The Hydrogeology of Northern Agago County in Pader District, Uganda
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The Hydrogeology of Northern Agago County in Pader District, Uganda Groundwater Programme Open Report OR/08/040 BRITISH GEOLOGICAL SURVEY GROUNDWATER PROGRAMME OPEN REPORT OR/08/040 The Hydrogeology of Northern Agago County in Pader District, Uganda Keywords M T Graham Groundwater; Uganda; Pader; Agago; hydrogeology; weathered basement. Latitude, Longitude SW corner 33.1305E, 2.7182N NE corner 33.6596E, 3.2992N Front cover View looking NNE from Parabong mountain, towards NE Parabongo and Paimol sub- counties Bibliographical reference GRAHAM, M. 2008. The Hydrogeology of Northern Agago County in Pader District, Uganda. British Geological Survey Internal Report, OR/08/040. 30pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2008. All rights reserved Keyworth, Nottingham British Geological Survey 2008 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com BGS Central Enquiries Desk 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference email [email protected] collection of BGS publications including maps for consultation. 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Office time to carry out preparatory work and to produce this report has been funded by the British Geological Survey (BGS). Travel and subsistence costs within Uganda were met by GOAL. Acknowledgements The production of this report would not have been possible without the help of a number of individuals and organisations. Firstly, the author would like to thank Peter Goodfellow, Water and Sanitation Coordinator at GOAL Kalongo, for making this project possible, for providing much of the data used and for guidance on the local area. Thanks must also go to Chris Wardle, Programme Manager at GOAL Kalongo and all of the members of the Water and Sanitation Department working in the Kalongo office. I am indebted to the BGS, for their continued support throughout the project. In particular, I would like to thank Jeff Davies and Alan MacDonald, for the provision of advice and contacts regarding Ugandan hydrogeology. Finally, I would like to thank CESVI and the Ugandan Directorate of Water Development (DWD) in Entebbe, for the provision of additional data. i OR/08/040; Draft 1 Last modified: 2008/05/20 15:41 Contents Preface i Acknowledgements i Contents ii Summary iv 1 Introduction 5 1.1 Study Area 5 1.2 Existing Water Supplies and Requirements 6 1.3 Project Aims 6 2 Available Data 7 2.1 Existing Data 7 2.2 Data Collection 7 3 Data Interpretation 12 3.1 Overview 12 3.2 Water Strike Depth 15 3.3 Aquifer Productivity 17 4 Conclusions 22 References 23 Appendix 24 FIGURES Figure 1: a) Map of Uganda showing the study area b) The five sub-counties which constitute GOAL’s area of operation in Pader District. ...................................................... 5 Figure 2: Folded quartz vein on Parabong mountain, surrounded by medium-grained granulite. ............................................................................................................. 8 Figure 3: Coarse-grained metamorphic rock with gneissose banding on Parabong mountain. 8 Figure 4: Coarse-grained granulite, with large quartz vein on Parabong mountain .................. 9 Figure 5: a) highly weathered soil profile, Kabala b) exposure of bedrock and broken, weathered rock on Parabong mountain. ........................................................... 10 Figure 6: Idealised weathering profile (from Fookes, 1997) ................................................... 11 Figure 7: Major deposits of sand near Ogili-Parabongo mountain. ......................................... 12 ii OR/08/040; Draft 1 Last modified: 2008/05/20 15:41 Figure 8: Typical resistivity profile and geological interpretation from Awelo, showing the characteristic 'U'-shape commonly seen in areas of deeply weathered basement. .......................................................................................................................... 13 Figure 9: Variations in porosity and permeability with depth in weathered basement (Ackworth , 1987) ............................................................................................ 14 Figure 10: Leaky response in a pumping test at Lokabar ........................................................ 15 Figure 11: Predicted depth to water and recorded first water strikes across the study area ..... 16 Figure 12: Depth to recorded first water strike versus land surface curvature. There is much greater variability in water strike depth above a curvature value of around - 0.001. ................................................................................................................ 17 Figure 13: Graph of transmissivity versus depth of weathering, taken from lithological descriptions in the drilling logs ........................................................................ 18 Figure 14: Hydrogeological domains assigned to the study area ............................................. 19 Figure 15: Transmissivity data and land surface curvature across the four hydrogeological domains. ........................................................................................................... 21 iii OR/08/040; Draft 1 Last modified: 2008/05/20 15:41 Summary This report was produced to assist GOAL, an Irish NGO working in Uganda, in the provision of water supplies for displaced persons in Agago County, part of Pader District in the north of Uganda. The work contained within the report has been carried out on a voluntary basis, although considerable support has been provided by GOAL in the provision of travel and subsistence costs within Uganda, spanning the period from the 22nd September to the 12th October 2007. Funding for preparatory work and for the writing of this report was provided by the British Geological Survey (BGS). The report describes the hydrogeology of five sub-counties (Lapono, Lukole, Paimol, Parabongo and Wol) within Agago County, which cover GOAL’s area of operation for water and sanitation in Pader district. The area currently benefits from a large number of deep boreholes, although many of these have proved to be dry at the time of drilling. GOAL aims to meet the requirement for further water supplies largely through the provision of shallow, hand-dug wells. There has been no systematic geological or hydrogeological survey of the area to date and geological maps are only available at scales of 1:1,000,000 and 1:1,250,000. Further data collection during this visit has been restricted by limited exposures of rock, a lack of drill cuttings and logistical difficulties arising from poor transport and continuing security concerns. In general, however, the study area can be divided into areas of deeply weathered crystalline basement and large inselbergs, exposing a range of high-grade metamorphic rocks. Given the current emphasis on shallow well construction in the area, GIS layers of