Ogallala-Aquifer

The Ogallala Aquifer, also known as High Plains Aquifer, is a large underground groundwater aquifer located beneath the Great Plains in the United States. As one of the world's largest aquifers, it covers an area of ​​more than 450,000 square kilometers of the eight American states of South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico and Texas. He was named in 1899 by Nelson Horatio Darton after the small town of Ogallala, Nebraska.

General

The deposition of groundwater- conducting layers can be dated back to the era of the late Miocene to early Pliocene, when piling up the Rocky Mountains. Given the country raised in the West, rivers and streams channels broke into East-West or West - East direction. The erosion in the Rocky Mountains led to wind and alluvial deposits, which filled up the old river beds and perhaps covered the entire area of ​​the present-day aquifer and today form the Ogallala waterproof layer. The depth of the deposits varies with the shape of the earth's surface before the start of the deposits and is at its deepest, where the old alluvial valleys and river cuts covered.

The thickness of the filled water of the Ogallala Formation ranges from a few centimeters to more than 160 meters ( 525 feet), being in the north of the Great Plains generally larger than in the south. The water itself is located at a depth of 122 meters ( 400 feet, to the north) to 30-60 meters (100-200 feet; south ). The reservoir now has no fresh water supply, but it fills only slowly with rain water that seeps through the soil back on. So the underground overlying water still comes mostly from the last ice age.

Ratio of water withdrawal and inflow

Each aquifer is a water storage and thus has influence on the water cycle. The USGS ( U.S. Geological Survey) has several studies of the Ogallala Aquifer hired to explore the relationship between water supply and water withdrawal for example, wells and pumps, and thus the development of the water level to strategies for conservation of the reservoir lake for the future to secure. This is very important because the aquifer today forms the basis for almost all agriculture in the Great Plains and its destruction, the end of thousands of small, medium and large enterprises would result.

Inflow of groundwater

The amount of the water supply is limited by various factors. So prevails in much of the Great Plains semi- arid climate with strong winds, which accelerate the evaporation of water. In many places, the aquifer is overlain by a limestone layer, which is almost completely impermeable to water, which greatly restricts the flow of water. The origin of the limestone is in turn funded by the climate and high evaporation, so the climate is a double obstacle to the filling of the reservoir lake.

Extraction of groundwater

The regions above the Ogallala Aquifer among the most productive livestock and agricultural regions of the United States. Here corn, wheat and soybeans are grown in very large amounts, which the Great Plains has been nicknamed the " bread basket of America" ​​introduced. The earnings of many large farm enterprises, often with only inadequate water supply are located in areas with rainfall and where it is not year round frame sufficient water at the surface, are highly dependent on groundwater, which with pump for watering the plants on the surface is promoted.

The aquifer was first in 1911 used for agricultural irrigation, but the mass use began in the 1930s and experienced a second attack in the 1950s, when the now almost universal coverage with electricity in the rural areas and the availability of cheaper and more efficient turbine pump better assistance to the water offered. Since the amount of water withdrawn soon had exceeded the amount of incoming water, the water level began to decline rapidly. Today's estimates, the ratio of retrieved to feed water is about 25, which means that only one liter continues to flow for 25 liters of water abstracted fresh water through seepage.

In some places a drop of the water level of up to 1.50 meters per year was measured.

In some extreme cases, holes for the pump had to be already driven deeper into the earth to still get to water, some parts of the aquifer are also already waterless, so parched. If this trend continues, the excessive water consumption in the medium term could make agriculture in this area is absolutely impossible.

Some rivers in the region such as the Platte River are sometimes even lower than the water level, which additionally removes the aquifer water.

Current Situation

Measures to reduce water consumption, such as crop rotation, more efficient irrigation methods and the reduction of irrigated land have recently led to a slight decline in the lowering of the water table. In some areas, such as the humid East and Zentralnebraska he has risen, however slightly. The graphs show the changes between 1980 and 1995.