Hydrogeology Journal

, Volume 21, Issue 4, pp 905–917 | Cite as

Groundwater supply and demand from southern Africa’s crystalline basement aquifer: evidence from Malawi

Report

Abstract

Failure of borehole sources in weathered and fractured crystalline basement aquifers in Malawi in southern Africa has been linked with poor borehole design, mechanical failure and badly sited boreholes. However, recent work in Malawi indicates that demand may now exceed long-term resource potential in some places and that this is also a cause of water point failure. An 11-year climate cycle (including a wet and dry period) necessitates overdraft from groundwater storage during the dry-cycle years before episodic rainfall events in the wetter part of the cycle again recharge the aquifers. Data, particularly groundwater hydrograph data, are sparse, but sufficient to evaluate the long-term renewable groundwater potential for both fractured and weathered basement-aquifer types in each of the 15 management areas in Malawi. The groundwater potential or long-term renewable resource (recharge) is given by the sum of Darcian throughflow and dry-season depletion of storage. Estimated rural demand exceeds the renewable resource in the fractured-rock aquifer in two management units and in the weathered-rock aquifer in two other units. Although there is inherent uncertainty in the water-balance estimates, the likelihood that rural demand is exceeding long-term average recharge in some areas is cause for concern.

Keywords

Malawi Crystalline rocks Groundwater development Groundwater recharge Over-abstraction 

Offre et demande en eau de l’aquifère du socle cristallin de l’Afrique australe : exemple du Malawi

Résumé

L’insuffisance du débit des forages dans les aquifères du socle cristallin altéré et fracturé du Malawi (Afrique australe) est liée à une conception défectueuse, un défaut mécanique et une mauvaise implantation de l’ouvrage. Cependant, un travail récent au Malawi indique que la demande peut maintenant excéder la ressource potentielle de long terme en plusieurs emplacements et que c’est aussi une cause d’échec du point d’eau. Un cycle climatique de 11 ans (comprenant une période humide et une période sèche) oblige à une surexploitation de la réserve en eau souterraine pendant les années du cycle sec, avant que les événements pluvieux épisodiques de la partie plus humide du cycle rechargent de nouveau les aquifères. Les données, particulièrement les données d’hydrologie souterraine, sont rares, mais suffisantes pour évaluer le potentiel à long terme en eau souterraine renouvelable des deux types d’aquifères du socle, fracturé et altéré dans chacune des 15 zones de gestion du Malawi. Le potentiel souterrain ou ressource renouvelable à long terme (recharge) est donné par la somme de l’écoulement de Darcy et de la diminution de l’emmagasinement en saison sèche. La demande rurale estimée dépasse la ressource renouvelable de l’aquifère rocheux fracturé dans deux unités de gestion et de l’aquifère rocheux altéré de deux autres. Bien qu’il y ait une incertitude inhérente aux estimations du bilan hydrique, la probabilité que la demande rurale dépasse la recharge moyenne à long terme dans plusieurs secteurs est une cause d’inquiétude.

Abastecimiento y demanda de agua subterránea del acuífero de basamento cristalino de África del Sur: evidencia de Malawi

Resumen

El fracaso de las fuentes de agua en pozos de acuíferos del basamento cristalino fracturado y meteorizado en Malawi en África del Sur se asocia a un deficiente diseño de los pozos, a fallas mecánicas y a la mala ubicación de los pozos. Sin embargo, trabajos recientes en Malawi indican que la demanda puede exceder los recursos potenciales a largo plazo en algunos lugares y que esta también es una causa del fracaso de las fuentes de agua. Un ciclo climático de 11 años (incluyendo períodos húmedos y secos) requiere la puesta a disposición del almacenamiento de agua subterránea durante los años del ciclo seco antes que eventos de lluvias episódicas en la parte más húmeda del ciclo produzcan una nueva recarga de los acuíferos. Los datos, particularmente los datos de hidrogramas de agua subterránea, son escasos, pero suficientes para evaluar la renovabilidad potencial de agua subterránea a largo plazo para los acuíferos fracturados y meteorizados del basamento en cada una de las 15 áreas de manejo en Malawi. El potencial de agua subterránea o la renovabilidad del recurso (recarga) a largo plazo está dada por la suma del flujo Darciano y la depleción del almacenamiento en la estación seca. La demanda rural estimada excede el recurso renovable en el acuífero de roca fracturada en dos unidades de manejo y en el acuífero de roca meteorizada en otras dos unidades. Aunque hay una incertidumbre inherente a la estimación del balance de agua, la probabilidad que la demanda rural exceda a la recarga promedio a largo plazo en algunas área es causa de preocupación.

Abastecimento e procura de águas subterrâneas no aquífero cristalino basal do sul de África: evidências do Malawi

Resumo

As falhas no abastecimento de água com base em furos localizados em sistemas alterados e fraturados dos aquíferos cristalinos basais no Malawi, no sul da África, têm sido associadas à conceção deficiente de furos, a falhas mecânicas e à localização desadequada. No entanto, o trabalho recente efetuado no Malawi indica que a procura atual pode ultrapassar o potencial a longo prazo do recurso em alguns lugares, sendo esta também uma causa de falha do recurso nalguns pontos de água. Um ciclo climático de 11 anos (incluindo períodos secos e húmidos) requere a identificação dos principais locais de armazenamento de águas subterrâneas durante os anos de seca, antes de eventos episódicos de precipitação durante a época mais húmida do ciclo recarregarem novamente os aquíferos. Os dados, especialmente de níveis piezométricos, são escassos, mas suficientes para avaliar o potencial de renovação de longo prazo, tanto para as águas subterrâneas em aquíferos basais fraturados, como alterados, em cada uma das 15 áreas de gestão no Malawi. O potencial de recursos de águas subterrâneas ou de recursos renováveis de longo prazo (recarga) é dada pela soma do escoamento de Darcy e pela diminuição do armazenamento na estação seca. A procura de água estimada para abastecimento rural excede o recurso renovável no aquífero em rochas fraturadas em duas unidades de gestão e no aquífero de rochas alteradas noutras duas unidades. Embora haja incertezas inerentes às estimativas de balanços de água, o risco da procura rural de água, a longo prazo, ser superior à recarga média em algumas áreas é já um motivo de preocupação.

References

  1. Alemau BF, Chaoka TR (2010) Investigation of borehole failure: experience from Botswana. In: Xu Y, Braune E (eds) Sustainable groundwater resources in Africa. CRC, Leiden, The Netherlands, pp 177–185Google Scholar
  2. Baron J, Seward P, Seymour A (1998) The groundwater harvest potential map of the Republic of South Africa. Technical report GH 3917, Directorate of Geohydrology, Department of Water Affairs and Forestry, Pretoria, South AfricaGoogle Scholar
  3. Baumann E, Danert K (2008) Operation and maintenance of rural water supplies in Malawi. SKAT Swiss Resource Centre and Consultancies for Development, St Gallen, SwitzerlandGoogle Scholar
  4. Betson M, Robins NS (2003) Using specific capacity to assign vulnerability to diffuse pollution in fractured aquifers in Scotland. In: Krasny J, Sharp JM (eds) Groundwater in Fractured Rocks: Selected papers from the Groundwater in Fractured Rocks International Symposium, Prague, Taylor and Francis, Leiden, The Netherlands, pp 495–505Google Scholar
  5. Bredehoeft JD (2002) The water budget myth revisited: why hydrogeologists model. Ground Water 40(4):340–345CrossRefGoogle Scholar
  6. Bredehoeft JD (2007) It is the discharge. Ground Water 45(5):523–523CrossRefGoogle Scholar
  7. Carl Bro, Cowiconsult and Kampsax-Kruger (1980) Water master plans for Iringa, Ravuma and Mbeya regions, the geomorphological approach to the hydrogeology of the basement complex. Carl Bro, Cowiconsult and Kampsax-Kruger report for Danish International Development Agency. www.sadcgwarchive.net. Accessed 30 July 2012
  8. Chilton PJ, Foster SSD (1995) Hydrological characterisation and water-supply potential of basement aquifers in tropical Africa. Hydrogeol J 3:36–49CrossRefGoogle Scholar
  9. Directorate of Water Development (2001) The national rural water supply atlas, 2001. Ministry of Water, Lands and Environment, Kampala, UgandaGoogle Scholar
  10. Engineers Without Borders (2012) Improving access to clean water in Malawi. www.ewb.ca/malawi. Accessed October 2012
  11. GTZ (2007) The groundwater resources of southern province, Zambia (phase 1), vol 1: technical report. Lusaka, ZambiaGoogle Scholar
  12. Harvey PA (2004) Borehole sustainability in rural Africa: an analysis of routine field data. Appendix A: 30th WEDC International Conference, Vientiane, Laos, October 2004, 8 ppGoogle Scholar
  13. Holland M (2011) Hydrogeological characterisation of crystalline basement aquifers within the Limpopo Province, South Africa. PhD Thesis, University of Pretoria, South AfricaGoogle Scholar
  14. Houston JFT (1988) Rainfall–runoff–recharge relationships in the basement rocks of Zimbabwe. In: Simmers I (ed) Estimation of natural groundwater recharge. Riedel, Dordrecht, The Netherlands, pp 249–265Google Scholar
  15. Hydrotechnica (1985) Accelerated drought relief programme, Victoria Province, Zimbabwe. Final report, vol 2. Hydrotechnica, Shrewsbury, UKGoogle Scholar
  16. Jones MJ (1985) The weathering zone aquifers of the basement complex areas of Africa. Q J Eng Geol 18:35–46CrossRefGoogle Scholar
  17. Lerner DN, Isar AS, Simmers I (1990) Groundwater recharge: a guide to understanding and estimating natural recharge. IAH International Contributions to Hydrogeology, 8. Heise, Hannover, GermanyGoogle Scholar
  18. Lewis MF, Walker GR (2002) Assessing the potential for significant and episodic recharge in southwestern Australia using rainfall data. Hydrogeol J 10(2):229–237CrossRefGoogle Scholar
  19. Lovell CJ, Simmonds L, Waughray DK, Semple AJ, Mazhangara E, Murata MW, Brown M, Thompson DM, Chilton PJ, Macdonald DMJ, Conyers D, Butterworth JA, Mugweni O, Moriarty P, Bromley J, Batchelor CH, Mharapara I, Mugabe FT, Mtetwa G, Dube T (1998) The Romwe Catchment Study, Zimbabwe: the effects of changing rainfall and land use on recharge to crystalline basement aquifers, and the implications for rural water supply and small scale irrigation. Technical report, Institute of Hydrology, Wallingford, UKGoogle Scholar
  20. Malherbe J, Engelbrecht FA, Landman WA, Engelbrecht CJ (2012) Tropical systems from the southwest Indian Ocean making landfall over the Limpopo River Basin, southern Africa: a historical perspective. Int J Climatol 32:1018–1032CrossRefGoogle Scholar
  21. Mandeville AN, Batchelor CH (1990) Estimation of actual evapotranspiration in Malawi. Technical report, Institute of Hydrology, Wallingford, UK, 110 ppGoogle Scholar
  22. Mkandawire PP (2002) Groundwater resources of Malawi. Proceedings of International Workshop, Tripoli, Libya, June 2002, pp 101–104Google Scholar
  23. Mwafulirwa ND (1999) Climate variability and predictability in tropical Southern Africa with a focus on drier spells over Malawi. MSc Thesis, University of Zululand, South AfricaGoogle Scholar
  24. National Statistics Office (2008) 2008 population and housing census preliminary report. National Statistics Office, Zomba, MalawiGoogle Scholar
  25. Renard P, de Marsily G (1997) Calculating equivalent permeability: a review. Adv Water Resour 20(5–6):253–278CrossRefGoogle Scholar
  26. Robins NS, Davies J, Hankin P, Sauer D (2003) Groundwater and data: an African experience. Waterlines 21(4):19–21CrossRefGoogle Scholar
  27. Robins NS, Davies J, Farr JL, Calow RC (2006) The changing role of hydrogeology in semi-arid southern and eastern Africa. Hydrogeol J 14(8):1483–1492CrossRefGoogle Scholar
  28. Simmers I, Hendrickx GP, Kruseman GP, Rushton KR (1997) Recharge of phreatic aquifers in (semi-) arid areas. IAH International Contributions to Hydrogeology, 19.Balkema, Rotterdam, The NetherlandsGoogle Scholar
  29. Singhal BBS, Gupta RP (2010) Applied hydrogeology of fractured rocks, 2nd edn. Springer, HeidelbergGoogle Scholar
  30. Sophocleous M (1997) Managing water resources systems: why “Safe Yield” is not sustainable. Ground Water 35(4):561CrossRefGoogle Scholar
  31. Taljaard JJ (1996) Atmospheric circulation systems, synoptic climatology and weather phenomena of South Africa., part 6: rainfall in South Africa. South African Weather Service Technical Paper 32. South African Weather Service, Pretoria, South AfricaGoogle Scholar
  32. Titus R, Friese A, Adams S (2009) A tectonic and geomorphic framework for the development of basement aquifers in Namaqualand: a review. In: Titus R, Beekman H, Adams S, Strachan L (eds) The basement aquifers of southern Africa. Report No. TT 428–09, Water Research Commission, Pretoria, South Africa, pp 5–18Google Scholar
  33. Van Wyk E (2010) Estimation of episodic groundwater recharge in semi-arid fractured hard rock aquifers. PhD Thesis, University of the Free State, Bloemfontein, South AfricaGoogle Scholar
  34. Van Wyk E, van Tonder GJ, Vermeulen D (2011) Characteristics of local groundwater recharge cycles in South African semi-arid hard rock terrains: rainwater input. Water SA 37(2):147–154Google Scholar
  35. Wright EP (1992) The hydrogeology of crystalline basement aquifers in Africa. In: Wright EP, Burgess WG (eds) The hydrogeology of crystalline basement aquifers in Africa. Geol Soc Lond Spec Publ 66:1–28Google Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.British Geological SurveyWallingfordUK
  2. 2.Wellfield Consulting ServicesGaboroneBotswana

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