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UNESCO-IHE Institute for Water Education, Delft (2006)

Groundwater recharge estimation and modelling of the Nyamandhlovu aquifer, Mid Zambezi basin, Zimbabwe

Sibanda T.

Titre : Groundwater recharge estimation and modelling of the Nyamandhlovu aquifer, Mid Zambezi basin, Zimbabwe

Auteur : Sibanda T.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science 2006

Résumé
The Nyamandhlovu aquifer is the main source of water in the semi arid Umguza district in Matebeleland North Province in Zimbabwe. Some water is piped to the Cityof Bulawayo to augment the urban water supplies. The rapid increase in groundwater demand for domestic and agricultural purposes coupled with an increase in population growth in the Province has initiated the need to quantify the available groundwater resources for efficient and sustainable utilisation. In order to exploit this resource in a sustainable manner with minimal impact on the environment there is a 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 the Chloride Mass Balance, Water Table Fluctuation, Groundwater Dating, Flow net Computation and Groundwater Modelling methods. The Chloride Mass Balance Method gave arecharge rate in the range of 19 to 62 mm/year with an average of 37 mm/year while the Water Table Fluctuation method gave a range of 2 to 50 mm/year. The Flow net computation and the 14C groundwater dating methods gave recharge rates of 22mm/year and 25 mm/year, respectively. Groundwater modelling also confirmed the recharge rate of 25 mm/year. Combining all the methods, an average recharge rate of25 mm/year can be considered an appropriate estimate for the study area. This represents 4.5% of the long term average annual rainfall of 555 mm in the area. The water budget from the groundwater model showed that total direct and indirect recharge into the Nyamandhlovu aquifer is 36.9 Mm3/year. The results obtained from different methods applied in recharge rate estimation give results in the same order of magnitude. The good correlation in the results obtained from both tracer and physical methods gives confidence in the results obtained. At hreshold annual rainfall of 400 mm/yr can be deduced below which recharge isnegligible.Ca-HCO3 is the dominant water type categorised as fresh groundwater occurring mainly in the recharge area. A Na-HCO3 water type occurs on the confined part of the aquifer and it shows depletion in ä18O and äH. The quality of groundwater in th eNyamandhlovu aquifer is generally good and it is suitable for domestic and agricultural consumption.

Mots clés : groundwater recharge ; groundwater modelling ; aquifer modelling ; sustainability ; Zimbabwe

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Page publiée le 26 décembre 2014, mise à jour le 19 octobre 2018