|Van Genuchten, Martinus|
Submitted to: Unsaturated Zone Modeling: Progress, Applications and Challenges
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2004
Publication Date: 10/1/2004
Citation: Gardenas, A., Simunek, J., Jarvis, N., Van Genuchten, M.T. 2004. Two-dimensional field-scale modeling of pesticide transport using different preferential flow and transport approaches. Unsaturated Zone Modeling: Progress, Applications and Challenges. [Poster abstract]. Oct. 3-5, 2004, Wageningen, Frontis, Wageningen University, The Netherlands. p. 98. Interpretive Summary:
Technical Abstract: Preferential flow can have a major effect on solute transport in the unsaturated zone and significantly increase the risk of groundwater contamination by pesticides or other solutes. Many Swedish agricultural fields have an undulating or hilly topography that can produce a substantial lateral flow component along the slope. Two- or three-dimensional modeling approaches are hence very appropriate for estimating pesticide leaching from such fields. The aims of this project were to (i) investigate the importance of preferential flow and/or transport to pesticide leaching, and (ii) test which modeling approach for preferential flow and/or transport best describes the measured peaks in pesticide loadings. Four different preferential flow and/or transport approaches were included in the HYDRUS-2D software package ('imunek et al. 1999; 2003), namely an equivalent porous media approach involving composite hydraulic properties, a mobile-immobile model, a dual-porosity model, and a dual-permeability model. The preferential flow approaches were applied to the Näsby Gård field, which represents a typical agricultural area in southern Sweden. The field is part of the Vemmenhög watershed formed in a glacial till. The dominant soil type is Eutric Cambisols (FAO). The landscape is strongly undulating with sequences of hilltops and hollows within short distances. Differences in texture and organic matter content between the landscape elements (hilltop, slope and hollows) can cause the elements to contribute differently to preferential flow and transport of pesticide. A 50-m-long transect from a hollow to a hilltop was chosen to represent the entire field. Soil texture was analyzed every two meters at 4 depths down to 1 m. We modeled field drainage rates and pesticide fluxes using the different modeling approaches and compared results with measured data. The dual-permeability model was found to the most promising approach since it best mimicked the dynamics in the measured drainage flux, although it slightly overestimated the total amount of drainage. The pesticides fluxes were underestimated.