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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.[1]
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.[2]
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[3]
- ^ "Glossary of Hydrologic Terms". www.nws.noaa.gov. Retrieved 2019-03-19.
- ^ Mirnezami, S.J.; Bagheri, A.; Maleki, A. (2018). "Inaction of Society on the Drawdown of Groundwater Resources: A Case Study of Rafsanjan Plain in Iran". Water Alternatives. 11 (3): 725–748 – via Content Server.
- ^ Lytle, Michael J.; Markowski, Paul (1989). "An Introduction to Well Drawdown" (PDF). Retrieved March 17, 2019.