THe Basics
What is an aquifer?
An aquifer is an underground volume of water found in permeable rock or another water bearing substrate such as gravel. Aquifers sit atop impermeable layers of earth referred to as aquicludes. Sometimes there are impermeable layers above aquifers as well. These aquifers are termed confined and are under pressure. If enough pressure exists in a confined aquifer, water can be accessed without the use of a pump. Wells utilizing this natural pressure are called artesian wells. If the geology above an aquifer is permeable it is termed unconfined. The top of an unconfined aquifer is called the water table and equates to the depth of groundwater from the surface.
An aquifer is an underground volume of water found in permeable rock or another water bearing substrate such as gravel. Aquifers sit atop impermeable layers of earth referred to as aquicludes. Sometimes there are impermeable layers above aquifers as well. These aquifers are termed confined and are under pressure. If enough pressure exists in a confined aquifer, water can be accessed without the use of a pump. Wells utilizing this natural pressure are called artesian wells. If the geology above an aquifer is permeable it is termed unconfined. The top of an unconfined aquifer is called the water table and equates to the depth of groundwater from the surface.
What about the Ogallala aquifer?
The Ogallala aquifer lies under 8 U.S. states and is one of the largest aquifers in the world. In total, it lies under an area of about 174,000 square miles in the plain states of Nebraska, South Dakota, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas (“Ogallala Aquifer,” 2014). In general, this unconfined aquifer is relatively shallow and easy to access. It ranges from several feet thick to about 1000 feet thick(“Ogallala Aquifer,” 2014). The substrate of the aquifer is made up of poorly sorted and unconsolidated clay, silt, sand, and gravel deposited by streams and wind, as well as fine-grained sandstone, siltstone, and interconnected fractures(“Ogallala Aquifer,” 2014). Water in the Ogallala aquifer generally flows from east to west at a rate of about one foot per day(“Ogallala Aquifer,” 2014). The Ogallala aquifer was estimated to contain 2.9 billion acre feet of water in 2009(“Ogallala Aquifer,” 2014). Recharge occurs through the percolation of precipitation through soils to the water table. The recharge rate of the Ogallala aquifer has been estimated to average about one half inch per year(“Ogallala Aquifer,” 2014).
The Ogallala aquifer lies under 8 U.S. states and is one of the largest aquifers in the world. In total, it lies under an area of about 174,000 square miles in the plain states of Nebraska, South Dakota, Wyoming, Colorado, Kansas, Oklahoma, New Mexico, and Texas (“Ogallala Aquifer,” 2014). In general, this unconfined aquifer is relatively shallow and easy to access. It ranges from several feet thick to about 1000 feet thick(“Ogallala Aquifer,” 2014). The substrate of the aquifer is made up of poorly sorted and unconsolidated clay, silt, sand, and gravel deposited by streams and wind, as well as fine-grained sandstone, siltstone, and interconnected fractures(“Ogallala Aquifer,” 2014). Water in the Ogallala aquifer generally flows from east to west at a rate of about one foot per day(“Ogallala Aquifer,” 2014). The Ogallala aquifer was estimated to contain 2.9 billion acre feet of water in 2009(“Ogallala Aquifer,” 2014). Recharge occurs through the percolation of precipitation through soils to the water table. The recharge rate of the Ogallala aquifer has been estimated to average about one half inch per year(“Ogallala Aquifer,” 2014).
RECHARGE & INFLUENTIAL FACTORS
Recharge refers to the amount of water that is able to find its way past the evapo-transpiration process and permeate into the deeper recesses of the Earth and the aquifers of the world. The amount of recharge of a particular area is determined by the climate, topography, geology, and flora. The Ogallala Aquifer sits beneath the “High Plains” of the central United States. The High Plains is a unique ecosystem lying between the Rocky Mountains and the central lowlands, which has been developing over millions of years and plays a large role in how the aquifer recharges.
The climate of the High Plains is described as a “dry continental climate” and is characterized by ample sunshine, minimal precipitation, low humidity, and therefore a high evaporation rate (Gutentag et al, 3). Precipitation, which falls mainly from April through September, increases from approximately 16 inches in the Western regions to upwards of 28 inches in the Eastern regions (Gutentag et al, 3). The topography of the area is mainly comprised of flatlands and mild rolling hills formed by permeable sediments deposited by ancient seas and streams stemming from the Rocky Mountains (Gutentag et al, 2).
The recharge of the Ogallala Aquifer is has an interesting recharge capability as it deals with low precipitation, sandy overlying soils, and the dominant grassland ecosystem. The sandy soils, which have high permeability and low moisture storage, naturally play an integral role to the recharge of the Ogallala Aquifer (Gutentag et al, 31). Below is a detailed map of the soils, which can help us gain an understanding about how permeable each region is. However, this form of recharge is minimal due to the low precipitation rates and high evaporation rate. In addition to precipitation, intermittent creeks produce infrequent high flows that play an important role in the recharge process. However, it must be noted that this form of recharge is not entirely steady and requires a few substantial high flows per decade to add a significant amounts of water (Gutentag et al, 31). This all points to the average annual recharge rates being quite minimal: ranging from .024 inches/year in Texas to 6 inches/ year in south-central Kansas, due to differences in the soil, topography, and climate of each respective region (see Table 7)(Gutentag et al, 31).
Recharge refers to the amount of water that is able to find its way past the evapo-transpiration process and permeate into the deeper recesses of the Earth and the aquifers of the world. The amount of recharge of a particular area is determined by the climate, topography, geology, and flora. The Ogallala Aquifer sits beneath the “High Plains” of the central United States. The High Plains is a unique ecosystem lying between the Rocky Mountains and the central lowlands, which has been developing over millions of years and plays a large role in how the aquifer recharges.
The climate of the High Plains is described as a “dry continental climate” and is characterized by ample sunshine, minimal precipitation, low humidity, and therefore a high evaporation rate (Gutentag et al, 3). Precipitation, which falls mainly from April through September, increases from approximately 16 inches in the Western regions to upwards of 28 inches in the Eastern regions (Gutentag et al, 3). The topography of the area is mainly comprised of flatlands and mild rolling hills formed by permeable sediments deposited by ancient seas and streams stemming from the Rocky Mountains (Gutentag et al, 2).
The recharge of the Ogallala Aquifer is has an interesting recharge capability as it deals with low precipitation, sandy overlying soils, and the dominant grassland ecosystem. The sandy soils, which have high permeability and low moisture storage, naturally play an integral role to the recharge of the Ogallala Aquifer (Gutentag et al, 31). Below is a detailed map of the soils, which can help us gain an understanding about how permeable each region is. However, this form of recharge is minimal due to the low precipitation rates and high evaporation rate. In addition to precipitation, intermittent creeks produce infrequent high flows that play an important role in the recharge process. However, it must be noted that this form of recharge is not entirely steady and requires a few substantial high flows per decade to add a significant amounts of water (Gutentag et al, 31). This all points to the average annual recharge rates being quite minimal: ranging from .024 inches/year in Texas to 6 inches/ year in south-central Kansas, due to differences in the soil, topography, and climate of each respective region (see Table 7)(Gutentag et al, 31).
(Gutentag et al, 32
(Gutentag et al, 33)
FRAGILITY OF THE SYSTEM
As one may be able to see, this aquifer is in a precarious situation. Mainly due to the High Plain's arid climate, there is little recharge for this old water body. As one can see below, the Aquifer is being stressed by minimal recharge coupled with high use
As one may be able to see, this aquifer is in a precarious situation. Mainly due to the High Plain's arid climate, there is little recharge for this old water body. As one can see below, the Aquifer is being stressed by minimal recharge coupled with high use