Drawdown (hydrology)

In hydrology, there are two similar but distinct definitions in use for the word drawdown: In subsurface hydrogeology, drawdown is the reduction in hydraulic head observed at a well in an aquifer, typically due to pumping a well as part of an aquifer test or well test. In surface water hydrology and civil engineering, drawdown refers to the lowering of the surface elevation of a body of water, the water table, the piezometric surface, or the water surface of a well, as a result of the withdrawal of water. In either case, drawdown is the change in hydraulic head or water level relative to the initial spatial and temporal conditions of the system. Drawdown is often represented in cross-sectional diagrams of aquifers. A record of hydraulic head, or rate of flow (discharge), versus time is more generally called a hydrograph (in both groundwater and surface water). The main contributor to groundwater drawdown since the 1960s is over-exploitation of groundwater resources. Drawdown occurs in response to: pumping from the bore interference from a neighbouring pumping bore in response to local, intensive groundwater pumping regional seasonal decline due to discharge in excess of recharge Aquifer is an underground layer of permeable rock or sand, that hold or transmit groundwater below the water table that yield a significant supply of water to a well. Aquifer test (or a pumping test) is a field experiment in which a well is pumped at a controlled rate and the aquifer's response (drawdown) is measured in one or more observation wells. Cone of depression is a conically-shaped depression that is produced in a water table as a result of pumping water from a well at a given rate. Groundwater is water located beneath the earth's surface in pores and fractures of soil and rocks. Hydraulic head (or piezometric head) is a specific measurement of the potential of water above a vertical datum. It is the height of the free surface of water above a given point beneath the surface. Pumping level is the level of water in the well during pumping.