Author(s): Linh Hoang; Arthur Mynett; Ann Van Griensven
Linked Author(s): Arthur Mynett
Keywords: Soil-water interaction; Landscape effects on surface/groundwater; SWAT; Flow modelling; Nitrogen modelling; River basin scale hydrology
Abstract: Several eco-hydrological models have been developed to compute the water and nitrogen processes at river basin scale. These models typically use DEM to divide the basin into several sub-basins to account for the spatial variability of the soil and land use characteristics in a fully or semi -distributed way. However, these models lack the representation and proper linking of different landscape units, such as hill slopes, floodplains or wetlands. The position and the connectivity of the different landscape elements have a determining influence on the retention and transformation of many pollutants such as nitrogen. In this study, we modified the Soil and Water Assessment Tool (SWAT), a widely used open source river basin model to account for the landscape position of the Hydrological Response Units (HRUs) which are the basic modeling units used in SWAT, and to explore the routing of water and nitrogen across different landscape elements. The objectives of this study are to (i) illustrate the application of the modified SWAT in a simple hypothetical case study which covers two landscape units: upland and lowland, and (ii) carry out a sensitivity analysis on flow and nitrogen simulation using the modified model and compare with the original SWAT model. The results show the parameter sensitivit ies of the two models, which leads to the conclusion that the added routing between landscape units can affect the water volume but does not influence the flow behaviour within the sub-basins. The difference in flow results from the two models is not only caused by the two most sensitive parameters which are curve number and depth of impervious layer, but also by the area proportion of the two landscape units. When comparing the flows, the modified SWAT version can deal with more significant changes in nitrate fluxes especially when the lowland area has a high nitrogen removal capacity.