Active Rain Recharge in a Desert Indicated in a Tritium Soil Profile

Figure 10.8 shows tritium profiles in soil moisture near Grootfontein, South Africa (Bredenkamp et al., 1974). A layered structure is seen, indicating a piston flow type of recharge in the soil. Another set of tritium soil profiles from the southern Kalahari, South Africa, is given in Fig. 10.9 (Verhagen et al., 1979). The value of 10 TU was adopted to indicate the arrival of the 1963 tritium front. The results of this study are of special interest in the light of a

Fig. 10.8 Variations of tritium concentration with depth in soil profiles near Grootfontein, South Africa. Such tritium profiles were an excellent means of demonstrating piston flow of infiltrating recharge water. (From Bredenkamp et al., 1974.)

long-standing controversy about whether recharge is effective at all in the sand-covered Kalahari dry land (Mazor, 1982). The 1963 recharge has penetrated 7-23 m, thus demonstrating active recharge. Profile B.H. 3 was taken below a large thorn tree. The depth of recharge penetration was only 8 m, about half the depth in the adjacent profiles. This was attributed to the water consumption of the tree.

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