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International Institute for Geo-Information Science and Earth Observation (ITC) 2003

Recharge and groundwater resources evaluation of the Lokalane - Ncojane basin Botswana using numerical modelling

Tefo Boyboy Rahube

Titre : Recharge and groundwater resources evaluation of the Lokalane - Ncojane basin Botswana using numerical modelling.

Auteur : Tefo Boyboy Rahube

Etablissement de soutenance : University of Twente International Institute for Geo-Information Science and Earth Observation (ITC)

Grade : Master of Science in Geo-Information Science and Earth Observation 2003

Résumé
The Kalahari, like most parts of Botswana is characterised by arid to semi-arid climatic conditions with low erratic and highly, temporally and spatially, variable rainfall. It is already known that fresh groundwater resource is available in the Ncojane-Nossop Karoo basin. To exploit this resource in a sustainable manner with minimal impact on the environment there is need to delineate the aquifers in the area and evaluate their potential in terms of water quantity, quality and replenishment. Thus, this study focuses on estimating groundwater recharge using indirect methods like hydrochemistry, iso- tope chemistry and the direct well hydrograph analysis method. A groundwater model simulated the groundwater flow system that gave a spatial recharge distribution and a water resources evaluation through the model water budget. Spatial recharge variability was assessed by the chloride balance method, which gave an average recharge value of 21.5mm/year and the carbon 14 assessment gave an average value of 0.68mm/year. The hydrograph analysis method, which gave an average value of 11mm/year, was based on four years of groundwater level fluctuations data. The results of these methods were compared to the re- sults from the ground water model, which gave a range of recharge values from 0mm/year to 1.46mm/year. The water budget from this model showed that net aerial recharge into the Ntane aqui- fer is 3.73 x10 3 m 3 /day, while the net aerial recharge into the Ecca aquifer is 2.045 m 3 /day.

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Page publiée le 4 février 2018