Editing Hydrograph (section)

==Subsurface hydrology hydrograph==
In subsurface hydrology ([[hydrogeology]]), a hydrograph is a record of the water level (the observed [[hydraulic head]] in wells screened across an [[aquifer]]).

Typically, a hydrograph is recorded for monitoring of heads in aquifers during non-test conditions (e.g., to observe the seasonal fluctuations in an aquifer). When an [[aquifer test]] is being performed, the resulting observations are typically called [[drawdown (hydrology)|drawdown]], since they are subtracted from pre-test levels and often only the change in water level is dealt with.