Showing papers by "Marcel G. Schaap published in 1999"
TL;DR: In this article, the porosity and its microscopic characteristics were directly measured using binary images collected with a backscattered electron detector from thin sections of soils, and the results were used to predict a formation factor from microscopic, macroscopic, and chemical data.
Abstract: Traditional models to describe hydraulic properties in soils are constrained by the assumption of cylindrical capillarity to account for the geometry of the pore space. This study was conducted to develop a new methodology to directly measure the porosity and its microscopic characteristics. The methodology is based on the analysis of binary images collected with a backscattered electron detector from thin sections of soils. Pore surface area, perimeter, roughness, circularity, and maximum and average diameter were quantified in 36 thin sections prepared from undisturbed soils. Saturated hydraulic conductivity Ksat, particle size distribution, particle density, bulk density, and chemical properties were determined on the same cores. We used the Kozeny-Carman equation and neural network and bootstrap analysis to predict a formation factor from microscopic, macroscopic, and chemical data. The predicted Ksat was in excellent agreement with the measured Ksat (R2=0.91) when a hydraulic radius rH defined as pore area divided by pore perimeter and the formation factor were included in the Kozeny-Carman equation.
50 citations
01 Jan 1999
TL;DR: A large number of conceptual models are now available to predict flow and transport in the vadose zone as discussed by the authors, and several useful approaches have recently become available to study and model preferential flow in structured media.
Abstract: Much progress has been made during the past several decades in attempts to more realistically simulate variably-saturated water flow and solute transport in the subsurface. A large number of conceptual models are now available to predict flow and transport in the vadose zone. In this paper we highlight recent advances in modeling at especially the local scale. Improved understanding of underlying processes, continued advances in numerical methods, and the introduction of increasingly powerful computers now permit comprehensive simulations of the most important physical, chemical and biological processes operative in the unsaturated zone. Examples include models for mass/energy transport in the soil-plant atmosphere continuum, multicomponent major ion chemistry, and multifluid flow. While the problem of preferential flow remains a challenge, several useful approaches have recently become available to study and model preferential flow in structured media. Increasingly accurate indirect methods, including pedotransfer functions, are now also available for estimating the unsaturated soil hydraulic properties from more readily available or easily measured data. A need still exists for more user-friendly software to enable more effective application of models to a variety of flow and transport problems in research and
19 citations