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sur le développement des zones arides et semi-arides

Titre : A spatial-temporal conceptualization of groundwater flow distribution in a granite fractured rock aquifer within the southern supersite research catchment of the Kruger National Park

Auteur : Van Niekerk, Ashton

Université de soutenance : University of the Western Cape

Grade : Magister Scientiae - MSc (Earth Science) 2014

Résumé partiel
Understanding the hydrogeology of fractured or crystalline rocks is complicated because of complex structure and a porosity that is almost exclusively secondary. These types of geologies exhibit strong heterogeneities and irregularities contrasted in hydraulic properties, spacing and flow direction within fractured rock aquifers. Therefore it is important to develop a conceptual model based on site specific data such as the hydraulic roles between groundwater and nearby hillslope/surface water bodies in order to understand its movement within the environment. Therefore this study intends to develop a hydrogeological conceptual model associated with the dominant groundwater flow processes at a 3 rd order scale within the Kruger National Park (KNP). Electrical resistivity Tomography (ERT) surveys were conducted in the KNP in the 3 rd order supersite catchments namely the southern granite (Stevenson Hamilton). This supersite is representative of the granite geology and land systems in the Southern region of KNPThese ERT surveys were used to characterize the hydrogeological components of weathering and depth to water level using the subsurface resistivity distribution. The initial ERT surveys conducted along the 1storder hillslope suggested that the weathering depths were deeper at the riparian zone and shallower at the crest. The weathering depth at the 2nd order hillslope was expected to be deeper at the riparian zone than at the crest. The weathering depth for the 3rd order hillslope interpretation was expected to be shallower at the riparian than at the crest. The surveys illustrated low resistivity values ranging from 3-75 Ωm at a depth of 8- 12m suggesting possible depth to groundwater across the 3 hillslopes. It was interpreted that two zones of saturation could be explored for groundwater along each hillslope, namely the low resistivity (3-75 Ωm) weathered aquifer and high resistivity (1875-5484 Ωm) hard rock aquifer. The close banding of resistivity values ranging between 219-641 Ωm suggest possible depth of weathering /hard rock interface. Based on the initial ERT survey interpretations, boreholes were drilled providing actual subsurface results in the form of borehole drilling logs, water levels, hydraulic data and in-situ groundwater quality parameters. Integrating the ERT survey data with the results from the intrusive measurements enabled an updated conceptualization of groundwater flow characteristics and distribution across the southern granite supersite.

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