Groundwater recharge is vital to the hydrological cycle, but difficult to estimate. It can be natural or human-made, but overuse, pollution, and human activities can disrupt it. Communities are taking steps to increase recharge and prevent pollution.
Groundwater recharge is an important part of the hydrological cycle, in which surface water makes its way underground, replenishing groundwater supplies. It can be difficult to estimate groundwater recharge rates because it is difficult to track the amount of water returning to groundwater supplies, although several techniques can be used to arrive at estimates. It is important to understand how much water is entering a groundwater supply, as this affects how much water can be safely withdrawn from groundwater supplies for human use.
In nature, groundwater recharge is provided by rain, snowmelt, rivers, lakes and streams. As some surface water evaporates or makes its way into another catchment area, more water drips through the land, gradually meeting up with a subsurface water reservoir. It can take a long time for groundwater to build up, or it can replenish very quickly, depending on a variety of environmental factors.
Humans can also create groundwater recharge. Public works agencies can reintroduce groundwater with techniques such as specialized tanks to restore groundwater to previous levels or to keep groundwater levels stable. This technique is used in areas where groundwater resources are heavily utilized and authorities are concerned about falling water table, accumulation of salts in the soil or complete depletion of water. Land is also one of the best places available to store water, so groundwater recharge is used as a storage technique.
Several things can disrupt this process. If aquifers are overused, the recharge will not compensate for the water withdrawn, which lowers the water table. When the water table drops, wells can dry out. Salts can also build up in the soil as the scrubbing action of the water gets rid of it. Human activities such as construction and logging can also impair groundwater recharge, preventing water from entering the ground altogether.
As concerns about water resources have increased around the world, many communities have begun to address the problem of groundwater recharge. Some communities have taken small steps to increase the amount of water flowing back underground, such as using permeable pavement that allows water to drip back into the subsoil, rather than allowing water to pool on the surface and evaporate. People are also concerned about pollution caused by the release of harmful chemicals; when groundwater flows past chemical deposits, the chemicals are collected and enter the water supply. Once in the water, the pollution is hard to remove.
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