Inverse estimation of parameters for multidomain flow models in soil columns with different macropore densities

Abstract

Soil and crop management practices have been found to modify soil structure and alter macropore densities. An ability to accurately determine soil hydraulic parameters and their variation with changes in macropore density is crucial for assessing potential contamination from agricultural chemicals. This study investigates the consequences of using consistent matrix and macropore parameters in simulating preferential flow and bromide transport in soil columns with different macropore densities (no macropore, single macropore, and multiple macropores). As used herein, the term“macropore density” is intended to refer to the number of macropores per unit area. A comparison between continuum-scale models including single-porosity model (SPM), mobile-immobile model (MIM), and dual-permeability model (DPM) that employed these parameters is also conducted. Domain-specific parameters are obtained from inverse modeling of homogeneous (no macropore) and central macropore columns in a deterministic framework and are validated using forward modeling of both low-density (3 macropores) and high-density (19 macropores) multiple-macropore columns. Results indicate that these inversely modeled parameters are successful in describing preferential flow but not tracer transport in both multiple-macropore columns. We believe that lateral exchange between matrix and macropore domains needs better accounting to efficiently simulate preferential transport in the case of dense, closely spaced macropores. Increasing model complexity from SPM to MIM to DPM also improved predictions of preferential flow in the multiple-macropore columns but not in the single-macropore column. This suggests that the use of a more complex model with resolved domain-specific parameters is recommended with an increase in macropore density to generate forecasts with higher accuracy.

Quantification of the influence of preferential flow on slope stability using a numerical modelling approach

“…7). Arora et al (2011) and Köhne and Mohanty (2005) did not consider the influence of coatings on the permeability, nor was this done in this study. It may be seen from Table 2 that the magnitude of the product α w K sa is similar for all studies, even though some of the other values (notably the ratios K sa /K sm and the values of α w ) differ by several orders of magnitude.…”

“…Köhne and Mohanty (2005) conceptualise the dual domain as a hollow cylindrical matrix that is filled with coarse sand in the middle to mimic the macropore domain. Arora et al (2011) based their parameters on a high density of macropore columns, and they calculated K a by averaging the hydraulic conductivities of the two pore domains (as adopted in this paper; see Eq. 7).…”

“…where α w (L −2 ) is the effective water transfer coefficient, and the relative hydraulic conductivity K a (L T −1 ) is calculated by averaging the hydraulic conductivities of the two pore domains (Arora et al, 2011;Laine-Kaulio et al, 2014):…”

Estimation and upscaling of dual-permeability model parameters for the transport of E. coli D21g in soils with preferential flow

“…The study of preferential flow and transport through artificial macropores provides an opportunity to overcome many modeling challenges in natural soils because the macropore geometry and hydraulic properties can be well defined and controlled in a repeatable manner (Arora et al, 2011(Arora et al, , 2012Castiglione et al, 2003;Guzman et al, 2009;Pivetz and Steenhuis, 1995). Artificial macropores can be systematically created by leaving small cylindrical openings in repacked columns (Castiglione et al, 2003;Pivetz and Steenhuis, 1995) or by packing different sized sands to generate layers and/or lens with contrasting hydraulic conductivities (Bradford et al, 2004;Fontes et al, 1991;Morley et al, 1998;Saiers et al, 1994;Wang et al, 2013Wang et al, , 2014.…”

Reactive transport codes for subsurface environmental simulation

“…Some of the commonly used continuum-scale models include (1) equivalent continuum model (ECM) [41]; (2) dual permeability model (DPM), dual or multiporosity model [42,43], multiple interacting continua approach (MINC) [44], and (3) discrete fracture and matrix model [45]. Among these three commonly used approaches, the dual-continuum approach has been extensively applied in different subsurface environments [46][47][48]. Broadly speaking, the dual-continuum approach considers two interacting regions, one associated with the less permeable intraaggregate pore region, or the soil matrix domain, and the other associated with the inter-aggregate pore region, or the fracture domain.…”