ADDIS ABABA UNIVERSITY School of Earth Sciences Groundwater Surface water Interaction along the main course of Awash River; Integrated approach A Thesis Submitted to School of Graduate Studies of Addis Ababa University In Partial Fulfillment of the requirements for Degree of Master of Science in Hydrogeology TSEDENYA AREGU TAFESSE MAY, 2018 ADDIS ABABA, ETHIOPIA Lake Afambo Addis Ababa University School of Graduate studies School of Earth Science Groundwater-Surface Water Interaction along the main course of Awash River; Integrated Approach A Thesis Submitted to School of Graduate Studies of Addis Ababa University In Partial Fulfillment of the requirements for Degree of Master of Science in Hydrogeology By Tsedenya Aregu Advisor Dr. Seifu Kebede 2018 Addis Ababa Addis Ababa University School of Graduate studies School of Earth Science Groundwater-Surface Water Interaction along the main course of Awash River; Integrated Approach By Tsedenya Aregu Approved by Board Examiners: Signature Dr. Tilahun Azagegn __________________________ (Examiner) Dr. Dessie Nadew __________________________ (Examiner) Dr. Seifu Kebede __________________________ (Advisor) Abstract In river basin hydrology the role of groundwater for being an integral part of the river basin water resources is often unrecognized. This is true in Ethiopia. Groundwater has multiple roles in river basins. It serves as source of water for socioeconomic activity, it maintains river flows during dry seasons and it could be the main pathway for solute and heat migration. In existing Awash Basin Master Plan groundwater is not accounted as one of the factor for increasing and imposing stress on existing surface water resources. There is increasing discussion among policymakers to learn more about the role of groundwater in the Awash Basin Hydrology. Through multiple methods, namely stable isotope of water (2H and 18O), isotope of Radon (222Rn), piezometeric evidences as well as field physico-chemical characteristics, investigation of groundwater surface water interaction along the main channel of Awash River has been carried out. The analysis of isotopic compositions of groundwaters from Upper Awash generally signifies, the groundwaters have similar isotopic composition to that of the present day rainfall. Whereas from middle and Lower Awash groundwaters here are mostly of older origin- because of lack of 14C data estimating the age of groundwater in the lower Awash Basin was not possible. From 222Rn measurements groundwater discharge into the river is observed, in Upper Awash, in the lower and middle Awash. There are some specific spots where groundwater discharge is noticed in the lower and middle Awash (e.g. around irrigation areas of-Wonji, Metahara and Amibara; and along thermal spring discharge zones downstream-e.g. Meteka). The Pizeometeric evidence also supports this observation. In which Upper Awash is generally a gaining river and the downstream river segments are generally loosing. Most of groundwater loss that occur in the lower part of Awash, takes place between Amibara and Mile and groundwater flows towards North Easterly direction and probably discharges into Lake Abe or into the sea or into other lower areas in Ethiopia. Evidences form various methods clearly indicate the presence of aquifer hydraulic link in the basin. This work generally showed that deep groundwater in the middle and Lower Awash can be considered as separate water resources, whereas, deep groundwaters in Upper Awash are hydraulically connected to Awash River. Therefore, areas where this interaction taking place is mapped based on the obtained results. This has a practical implication in finding way for water resource management, which can solve the current unbalanced usage of water resource. Key Words: - Awash Basin Groundwater-Surface Water interaction 222Rn Stable Isotopes Pizeometeric evidence Groundwater Management Acknowledgement Foremost, I would like to express my sincere gratitude to my advisor Dr. Seifu Kebede, for his continuous support, with his amazing patience, motivation, enthusiasm, and immense knowledge sharing. His guidance has helped me in all the time of my research work and writing of this thesis. I could not have imagined having a better advisor and mentor for this research. He also gave me the opportunity to have a support from Reach Programme. I would like to express my greatest gratitude towards Reach program that fully sponsored my research work. The whole course of the research was funded by UK Aid from the UK Department for International Development (DFID). The program has supported the research work, starting from the field work during two campaigns and after on each event of the field work the Programme has paid fees for the water sample analysis that has been carried out at Morocco Laboratory of CNESTEN. I would like to thank also, Laboratory CNESTEN, for timely report for the analysis results. I am thankful to the University of Oxford for facilitating every condition for laboratory analysis. I am heartily thankful to Dr. Meron Taye for providing me any information I was up to. My thanks and appreciations also go to my colleague and friends at ECDSW-WEDSWS for their kind co-operation and encouragement which help me in completion of this research. Finally, I would like to express my very profound gratitude to my mother and to my father and to my sisters, for providing me with unfailing support and continuous encouragement throughout my years of study and through the process of researching and writing this thesis. This accomplishment would not have been possible without them. *** This document is an output from the REACH Programme funded by UK Aid from the UK Department for International Development (DFID) for the benefit of developing countries (Aries Code 201880). However, the views expressed and information contained in it is not necessarily those of or endorsed by DFID, which can accept no responsibility for such views or information or for any reliance placed on them. Table of Contents Abstract ................................................................................................................................................. i Acknowledgement ..............................................................................................................................iii 1. Introduction ...................................................................................................................................... 1 1.1 Background ............................................................................................................................... 1 1.2 Literature review ....................................................................................................................... 3 1.3 Objectives .................................................................................................................................. 5 1.3.1 General objective ................................................................................................................. 5 1.3.2 Specific Objective ............................................................................................................... 5 1.4 Statement of the Problem .......................................................................................................... 5 1.5 Significance of the research ...................................................................................................... 5 1.6 Materials Used and Sampling .................................................................................................... 6 2. Methodologies.................................................................................................................................. 9 2.1 Radon (222Rn) ............................................................................................................................ 9 2.2 Stable Isotopes ......................................................................................................................... 11 2.3 Pizeometeric Evidences ........................................................................................................... 14 3. Characteristics of Awash Basin ..................................................................................................... 16 3.1 Location ................................................................................................................................... 16 3.2 Physiography ........................................................................................................................... 18 3.3 Climate .................................................................................................................................... 20 3.4 Land use land cover ................................................................................................................. 23 3.5 Geology ................................................................................................................................... 26 3.5.1 Geology of Awash Basin ................................................................................................... 26 3.5.2 Geomorphology of Awash Basin ...................................................................................... 28 3.5.3 Geological structures in Awash Basin ............................................................................... 32 3.6 Hydrology ...............................................................................................................................