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.
Author(s): Chalachew Abebe Mulatu
Series: IHE Delft PhD Thesis Series
Publisher: CRC Press/Balkema
Year: 2022
Language: English
Pages: 158
City: Leiden
COVER
TITLE PAGE
COPYRIGHT PAGE
CONTENTS
ACKNOWLEDGMENTS
SUMMARY
SAMENVATTING
CONTENTS
1 INTRODUCTION
1.1 Background
1.2 Research Aims
1.3 Research Questions
1.4 General Approach
1.5 Structure of the Thesis
2 THE LAKE TANA BASIN
2.1 Description of the Basin
2.2 Topography, Land use and Land cover Conditions
2.3 Geology and Soil Characteristics
2.4 Rainfall and Climatic Condition
2.5 Water Resources Developments
2.5.1 Hydropower Developments
2.5.2 Irrigation Developments
2.6 Description of the Study Watersheds and River Reaches
2.6.1 The Ribb River Watershed and the River Reaches
2.6.2 The Gumara River Watershed
2.6.3 The Fogera Plain
3 MORPHODYNAMIC TRENDS OF THE RIBB RIVER PRIOR TO DAM CONSTRUCTION
3.1 Introduction
3.2 Description of Study River Reaches
3.3 Materials and Methods
3.3.1 River Flow Regime
3.3.2 Bed Level Changes and Sediment Transport Rates
3.3.3 Historical Channel Evolution
3.3.4 River Slope Adjustment to Interventions
3.3.5 Assessment of Propagation of Bed Level Adjustment to Lake Tana Regulation
3.4 Results
3.4.1 River Discharge Characterization
3.4.2 Bed Level Changes and Sediment Transport Rates
3.4.3 Historical Channel Evolution
3.4.4 River Slope Adjustment to Interventions
3.4.5 Propagation of River Bed Level Adjustment to Lake Tana Regulation
3.5 Discussion
3.5.1 River Channel Changes
3.5.2 River Response to Sand Mining and Water Withdrawal
3.5.3 Effects of the Embankments
3.5.4 Application of the Equilibrium Theory
3.6 Conclusions
4 LONG-TERM EFFECTS OF RIBB DAM OPERATION FOR IRRIGATION ON DOWNSTREAM RIVER REACHES
4.1 Introduction
4.2 Study case: The Ribb River
4.3 Material and Methods
4.3.1 Data Sources
4.3.2 Dam Operation Scenarios
4.3.3 Sediment Transport Capacity
4.3.4 Reach-Scale Morphodynamic Equilibrium Theory
4.3.5 Morphodynamic Model Application
4.4 Results
4.4.1 Pre and Post-Dam River Discharges
4.4.2 Pre and Post-Dam Reach-Averaged Sediment Transport Capacity
4.4.3 Results of the Equilibrium Theory
4.4.4 Calibration and Validation of 1D Morphodynamic Model
4.4.5 1D Model Application on the Ribb River
4.4.6 Comparison of Method Results
4.5 Discussion
4.6 Conclusions
5 ALTERATION OF THE FOGERA PLAIN FLOOD REGIME DUE TO RIBB DAM CONSTRUCTION
5.1 Introduction
5.2 Description of the Study Area
5.3 Data Sources
5.4 Methodology
5.4.1 Pre-dam Discharge Analysis
5.4.2 Post-dam Discharge Analysis
5.4.3 Pre-dam Flooding
5.4.4 HEC-RAS 2D Modeling for the Pre-and Post-dam Fogera Plain Flooding
5.4.5 Effect of the Ribb Dam on the Fogera Plain Wetlands
5.5 Results
5.5.1 Hydrological Modeling
5.5.2 Observed Pre-dam Fogera Plain Flooding
5.5.3 HEC-RAS 2D Modeling of the Pre- and Post-dam Flooding
5.5.4 Effect of River Regulation on Wetland Dynamics
5.6 Discussion
5.7 Conclusions
6 CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
6.2 Recommendations
REFERENCES
LIST OF ACRONYMS
LIST OF TABLES
LIST OF FIGURES
ABOUT THE AUTHOR
