Considerations of past and present geological conditions are crucial for site selection of any engineering works and environmental activities. The need of engineering geological involvements in the above mentioned activities increase day to day since its commencement. Due to severe problems of water supply to the Mekelle town from other resources, Tigray Water Resource Bureau proposed the Giba dam across Elala River. As previous study shows, more than 20 micro and small dams were constructed within the Mekelle drainage basin. But most of them were failed due to many reasons and consideration of the past and present geological condition of the proposed sites. A preliminary development of the geological model of the study area and rock mass characterization of the Mekelle fault and its associated structures will minimize/reduce any unexpected risk from the past and present geological conditions at the feasibility stage. In addition, such study could be used in the future as a tool for the feasibility study of site selection for similar engineering works. This book should help for researchers , students and should be especially useful to professionals working on dam ,tunnel..etc.