Northern aquifer probe raises stakes

The latest information available on the Ohangwena aquifer known as KOH II, shows that it holds four times the amount of water than was originally estimated and that it is twice as large.New evidence presented on the aquifer yesterday indicates that it can hold 20 billion cubic metres of water while in 2013 it was estimated to hold five billion cubic metres. The aquifer covers 5 170 square kilometres while 2013 parameters indicated it was roughly 2 500 square kilometres big. Bertman Swartz, the deputy director of geology at the agriculture ministry, presented the new evidence that has been found with core drilling on the Cubango megafan. The new knowledge on the aquifer was discovered when geologists from Germany and Namibia cut a continuous core in the centre of a huge sedimentary fan known as the Cubango megafan which comprises a former gigantic river delta in the north of Namibia.A megafan, simply put, is a large base of sediment deposited by a flowing river than fans out from a mountainous area.According to Swartz a core borehole was drilled to a depth of 400m. “The cores obtained from this drilling were the basis for a detailed lithological (rock) description and the analysis of the sediment of the aquifer.” Swartz said that is now known that the actual recharge of the aquifer is 635 000 cubic metres, while this was previously not known. This figure was estimated for the 2011/2012 season, one of the best in recent memory. Furthermore the average depth of the aquifer has been identified at 235 metres, while it was previously thought to be a little deeper at 250 metres. For every metre the water level in the borehole dropped, yields were between 0.28 and 5.29 cubic metres per hour. The average was calculated at 1.4 cubic metres per hour.“We were able to answer a lot of unanswered questions about the aquifer,” he said. Elaborating further on the groundwater project in northern Namibia and the drilling at the Cubango megafan, Swartz went into the background and objectives of the projects. He said access to safe, fresh water is the main limiting factor for the economic and social development of Namibia. “Surface water is mainly restricted to four perennial rivers at the northern and southern borders, and damming of ephemeral rivers inland. Therefore groundwater, as in many arid countries, plays a vital role for the supply of wide areas in Namibia.”According to him most of the population in the central northern areas of Namibia, and of the Cuvelai Etosha Basin, is currently supplied with drinking water by a pipeline system conveying water into the basin from the Kunene River, via the Calueque Dam in Angola. Swartz said intermittent droughts and floods and population growth has led to an increasing demand and has increased pressure on the existing water resources.Between 2007 and 2014 the project identified and delineated a vast multi-layered groundwater system, the Ohangwena Groundwater System (OGS), with its main aquifers KOH I (Kalahari Ohangwena I) and KOH II (Kalahari Ohangwena II) . “The Ohagwena Groundwater System is a high-yield aquifer system with a significant volume of stored potable water,” said Swartz. He said as part of the technical cooperation between Namibia and Germany, the German government provided financial and technical support to the project, which started in 2014 as a follow-up to the project that ran from 2007 to 2014.The target was to provide fundamental information on the groundwater potential, protection and sustainable utilisation of the Ohangwena Aquifer System to Namibian decision-makers and especially to the department for water and forestry.“For a full understanding of the aquifer system, it was essential that the properties of these aquifers and aquitards (a bed of low permeability which runs along an aquifer) were well understood, thus good drilling and coring of the system was proposed.”These results enable a detailed conceptual model of the aquifer system to be developed and to support the development of a numerical groundwater model to calculate scenarios of future water supply.He also explained that the main goal of the project is to provide fundamental information on the groundwater potential, protection and sustainable utilisation of the Ohangwena Groundwater System (OGS).It also aims to determine the potential of the Ohangwena Aquifer System and to provide information on the effect of water supply scenarios from that resource.The groundwater monitoring network in the region permits immediate assessment of the aquifer's status under production conditions.Swartz concluded that groundwater can be considered as a secure back-up supply option for the region if developed accordingly. He added that the protection and sustainable use of the resource requires careful monitoring and very close cooperation with all stakeholders. “A trans-boundary approach is the best way towards sustainability.”A sound legal framework must also be in place along with joint efforts of all stakeholders to protect the resource.Agriculture deputy permanent secretary Abraham Nehemia added the aquifer is a valuable resource to the Namibian people, as it ensures water security for the people, withstanding its proper management.Hydro-geologists will now be able to draw conclusions about production capacity of the aquifer, as we proceed into the utilization of this very important resource, Nehemia said. ELLANIE SMIT

Northern aquifer probe raises stakes

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Namibian Sun 2025-07-02

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Northern aquifer probe raises stakes

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Namibian Sun 2025-07-02

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