VARIABLE DENSITY GROUNDWATER FLOW: HISTORICAL ACHIEVEMENTS AND FUTURE CHALLENGES (Invited Presentation)

Over the last few decades, there has been significant growth in the field of variable density flow because of global concern about the future of water and energy resources and environmental contamination. Recent exhaustive review articles on this topic by Simmons (2005), Diersch and Kolditz (2002) and Simmons et al. (2001) clearly illustrate the widespread importance, diversity and interest in applications of variable density flow phenomena in groundwater hydrology. These include seawater intrusion, fresh-saline water interfaces and saltwater upconing in coastal aquifers, subterranean groundwater discharge, dense contaminant plume migration, DNAPL studies, density driven transport in the vadose zone, flow through salt formations in high level radioactive waste disposal sites, heat and fluid flow in geothermal systems, palaeohydrogeology of sedimentary basins, sedimentary basin mass and heat transport and diagenesis, processes beneath sabkhas and salt lakes and buoyant plume effects in applied tracer tests. This presentation will discuss the importance of variable density flow phenomena, the evolution of this field of research from early developments in classical fluid mechanics through to applications in groundwater hydrology and some of the important research challenges in this field of research. It describes the major scientific contributions made by John M. Sharp Jr. to this field of science. Current challenges and opportunities in understanding, conceptualizing, predicting, measuring and explaining variable density groundwater behavior are discussed. Using examples from current research, particular challenges and solutions are described in areas of inquiry including numerical modelling and model testing, the controls of geologic heterogeneity on variable density flow processes and field scale detection of free convection.