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:
Stream Base Flow	Streamflow	Watershed	Years	Net Recharge	Easy	Low	Low
Base flow is the part of streamflow usually attributed to groundwater discharge. Although base flow is not recharge, it is sometimes used as an approximation of long-term recharge when underflow, evapotranspiration from riparian vegetation, and other losses of groundwater from the watershed are thought to be minimal. When used as a proxy for recharge, base flow has sometimes been referred to as “effective recharge”, “base recharge” , or “observable recharge” to acknowledge that it probably represents some amount less than that which recharged the aquifer. Numerous computerized methods of hydrograph separation have been developed, making estimates of base flow easy and inexpensive. Drawbacks are that the hydrograph separation methods are arbitrary and the base discharge may have been significantly reduced compared to the amount which recharged the aquifer.