When groundwater aquifers and river systems are found within the same basin, they may be managed as one interconnected resource. This practice is known as “conjunctive use,” and it can enable very efficient use of both surface and groundwater resources.
Conjunctive management plans, in the simplest sense, may simply alter water usage patterns. Community managers may decide to leave groundwater resources untouched in wet years or during the monsoon season when surface water is plentiful. Such a policy would conserve underground water for times of seasonal or prolonged drought.
Other conjunctive use systems are much more complex and may involve extensive infrastructure investments. Many are designed to capture rainwater, or to divert and store surface water runoff. In such systems excess surface water may be channeled to ponds, wetlands, or other natural features from which it can seep into the earth and naturally recharge the groundwater stores below.
In some cases excess surface water may be more aggressively moved underground by employing wells that inject water rather than pumping it out, and other technologies designed to rapidly boost groundwater reserves. These processes are known as artificial recharge. Groundwater aquifers promise several advantages over surface storage, such as immunity from evaporation, and artificial recharge can replenish even confined aquifers that are isolated from the surface water system. However, dams and reservoirs can accommodate large volumes of excess water in a short time—something that artificially recharged aquifers cannot do.
Conjunctive use enables managers to use the advantages of both surface and groundwater resources while minimizing their drawbacks. The result is a more efficient use of water.