SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Modeling flow and nitrate fate at catchment scale in Brittany (France) 
Authors:Conan, C., F. Bouraoui, N. Turpin, G. de Marsily and G. Bidoglio 
Journal:Journal of Environmental Quality 
Volume (Issue):32(6) 
Article ID: 
URL (non-DOI journals): 
Broad Application Category:hydrologic and pollutant 
Primary Application Category:model and/or data interface 
Secondary Application Category:pollutant cycling/loss and transport 
Watershed Description:12 km^2 Coët-Dan River, located in the Province of Brittany in northwest France. 
Calibration Summary:daily 1995-96 E = .79 
Validation Summary:daily (1994, 1997-99) E = .42 --------------------------- Monthly 1994-99 E values: daily = .66 outlet = .87 subwatershed (Villeneuve sampling site) = .83 
General Comments:Study describes an interface between SWAT 99.2 and the MODLFOW groundwater model. Very minor improvement in flow resulted from coupled model approach. However, subsurface nitrate was not tracked by SWAT, which resulted in nitrate losses at the outlet being greatly underestimated. Nitrate movement was much more accurately simulated with the coupled modeling system (nitrate E = 0.87 at outlet on a monthly basis with coupled model system). Fertilizer application rate scenarios of 210 and 170 kg/ha (based on EU Nitrates Directive), relative to the baseline rate of 282 kg/ha on cropland, resulted in groundwater concentration reductions of 15 and 22 mg/L. 
Abstract:In the intensive pig-farming (Sus scrofa) area of Brittany (western France), many surface and subsurface water resources are contaminated by nitrate (NO3) with concentrations that chronically exceed the European Community 50 mg L-1 drinking standard. To ensure sustainable water supply, the fate of NO3 must be considered in both surface water and ground water. The fate of N was investigated in a Britain catchment, the Coët-Dan watershed, with an integrated management tool: the hydrological SWAT model coupled with the ground water model MODFLOW, and its companion contaminant and solute transport model MT3DMS. The model was validated with respect to water quantity during a 6-yr period and for the NO3 concentration during a 44-mo period, at two gauging stations in the catchment. The coupled models reproduced accurately the measurements. At the basin outlet, the Nash-Sutcliffe coefficients were 0.88 for monthly flow for the entire period and 0.87 for monthly N load. Alternative scenarios were simulated and showed potential benefits of decreasing manure application from 210 to 170 kg N ha-1 as required by the European Commission Nitrates Directive.