Aquifer – a body of permeable rock which can contain or transmit groundwater. Aquifers supplied 55 percent of the water used in Texas in 2020.
Ogallala Aquifer– the largest source of fresh groundwater in the United States, underlying parts of Texas, New Mexico, Oklahoma, Kansas, Colorado, South Dakota, Nebraska and Wyoming. It covers more than 36,000 square miles. The Ogallala provides significantly more water for users than any other aquifer in the state. (Check out 5 things that you absolutely need to know about the Ogallala Aquifer.)
Groundwater – water that exists underground in saturated zones beneath the land surface. It does not form underground rivers or lakes, Instead, it fills the pores and fractures in underground materials such as sand, gravel and other rock, in much the same way as water fills a sponge.
Water table – the upper surface of a saturated zone in a groundwater aquifer
Confined Aquifer –A confined aquifer is an underground water-bearing layer trapped between layers of impermeable rock or clay, meaning rainwater or snowmelt is prevented from easily flowing from the surface. Confined aquifers are often fed from recharge areas at higher altitudes than the aquifer itself, and the water moves downward underground due to gravity. The downward movement causes a build-up of pressure within the aquifer. So, when you drill a well into it, the pressure will cause the water to rise in the well, sometimes even to the surface without pumping.
Unconfined Aquifer – Unconfined aquifers lack the layers of impermeable material above sealing the aquifers from the surface, meaning water can get in and out. They are subject to atmospheric pressure and are directly connected to the surface, allowing rainwater and snowmelt to infiltrate them. Because they are directly connected to the surface, unconfined aquifers are generally more susceptible to contamination from surface sources than confined aquifers. Unconfined aquifers are usually closer to the Earth’s surface than confined aquifers and are, therefore, impacted by drought conditions sooner than confined aquifers.
The Ogallala Aquifer is an unconfined aquifer. It’s not trapped by an impervious layer and is recharged by rainfall or snowmelt infiltrating from the surface. In the High Plains region, it also is recharged by playa lakes, which contain a special kind of clay that cracks during dry weather conditions. When rain falls, the water flows into the playa and starts a long journey to the aquifer. As the playa goes wet, the cracks seal, cutting off the downward flow of water, and the lake fills up. Grassy areas beyond the banks of playas in their natural state help to clean the water as it flows in.
Sources: The Texas Water Development Board, U.S. Geological Survey
