A Century of Denial: Preferential and Nonequilibrium Water Flow in Soils, 1864‐1984

Abstract

This review provides a historical summary of the development of knowledge on preferential and non-equilibrium flows in soils, particularly in the period 1864 to 1984. It is pointed out that preferential flows were recognized long before the equilibrium concepts of Edgar Buckingham and Lorenzo A. Richards were developed and became the dominant underpinnings of soil physics in the 20th century, effectively in denial of all the evidence that the Buckingham-Richards theory was inadequate to deal with water flows in field soils. Summaries of evidence from soil microscopy, tracing and breakthrough curve experiments, infiltration and throughflow observations, and studies of natural pipes are presented. Approaches to modeling preferential flows at soil profile and hillslope responses are also reviewed, including viscous flow theory and particle tracking methods. Further research is required into the integration of viscosity and capillarity-dominated flows, into nonlaminar flows in larger pores, and into upscaling from core and profile experiments to larger hillslope scales. Also, more rigorous hypothesis testing is required in soil physics and hillslope hydrology using both flow and tracer data. This might lead to a new paradigm in representing the detail complexity of flow in soils in applications at larger scales.Abbreviations: ADE, advection-dispersion equation; B-R, Buckingham-Richards.Lancaster Environment Centre, Lancaster Univ., Lancaster LA1 4YQ, UK. *Corresponding author (k.beven@lancaster.ac.uk).

Land cover effects on soil infiltration capacity measured using plot scale rainfall simulation in steep tropical lowlands of Central Panama

“…The soil beyond the immediate vicinity of this decayed root cast did not show any seepage and was not saturated. These field observations and measurements are evidence that surface runoff and macropore flow in the ASP can occur regardless of saturation conditions, as has been shown in other field and theoretical work (Beven, ; Beven & Germann, ; Jarvis, ).…”

Viscosity Controls Rapid Infiltration and Drainage, Not the Macropores

“…Beven (2018) [28] argued that, for about a century, the hardly questioned preference given to capillarity denied recognition of concepts considering flow along macropores, pipes, and cracks. Indeed, there is an increasing number of contributions focusing on the dimensions and shapes of flow paths, their 3-D imaging, and trials to derive flows from them [4].…”

“…Imaging procedures visualize flow in 2-D and 3-D in voids as narrow as some 10 µm, rising hope that the wealth of information gained so far at the hydro-dynamic scale will eventually lead to macroscopic models at the soil profile scale of meters [4]. Thus, Beven's (2018) [28] denial of progress in infiltration research is here carried a step further. The obsession with pores, channels, flow paths, and their connectivity, tortuosity, and necks actually retarded research progress towards more general infiltration that has to be based on hydro-mechanical principles.…”

Current Insights into Nonuniform Flow across Scales, Processes, and Applications

“…As an invited contribution to this special section, Beven (2018) outlines the historic evolution of knowledge about preferential flows, focusing on the period between 1864 and 1984. Her summarizes a century‐old general denial of theoretical and multiscale experimental evidence of preferential flow, even though the initial discovery and documentation of these processes predate the establishment of equilibrium concepts by Edgard Buckingham and Lorenzo Richards.…”