An aquifer is a body of porous rock or sediment saturated with groundwater. Groundwater enters an aquifer as precipitation seeps through the soil. It can move through the aquifer and resurface through springs and wells.
Beneath your feet is part of the largest aquifer in the United States. It occupies an area of 174,000 square miles, spreading across 8 American Great Plains States, according to the US Geological Survey. These states are Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. The Ogallala Aquifer is one of the largest aquifers in the world underlying parts of eight states in the United States. This aquifer is considered to be a non-renewable resource because of the low rate of natural recharge compared to the amount of groundwater extracted every year. The aquifer is part of the High Plains Aquifer System, and resides in the Ogallala Formation, which is the principal geologic unit underlying 80% of the High Plains. Large scale extraction for agricultural purposes started after World War II due partially to center pivot irrigation and to the adaptation of automotive engines for groundwater wells.
There are 4 different types of aquifers - each with their own unique characteristics:
1. Unconfined Aquifer:
An aquifer which is not overlain by any confining layer but has a confining layer at its bottom is called unconfined aquifer. It is normally exposed to the atmosphere and its upper portion is partly saturated with water. The upper surface of saturation is called water table which is under atmospheric pressure therefore this aquifer is also called phreatic aquifer.
2. Perched Aquifer:
It is a special case of an unconfined aquifer. This type of aquifer occurs when an impervious or relatively impervious layer of limited area in the form of a lens is located in the water bearing unconfined aquifer. As shown in Fig. 16.3 the water storage created above the lens is perched aquifer and its top layer is called perched water table.
3. Confined Aquifer:
It is also called artesian aquifer. It is a type of aquifer overlain as well as underlain by confining layers. The water within the aquifer is therefore held under pressure. It is sometimes called pressure aquifer also. If the aquifer has high outcrop laterally than the ground surface there will be positive hydrostatic pressure to create conditions for a flowing well. Water from such well comes to the surface without pumping. The imaginary level upto which the water will rise is called piezometric surface.
4. Leaky Aquifer:
In nature, truly confined aquifers are rare because the confining layers are not hundred per cent impervious. An aquifer which is overlain or underlain by a semi- pervious layer (aquitard) through which vertical leakage takes place due to head difference is called leaky aquifer or semi-confined aquifer.
The permeability of the semi-confining layer is usually very small as compared to the permeability of the main aquifer. Thus the water which seeps vertically through the semi-confining layer is diverted internally to proceed horizontally in the main aquifer.
The Role of Playas in the Ogallala Aquifer
Playas — also called mud holes, buffalo wallows, and lagoons — are round, shallow depressions found at the lowest point of a watershed. Their basins, which are lined with clay soil, collect and hold water from rainfall and runoff, creating temporary wetlands. The water then seeps into the soil and slowly moves toward the aquifer or evaporates.
With more than 80,000 scattered across six states from Nebraska and Colorado south to Texas and New Mexico, playas are the most numerous wetlands in the region and have a critical role in recharging the Ogallala aquifer and providing habitat and food for birds as well as many other wildlife species.
A healthy playa has an intact clay basin — without excavated pits or ditches — that is not buried by sediment from nearby fields. Water from the surrounding watershed freely enters the basin through a native vegetative buffer without being diverted from the playa by roads, terraces or other impediments.
To claim this cache answer the following questions and send the answers via the messaging service or email.
1) What type of Aquifer do you believe the Ogallala Aquifer is - explain your answer based on what you see in the area.
2) To the East of you is a Playa - based on what you see how would you describe the health of this playa?
3) What man-made factors do you see that have affected the health of this aquifer?
4) How does this Playa recharge the Ogallala aquifer?
5) Optional - Take a picture of you/your group at GZ.