Comparison of Selected Methods for Estimating Groundwater Recharge In Humid Regions

Method:	Category:	Spatial Scale:	Temporal Scale:	Quantity Estimated:	Ease of Use:	Data Needs:	Cost:
Water-Table Fluctuations	Groundwater	Local	Day to Years	Recharge	Easy	Low	Low
The water-table fluctuation method provides a point value of recharge computed from the water-level rise in a well multiplied by the specific yield of the aquifer. It assumes that a water-level rise is caused by recharge arriving at the water table and that the specific yield is constant. The method is simple to apply and inexpensive if water-level records are available from existing observation wells. It should work best for wells that show a relatively rapid water-level rise in relation to the rate that water moves away from the water table. Although simple in concept, the water-table fluctuation method has drawbacks in its application related to accurate estimation of specific yield and water-level rise. Other complications include water-level rises that are not associated with recharge – such as those caused by changes in atmospheric pressure, earth tides, and entrapped air.