Flood Risk Assessment of the Crocodile River, Mpumalanga By: Siyasanga Sauka Student No: 0504584n Supervisor: Prof. Jasper Knight A dissertation submitted to the School of Geography, Archaeology and Environmental Studies, Faculty of Science at the University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016 Student No: 0504584n DECLARATION I declare that this dissertation is my own, unaided work. It is being submitted for the degree of Master of Science at the University of the Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination in any other university. ___________________________________ Signed by: Miss S. Sauka (0504584n) i Student No: 0504584n ABSTRACT The Crocodile River East in Mpumalanga Province, South Africa, has seen three major floods in a twenty-four-month period, specifically January 2011, January 2012 and January 2013. The damage included the loss of life, damage and/or loss of public or private properties, agricultural land loss, and damage to biodiversity and river geomorphology. The purpose of this study was to understand the consequences and risks to livelihoods and river basin systems due to flooding of the river. The study focused on a segment of the Crocodile River East, between Riverside and Tekwane. The study used historic hydro-climatic data for the Crocodile River to determine the critical threshold for past flood events and to predict the extent of future flood events. Hydrological modelling coupled with the HEC-RAS hydraulic model enabled the simulation of these future flood events. The use of orthophotos and digital elevation models (DEMs) allowed for a spatial representation of the areas affected during the flood events. Flood hazard maps and flood risk maps were then developed for the identified flood events within a Geographical Information System (GIS). The maps enabled the identification of high risk and flood prone areas along this segment of the Crocodile River Basin. The results showed that when discharge reaches 241.75 m3/s, both locations (Riverside and Tekwane) are at risk to flooding. This is therefore the threshold for which the two locations are likely to be flooded. This study provides a methodology to determine the spatial extent of past and modelled future river flood events. As such, outcomes of this study may aid in the understanding of flood hazard extent and flood prone areas, and may thus help catchment management authorities and institutions in flood reconstruction and flood risk management. The employed methodology can aid effective spatial planning, and can also be extended at the basin scale through integration with the existent flood warning system to gain an estimate of flood extent and flood risk. ii Student No: 0504584n ACKNOWLEDGEMENTS I want to thank Prof. Jasper Knight for his valuable support and constantly guiding me throughout this research. In particular, I would like to thank him for providing critical and valuable comments and advice that informed this research. In spite of my relocation, he was accommodative and extremely adaptable, for which I will forever be grateful for. His help has been indispensable and I cannot imagine how I would have achieved this research without his guidance, patience and support. I would like to thank the NASA Land Processes Distributed Active Archive Centre User Services and the Customer Services Department at the USGS Earth Resources Observation and Science (EROS) for their assistance with obtaining Digital Elevation Models (DEMs) for my research. Your assistant with the various packages and with navigating the USGS website was indispensable. And lastly, I would also like to thank the Department of Water Sanitation (DWS) for making hydrological and meteorological data available on their website, without which this study would have been impossible. iii Student No: 0504584n CONTENTS PAGE ABSTRACT ......................................................................................................... II ACKNOWLEDGEMENTS .................................................................................. III LIST OF FIGURES ............................................................................................ VII LIST OF TABLES ............................................................................................... IX 1. INTRODUCTION .......................................................................................... 1 1.1 Problem Statement ................................................................................................. 3 1.2 Research Question, Aims and Objectives .............................................................. 5 1.2.1 Research Question.......................................................................................... 5 1.2.2 Research Aims ................................................................................................ 5 1.2.3 Research Objectives ....................................................................................... 6 1.3 Research Methodology ........................................................................................... 6 1.4 Structure of Dissertation .......................................................................................... 8 2. LITERATURE REVIEW .............................................................................. 10 2.1 Introduction ............................................................................................................ 10 2.2 Flood Typology ...................................................................................................... 11 2.2.1 Flood Prone Areas ........................................................................................ 12 2.2.2 Flood Frequency ........................................................................................... 12 2.3 Causes of Floods .................................................................................................. 13 2.3.1 Weather Systems .......................................................................................... 14 2.3.2 Land-Use and River Basin Characteristics ................................................... 15 2.4 Flood Risk ............................................................................................................. 18 2.4.1 Flood Risk Framework .................................................................................. 18 2.4.2 Flood Risk Assessment ................................................................................. 24 2.5 Flood Distribution and Flood Mapping .................................................................. 26 2.5.1 Hydrological Modelling .................................................................................. 27 2.5.2 Hydraulic Modelling ....................................................................................... 32 2.5.3 Geographical Information Systems ............................................................... 37 2.5.4 Flood Hazard Mapping .................................................................................. 39 2.6 Floods under Changing Climate Futures .............................................................. 41 2.6.1 Southern Africa .............................................................................................. 42 2.6.2 South Africa ................................................................................................... 44 2.6.3 Mpumalanga Province .................................................................................. 46 2.6.4 Limitations and Uncertainties of Future Climate Projections ........................ 48 2.7 Conclusions ........................................................................................................... 49 3. STUDY AREA ............................................................................................ 50 3.1 General Description of Study Area........................................................................ 50 3.2 Physical Properties of the Study Area .................................................................. 52 3.2.1 Topography ................................................................................................... 52 3.2.2 Geology ......................................................................................................... 54 iv Student No: 0504584n 3.2.3 Soil Typology ................................................................................................. 55 3.2.4 Ecology .......................................................................................................... 56 3.2.5 Land Cover and Land Use Typology............................................................. 56 3.2.6 Settlement Patterns ....................................................................................... 57 3.3 Climatological Properties of the Study Area ......................................................... 58 3.3.1 Rainfall .......................................................................................................... 58 3.3.2 Temperature .................................................................................................. 60 3.4 Hydrological Properties of the Study Area ............................................................ 61 3.5 Conclusions ........................................................................................................... 62 4. DATA ACQUISITION, ANALYSIS AND METHODOLOGY .......................