Modeling dynamic non-equilibrium water flow observations under various boundary conditions

Diamantopoulos, Efstathios; Durner, Wolfgang; Iden, Sascha C.; Weller, Ulrich; Vogel, Hans‐Jörg

doi:10.1016/j.jhydrol.2015.07.032

Cited by 21 publications

(21 citation statements)

References 25 publications

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“…For the finer soils, this effect is even more pronounced and flow equilibrium is hardly reached, even after providing a relatively long time with constant suction (couple of hours). This observation is in contrast to our numerical findings and indicates ''hydraulic non-equilibrium'', i.e., a nonuniqueness of the relation between local water content and local pressure head, as discussed by Diamantopoulos and Durner (2012) and experimentally found in many types of transient flow experiments (Diamantopoulos et al, 2015). The effect of hysteresis can also be observed from the graphs of flow rates.…”

Section: Kusat and Ksatcontrasting

confidence: 99%

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Sarkar

Germer

Maity

et al. 2019

J. Plant Nutr. Soil Sci.

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Sarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method.

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Section: Kusat and Ksatcontrasting

confidence: 99%

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Sarkar

Germer

Maity

et al. 2019

J. Plant Nutr. Soil Sci.

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“…This could be done by decoupling both state variables and introducing a term describing the dynamics toward equilibrium while still adhering to the basic concept of the Richards equation (i.e., to link the gradient in soil water potential to the flux by an effective hydraulic conductivity). Such a decoupling was proposed by Ross and Smettem (2000) and extended by Diamantopoulos et al (2015), who separated fast and slow equilibrating pore domains.…”

Section: Challenges At the Pedon Scalementioning

confidence: 91%

Scale Issues in Soil Hydrology

Vogel

2019

Vadose Zone Journal

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Core Ideas The soil profile is the critical scale for representation of soil hydrology also at larger scales. Natural soils do not follow well‐defined hydraulic properties. Concepts are needed to model hydraulic nonequilibrium and hysteresis. Spatial patterns of functional soil types need to be identified. These can account for vertical stratification of hydraulic properties and structural attributes. Soil hydrology is a key control for the functioning of the terrestrial environment. Many environmental issues that we need to tackle today are directly linked to soil water dynamics. This includes agricultural production and food security, nutrient cycling and carbon storage, prevention of soil degradation and erosion, and last but not least, clean water resources and flood protection. However, these problems need to be addressed at the scales of fields, regions, and landscapes, while soil water dynamics and soil hydraulic properties are well understood and typically measured at much smaller scales—the comfort zone of soil physics. An obvious problem is how to link these vastly different scales and how to profit from small‐scale understanding to improve our capability to predict what is going on at the large scale. In this update, this problem is discussed based on insights gained during the last decades. As a synthesis, a two‐step scaling approach is proposed for modeling soil water dynamics from local to landscape scales where the scale of the soil profile is the stepping stone.

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“…It has also been defined, by Ross and Smettem (), as a parameter relating the difference ( θ eq − θ ) [ M L − 3 ] between the water content in the equilibrium state and the actual water content to the rate of change in the actual water saturation of a porous medium, ∂θ/∂t [ M L − 3 T − 1 ]. These characterizations of DNE facilitate the description or modeling of pore‐scale dynamic water flows in porous media (Diamantopoulos et al, ). The variations in water content‐capillary pressure functions are mainly manifested in the differences in: capillary pressure at a given water saturation, water saturation at a given capillary pressure under different test conditions, and time lags between corresponding water saturation and capillary pressure values during a drainage or imbibition process.…”

Section: Introductionmentioning

confidence: 99%

Factors Influencing Dynamic Nonequilibrium Effects in Drainage Processes of an Air‐Water Two‐Phase Fine Sandy Medium

Li¹,

He²,

et al. 2019

Water Resources Research

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In efforts to reduce uncertainties about effects of minor changes in the pore structure of porous media on dynamic nonequilibrium effects (DNEs), we monitored water saturation‐capillary pressure relationships in both dynamic flow and static states in stepwise drainage processes of a sandy medium. The acquired data were used to detect DNE and their changes with time in each drainage step and construct new parameters to characterize DNE. Effects of factors affecting water flow—including capillary number, water saturation, rate of change of water saturation with time (△Sw/△t), and the maximum value of this rate (RSMAX)—on the magnitude of the DNE were then determined. Results show that entry pressures are considerably larger under dynamic flow conditions than under static flow conditions, and DNE only occurs when the water saturation exceeds a threshold value in a drainage process. During either a smooth drainage or drainage step, the maximum capillary pressure (PMAX) is reached before the minimum water saturation (SMIN). Moreover, in drainage steps RSMAX occurs before the maximum difference between the capillary pressures associated with the static and dynamic states (DPMAX), except when they start from the saturated state. Accordingly, DNEs in a drainage step are mainly reflected in the time between PMAX and SMIN (△t), DPMAX, the average sum of the squares of the difference between capillary pressures of the static and dynamic states (DPAVE), and the dynamic coefficient τ (which is often used to characterize DNE). Furthermore, our results indicate that the water saturation and its rate of change with time are more important parameters than the capillary number for modeling DNE in a drainage process, and we detected no clear correlation between either maximum or minimum values of τ and the timing of the most significant DNE during drainages. τ appears to characterize DNE effectively in smooth drainage processes, while △t, DPAVE, and DPMAX constitute meaningful supplementary parameters for the characterization of DNE in a drainage step of a stepwise drainage.

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Modeling dynamic non-equilibrium water flow observations under various boundary conditions

Cited by 21 publications

References 25 publications

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Scale Issues in Soil Hydrology

Factors Influencing Dynamic Nonequilibrium Effects in Drainage Processes of an Air‐Water Two‐Phase Fine Sandy Medium

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