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Both physical and chemical methods have been used to estimate recharge in arid and semiarid areas. Our review indicates that indirect, physical approaches, such as water balance and Darcy flux measurements, are the least successful, while methods using tracers (e.g., Cl, 3H, and 36Cl) have been the most successful in estimating ground‐water recharge in dry regions. Lysimeters, which can directly measure root‐zone drainage, have been useful in quantifying recharge, particularly for coarse soils, but are costly to construct and operate. Of the tracer techniques available, Cl balance techniques appear to be the simplest, least expensive, and most universal for recharge estimation. In Australian studies, under native vegetation in semiarid areas, Cl profiles were found to be remarkably uniform, indicating very low and relatively uniform rates of groundwater recharge. Following changes in land use, recharge appeared to become much more variable, increasing more than two orders of magnitude. Methods for scaling point estimates of recharge to large areas using indirect techniques (such as nondestructive electromagnetic induction) have also been developed. In deep unsaturated zones, the pressure response in the soil water may be recorded in the profile, and simple field measurements may be used to obtain semi‐independent verification of recharge rates determined by using Cl balance techniques.

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A portion of the Gambier Plain underlain by an unconfined aquifer with readily definable hydrologic boundaries has been divided into a number of areas within which soil types have similar hydrologic properties. Mean annual recharge has been estimated for each area using both the tritium concentration and the chloride concentration of water within the soil profile. Good agreement was obtained between the two methods with local recharge varying between 50 and 250 mm year-1. Total mean annual recharge for the area has been estimated to be 2.4 � 0.3 x 108 m3 year-1, and this compares favourably with an estimated discharge of 2.5 � 0.3 x 108 m3 year-1.