INTEGRATED MODELING OF VADOSE ZONE FLOW AND TRANSPORT PROCESSES

Authors: Van Genuchten, Martinus; SIMINEK, JIRKA - U.C. RIVERSIDE, CA

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 11/5/2004
Publication Date: 1/10/2005
Citation: Van Genuchten, M.T., Siminek, J. 2005. Integrated modeling of vadose zone flow and transport processes. Book Chapter. In: Unsaturated Zone Modeling: Progress, Challenges and Applications, Wageningen UR Frontis Series, Kluwer Academic Publishers, Dordrecht, The Netherlands. Vol. 6, Chapter 2, pp. 37-69, x-xi.

Interpretive Summary: Tremendous advances have been made during the past several decades in our understanding and ability to predict water flow and contaminant transport processes in the subsurface. We have come to a point in history where truly unique opportunities exist for developing models that integrate the most pertinent processes affecting water, heat and solute movement in the subsurface. Historically, much of the research in subsurface flow and transport has progressed mostly along disciplinary lines (e.g., soil physics, hydrogeology, geochemistry, microbiology, plant physiology). As such, physical, chemical and microbiological processes were often studied and implemented in relative isolation. The same is true for studies of surface and subsurface flow processes, and for flow and transport in the unsaturated zones and in groundwater. The introduction of increasingly powerful computers, advanced numerical methods and improved understanding of subsurface flow and transport processes, now provide tremendous opportunities for integrating the various processes involved. This paper highlights several exciting approaches for coupling physical, chemical and other processes into integrated descriptions of the subsurface, while focusing especially on the vadose zone between the soil surface and the groundwater table. Besides relatively standard current approaches for modeling flow and transport, we discuss in the paper (1) multicomponent geochemical transport, (2) colloid and colloid-facilitated transport, (3) integrated surface/subsurface modeling, and (4) process-based descriptions of preferential flow. Continued progress in the above four areas of research still requires significant advances in both numerical modeling and the underlying science.

Technical Abstract: Enormous advances have been made during the past several decades in our understanding and ability to model flow and transport processes in the vadose zone between the soil surface and the groundwater table. A large number of conceptual models are now available to make detailed simulations of transient variably-saturated water flow, heat movement and solute transport in the subsurface. In this paper we highlight four examples illustrating such advances: (1) coupling physical and chemical processes, (2) simulating colloid and colloid-facilitated transport, (3) integrated modeling of surface and subsurface flow processes, and (4) modeling of preferential flow in the subsurface. The examples show that improved understanding of underlying processes, continued advances in numerical methods, and the introduction of increasingly powerful computers now permit us to make comprehensive simulations of the most important coupled, nonlinear physical, chemical and biological processes operative in the unsaturated zone.