Viscous‐Flow Approach to In Situ Infiltration and In Vitro Saturated Hydraulic Conductivity Determination

Authors:
Publisher website
Google Scholar
Abstract
Core Ideas: Viscous film flow can explain non‐equilibrium in the Richards equation. Parameters of viscous flow were determined in situ and in vitro. If macropore‐flow restriction applies, then kinematic wave theory is applicable. Infiltration is dominantly gravity driven, and a viscous‐flow approach was developed. Laminar film flow equilibrates gravity with the viscous force and a constant flow velocity evolves during a period lasting 3/2 times the duration of a constant input rate, q S . Film thickness F and the specific contact area L of the film per unit soil volume are the key parameters. Sprinkler irrigation produced in situ time series of volumetric water contents, θ( z , t ), as determined with TDR probes. The wetting front velocity v and the time series of the mobile water content, w ( z , t ) were deduced from θ( z , t ). In vitro steady flow in a core of saturated soil provided volume flux density, q ( z , t ), and flow velocity, v , as determined from a heat front velocity. The F and L parameters of the in situ and the in vitro experiments were compared. The macropore‐flow restriction states that, for a particular permeable medium, the specific contact area L must be independent from q S i.e., d L /d q S = 0. If true, then the relationship of q S ∝ v 3/2 could scale a wide range of input rates 0 ≤ q S ≤ saturated hydraulic conductivity, K sat , into a permeable medium, and kinematic‐wave theory would become a versatile tool to deal with non‐equilibrium flow. The viscous‐flow approach is based on hydromechanical principles similar to Darcy's law, but currently it is not suited to deduce flow properties from specified individual spatial structures of permeable media.

This publication has 20 references indexed in Scilit: