An Investigation of Sub-soil Water Penetration in the Mokobulaan Research Catchments, South-eastern Transvaal

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Abstract
Two bore holes were sunk within the Mokobulaan hydrological research catchments in the south-eastern Transvaal to investigate the depth to which water penetrates below the soil profile. Moist material was found to exist to depths of 30 and 45 m respectively. Comparison of the amount of plant-available water in the soil profile to inferred transpiration by Eucalyptus trees during winter suggests that deeper strata below the soil profile may be an important source of water to the trees. The presence of a large, buffering soil water store could introduce lags in streamflow response to forestry management practices. Further information on the importance of sub-soil water to forest plantations is required, especially at drought-prone sites, to predict annual water use as well as periods of water deficit and reduced growth. Information on streamflow generation is also necessary to link afforestation practices to altered streamflow regimes.