This study assessed the downstream river system adaptation in response to upstream damming on the Ribb River, Ethiopia, to irrigate 15,000 ha. It combined primary and secondary data, and the application of remote sensing and mathematical modeling. The pre-dam morphodynamic trends of the Ribb River were analyzed for 59 years based on aerial photographs, satellite images, and newly collected field data. Three dam operation scenarios were developed to analyze the long-term hydro-morphological effects of the dam on the downstream river reaches. It also assessed the applicability of physics-based analytical equations (Equilibrium Theory) compared to a 1D numerical model (SOBEK-RE) to determine the least-morphologically impactful dam operation scenario on the river reaches downstream of the dam. Moreover, a HEC-RAS 2D hydrodynamic model was developed to assess the effect of the dam on the flooding extent of the Fogera Plain. This was used to study the potential implications of hydrological alteration on the ecology of the floodplain wetlands, as they are the habitats of important fish and bird species. The results contribute to knowledge on the hydro-morphological and environmental impacts of dams on downstream river systems. The developed methodologies and findings may be used to study future hydro-morphological and ecological changes that may arise due to other dam operations or climate change.

Chalachew Abebe Mulatu was born in Dangila, Ethiopia, in 1977. He obtained his B.Sc. degree in Hydraulic Engineering from Arba Minch Water Technology Institute, Ethiopia, and M.Sc. degree in Water Science and Engineering, specialization Hydraulic Engineering and River Basin Development, from UNESCO-IHE, Delft, the Netherlands. His Ph.D. research work focuses on the effects of dam construction on the downstream river system, focusing on the Ribb River, Ethiopia. He has been working for more than 16 years in different governmental and non-governmental organizations in Amhara Region, Ethiopia, mainly on capacity development, and as a team leader and design, engineer to study and design water resources projects. In May 2009, he joined the Faculty of Civil and Water Resources Engineering, Bahir Dar Institute of Technology, Bahir Dar University in a position of lecturer. He has been the Director for the school of Civil and Water Resources Engineering from October 4, 2011, to December 24, 2012. He teaches Hydraulic Structure-II and Embankment Dam Engineering for Postgraduate Hydraulic Engineering students, and hydraulic structure-I and II, and hydropower development for an undergraduate student. He has been the main advisor for two M.Sc. students in river morphology and sediment transport. Moreover, he is a co-founder of KIM FC Water Works Consultancy PLC, registered in Category Five, which provides engineering consultancy services in study, design, and construction supervision of Irrigation and water supply systems since 2011. His research interest includes sediment transport and river morphology, flood modeling, and water resources management and modeling.