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United States Department of Agriculture

Agricultural Research Service

Title: SIMULATING UNSATURATED FLOW AND TRANSPORT IN A MACROPOROUS SOIL TO TILE DRAINS SUBJECT TO AN ENTRANCE HEAD: MODEL DEVELOPMENT AND PRELIMINARY EVALUATION

Authors
item Kohler, A - SWISS FED INST OF TECH
item Abbaspour, K - SWISS FED INST FOR EAWAG
item Fritsch, M - BOB PARTNERS GMBH
item Van Genuchten, Martinus
item Schulin, R - SWISS FED INST OF TECH

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 3, 2001
Publication Date: October 9, 2001
Citation: Kohler, A., Abbaspour, K.C., Fritsch, M., Van Genuchten, M.T., Schulin, R. 2001. Simulating unsaturated flow and transport in a macroporous soil to tile drains subject to an entrance head: model development and preliminary evaluation. Journal of Hydrology. Vol 254:67-81

Interpretive Summary: Although public awareness about environmental issues has increased sharply over the past several decades, many situations and management practices keep contributing to contamination of our soil and water resources. These include agricultural management practices such as nutrient and pesticide applications, the use of septic fields, and the construction of landfills, radioactive waste disposal sites, wastewater and sewage lagoons, and mine tailing embankments. Reliable analyses of these contamination problems require models that account for the most important physical, hydrological, and chemical processes. This study focused on two important flow processes in tile-drained agricultural fields: preferential flow and discharge through tile drains. To better account for these two processes, we extended an existing two-dimensional model (SWMS-2D) by adding a macropore flow component as well as an improved description of the flow processes at and near the tile-drain/soil boundary. The macropore component was necessary to account for water and solutes short-circuiting the soil between the soil surface and the tile drain, while the modified drain boundary condition was needed to account for the contraction of streamlines around the drains, a feature that causes delayed discharge. The model was calibrated against observed hourly discharge data from a landfill in Switzerland, and subsequently used to simulate solute transport through and from the landfill. The modified model performed satisfactorily, with the predicted tile discharge rate comparing well with results of other models. This study should be of interest to scientists and engineers trying to better understand and predict water flow and solute transport processes in tile-drained field systems.

Technical Abstract: Accurate prediction of water flow and chemical transport in agricultural soil profiles requires the use of a simulation model that considers the most important physical, hydrological and chemical processes. Two important flow-related processes in tile-drained field systems are macropore flow and water discharge from the tile drains. To better account for these two processes, we extended an existing two-dimensional model (SWMS-2D) by adding a macropore flow component as well as a Hooghoudt type boundary condition that considers the presence of an entrance head at the tile drain. The macropore component is necessary to account for water and solutes short-circuiting the soil matrix, while the drainage entrance head is needed to account for the contraction of streamlines around the drains, a feature that causes delayed discharge. The applicability of the new model to a landfill problem was examined. The simulation results, which included water flow and solute transport, compared well with other models.

Last Modified: 9/1/2014
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