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Estimation of Flow Characteristics of Ungauged Catchments Estimation of Flow Characteristics of Ungauged Catchments Case Study in Zimbabwe Dominic MAZVIMAVI Promotor: Prof. dr. Alfred Stein Professor of Spatial Statistics Wageningen University, Wageningen, and International Institute for Geo-information Science and Earth Observation, Enschede. Co-Promotors: Prof. dr. A.M.J. Meijerink Professor of Water Resources Surveys and Watershed Management International Institute for Geo-information Science and Earth Observation, Enschede. Prof. dr. ir. H.H.G. Savenije Professor of Water Resources Management UNESCO-IHE, Delft. Members of the Examination Committee Prof. dr. C. C. Mutambirwa, University of Zimbabwe Prof.dr. P. Troch, Wageningen University Dr. C.J.F. Ter Braak, Biometris Dr. E. Seyhan, Free University Amsterdam ii Estimation of Flow Characteristics of Ungauged Catchments Case Study in Zimbabwe Dominic MAZVIMAVI Thesis to fulfil the requirements for the degree of doctor on the authority of the rector magnificus of Wageningen University Prof.dr.ir. L. Speelman to be publicly defended on 18 December 2003 at 11.00 hours in the auditorium of ITC, Enschede ISBN 90-5808-950-9 ITC Dissertation number 107 Dominic Mazvimavi, 2003 Estimation of Flow Characteristics of Ungauged Catchments: Case Study in Zimbabwe/ Mazvimavi, D. Ph.D. Thesis, Wageningen University – with references and summaries in English and Dutch. iv ACKNOWLEDGEMENTS I have received tremendous assistance and encouragement from several people during my PhD studies in both the Netherlands and Zimbabwe. Firstly, I would like to express my gratitude to Prof. dr. A.M.J. Meijerink who accepted the challenge of supervising a student who was going to spend most of the time away from ITC, knowing fully well problems associated with such an arrangement. Several discussions we had with Prof Meijerink and his comments on several drafts of this thesis have been very illuminating. At all stages of preparing this thesis Prof Meijerink went out of his way to provide me with the necessary support. I am most grateful to Prof. dr. A. Stein for accepting to be my promotor. Prof Stein meticulously went over several drafts of this thesis, and each time I handed some material for his consideration, I always looked forward to receive his comments. Prof H.H.G. Savenije, my co-promotor, encouraged me to embark on a PhD on several occasions we met in Africa, and I am most grateful for the assistance he has provided. He always created time for discussions during his short but busy visits to the University of Zimbabwe. I am thankful to Prof D. Hughes of the Institute of Water Research, Rhodes University, South Africa, who kindly assisted me on rainfall-runoff modelling. The Institute of Water Research provided me with an office, and this is sincerely acknowledged. My PhD studies would not have been possible without the financial support provided by the Netherlands Government funded ITC/Dept of Geography & Environmental Science (University of Zimbabwe) Project on Strengthening the Masters in Environmental Policy (MEPP). Dr Herman Huizing (ITC MEPP Project Director) and Dr Charles Kunaka (Dept of Geography, University of Zimbabwe, MEPP Project Director) were instrumental in encouraging me to start on a PhD. Dr Huizing went out of his way organizing my several visits to ITC. His comments which he termed “layman comments” on my thesis were very encouraging. To both Herman and Charles, thank you. The support provided by my colleagues in the Department of Geography and Environmental Science, University of Zimbabwe, is greatly appreciated. They took over my teaching obligations despite the department not having a full staff complement. Prof C.C. Mutambirwa’s encouragement, and comments are greatly appreciated. Dr Pieter van der Zaag at the University of Zimbabwe has been very supportive over the years. He translated the English Summary of this thesis into Dutch, and I am very grateful for all the assistance that Pieter has provided. Sam Kusangaya and Tinos Madondo worked tirelessly even during i off-working hours capturing data, and I am grateful for their assistance. The University of Zimbabwe is thanked for granting me leave to undertake my PhD studies. During periods when I was at ITC, Zimbabwean students; Onisimo Mutanga, Amon Murwira, Liliosa Magombedza, Angela, Robert Maruziva, Gilbert Mhlanga and Itai made me feel at home. Onisimo, Amon and Karin, fellow PhD students have been such wonderful colleagues and I thank them. Other Zimbabweans in the Netherlands, Sam and Patience Matsangaise, Joyce Nyanyira welcomed me in their homes whenever I needed to take a break and be out of a student environment. Their support is gratefully acknowledged. Staff in the Department of Water Resources, and the Cluster Manager at ITC were helpful during my stay at ITC. I thank them all. The support provided by fellow PhD students; Mobin-ud-Din Ahmad, Masoud Kheirkhah, and Obokile Obakeng whom I shared an office with is greatly appreciated. Data used in this study were provided by the Zimbabwe National Water Authority, and the Department of Meteorological Services. The assistance provided by these organizations is gratefully acknowledged. The encouragement from several friends in Zimbabwe in particular Stan and Grace Mangoma, Charles Kunaka, Lazarus Zanamwe, Davison Gumbo, Chris and Esther Mandizvidza, Felicitus, Netsai, Gladys, Tendai and Bathsheba Biti is sincerely appreciated. I am most grateful for the support and encouragement throughout my education from my father and late mother. I am thankful for the continuous encouragement from my brothers and sisters. My PhD studies have required that every year I was in the Netherlands for about three months, during which my family had to stand on their own. I wish to express my gratitude for their sacrifice, support and encouragement. To my wife Gertrude, and children Tafadzwa, Vimbiso and Tapiwa, thank you. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS.................................................................................... i TABLE OF CONTENTS ..................................................................................... iii LIST OF FREQUENTLY USED SYMBOLS....................................................... vi 1 INTRODUCTION...................................................................................... 1 1.1 Background ............................................................................................... 1 1.2 Research objectives................................................................................... 3 1.3 Outline of the thesis .................................................................................. 4 2 THE STUDY AREA ................................................................................... 5 2.1 Introduction............................................................................................... 5 2.2 Selection of the catchments....................................................................... 8 2.3 Derivation of flow characteristics ........................................................... 11 2.3.1 Base flow and recession constant............................................................ 12 2.4 Selection and derivation of catchment characteristics ............................ 14 2.4.1 Mean annual precipitation and number of rainy days............................. 15 2.4.2 Maximum, average and minimum elevations, and relief ........................ 17 2.4.3 Slope ....................................................................................................... 18 2.4.4 Drainage density..................................................................................... 20 2.4.5 Geology................................................................................................... 22 2.4.6 Land cover...............................................................................................26 2.4.7 Normalized Difference Vegetation Index ............................................... 28 2.4.8 Evaporation ............................................................................................. 30 2.5 Flow characteristics................................................................................. 33 3 PREDICTION OF FLOW CHARACTERISTICS .................................... 37 3.1 Introduction............................................................................................. 37 3.2 Neural networks ...................................................................................... 37 3.3 Results..................................................................................................... 40 3.3.1 Correlation between flow and catchment characteristics........................ 40 3.3.2 Mean annual runoff................................................................................. 42 3.3.3 Base flow index....................................................................................... 46 3.3.4 Flow duration curves............................................................................... 50 3.3.5 Average number of days with zero flows ( N DZ )................................... 53 3.3.6 Mean monthly runoff distribution........................................................... 53 3.4 Summary ................................................................................................. 56 4 ORDINATION......................................................................................... 59 4.1 Introduction............................................................................................. 59
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