Groundwater is water that is found underground in the cracks and spaces in soil, sand and rock. Groundwater is stored in--and moves slowly through--layers of soil, sand and rocks called aquifers. Aquifers typically consist of gravel, sand, sandstone, or fractured rock, like limestone. These materials are permeable because they have large connected spaces that allow water to flow through. Groundwater is potable water which is stored underground. Around 20% of the world's freshwater is groundwater. Ground water recharge is a vital part of the “hydrologic cycle”. The hydrologic cycle is a constant movement of water above, on, and below the earth's surface. It is a cycle that replenishes ground water supplies. It is not easy to estimate groundwater recharge rates because it is tough to track the amount of water which returns to subsurface water supplies, even though several different techniques can be used to arrive at estimates. It is important to understand how much water is entering a supply of groundwater, as this influences how much water can safely be taken from groundwater supplies for human use.
Rates of groundwater recharge are difficult to quantify. Some of the methods are:
Groundwater recharge is water that has soaked into (infiltrated) the ground, and moved through pores and fractures in soil and rock to the water table. The water table is the depth at which soil and rocks are fully saturated with water. Recharge maintains the supply of fresh water that flows through the groundwater system to wells, streams, springs, and wetlands, which support the plants and animals that are part of the surrounding ecosystem.
In some places (where there are no nearby rivers or large lakes), almost all water-supply needs are met by groundwater, and recharge is critical to maintaining the abundance and quality of groundwater. Groundwater contributes to wells as well as flow to streams, springs, and wetlands year-round, sustaining them during droughts and dry summer months.
In locations where the withdrawal of water is more than the rate of recharge, an imbalance in the groundwater reserves is created. Recharging of aquifers is carried out with the following objectives:
Yes, humans can also facilitate groundwater recharge. Public works agencies can reintroduce water to the ground with procedures such as specialized reservoirs to restore groundwater to previous levels or to keep groundwater levels stable. This method is used in regions where groundwater supplies are heavily utilized and authorities are worried about a dropping water table which makes the wells go dry, salt build-up in the soil, or about water scarcity. The earth also makes one of the best available places to store water, so groundwater recharge is utilized as a storage technique.
The computer model of groundwater recharge map calculates deep infiltration based on land cover, the water holding capacity of the soil, and the daily precipitation and temperature. The final result is an estimate of groundwater recharge in inches per year.