Windhoek, Namibia: from conceptualising to operating and expanding a MAR scheme in a fractured quartzite aquifer for the city’s water security
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The city of Windhoek lies in the centre of Namibia some 700 km from the nearest perennial river. The concept of recharging the highly complex Windhoek aquifer was first considered in 1997 as an alternative to piping water from the distant Okavango River. This fractured quartzitic aquifer was studied in detail to establish its flow characteristics and boundaries. Four borehole injection tests were conducted and they provided the confidence to design and construct the first stage of the scheme which initially included six injection boreholes with a combined recharge capacity of 10,000 m3/day. Borehole injection started in 2006 and continued until 2012 when the targeted recharge area could not receive any more water. The scheme’s success led to two expansion phases with a third planned for 2017. The expansion phases consisted of drilling additional injection boreholes and “deep” abstraction boreholes. Most of the existing abstraction boreholes are less than 250 m deep, but to maximize the aquifer’s available storage, it became necessary to drill “deep” boreholes with depths ~ 300–500 m. The first expansion phase resulted in drilling an additional ten recharge boreholes with a combined injection capacity of 16,000 m3/day and ten “deep” abstraction boreholes with a combined recovery capacity of 18,000 m3/day. The second drilling phase will be completed in June 2017. Eleven of the planned 12 “deep” abstraction boreholes have been drilled and their abstraction capacities range up to 3600 m3/day. The aim is to be able to utilize as much of the aquifer’s available storage space as possible. The source water is surface water from the city’s supply dams and a portion of reclaimed water; both of which are treated to drinking quality standards prior to recharge.
KeywordsFractured aquifer Hard-rock aquifer Borehole injection Artificial recharge Water banking, aquifer storage and recovery (ASR)
Dr R Murray, the project’s hydrogeologist, assessed the feasibility of the scheme, delineated the aquifer, assessed the storage capacity, identified the prime sites for recharge and abstraction and quantified the recharge and abstraction rates. Mr D. Louw is the municipality’s hydrogeologist and is responsible for data management. Mr B. van der Merwe initiated the pilot recharge tests (1996), made an assessment of the technical and financial viability of the project including optimization of abstraction and injection infrastructure, and is the project leader in the current expansion phase of the project. Mr H. I. Peters was responsible for the implementation and continuation of the project until the end of October 2015 when he retired from the Windhoek municipality. He is now involved as a consultant to the city of Windhoek on this project.
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