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Groundwater

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Abstract

An aquifer is an underground body of water perched on top of bedrock or other impermeable layer. Most usable freshwater storage is within aquifers (Table 10.1). The residence time of groundwater can vary from days to millennia (Fig. 10.1). Groundwater’s often long period of water exchange (Table 10.1) makes it useful as a stable source of water but also leads to its susceptibility to long term degradation by aquifer contamination. Groundwater supplies approximately 40 % of the water used by irrigated agriculture. Wells are drilled into high conductivity layers in geologic formations. Sand and gravel aquifers are the primary source of groundwater for irrigation. Measurement of the piezometric gradient and aquifer hydraulic conductivity enables hydrologists to calculate aquifer flow velocity and direction. The product of aquifer thickness and hydraulic conductivity is the transmissivity. The Thiem equation calculates aquifer transmissivity in confined aquifers based on steady-state pumping in a pumping well and draw down (decline in water table) in an observation well. The steady-state unconfined aquifer equation adds aquifer thickness to the equation. The Theis equation evaluates transient drawdown in an observation well.

Keywords

Aquifer Water table Confined aquifer Unconfined aquifer Specific capacity Wells 

Supplementary material

References and Resources

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Copyright information

© Springer International Publishing Switzerland 2016

Authors and Affiliations

  1. 1.Agricultural and Biosystems EngineeringUniversity of ArizonaTucsonUSA

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