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University of the Witwatersrand (2021)

Surface water and groundwater interaction in the (semi-arid areas) Vredefort Dome, South Africa

Welguś, Marcja Natalja

Titre : Surface water and groundwater interaction in the (semi-arid areas) Vredefort Dome, South Africa

Auteur : Welguś, Marcja Natalja

Université de soutenance : University of the Witwatersrand

Grade : Master of Science (MS) 2021

Résumé partiel
The growing importance of groundwater as freshwater supply in semi-arid areas such as the Vredefort Dome World Heritage Site (VDHS) demands the judicious management of this vital resource. A comprehensive understanding of the mechanisms operating during hydrological connectivity is, therefore, necessary to achieve sustainable groundwater development. An integrated study based on hydrochemical multivariate statistical techniques, baseflow separation, microorganisms, stable water isotopes, and groundwater level mapping has been conducted to investigate the nature of surface water-groundwater (SW-GW) interaction under the influence of anthropogenic practices, coupled with a structurally complex geological setting. Surface water loss to the underlying fracture network was observed in the northern and south-western river reaches, underlain by metamorphosed sedimentary and lava units. These areas exhibit declining groundwater levels that are below the riverbed. The continuous wastewater discharge released into the Vaal River coupled with increased groundwater exploitation may be prompting induced recharge conditions. Analysis of seasonal baseflow from 2013 to 2016 indicates that subsurface contribution occurs primarily during the dry season (BFI 7%) as opposed to the wet season (BFI 1%). The limited baseflow that was detected has an isotopic composition consistent with springs and shallow groundwater near the channel in the south-eastern river reach, underlain by the crystalline basement complex. Principal Component Analysis reveals the combined effect of natural hydrochemical processes and anthropogenic sources as controlling factors of groundwater composition.

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