The High Plains aquifer (which includes the Ogallala aquifer) lies under parts of eightStates and has been intensively developed for irrigation. The aquifer is ‘Unconfined’ ,sometimes also called water table  or phreatic  aquifers, because their upper boundary isthe water table.

Present-day recharge of the aquifer with fresh water occurs at an exceedingly slow rate suggesting that much ofthe water in its pore spaces is paleowater, dating back to the last ice age and probably earlier. Withdrawals fromthe Ogallala are in essence mining ancient water. 

Utilizing treated recycled sources of water in agriculture is one approach at safeguarding the future of the aquifer. Another method to reducing the amount of water use is changing to crops that require less water, suchas sunflowers. Water conservation practices (e.g. crop rotation), more efficient irrigation methods (center pivot anddrip), and simply reduced area under irrigation have helped to slow depletion of the aquifer, but levels are gener-ally still dropping.

Mass balance = Water In - Water out

Much of the plains region is semi-arid. Steady winds accelerate evapora-tion of surface water and precipitation. In many locations, the aquifer iscovered by a shallow layer of caliche (calcium carbonate) that is practi-cally impermeable; this limits the amount of water able to recharge theaquifer from the land surface. However, where you have playa lakes thesoil doesn’t have this so the aquifer can re-charge. However farming destroys the playalakes, creating the layer of caliche as soilmoisture evaporates. The increased aridityincreases the amount of evaporation, which

Water levels have declined more than 100 feet in some areas and the saturateddepth has been reduced by more than half in others. Water levels are recovering insome areas due to management by State and local agencies, improved irrigationefficiency, low crop prices, and agricultural programs (McGuire and others, 2003). 

In some places, the water table has dropped more than five feet (1.5 m) per year.In extreme cases wells have been deepened to reach the steadily falling water table.In some places, the water table has been drained, e.g. Northern Texas.

High Plains Aquifer

 

Ground surface

1925

1955