply but can be depleted if over-extracted. In a conjunctive use scheme, surplus surface water during wet periods is used to recharge aquifers through spreading basins, injection wells, or in-lieu recharge (substituting surface water for groundwater pumping to allow aquifer recovery). During dry periods or droughts, the stored groundwater is then extracted to supplement reduced surface water supplies. California's Central Valley is a prominent example where conjunctive use is practiced to manage the state's highly variable hydrology. Effective conjunctive use requires understanding of the hydrogeologic system, coordination among surface water and groundwater users, appropriate infrastructure for recharge and extraction, and institutional frameworks that allow flexible water management. Benefits include increased total usable supply, reduced peak demand on surface systems, mitigation of land subsidence from groundwater overdraft, and improved water quality through aquifer recharge.