Boreholes and their effect on aquifers

• Groundwater is a valuable source of water
• Groundwater is mainly used for drinking water and domestic and agricultural purposes (irrigation)
• Groundwater supplies are naturally replenished by rain and melting snow that infiltrates the soil, as well as by rivers and lakes
• The water slowly moves through the upper layers of soil until it reaches a depth where the soil becomes saturated with water.
• The top level of the saturated layer is called the water table
• This underground layer of permeable rock that is saturated with water and from which groundwater can be extracted through a borehole, is known as an aquifer
• Under natural conditions, water is brought to the surface from an aquifer by means of a fountain/spring, or is seeps into a river or lake
• We can extract groundwater by sinking a borehole that penetrates the aquifer
• Once the water is extracted, it is naturally replensihed
• Some groundwater sources take a long time to be replenished
• When water is extracted from the ground faster than it is replenished, it can have adverse consequences
• The water table is lowered and aquifers are depleted
• Water in rivers and lakes is reduced- the water in rivers and lakes is partially supported by water seeping from underground aquifers to the riverbeds
• Soil subsidence- when groundwater is extracted, the soil may collapse as a result of a loss of the underground support of water
• Salinisation of groundwater- when groundwater is extracted near the coast, salt water may seep in to replace the freshwater, thus reducing the available freshwater