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In water-related science and engineering there are two similar but distinct definitions in use for drawdown. *In subsurface hydrogeology, drawdown is the change 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 water level in a man-made reservoir or tank. In either case, drawdown is the change in head or water level relative to background condition, indicating the difference in head which has occurred at a given location relative to an initial time at the same location. A record of hydraulic head through time is more generally called a hydrograph (in both groundwater and surface water). ==Effects== Aquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise.〔(【引用サイトリンク】title=Rising sea levels attributed to global groundwater extraction )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Drawdown (hydrology)」の詳細全文を読む スポンサード リンク
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