Conjunctive Use—Advantages, Constraints, and Examples

Conjunctive use of surface water and ground water can usually increase yields at lower costs than more dams and reservoirs operated separately. There are three main types of conjunctive use projects: (1) Stream diversions; (2) dam and reservoir only; and (3) total system. There are many advangates of ground‐water storage compared with surface storage, and of conjunctive use compared to independent use. Physical, operational, financial, and institutional constraints may be encountered by the project proponents. Institutional issues may be the most difficult to resolve. Often, several governmental agencies may provide funds and have responsibilities for various features of conjunctive‐use projects. Implementation is more difficult in countries where surface‐water development has historically dominated water‐supply project formulation. Court decisions in California have provided guidelines for conjunctive‐use programs, especially in defining the rights of public agencies. Four areas in California that have experienced basin overdraft and increasing water demands, and where conjunctive‐use operations have been implemented, are described.