Groundwater - Will it always be there?
Over-exploitation of our groundwater resources is a big problem, where much is used for irrigation only to evaporate again. And climate change also affects the availability of groundwater. Hear Professor Anders Vest Christiansen talk about the threats facing groundwater reserves.
Groundwater is a very useful resource. If handled properly, it delivers clean and sustainable water.
If we're not careful we risk depletion or devastation of the groundwater resource. This may have severe consequences.
Groundwater is recharged from precipitation seeping through soil layers.
The recharge depends on a number of factors - but the amount and duration of the precipitation are the main ones.
This means that during wet seasons - the aquifer is recharged and the groundwater table rises.
Similarly, in dry seasons the groundwater table declines. Pumping water will impact this balance, but in large parts of the world - there's plenty of room for sustainable groundwater extraction.
The equation is simple: If more water is extracted than the recharge delivers - the groundwater level drops and the aquifer is depleted. Continued depletion will eventually dry out any aquifer.
Groundwater is used for two main purposes: drinking water and irrigation. In many countries, irrigation is by far the largest component. The alternative to groundwater is surface water from rivers, lakes and dams. That comes without the cleaning effect from the precipitation - filtering through soil layers in the ground.
In some dry regions, the groundwater depletion has been going on for years - with the effect that the groundwater table has seen significant drops. The consequence is not only that we need to extract the water from deeper levels - but also that we may see land subsidence due to the decreased pressure support - from the water in between the grains.
The solution to groundwater depletion may come in many forms. The simplest one is to extract less water.
Quite often there are other solutions, like spreading the load on an aquifer - by installing more wells distributed over a larger area.
The other parameter that may be manipulated is the recharge. In the natural setting, the recharge is from precipitation. But precipitation may be highly irregular over the course of a year - with dry seasons and wet seasons.
In the wet seasons, a lot of the excess rain runs off directly from the surface - through rivers and back into the ocean. Recently, several experiments have taken place - where the excess water in the wet seasons is stored in basins and pools - and is allowed to re-infiltrate into and recharge the aquifer.
The water is stored in the wet seasons and can be reused in the dry seasons. The groundwater is there. It's constantly being recharged from precipitation. If we withdraw less water than the recharge - groundwater is a safe and sustainable resource - for drinking water as well as irrigation.