MODELING RAINFALL-RUNOFF RELATIONSHIP AND ASSESSING IMPACTS OF SOIL CONSERVATION RESEARCH PROGRAM INTERVENTION ON SOIL PHYSICAL AND CHEMICAL PROPERTIES AT MAYBAR RESEARCH UNIT, WOLLO, ETHIOPIA A Thesis Presented to the Faculty of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Masters of Professional Studies By Haimanote Kebede Bayabil August 2009 © 2009 Haimanote Kebede Bayabil ABSTRACT This study focuses on characterizing subsurface water flow and ground water table fluctuations in response to rainfall that leads to saturation excess runoff, the basic principle of variable source area hydrology In particular, this study concentrates to develop a model that efficiently simulates the location of saturated runoff areas and predict river discharge, which finally could help in realistic planning of watershed interventions Furthermore, the study assesses the impact of soil conservation research program intervention on selected physical and chemical soil properties of the study area Long-term discharge and rainfall data was available at the watershed outlet and for four test plots In addition, 29 piezometers were installed in 2008 and water table measurements were taken during the main rainy season Based on major runoff mechanisms identified at the catchment-level, a conceptual rainfall-runoff model was developed to compute runoff The model incorporates saturated excess overland flow from both bottomlands and subsoil exposed areas and baseflow and interflow from the hillsides The model was tested on a daily, weekly, and monthly basis and fitted well the discharge data at the bottom of the watershed In addition, the distributed model output agreed well with the ground water table measurements The watershed was saturated (and produced runoff) in the flat areas near the river while the hillsides were unsaturated with a perched water table that responded rapidly to rainfall Data from test plots showed that flatter areas produced more runoff than test plots at steeper slope areas The model has potential to predict runoff in ungauged basins but should be further tested to so On the other hand, soil samples were tested for selected physical and chemical properties The result indicated that AP and % OC contents of the soil were found in lower amount than before/early project intervention period, while the Db value has shown an increase BIOGRAPHICAL SKETCH Haimanote Kebede was born and raised in East Gojjam, in 1981 After successfully completing his secondary school study at Debre Markos C.S.S School, he joined Alemaya Universiy in 1999 During his four-year stay at university, he studied plant science and received his Bachelor degree in June 2003 In September 2003, he was employed by Elfora Agro Industries P.L.C where he served as Junior Agricultural Expert for eight months Then in May 2004, he moved to Finchaa Sugar Factory as a Plantation Section Manager and was assigned to manage a plantation section, including the 1300-hectare farm cultivated under irrigation and all the working staff under this section In April 2005, he had an opportunity to participate in a training entitled ‘Sugarcane Micro-Propagation Techniques’ conducted in Havana, Cuba for six months After his return to Ethiopia, he continued to work at the Finchaa Sugar Factory until he left the organization in November 2007 for his Masters degree iii iv ACKNOWLEDGMENTS First and for most I am ever grateful to the Almighty God, without his support and blessings, this piece of work would never have been accomplished My sincere gratitude goes to my major advisor Prof Tammo S Steenhuis, from Cornell University, USA, for his sympathy, encouragement, endless patience, and strong belief in me He has been sensitive and softhearted; he always tried to take care of every problem I had during my entire study and research period He was more like a friend than just a professor Dr Amy S Collick was so wonderful She helped me organize things, gave me valuable ideas, edited my manuscript, and was always in the front line to help me during hard times Thank you so much Very special thanks go to my co-advisor Dr Ingr Sileshi Bekele, East Africa Director of International Water Management Institute (IWMI), for his constructive ideas, encouragement, and worthy comments I am thankful to ARARI, for allowing me to work at the Maybar research site and providing long term hydrological and sediment data The support and help I got from Mr Derese G / Wold, former SCRP staff, was more than I could express; he was always generous, cooperative, and friendly He is an amazing person with never changing smile International Water Management Institute and Bahir Dar University are acknowledged for their financial support and Dr Ayalew Wondie helped me in facilitating the financial issues with Bahir Dar University finance division I am also greatly indebted to the technicians at Maybar Research Station: Gash Ali Ahmed, Seid Hussien, and Seid Belay They were welcoming and allowed me to share everything they have The life experience I got from them was invaluable v I would also like to thank my family for the unconditional love and support they provided me throughout my life and in particular, I must acknowledge my younger sister Nitsuh Kebede, who has always believed in my potentials, and she was the reason and my strength to join this program Finally, I would like to express my gratitude for all my friends, who have been helping and encouraging me by telephone and e-mail during the study and thesis writing periods vi TABLE OF CONTENTS BIOGRAPHICAL SKETCH III ACKNOWLEDGMENTS V TABLE OF CONTENTS VII LIST OF FIGURES X LIST OF TABLES .XII LIST OF ABBREVIATIONS XIII CHAPTER ONE RESEARCH BACKGROUND .1 STUDY AREA Location and Topography Soils Agro Climate, Land Use, and Cropping Pattern .5 REFERENCES .9 CHAPTER TWO 10 INTRODUCTION 10 MODEL DEVELOPMENT 12 MATERIALS AND METHODS 16 Discharge from Runoff Plots 17 Saturated Area Delineation .20 Data Checking and Analysis 20 MODEL EFFICIENCY EVALUATION 20 Calibration and Validation of Rainfall – Runoff Model 20 RESULTS AND DISCUSSION 21 Rainfall Amount, Intensity and Infiltration Capacity .21 vii Rainfall Intensity and Soil Infiltration Rate 23 Runoff from Test Plots 25 Groundwater in the watershed 28 Ground water level at different slope range 30 Ground water level at different land use areas 31 Simulating Watershed Discharge 32 Calibration and simulation 33 Runoff Source Area in the watershed .43 CONCLUSION .45 REFERENCES .46 CHAPTER THREE .51 INTRODUCTION 51 RESEARCH METHODS 52 Soil Sampling Techniques, Site Selection, and Sample Preparation 52 Laboratory Analyses .53 Soil Chemical Property Analyses 53 Organic Matter Content (%OC) 54 Available Phosphorous (AP) .54 Soil Physical Property Analysis 55 Bulk Density Determination (Db) .55 Statistical Analysis 56 RESULTS AND DISCUSSION 56 Available Phosphorous (AP) 56 Percentage Organic Carbon (% OC) .57 Bulk Density (Db) 58 CONCLUSION .59 viii REFERENCES .61 APPENDICES 63 ix Hypothesized Mean Difference df t Stat P(T