Multiple data sources and integrated hydrological modelling for groundwater assessment in the Central Kalahari Basin Moiteela Lekula PhD Graduation committee: Chairman/Secretary Prof.dr.ir. A. Veldkamp University of Twente Supervisor Dr.ir. M.W. Lubczynski University of Twente Co-Supervisor Prof.dr.ing. W. Verhoef University of Twente Prof.dr. E. Shemang Botswana Int. Univ. of Science and Technology (BIUST) Members Prof.dr. Z. Su University of Twente Prof.dr. V.G. Jetten University of Twente Prof.dr. F.J. Samper Cavete University of La Coruna Prof.dr. M. Leblanc University of Avignon Prof.dr. P.K. Kenabatho University of Botswana ITC dissertation number 333 ITC, P.O. Box 217, 7500 AE Enschede, The Netherlands ISBN 978-90-365-4639-3 DOI 10.3990/1.9789036546393 Cover designed by Benno Masselink Printed by ITC Printing Department Copyright © 2018 by Moiteela Lekula MULTIPLE DATA SOURCES AND INTEGRATED HYDROLOGICAL MODELING FOR GROUNDWATER ASSESSMENT IN THE CENTRAL KALAHARI BASIN DISSERTATION to obtain the degree of doctor at the University of Twente, on the authority of the Rector Magnificus, prof. dr. T.T.M. Palstra, on account of the decision of the graduation committee, to be publicly defended on Wednesday 17 October 2018 at 14:45 hrs by Moiteela Lekula born on 7 November 1975 in Francistown, Botswana This thesis has been approved by: Dr.ir. M.W. Lubczynski, Supervisor Prof.dr. W. Verhoef, Co-supervisor Prof.dr. E. M. Shemang, Co-supervisor Acknowledgements Let me take this opportunity to extend my gratitude to all the people that directly and/or indirectly supported my PhD research. Firstly I would like to thank Botswana International University of Science and Technology (BIUST) for offering me scholarship and the then Ministry of Minerals Energy and Water resources (Now Ministry of Mineral Resources, Green Technology and Energy Security) for granting me study leave to pursue my PhD. I would like to extend my gratitude to Dr. Ir. Maciek Lubczynski for his patience and guidance from initial discussion through my PhD tour, especially technical and scientific assistance on my manuscripts. To Prof. Wouter Verhoef, for his active and timely support in my PhD. My PhD could not be successful without the fieldwork support. My sincere gratitude to Prof. Elisha M. Shemang (BIUST) for going an extra mile in providing necessary field equipment and transport logistics of top technical and scientific assistance on my manuscripts. Mr. Phemelo “Picture” Makoba for his efforts during the fieldwork campaigns, especially during equipment setup and data downloads. You are a star Picture and God will bless you more. Mr. Ofentse Gabaitse and Ms Tshiamo Motlhetlhi, Ghanzi DWA, for extending their helping hands during the fieldwork. BIUST drivers who made sure that I access my study area with ease. Addition data was also vital for the successful completion of my PhD. Special thanks goes to the Department of Meteorological Services, Botswana, which provided the rain gauge data used in this study. Dr. Nicolas Novella from National Oceanic and Atmospheric Administration (NOAA) is highly acknowledged for proving information on RFE processing. The developers and managers of the free online databases of the satellite-based rainfall products used in this study, are also acknowledged. Special thanks also goes to the Department of Water Affairs in Botswana, Botswana Geoscience Institution, Debswana Diamond Mining Company, especially Mr. Banda Maswabi, Mr. Tefo Rahube, Mr. Ceasor Sebina and Mr. Obone Mabote, and Directorate of Water Resources Management in Namibia, for providing the geological and hydrogeological data, which made this study possible. Dr Richard G Niswonger and Dr Richard B Winston from USGS are highly acknowledged for the interactive discussion about the UZF1 package during the groundwater flow model development. Additionally, I am thankful to all my PhD colleagues at ITC, who we interacted a lot especially in the WPW sessions. To Cesar Cisneros Vaca, Peiqi Yang, Tebogo Sox Masaka, Webster Gumindoga, Donald Rwasoka, Sammy Njuki, Marc Manyifika, Margaret Kimani, Chandra Ghimire, Tina Butt-Castro and Anke De Koning, you made my stay in water resources comfortable and I will miss you. All ITC hotel staff members are acknowledged for making it may second home. I would like to also extend my sincere gratitude to the many people that I have not mentioned by name whose contribution was fundamental in the success of my PhD. Finally, I would like to thank my wife Keitimetse Maopere Lekula for taking care of my daughter Katlego and my son Letshwao Larona during the tough times through my PhD trajectory. ii Table of Contents Acknowledgements ............................................................................... i List of figures ...................................................................................... v List of tables..................................................................................... viii List of symbols and abbreviations .......................................................... ix Chapter 1 : General introduction ............................................................1 1.1 Background ...........................................................................1 1.2 Research problem and objectives ..............................................3 1.3 Thesis outline .........................................................................4 Chapter 2 : Description of study area ......................................................7 2.1 Study area .............................................................................7 2.1.1 General geology ..................................................................8 2.1.1.1 Pre-Karoo Groups .............................................................9 2.1.1.2 Karoo Supergroup ............................................................9 2.1.1.3 Post Karoo Group (Kalahari Sand) .................................... 12 2.1.2 Structural geology ............................................................ 12 2.1.3 Hydrogeology .................................................................. 12 Chapter 3 : Hydrogeological conceptual model of large and complex sedimentary aquifer systems – the Central Kalahari Basin. ....................... 15 3.1 Abstract .............................................................................. 15 3.2 Introduction ......................................................................... 16 3.3 Methodology of setting up CKB conceptual model ...................... 18 3.3.1 Borehole and spatial data ................................................... 18 3.3.2 Geological modelling and hydrostratigraphic units .................. 18 3.3.3 System parameterization .................................................... 20 3.3.4 Flow system analysis ......................................................... 20 3.3.5 Preliminary water balance ................................................... 21 3.3.6 Hydrogeological boundary conditions .................................... 21 3.4 CKB conceptual model ........................................................... 21 3.4.1 Geological modelling and hydrostratigraphic units .................. 21 3.4.2 System parameterization .................................................... 26 3.4.3 Flow system, water balance and hydrogeological boundary conditions ........................................................................ 28 3.4.3.1 Kalahari Sand Unit (KSU) ................................................ 28 3.4.3.2 Lebung Aquifer (LA) ....................................................... 29 3.4.3.3 Ecca Aquifer (EA) ........................................................... 31 3.4.3.4 Ghanzi Aquifer (GA) ....................................................... 32 3.5 Discussion ........................................................................... 33 3.6 Conclusions .......................................................................... 37 Chapter 4 Validation of satellite-based rainfall in Kalahari......................... 39 4.1 Abstract .............................................................................. 39 4.2 Introduction ......................................................................... 40 4.3 Datasets .............................................................................. 42 iii 4.3.1 Meteorological data ............................................................ 42 4.3.2 Satellite data .................................................................... 43 4.4 Methodology ........................................................................ 44 4.4.1 Satellite rainfall evaluation .................................................. 44 4.4.1.1 Scatter plots .................................................................. 45 4.4.1.2 Descriptive statistics ....................................................... 45 4.4.1.3 Categorical statistics ....................................................... 45 4.4.1.4 Bias decomposition ......................................................... 46 4.4.2 Spatio-temporal variability of rainfall in CKB .......................... 47 4.4.3 Bias correction .................................................................. 48 4.5 Results and discussion ........................................................... 49 4.5.1 Satellite rainfall evaluation .................................................. 49 4.5.2 Bias decomposition ............................................................ 53 4.5.3 Spatio-temporal variability