Macropores and water flow in soils

TLDR

Macropores create spatially concentrated water flow in unsaturated soils that is poorly captured by Darcy’s law, leading to rapid solute and pollutant transport and revealing limitations of models that treat macropores and matrix porosity as separate flow domains. The paper reviews the importance of macropores for soil water flow and identifies gaps, calling for a coherent theory of flow through structured soils that would eliminate the need for a separate macropore domain concept. The authors review definitions and nomenclature of macropores, and discuss their influence on infiltration and subsurface storm flow using experimental evidence and theoretical studies. Experimental evidence and theoretical studies show that macropores significantly influence infiltration and subsurface storm flow.

Abstract

This paper reviews the importance of large continuous openings (macropores) on water flow in soils. The presence of macropores may lead to spatial concentrations of water flow through unsaturated soil that will not be described well by a Darcy approach to flow through porous media. This has important implications for the rapid movement of solutes and pollutants through soils. Difficulties in defining what constitutes a macropore and the limitations of current nomenclature are reviewed. The influence of macropores on infiltration and subsurface storm flow is discussed on the basis of both experimental evidence and theoretical studies. The limitations of models that treat macropores and matrix porosity as separate flow domains is stressed. Little‐understood areas are discussed as promising lines for future research. In particular, there is a need for a coherent theory of flow through structured soils that would make the macropore domain concept redundant.