C1. Macro-scale Evidence of Pore-scale Processes: The Promise and Peril seen in 40 years of Studying Fingered Flow

Abstract

Fingered flow in coarse textured media has long been studied as an exemplar system for exhibiting the interplay between gravity and capillarity at easily observable scales. Early work by Parlange and Hill explained the system using linear stability analysis of solutions to the Richard’s equation, and were able to explain the relationship between finger width and media texture. These results were largely confirmed by the doctoral work of Glass, under the supervision of Parlange and Steenhuis. However thereafter several tests of the fundamental behavioral dependencies have been seen as being inconsistent with the theory, and have remained actively examined. Recent strategies to explain fingered flow behavior have seemingly given up on mechanistic physics and invoked new sources of hydrodynamic potential based on curvature of the wetting front. Others attribute the results to an expression of time-dependency in the soil characteristic curve. This talk presents highlights of this history illustrating the outstanding issues in this field, as well as pointing out the remarkable insights and conundrums that this easily-seen behavior has evoked over the 40 years since being reported in the literature.