At the interface between terrestrial and aquatic ecosystems, the riparian zone plays an important role in nitrogen removal, despite the minor proportion of the land area that it covers. Very limited studies are carried out in modelling these effects at the river basin scales. The Soil and Water Assessment Tool (SWAT) is a well-known river basin scale model to simulate hydrological processes and nutrient dispersal. So far, SWAT followed a lumped approach that did not take into account the effect of the particular position of the hydrological units and their interaction, which implied that SWAT could not model riparian zones as discrete units and take into account the effects from upland areas.
This thesis presents two modifications in SWAT: (i) an approach to represent landscape variability and landscape routing across different landscape units, and (ii) a Riparian Nitrogen Model that simulates the denitrification process in riparian zones. This enhanced landscape SWAT model, referred to as SWAT_LS, was tested on a hypothetical case study and then applied to the Odense river basin, an agriculture-dominated and a densely tile-drained river basin.
Case study results show that SWAT_LS is able to evaluate the effect of denitrification in riparian zones, taking into account their specific locations as interfaces between terrestrial and aquatic ecosystems. These modifications enable the SWAT model to be used for flow and nitrogen modelling in riparian zones.
2: Literature review
3: Study area: Odense river basin, Denmark
4: Model set-ups for the Odense river basin
5: Comparison and evaluation of model structures for the simulation of flow and nitrogen fluxes in a tile-drained river basin
6: The approach to represent the landscape variability in the SWAT model
7: Integrating a conceptual riparian zone model in the SWAT model
8: Application of the SWAT_LS model in the Odense river basin
9: Conclusions and recommendations
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.