General Characteristics
Most commonly an aquifer test is conducted by pumping water from one well at a steady rate and for at least one day, while carefully measuring the water levels in the monitoring wells. When water is pumped from the pumping well the pressure in the aquifer that feeds that well declines. This decline in pressure will show up as drawdown (change in hydraulic head) in an observation well. Drawdown decreases with radial distance from the pumping well and drawdown increases with the length of time that the pumping continues.
The aquifer characteristics which are evaluated by most aquifer tests are:
- Hydraulic conductivity The rate of flow of water through a unit cross sectional area of an aquifer, at a unit hydraulic gradient. In English units the rate of flow is in gallons per day per square foot of cross sectional area.
- Specific storage or storativity: a measure of the amount of water a confined aquifer will give up for a certain change in head;
- Transmissivity The rate at which water is transmitted through a unit thickness of an aquifer under a unit hydraulic gradient. It is equal to the hydraulic conductivity times the thickness of an aquifer;
Additional aquifer characteristics which are sometimes evaluated, depending on the type of aquifer, include:
- Specific yield or drainable porosity: a measure of the amount of water an unconfined aquifer will give up when completely drained;
- Leakage coefficient: some aquifers are bounded by aquitards which slowly give up water to the aquifer, providing additional water to reduce drawdown;
- The presence of aquifer boundaries (recharge or no-flow) and their distance from the pumped well and piezometers.
Read more about this topic: Aquifer Test
Famous quotes containing the word general:
“The man who would change the name of Arkansas is the original, iron-jawed, brass-mouthed, copper-bellied corpse-maker from the wilds of the Ozarks! He is the man they call Sudden Death and General Desolation! Sired by a hurricane, dam’d by an earthquake, half-brother to the cholera, nearly related to the smallpox on his mother’s side!”
—Administration in the State of Arka, U.S. public relief program (1935-1943)