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sur le développement des zones arides et semi-arides

Titre : Characterisation of groundwater and surface water interaction in the eThekwini Metropolitan District, KwaZulu-Natal, South Africa.

Auteur : Mtshali, Sphindile

Université de soutenance : University of KwaZulu-Natal

Grade : Master of Science (MS) in Hydrogeology 2021

Résumé partiel
The expansion of the city of Durban is proceeding rapidly due to rural to urban population migration and economic development. The urban development has been changing the mode of groundwatersurface water interactions, groundwater recharge, and water quality. These impacts of urbanization on groundwater-surface water interaction in the eThekwini Metropolitan District including the impact on groundwater-dependent ecosystems are not well understood. This study aims to contribute towards an improved understanding of groundwater-surface water interaction in the greater eThekwini district and understand the impact of urbanization thereof. The study was conducted by collecting primary data through a serious of field measurements and sampling of rivers, wetlands, springs and groundwater and complemented by secondary data obtained from Umgeni Water, eThekwini Municipality, the Groundwater Resource Information Projects (KZN-GRIP) database of the Department of Water and Sanitation (DWS), National Groundwater Archives (NGA) and consulting reports. The web-based hydrograph analysis tool (WHAT) was used to separate baseflow components from river discharge. The hydrochemical and environmental isotope data were analysed via diagnostic plots and multivariate statistical analyses. Kriging was used to interpolate groundwater level and generate groundwater flow directions. The results of data analyses indicate that groundwater in the study area occurs mainly in intergranular and fractured aquifers. Groundwater flows from west to east, towards the Indian Ocean, following the topographic gradient. The groundwater flow converges at rivers and wetlands, indicating that groundwater discharge contributes to the flow of streams and sustains wetlands in riparian areas. The groundwater contribution to stream flow is confirmed by baseflows separated from the river discharge. However, due to variation in hydraulic heads and aquifer properties, rivers also loose water to groundwater at some reaches, recharging the groundwater. Major ion hydrochemical data indicates that groundwater samples are dominated by Na-Cl-HCO3 facies, while surface water samples are mainly Na-Mg-Ca-HCO3 water type. Durov diagram of major ion hydrochemical data shows that the hydrochemical composition of groundwater in the area is influenced by dissolution and mixing processes. The Schoeller diagram plots the hydrochemical data of groundwater, rivers, springs, and wetlands parallel to each other indicating similar origin and appears to indicate groundwater and surface water interactions.

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