Tritium Concentrations and Time Series Providing Insight Into the Local Recharge Regime

Seasonal variations in the tritium concentration in two shallow tribal wells in the Kalahari are seen in Fig. 10.6. Variations in tritium were noticed to follow variations in the water table. This observation provided insight into the local recharge mechanism. The tritium-rich recharge of the rainy season formed an upper layer in the aquifer. As abstraction, mainly during the dry season, advanced lower water layers were encountered, having been stored in the aquifer for several years. The seasonal tritium peak was observed to arrive at the wells several months after the rain peak. Thus the recharge water moved in the aerated zone not through conduits, but in a porous

Fig. 10.6 Seasonal variations in tritium concentration in shallow wells in the Kalahari, indicating recharge in a piston-flow mode. (From Mazor et al., 1973.)

& u medium, in a piston flow mode (section 2.1, Fig. 2.2). The time lag provided an idea of the storage capacity of the aerated zone.

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