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Volume 11, Issue 1, January - March 2022
CONTENT
Chair's Foreword
The Importance of Groundwater in Africa - New Perspectives
Earth Science Events
References and Selected Reading
Chair's Foreword*
This quarter we look forward to the first international meeting of the Society (Climate Change in Africa: Geosciences and Sustainable Development) which, due to continued travel restrictions, is held online on 15th May 2022. Dr Enas Ahmed agreed to deliver a presentation on the role of Geoparks in sustainable development in Africa, particularly in regard to the achievement of SDGs for 2050, 2063 and COP27, which is to be hosted in Egypt in November 2022.
In this issue we return to the subject of African groundwater resources. In early newsletters the importance of groundwater as a source of freshwater for African communities was emphasized and readers were made aware of the online resources provided by organisations such as the International Association of Hydrogeologists [1]. In 2012 a British Geological Survey mapping research exercise revealed just how vast Africa's sources of groundwater are[2]. A more recent study in 2021 complements this work by showing that not only are these resources substantial, but also that these groundwater resources have the potential to rapidly recharge after sustained rainfall.
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| Source: US Geological Survey |
The Importance of Groundwater in Africa - New Perspectives
A recent publication by researchers presented in Environmental Letters [3] has created a new focus or even perspective on African water resources and how these ought to be managed. The findings represent a new opportunity to review how we manage groundwater to meet much of African community freshwater needs, even withstanding drought and climate change effects.
The vast resources mean that Africa's water problem is not the lack of an abundance of water resources, but rather how to extract this resource in a way which is convenient and cost effective. We are encouraged by the work of Dr Alaa Ahmed et al [4], which illustrates how groundwater in Africa could be more easily and cheaply extracted. Dr Ahmed and his team at the University of South Australia, were able to use Flinders Ranges to demonstrate how groundwater can be located without resort to expensive drilling. Using satellite imagery, geospatial techniques and adding information on drainage, rock types, fractures, and rainfall, Dr Ahmed and his team mapped the region into 3 distinct classifications for groundwater, making areas harbouring groundwater as a resource more easy to locate. For example, the study implied that the most effective groundwater recharge zones (where water collects as it moves downward) were located where there are numerous rock fractures, low drainage and a gentle slope. Conversely, the least effective groundwater recharge area, where we were then less likely to find groundwater, lay on top of shale and siltstone beds. Indeed by creating satellite maps of where groundwater is more likely to be found we go a long way to improving Africa's access to water resources at an affordable cost.
The study of Scanlon/McDonald et al[4a] is encouraging in revealing the potential for the rapid recharge of aquifers in the sub-Saharan Africa region. The study shows that even though certain sub-Saharan African aquifers face water level declines, the levels consistently and quickly recovered during rainy periods. These conclusions are based on data from a 18 year study conducted from 2002 to 2020. The robustness of the data is such as to lead one author to state quite confidently one could simply assume that these aquifers are guaranteed to recharge fully every several years. The researchers estimated that the annual groundwater recharge of the African continent exceeds the flow of the Congo, Nile, Niger and Zambezi rivers each year. According to reports this amounts to 15,000 cubic km per decade (or 1500 cubic km per year)[5].
Readers are reminded of modern studies (Pathak and Singh)[6], which avail the researcher of the mathematical tools to model the recharge of sub-Saharan African aquifers under the assumption of one-dimensional flow in unsaturated porous media on gentle slopes. For instance the authors cite the following expression of the flow through an aquifer used by Hantush and Cruz [7]
q = -K(y-mx)[dy/dx], where m = tan (theta) (1)
K is the coefficient of permeability regarded either as a constant or a function of distance in the direction of flow, x. Whilst y is distance from the floor of the aquifer perpendicular to direction of flow. The gentle slope of the floor of the aquifer is given by m, with slope angle, theta.
The study by Scanlon/McDonald et al found that most of the 13 African aquifers studied increased their storage over the period of the study. There were also swings in the water storage which were linked to climate patterns such as El Nino and the Indian Ocean Dipole, which tended to increase rainfall in East Africa; whilst La Nina climate pattern had the opposite effect decreasing rainfall in Southern Africa. West Africa saw an increase in water levels in aquifers probably due to land use changes. The researchers reported rising groundwater levels where the area of deep-rooted shrubland had been cleared for crops with shallow roots.
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References
[1] Groundwater/hydrogeology links: http://iah.org/general-public/groundwater-links-videos
[2] BBC, Science and Environment, Huge Water Resources Exist Under Africa, April 2012.
[3] Bridget Scanlon, Ahraf Rateb, Asaf Anyamba, Seifu Kibede, Alan M. McDonald, Mohammad Shamsudduha, Jennifer Small, Alexander Sun, Richard G Taylor and Hua Xie, Linkages Between GRACE Water Storage, Hydrologic Extremes and Climate Teleconnections in Major African Aquifers, Environmental Research Letters 2022.
[4] A. Ahmed, A. Alrajhi, S. Alquwaizany, Identification of Groundwater Potential Recharge Zones in Flinders Ranges, Water, 2021; 13(18): 257DOI:10.3390/w131182571
[4a] Bridget Scanlon, Alan M. McDonald et al, ibid.,
[5] Ibid.,
[6] Shreekant P. Pathak, Twinkle Singh, An Analysis on Groundwater Recharge by Mathematical Model in Inclined Porous Media, International Scholarly Research Notices, Volume 2014, Article ID 189369, 4 pages. http://dx.doi.org/10.1155/2014/189369
[7] Hantush, M. M. and Cruz, J., Hydrogeologic foundations in support of ecosystem restoration. United States Environmental Protection Agency. 1999; EPA/600/R-99/104.
*Board of the Society of African Earth Scientists: Dr Enas Ahmed (Egypt), Osmin Callis (Secretary - Guyana/Nigeria), Mathada Humphrey (South Africa), Ndivhuwo Cecilia Mukosi (South Africa), Damola Nadi (Nigeria), Dr Chukwunyere Kamalu (Chair - Nigeria).
