Mapping riparian vegetation and charactersing its groundwater dependency at the modder river government water scheme

Abstract Groundwater use by riparian vegetation transpiration commonly results in a drawdown of the water table which may significantly reduce groundwater discharge to streams and even change the status of streams from gaining to losing. Therefore, the significance of the riparian transpiration process, due to the continuously increasing demand for integrated sustainable water resources management policies, deserves great attention. It is for this reason that the present work was evoked to research the riparian groundwater dependency and consumptive groundwater use by the streamside flora. Observations of the daily groundwater multiple hydrographs, in conjunction with average daily temperature and solar radiation, indicated that the groundwater fluctuations were due to water losses from the riparian flora. The Diospyros lycioides (shrub) and Acacia karroo (tree) communities were found to be the two dominant riparian species along the subject area. However, the results indicated that only the Acacia karroo sourced their water primarily from the groundwater storage because: 1) the isotopic signature of twig xylem water was similar to that of groundwater and 2) the rooting depth was at the water table. This species was found to abstract approximately 121,100 m 3 /month from the riparian groundwater. This is considerably a voluminous abstraction which is most likely to pose a problem of water competition; therefore, groundwater dependency of the riverine flora must be considered in the formulation of any integrated sustainable water resources management policies in the subject area and/or similar areas for the co-existence of human society and nature.