SWAT


SWAT (Soil and Water Assessment Tool) (Arnold et al., 1998) is a semi-distributed mathematical model to represent the water and nutrient cycle at the watershed scale, which is developed by the USDA-ARS (United States Department of Agriculture-Agricultural Research Service). It relies on conceptually and physically based process descriptions which describe the hydrologic and nutrient cycles in the watershed. It also contains sub-modules where agricultural practises like tillage operations, crop cultivation as well as fertilizer and pesticide applications can be simulated. This enables the model to simulate the effects of agricultural management on the water quality in watersheds. Typical SWAT applications are hydrological studies, assessment of best management practices in order to improve river water quality, scenario analysis to assess the impacts of land use and climate change on the water and nutrient balance on the watershed scale (Breuer et al., 2009 among others) as well as pollutant fate model (mainly pesticides, Holvoet et al. 2005, Holvoet et al. 2007, among others). Furthermore several studies dealing with uncertainty and sensitivity analyses of SWAT exist (Abbaspour et al., 2007, Bekele and Nicklow, 2007 among others).

Within the M3 project SWAT will serve as the main eco-hydrological model which calculates the discharge and nutrient as well as pollutant fluxes over the whole water basins The model will be applied in Luxembourg to two study catchments which are subjected to intense pressures by emissions of nutrients and micro-pollutants from agricultural and urban areas. For several river stretches of interest the hydrological and pollutant/nutrient fluxes are passed to the Aquatox model for ecotoxicological simulations.

In order to make sound predictions SWAT is verified with measured discharge data provided by the Water administration Luxembourg (AGE) and data from own monitoring campaigns in both case studies.


For the simulations of the Wark watershed information about crops cultivated in the catchment as well as information about the use of pesticides is provided by the public authorities. In this catchment simulations regarding pesticide emissions are verified by data of an auto sampler located at the outlet of the watershed and passive samplers (POCIS) distributed over the watershed at several points e.g. confluences of smaller streams.

In the case study of the Mamer catchment SWAT will be complemented by the sewer system model KOSIM-MW for urban sanitation structure inputs, since SWAT is not capable of simulation combined sewer overflows (CSO). KOSIM-MW is a software package distributed by itwh Hannover (Institut für technisch-wissenschaftliche Hydrologie GmbH). It is mainly used in Germany for designing combined sewage storage structures with the help of long-term simulations. The KOSIM modelling tool (Paulsen (1987) is designed for long-term simulations of dry weather generation, rainfall-surface runoff and transport in the sewer system in a tanks in series hydrological set-up.. The model is able to give pollutant loads (for up to 6 components) in response to individual rain events. The simulation results regarding the CSOs of KOSIM-MW are used as input data for the SWAT model. The simulations of SWAT/KOSIM-MW are verified by data from auto samplers located nearby the largest waste water treatment plant in the Mamer catchment.

The villages in the Mamer catchment are represented in aggregated model structures (see Figure) including all main components like e.g. transport sewer sections, connected population equivalents, connected area, slope, and the combined sewer overflow structures and treatment plants as emission points of the urban sewer system into the river Mamer.

The application of SWAT and KOSIM-MW provides the opportunity to get an overview over emissions of nutrients and pollutants from agricultural and urban areas. Both models will be used in a scenario analysis where different program of measures (POM) are tested in order to reach the good ecological status of river water in the context of the Water Framework Directive.

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