PHYSICALLY BASED RAINFALL- RUNOFF MODELLING IN THE NORTHERN ETHIOPIAN HIGHLANDS:- THE CASE OF MIZEWA WATERSHED TEWODROS TAFFESE WATER RESOURCE ENGINERING ISTITUTE OF TECHNOLOGY BAHIR DAR UNIVERSITY FEBRUARY, 2012 PHYSICALLY BASED RAINFALL- RUNOFF MODELLING IN THE NORTHERN ETHIOPIA N HIGHLANDS:- THE CASE OF MIZEWA WATERSHED Thesis Submitted In Partial Fulfillment of the Requirements for the Degree of Master of Science in Water Resource Engineering. By Tewodros Taffese Advisor Birhanu Zemadim (PHD) Water Resource Engineering Institute of Technology Bahir Dar University December, 2011 The thesis titled “Physically based rainfall runoff modeling in the northern Ethiopian highlands:- the case of Mizewa Watershed” by Mr. Tewodros Taffese is approved for the degree of “Master of Science in Water Resource Engineering”. Board of Examiners Name Signature Advisor ---------------------- -------------------------- External Examiner ---------------------- -------------------------- Internal Examiner ---------------------- -------------------------- Date: -------------------- - Acknowledgment First of all I would like to thank the Almighty God for his great help during the entire study period and every aspect. I am so much grateful to Birhanu Zemadim (PHD), Matthew McCartney (PHD), Amy S.collick (PHD), Essayas Kaba (PHD candidate), Seifu Tilahun (PHD candidate), Abiyu Wale (PHD candidate), and Demeke Amena (MSc) for their advise, comment, kindness and help for the accomplishment of this study. I would like to extend my sincere gratitude to International Water Management International (IWMI) for financial support and providing every facility needed for study. I am also thankful to Amhara National Regional Water Resource and Development (ANRS – BoWRD) , ANRS – Bureau of Agriculture and National Meteorological Agency (NMA) Bahir Dar branch for their help by providing necessary data for these study. Contents List of Tables ............................................................................................................................................... iii List of Figures .............................................................................................................................................. iv List of Maps .................................................................................................................................................. v List of Abbreviations ................................................................................................................................... vi CHAPTER ONE ........................................................................................................................................... 1 1. INTRODUCTION ................................................................................................................................ 1 1.1. Back Ground ................................................................................................................................. 1 1.2. Statement of the Problem .............................................................................................................. 1 1.3. Objective ....................................................................................................................................... 2 1.3.1. Specific objectives ................................................................................................................ 2 1.4. Outline of the Research ................................................................................................................. 2 CHAPTER TWO .......................................................................................................................................... 3 2. LITRATURE REVIEW ........................................................................................................................ 3 2.1. General overview .......................................................................................................................... 3 2.2. Previous studies and approaches ................................................................................................... 4 2.3. Gaps .............................................................................................................................................. 7 CHAPTER THREE .................................................................................................................................... 11 3. MATERIALS AND METHODS .................................................................................................... 11 3.1. Description of the study Area ..................................................................................................... 11 3.1.1. Location .............................................................................................................................. 11 3.1.2. Farming System .................................................................................................................. 12 3.2. Data Collection and Preparation ..................................................................................................... 13 3.2.1. Identification of key water Resource issues ........................................................................ 13 3.2.2. Detail Review of Existing RM interventions ...................................................................... 15 3.2.3. Identification of Potential RM interventions ....................................................................... 17 3.2.4. Digital elevation Model ...................................................................................................... 19 3.2.5. Land use/Land cover ........................................................................................................... 20 3.2.6. Soil data .............................................................................................................................. 21 3.2.7. Slope ................................................................................................................................... 21 3.2.8. Parameter derivation ........................................................................................................... 22 i 3.2.9. Hydro meteorological data .................................................................................................. 24 3.2.10. Rating curve development .................................................................................................. 27 CHAPTER FOUR ....................................................................................................................................... 31 4. HYDROLOGICAL MODELLING .................................................................................................... 31 4.1. SWAT (Soil and Water Assessment Tool) ................................................................................. 31 4.1.1. Hydrologic Water Balance .................................................................................................. 31 4.1.2. SWAT-CN Method ............................................................................................................. 33 4.1.3. SWAT–WB method ............................................................................................................ 35 4.2. Model Setup ................................................................................................................................ 37 4.2.1. Watershed Delineation ........................................................................................................ 37 4.2.2. HRU Definition ................................................................................................................... 37 4.2.3. Weather Data Definition ..................................................................................................... 38 4.3. Sensitivity Analysis, Calibration and Validation ........................................................................ 38 4.4. Model Performance ..................................................................................................................... 40 4.5. General Methodology ................................................................................................................. 40 CHAPTER FIVE ........................................................................................................................................ 42 5. RESULT AND DISCUSSION ........................................................................................................... 42 5.2. Model Calibration and Validation ............................................................................................... 44 5.4. Impact of land use and soil ......................................................................................................... 52 5.5. Impact of sub watershed discretization ....................................................................................... 55 CHAPTER SIX ........................................................................................................................................... 56 6. CONCLUSION AND RECOMMENDATION .................................................................................. 56 7. References ........................................................................................................................................... 57 Appendix ......................................................................................................................................................