Simulating unsaturated flow and transport in a macroporous soil to tile drains subject to an entrance head: model development and preliminary evaluation

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.