This study aims at improving the hydrological process understanding of the semi-arid and transboundary Incomati river basin to enable better water management. Comprehensive statistical and trend analysis of rainfall and streamflow were conducted, and the Indicators of Hydrological Alteration tool was deployed to describe the streamflow regime and trends over time. Land use and land cover change, particularly the conversion of natural vegetation into forest plantation, the expansion of irrigated agriculture and the flow regulation due to dam operation were identified as critical drivers of flow regime alteration. Hydrograph separation using long-term hydrochemical data at seasonal scale, and hydrochemical and isotope data at event scale were performed to quantify runoff components. A novel methodology to calibrate recursive digital filters using routinely collected water quality data was developed and tested in the catchment. This method allows for estimation of daily baseflow from readily available daily streamflow data. Dominant runoff generation zones were mapped using the Height Above Nearest Drainage approach. The hydrological model STREAM was then employed, informed by the runoff generation zones mapping and the process understanding gained in the catchment, as well as remote sensing data. The study provides the basis for better operational water management in the catchment.
1 General introduction
1.2 Problem definition
1.3 Research objectives
1.4 Outline of the thesis
2 Description of the study area
2.1 Location and sub catchments
2.2 Topography and climate
2.3 Geology and soils
2.4 Land cover and land use
2.5 Water use, infrastructure and economy
2.7 Past research on the hydrology and water resources of the Incomati river basin
3 Drivers of spatial and temporal variability of streamflow in the Incomati river basin
4 Isotopic and hydrochemical river profile of Incomati river basin
4.2 Methods and data
4.3 Results and Discussion
5 Hydrograph separation using tracers and digital filters to quantify runoff components
5.6 Supporting documentation
6 Understanding runoff processes in a semi-arid environment through isotope and hydrochemical hydrograph separations
6.2 Study area
6.3 Data and methods
7 Hydrological modelling of the Kaap catchment
7.2 Materials and methods
8 Conclusions and recommendations
8.1 General conclusions
8.2 Main scientific contributions
8.3 Novelty of this PhD
8.4 Recommendations for future research
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.