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:
Recession-Curve Displacement	Streamflow	Watershed	Event to Years	Net Recharge	Moderate	Low	Low
The computer program RORA provides estimates of groundwater recharge from the displacement of the streamflow-recession curve from equations developed by Rorabaugh (1964) and Glover (1964). RORA estimates values of recharge for individual events on a daily basis from streamflow records, but it is recommended that results be reported at no smaller than a seasonal (3-month) time scale. The method assumes that streamflow recessions represent groundwater discharge from areal precipitation on the aquifer. Snowmelt runoff, streamflow regulation, storage and release of water from wetlands or bank storage could be other sources that affect the shape of the recession curve. Application of RORA requires an estimate of the slope of the streamflow-recession curve (recession constant K) representing periods when all streamflow is from groundwater discharge. The recession index can be computed by constructing a master-recession curve from the streamflow record by use of the program RECESS. Application to a long period of streamflow record gives an estimate of long-term average groundwater recharge.