Tuesday, November 6, 2007
184-8
Simulation of Two-Dimensional Surfactant-Induced Unsaturated Flow with Hysteretic Moisture Retention Functions.
R. Bashir1, J.E. Smith1, and E.J. Henry2. (1) Department of Civil Engineering, McMaster University, Hamilton, ON L8S 4L8, Canada, (2) Department of Geography and Geology, University of North Carolina Wilmington, Wilmington, NC 28403
In their 2002 work, Henry, Smith, and Warrick used a modified version of the HYDRUS-2D model (Simunek et al., 1999) to simulate surfactant-induced unsaturated flow and transport in a laboratory-scale experimental system. The model successfully captured the major processes associated with surfactant-induced flow during the infiltration of a surfactant solution from a point source into a shallow vadose zone. Those processes included transient drainage/rewetting associated with the advancing surfactant solute front within the unsaturated zone. As the surfactant solution reached the capillary fringe, drainage of the capillary fringe below the point source occurred, resulting in a depressed capillary fringe in the surfactant contaminated region. Finally, the drained zone propagated in the direction of groundwater flow as a “drainage wedge”, with the leading edge of the wedge corresponding approximately to the location of the surfactant solute front within the depressed capillary fringe. The wedge shape of the drainage front was due to the fact that surfactant was transported horizontally more quickly in the depressed capillary fringe than it was within the drained regions of the unsaturated zone, a mechanism that was confirmed by the numerical modeling. Differences between the numerical and experimental results were attributed, in part, to the fact that the simulations did not account for hysteresis. In the present work we revisit Henry et al. (2002) and compare their results to recent hysteretic numerical simulations in order to assess the potential importance of considering hysteresis in simulations of systems with surfactant-induced unsaturated flow.