When groundwater aquifers and river systems coexist in the same basin, they can be managed as a single integrated resource. This is referred to as “conjunctive usage,” because it allows for the effective utilization of both surface and groundwater resources.
Conjunctive management schemes, in their most basic form, may simply change water usage patterns. In wet years or during the monsoon season, when surface water is abundant, community managers may decide to leave groundwater resources alone. A scheme like this would save subsurface water for times of seasonal or long-term drought.
Aquifers are left untapped during wetter periods, allowing them to replenish naturally through seepage and other water cycle processes.
Other conjunctive usage systems are far more complicated, and they may necessitate substantial infrastructure investments. Many are designed to collect rainwater or divert and store runoff from the surface. Excess surface water in these systems can be diverted to ponds, marshes, or other natural features, where it can seep into the ground and naturally recharge the groundwater storage below.
Excess surface water may be pushed underground more aggressively in some circumstances by using wells that inject water rather than pump it out, as well as other methods designed to rapidly improve groundwater reserves. Artificial recharge is the term for these methods. Artificial recharge can replenish even confined aquifers that are isolated from the surface water system, and groundwater aquifers offer several advantages over surface storage, including evaporation resistance and the ability to replenish even confined aquifers that are isolated from the surface water system. Dams and reservoirs, on the other hand, can accept massive amounts of extra water in a short period of time, whereas artificially replenished aquifers cannot.
Conjunctive use allows managers to take advantage of both the benefits and downsides of surface and groundwater resources. As a result, water is used more efficiently.