I. Simmers
Groundwater recharge; an overview of estimation "problems" and recent developments (in Groundwater pollution, aquifer recharge and vulnerability, Robbins,)
Geological Society Special Publications (1998), 130 107-115

Abstract:
Since the mid-1980s there has been a relative explosion of recharge studies for (semi-)arid regions reported in the scientific literature. It is therefore relevant to assess what we now know and to offer guidance to the water resources development practitioner. This paper summarizes recurring recharge estimation "problems" and reviews some recent advances in (inter alia) estimation techniques and recharge time space variability. The determination of recharge fluxes in (semi-)arid regions remains fraught with uncertainty; multiple tracer approaches appear to offer the best potential for reliable results in local studies which require "at-point" information. It is also clear that sufficient advances have been made in recent years to show that the value of water balance and Darcian approaches should not be under-estimated. The frequently studied issues of localized recharge and spatial variability need not be a problem if concern is with regional estimates. The key for the practitioner is the project objective: this will dictate whether multiple "at-point" or area-based estimation methods are appropriate. For the latter, a combination of reliable local data, remote sensing, GIS and geostatistical techniques offers considerable promise for a better understanding and determination of recharge over extended areas.