1st Edition
Understanding Catchment Processes and Hydrological Modelling in the Abay/Upper Blue Nile Basin, Ethiopia
The Abay / Upper Blue Nile basin contributes the largest share of discharge to the river Nile. However, the basin exhibits large spatio-temporal variability in rainfall and runoff. Moreover, human activities also impact hydrological processes through intensive agriculture, overgrazing and deforestation, which substantially affect the basin hydrology. Thus, understanding hydrological processes and hydro-climatic variables at various spatio-temporal scales is essential for sustainable management of water resources in the region.
This research investigates the hydrology of the basin in depth using a range of methods at various spatio-temporal scales. The methods include long-term trend analysis of hydroclimatic variables, hydrologic responses analysis of land cover change, stable isotope techniques and process based rainfallrunoff modelling. A combination of field investigations with new measurements of precipitation, water levels and stable isotopes as well as existing hydro-climatic data offered gaining new insights about runoff generation processes in headwater catchments. The use of rainfall-runoff modelling in two meso-scale catchments of the Abay basin depict that a single model structure in a lumped way for the entire Abay basin cannot represent all the dominant hydrological processes. The results of the different approaches demonstrated the potential of the methods to better understand the basin hydrology in a data scarce region.
ACKNOWLEDGEMENTS
SUMMARY
LIST OF SYMBOLS
LIST OF ACRONYMS
1 INTRODUCTION
1.1 BACKGROUND
1.2 UNDERSTANDING HYDROLOGICAL PROCESSES
1.3 HYDROLOGICAL MODELLING
1.4 PROBLEM STATEMENT
1.5 RESEARCH OBJECTIVES
1.6 DISSERTATION STRUCTURE
2 STUDY AREA: THE ABAY/UPPER BLUE NILE RIVER BASIN
3 HYDROCLIMATIC TRENDS IN THE ABAY/UPPER BLUE NILE BASIN
3.1 INTRODUCTION
3.2 STUDY AREA AND DATA SOURCES
3.2.1 Study area
3.2.2 Data sources
3.3 METHODOLOGY
3.3.1 MannKendall test
3.3.2 Pettitt test for change point detection
3.4 RESULTS AND DISCUSSION
3.4.1 Trends analysis of precipitation, temperature and streamflow
3.4.2 Analysis of change points
3.5 CONCLUSIONS
4 WATER BALANCE MODELLING OF THE UPPER BLUE NILE CATCHMENTS USING A TOPDOWN APPROACH
4.1 INTRODUCTION
4.2 STUDY AREA AND INPUT DATA
4.2.1 Study area
4.2.2 Input data
4.3 METHODOLOGY
4.3.1 The Budyko framework
4.3.2 Catchment water balance model at annual time scale
4.3.3 Catchment water balance model at monthly time scale
4.3.4 Parameter estimation, sensitivity and uncertainty assessment
4.4 RESULTS AND DISCUSSIONS
4.4.1 Annual water balance
4.4.2 Modelling streamflow on monthly timescale
4.5 CONCLUSIONS
5 HYDROLOGIC RESPONSES TO LAND COVER CHANGE: THE CASE OF JEDEB MESOSCALE CATCHMENT, ABAY/UPPER BLUE NILE BASIN, ETHIOPIA
5.1 INTRODUCTION
5.2. STUDY AREA
5.3 DATA SOURCES
5.3.1 Hydrometeorological data
5.3.2 Land use land cover data
5.4. METHODOLOGY
5.4.1 Flow variability analysis
5.4.2 Monthly Flow duration curve
5.4.3 Hydrological simulation model
5.5 RESULTS AND DISCUSSION
5.5.1 Flow variability analysis
5.5.2 Indicators of hydrologic alteration
5.5.3 The hydrological simulation model
5.5.4 Evaluation of the flow regime based on the flow duration curve
5.5.5 Effects of land use/land cover (LULC) change on streamflow
5.6 CONCLUSIONS
6 CHARACTERISATION OF STABLE ISOTOPES TO IDENTIFY RESIDENCE TIMES AND RUNOFF COMPONENTS IN TWO MESOSCALE CATCHMENTS IN THE ABAY/UPPER BLUE NILE BASIN, ETHIOPIA
6.1 INTRODUCTION
6.2. STUDY AREA
6.3 METHODOLOGY
6.3.1 Hydrometeorological data collection
6.3.2 Field measurements and sampling
6.3.3 Laboratory analysis
6.3.4 Hydrograph separation on a seasonal timescale
6.4 RESULTS AND DISCUSSION
6.4.1 Meteoric water lines
6.4.2 Spatiotemporal variation of isotope composition in precipitation, spring water and streamflow
6.4.3 Potential moisture source areas for the study area
6.4.4 Hydrograph separation on a seasonal timescale
6.4.5 Uncertainty analysis of the hydrograph separations
6.4.6 Estimation of mean residence times
6.5 CONCLUSIONS
7 CATCHMENT MODELLING THROUGH THE USE OF STABLE ISOTOPE DATA AND FIELD OBSERVATIONS IN THE CHEMOGA AND JEDEB MESOSCALE CATCHMENTS, ABAY/UPPER BLUE NILE BASIN, ETHIOPIA
7.1 INTRODUCTION
7.2. DATA SOURCE
7.2.1 The rating curve
7.3. METHODOLOGY
7.3.1 Model setup
7.3.2 Calibration of parameters
7.3.3 Constraining model parameters using isotope data
7.3.4 Parameter sensitivity and uncertainty analysis
7.4 RESULTS AND DISCUSSIONS
7.4.1 Model development
7.4.2 The value of stable environmental isotope data
7.4.3 The dominant runoff mechanism
7.4.4 Sensitivity and Uncertainty Analysis
7.4.5 Limitations of the method
7.5 CONCLUSIONS
8 CONCLUSIONS AND RECOMMENDATIONS
8.1 CONCLUSIONS
8.2 RECOMMENDATIONS
REFERENCES
APPENDIX A
APPENDIX B
SAMENVATTING
ABOUT THE AUTHOR
Biography
Mr. Sirak Tekleab Gebrekristos is a lecturer at Hawassa University, Institute of Technology, Ethiopia. By profession he is a catchment hydrologist with an engineering background working extensively on planning and designing of water resources development projects. He has been involved in designing small scale irrigation development projects in Ethiopia. From 2008 to 2014, he has worked as PhD research fellow at UNESCO-IHE/TU-Delft, The Netherlands. During the course of his PhD, he studied the Abay/Upper Blue Nile basin hydrology at various spatio-temporal scales using a combination of different methods. Moreover, he has supervised MSc students and served as a reviewer for different international journals. Furthermore, he attended the course requirement for the Research School SENSE (Socio-economic and Natural Sciences of the Environment). Mr. Sirak published several articles in peer reviewed journals and presented his research outputs at different international conferences.
His research interests include catchment processes understanding through modelling, stable isotopes for hydrological application, stochastic modelling, remote sensing application to water resources, water system analysis, surface water-groundwater interactions, climate change and water resources management.
