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Understanding and Quantifying Channel Transmission Loss Processes in the Limpopo River Basin

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UNDERSTANDING AND QUANTIFYING CHANNEL TRANSMISSION LOSS PROCESSES IN THE LIMPOPO RIVER BASIN A thesis submitted in fulfilment of the requirements for the degree of MASTER OF SCIENCE in the FACULTY OF SCIENCE of RHODES UNIVERSITY Grahamstown South Africa by Vuyelwa MVANDABA MARCH 2018 UNDERSTANDING AND QUANTIFYING CHANNEL TRANSMISSION LOSS PROCESSES IN THE LIMPOPO RIVER BASIN by Vuyelwa MVANDABA SUPERVISOR PROF D.A. HUGHES INSTITUTE FOR WATER RESEARCH, RHODES UNIVERSITY CO-SUPERVISORS DR E. KAPANGAZIWIRI COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH DR J. MWENGE KAHINDA COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH DEGREE: Master of Science (HYDROLOGY) i ABSTRACT Water availability is one of the major societal issues facing the world. The ability to understand and quantify the impact of key hydrological processes on the availability of water resources is therefore integral to ensuring equitable and sustainable resource management. A review of previous hydrological studies conducted in the Limpopo River Basin has revealed a gap in the understanding of surface water-groundwater interactions, particularly channel transmission loss processes. These earlier studies, focused largely on the Limpopo River’s main stem, have attributed the existence of these streamflow losses to the presence of significant alluvial aquifers and indicated that the losses account for about 30 percent (or 1000 Mm3 a-1) of the basin’s water balance. The work conducted in this dissertation reports on the delineation of alluvial aquifers across three sub-basins of the Limpopo River Basin namely, the Mokolo (South Africa), Motloutse (Botswana) and Mzingwane (Zimbabwe) sub-basins and the estimation of potential channel transmission losses based on the alluvial aquifer properties. Additionally, an assessment of the different approaches that can be applied to simulate these channel transmission losses in the Pitman Model is presented. To delineate alluvial aquifers, general land cover classes including alluvial aquifers were produced from Landsat-8 imagery through image classification. The areal extent of the delineated alluvial aquifers was calculated using ArcMap 10.3. To quantify channel transmission losses and determine the effects on regional water resources, three approaches using the Pitman model were applied. The three approaches include an explicit transmission loss function, the use of a wetland function to represent channel- floodplain storage exchanges and the use of a ‘dummy’ reservoir to represent floodplain storage and evapotranspiration losses. Results indicate that all three approaches were able to simulate channel transmission losses, although with differing magnitudes. Observed monthly flow data were used to ii as a means of validating loss simulations however for each sub-basin, medium and low flows were over-simulated which accounts for water uses that were inefficiently represented due to lack of data. Knowledge of the structure of the transmission loss function dictates that it is better at representing the dynamics of channel transmission losses, as it takes into account the contribution of losses to groundwater recharge whereas the other two functions simply store water and release it back to the channel. Overall, the hydrological modelling results demonstrate the potential of each approach in reproducing the dynamics of channel transmission losses between channel and alluvial aquifer within an existing sub-basin scale hydrological model. It is believed that better quantification of losses and more efficient qualitative determination of the function which best represents transmission losses, can be attained with more reliable observed data. In conclusion, a study of this nature can be beneficial to water resource estimation programmes as it highlights the uncertainties related with quantifying channel transmission loss processes in a semi-arid environment. KEYWORDS: Alluvial aquifers; Channel transmission losses; Hydrological modelling; Landsat-8; Limpopo River Basin; Pitman Model iii Declaration I declare that the dissertation entitled Understanding and Quantifying Channel Transmission Loss Processes in the Limpopo River Basin which I hereby submit for the degree of MSc (Hydrology) at Rhodes University, is my own work. I also declare that this dissertation has not previously been submitted by me for a degree at this or any other tertiary institution and that all the sources that I have used or quoted have been indicated and acknowledged by means of complete references. Vuyelwa MVANDABA iv Acknowledgements To my supervisor, Professor Denis Hughes and co-supervisors Drs. Evison Kapangaziwiri and Jean-Marc Mwenge Kahinda: I would like to thank you for your guidance and consistently clear and strategic advice. I value your critique and most importantly, your patience! To my sponsors, the Council for Scientific and Industrial Research (CSIR) and Water Research Commission (WRC) in South Africa: I have benefitted immensely from being involved in the project and hope to continue contributing to this field of work. Thank you for sponsoring my MSc journey. To my colleagues at the CSIR, Nadia Oosthuizen, Nompumelelo Mandlazi, Shirley Malema, Sabelo Madonsela: I am grateful for your moral support, assistance and friendship. To my parents, Lineo Molingoana and Ramatedile Motseko, my grandmother Matshiliso Moji, my partner, Siviwe Vutha and my friends: Thank you for the encouragement that you have given me over the years and for understanding when I had to work over weekends! To God: thank you for carrying me through this journey! v Table of Contents Chapter 1 Chapter 1 Introduction 13 1.1 Introduction and background _________________________________________________ 13 1.1.1 Water resource management in the Limpopo River Basin ________________________________ 15 1.1.2 Understanding hydrological processes in arid/semi-arid environments of southern Africa 18 1.1.3 Channel transmission losses _______________________________________________________________ 19 1.2 Problem statement and research justification _________________________________ 21 1.3 Study aim and objectives _____________________________________________________ 21 1.4 Expected Outcomes ___________________________________________________________ 23 1.5 Organisation of the dissertation ______________________________________________ 24 Chapter 2 Introduction ___________________________________________________________ 25 2.1 Introduction ___________________________________________________________________ 25 2.2 Channel transmission losses __________________________________________________ 25 2.2.1 Definition of channel transmission losses__________________________________________________ 25 2.2.2 Significance of channel transmission losses _______________________________________________ 29 2.2.3 Methods of estimating channel transmission losses ______________________________________ 29 2.2.4 Examples of estimation of transmission losses in semi-arid/arid environments __________ 31 2.2.4.1 Estimation of transmission losses in the World and Africa ___________________________ 31 2.2.4.2 Estimation of transmission losses in South Africa ____________________________________ 35 2.2.4.3 Estimation of transmission losses in the Limpopo River Basin _______________________ 38 2.3 Alluvial aquifers _______________________________________________________________ 41 2.3.1 Definition and classification of alluvial aquifers ___________________________________________ 41 2.3.2 Significance of alluvial aquifers ____________________________________________________________ 43 2.3.3 Hydrological processes associated with alluvial aquifers __________________________________ 44 2.3.4 Alluvial aquifers in the Limpopo River Basin _______________________________________________ 44 2.3.5 Alluvial aquifer delineation techniques ____________________________________________________ 45 2.4 Hydrological (Rainfall-runoff) Modelling ______________________________________ 48 2.4.1 Definition and significance _________________________________________________________________ 48 1 2.4.2 Classification of hydrological models ______________________________________________________ 49 2.4.3 Model calibration and validation __________________________________________________________ 50 2.5 Conceptual framework ________________________________________________________ 51 2.5.1 Definition and significance of a conceptual framework ___________________________________ 51 2.5.2 Components of a conceptual hydrological framework ____________________________________ 52 2.6 Closing Remarks ______________________________________________________________ 53 Chapter 3 Studyareas _____________________________________________________________ 55 3.1 Introduction ___________________________________________________________________ 55 3.2 Selection of case study areas __________________________________________________ 55 3.3 The Mokolo sub-basin ________________________________________________________ 56 3.3.1 Physiography of the Mokolo sub-basin ____________________________________________________ 56 3.3.2 Geology and soils of the Mokolo sub-basin _______________________________________________ 57 3.3.3 Climate and hydrology of the Mokolo sub-basin __________________________________________ 58 3.3.4 Water and land use in the Mokolo sub-basin _____________________________________________ 59 3.4 The Motloutse sub-basin ______________________________________________________ 60 3.4.1 Physiography of the Motloutse sub-basin _________________________________________________
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