01 Jun 2022
01 Jun 2022
Status: this preprint is currently under review for the journal HESS.

Technical Note: Extending the SWAT model to transport chemicals through tile and groundwater flow

Hendrik Rathjens1, Jens Kiesel1, Michael Winchell1, Jeffrey Arnold2, and Robin Sur3 Hendrik Rathjens et al.
  • 1Stone Environmental, 535 Stone Cutters Way, 05602 Montpelier (VT), USA
  • 2USDA-ARS, Grassland Soil and Water Research Laboratory, 808 East Blackland Rd., 76502 Temple (TX), USA
  • 3Bayer AG, Research & Development Crop Science, Environmental Safety Ass. & Strategy, Building 6692 2.14, 40789 Monheim, Germany

Abstract. The SWAT model is frequently used to simulate the transport of water-soluble chemicals in the environment such as pesticides and their metabolites originating from agricultural applications. However, the model does not simulate the transport of chemicals through subsurface tile drains and groundwater. This limitation is particularly significant in lowland regions and when simulating stable chemicals that can leach to and accumulate in groundwater. To fill this gap, the publicly available SWAT code was modified to complement the simulation of chemicals by adding transport capabilities through tile and groundwater flow. The extended model was tested in two agricultural catchments with a typically used pesticide and one of its metabolites. Results show that the transport of the pesticide is mainly governed by surface runoff and that shallow surface tile flow contributions can be significant. Metabolite concentrations in streamflow are, however, driven by a complex spatial-temporal interplay of all surface and subsurface transport components. This highlights the advantages of applying the modified code in catchment-scale environmental exposure studies and for developing best management practices or mitigation strategies. The new code is made available as an electronic supplement to this technical note.

Hendrik Rathjens et al.

Status: open (until 27 Jul 2022)

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Hendrik Rathjens et al.

Model code and software

Modified SWAT code for routing chemicals through tile drains and groundwater Jeffrey Arnold, Hendrik Rathjens, Michael Winchell

Hendrik Rathjens et al.


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Short summary
The SWAT model can simulate the transport of water-soluble chemicals through the landscape, but neglects the transport through groundwater or agricultural tile drains. These transport pathways are, however, important to assess the amount of chemicals in streams. We added this capability to the model, which significantly improved the simulation. The representation of all transport pathways in the model enables watershed managers to develop robust strategies for reducing chemicals in streams.