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:
Chloride	Tracer	Point	Years	Recharge	Easy	Moderate	Moderate
The chloride-tracer method provides an estimate of recharge by use of a mass-balance equation. The premise of the method is that the chloride concentration of wet and dry deposition times the quantity of precipitation equals the chloride concentration of recharge times the quantity of recharge. Overland runoff is often assumed to be negligible; if not, its quantity and chloride concentration can be measured and these terms added to the equation. Long-term recharge can be estimated if the other terms are known. Significant error is inherent in the estimate of chloride concentration precipitation (including dry deposition) and in the assumption that other sources of chloride, such as road salt, are insignificant. The method is easy to apply and inexpensive.