where R(tj) (cm) is recharge occurring between times t0 and tj, Sy is specific yield (dimensionless), and DH(tj) is the peak water level rise attributed to the recharge period (cm).
Although simple in theory, some key assumptions and critical issues inherent in the WTF method have great bearing on its successful application: (1) the observed well hydrograph depicts only natural water-table fluctuations caused by groundwater recharge and discharge; (2) Sy is known and constant over the time period of the water-table fluctuations, and (3) the pre-recharge water-level recession can be extrapolated to determine DH(tj).