Soil Moisture Transport Research Articles

Interaction between soil hydrology and boundary-layer development

A two-layer model of soil hydrology and thermodynamics is combined with a one-dimensional model of the planetary boundary layer to study various interactions between evolution of the boundary layer and soil moisture transport. Boundary-layer moistening through surface evaporation reduces the potential and actual surface evaporation as well as the boundary-layer growth. With more advanced stages of soil drying, the restricted surface evaporation allows greater sensible heat flux which enhances boundary-layer growth and entrainment drying.

Deterministic hydrological site and catchment models for the analysis of agroecosystems

Summary This paper discusses two physical models which describe the water transport at sites and in catchments. The Deterministic Site Model consists of the submodels Evaporation, Transpiration, Interception, Heat Flux in the Soil, Soil Moisture Transport in the Matrix Pores and in the Macro Pores, Characterization of the Soil Physical Properties, Surface Crusting, Water Flux caused by Tile Drains and Lateral Water Flux. This model was tested using extensive data sets. The European Hydrological System/Systeme Hydrologique Europeen (SHE) is a distributed catchment model which was applied and tested. Based on first tests some components which had been tested successfully in applications of the Deterministic Site Model were substituted. Detailed validations showed the ability of the modified SHE to simulate water transports in agroecosystems.

Reply [to “Comment on ‘Kinematic Models for Soil Moisture and Solute Transport’ by Randall J. Charbeneau”

Reply [to “Comment on ‘Kinematic Models for Soil Moisture and Solute Transport’ by Randall J. Charbeneau”

Comment on “Kinematic Models for Soil Moisture and Solute Transport” by Randall J. Charbeneau

Comment on “Kinematic Models for Soil Moisture and Solute Transport” by Randall J. Charbeneau

Two-Dimensional Model of Coupled Heat and Moisture Transport in Frost-Heaving Soils

A two-dimensional model of coupled heat and moisture flow in frost-heaving soils is developed based upon well known equations of heat and moisture flow in soils. Numerical solution is by the nodal domain integration method which includes the integrated finite difference and the Galerkin finite element methods. Solution of the phase change process is approximated by an isothermal approach and phenomenological equations are assumed for processes occurring in freezing or thawing zones. The model has been verified against experimental one-dimensional freezing soil column data and experimental two-dimensional soil thawing tank data as well as two-dimensional soil seepage data. The model has been applied to several simple but useful field problems such as roadway embankment freezing and frost heaving.

Kinematic Models for Soil Moisture and Solute Transport

The kinematic theory of soil moisture and solute transport in the vertical direction for unsaturated groundwater recharge is considered. The general theory of kinematic models is reviewed and applied for an isolated wetting event wherein the soil starts at and eventually drains to field capacity. Analytical expressions are developed for the water content and moisture flux as a function of depth and time. The approach is extended for an arbitrary sequence of surface flux or water content boundary conditions. The transport of a solute with a general nonlinear sorption isotherm is also considered. It is shown that for the general isotherm the vertical displacement of a solute isochore during an arbitrary wetting sequence depends only on the total depth of water infiltrated and not on how the infiltration rate varies with time.

Soil moisture transport through the unsaturated zone: tritium tagging studies in Sabarmati basin, western India

ABSTRACT This paper describes a study for groundwater recharge estimation in the Sabarmati basin, western India, by means of the tritium tagging method. The estimation of areal average recharge for the basin from the point recharge estimates obtained at various field stations is discussed. A considerable variability of recharge estimates is observed at nearby locations having apparently similar conditions of soil and climate. In spite of the observed spatial variability in recharge estimates, data from the tritium tagging experiment in combination with conventional hydrogeological information (i.e. grain size, water level of the unconfined aquifers and other geological information) enable us to divide the alluvial parts of the basin into three recharge zones. On an average basis, about 14% of the precipitation input is estimated to be recharged annually in the alluvial parts of the Sabarmati basin.

Application of environmental isotope tracers to modeling in hydrology

Advances in nuclear science and computer development have made practicable chemical-transport models employing the environmental isotopes found in natural waters. The heavy isotopes of hydrogen, deuterium (stable) and tritium (radioactive), forming part of the water molecule, are the most conservative tracers of water known. The heavy stable oxygen isotope, 18O, circulates in tandem with deuterium in the hydrologic cycle. Tritium fallout varies seasonally and annually in a systematic fashion, and due to its property of radioactive decay is highly useful for dating time of recharge of soil moisture and groundwater. 14C is valuable for tracing old groundwater owing to its relatively long half-life of 5568 yr., but detailed knowledge of the hydrochemistry of the system is required for successful modeling. Deuterium and 18O are of principal value because they reflect the temperature at which precipitation condensed. Thus, they show pronounced seasonal variability and also the effects of altitude, latitude, distance from the sea, amount of precipitation, history of evaporation, and long-period climatic cycles. Principal areas of application of environmental isotopes to hydrologic modeling have been in soil-moisture transport, modeling of mixing and evapotranspiration in large lakes and swamps, glacial-ice movement, groundwater flow, and transport of contaminants in groundwater.

Improved linear trial function finite element model of soil moisture transport

Two methods of modeling a higher‐order approximation function of soil moisture transport by an improved linear trial function approximation are presented. The first approach considered is based upon use of the alternation theorem and a finite element capacitance matrix that incorporates the Galerkin finite element, subdomain, finite difference, and proposed nodal domain integration methods. The second approach extends the first approach by developing a temporal relationship for element matrices such that a higher‐order approximation function can be modeled by a linear approximation function. Comparison of model results produced from a nodal domain integration model incorporating these improved linear trial function approximations to the finite element, subdomain, and finite difference methods indicates that this approach may lead to a generalized modeling method for soil moisture transport problems.

A note on time integration of unsaturated soil-moisture transport

The non-linear soil-moisture diffusivity model can be approximately linearized by using values of diffusivity assumed constant for small intervals of space and time. By a series expansion of the diffusivity function and integrating the resulting series of differential equations with respect to time, an improved numerical model is developed. Results from application of this new approach to a sharp wetting-front soil infiltration problem indicates that a 67% saving in numerical effort is achieved at comparable estimation accuracy levels when using the traditional finite timestep Crank-Nicolson approach.

Numerical mass balance for soil-moisture transport problems

The Galerkin finite element method coupled with the Crank-Nicolson time advance procedure is often used as a numerical analog for unsaturated soil-moisture transport problems. The Crank-Nicolson procedure leads to numerical mass balance problems which results in instability. A new temporal and spatial integration procedure is proposed that exactly satisfies mass balance for the approximating function used. This is accomplished by fitting polynomials continuously throughout the time and space domain and integrating the governing differential equations. To reduce computational effort, the resulting higher order polynomials are reduced to quadratic and linear piece-wise continuous polynomial approximation functions analogous to the finite element approach. Results indicate a substantial improvement in accuracy over the combined Galerkin and Crank-Nicolson methods when comparing to simplified problems where analytical solutions are available.

Use of a laboratory lysimeter to determine soil moisture transport properties

Use of a laboratory lysimeter to determine soil moisture transport properties

Soil Moisture Transport Due to Thermal Gradients: Practical Aspects

AbstractThe present status of knowledge concerning thermally induced transport of moisture in soil is reviewed. This includes the various theories on mechanisms of transport and experimental data showing the magnitude of moisture flow in various porous materials. Wherever possible these data were chosen to show the relative importance of thermal versus head‐type flow and some general trends are noted.Simple equations are developed to describe the thermally induced moisture flow near the soil surface which arises from transient thermal gradients produced by the diurnal temperature cycle. Calculations of the moisture flux over 2 ten‐hour time intervals for a typical field situation indicate that thermal water transport should be considered whenever moisture, salt, or heat fluxes are being studied in the soil's surface layers.The upward flow of soil water against a moisture content gradient in the winter is also considered. A sample calculation of the amount of thermally driven moisture was made using data available in the literature. The result suggested that the thermal moisture flow was too small to account for the net movement of soil moisture into the frost zone.

WATER FLUX IN MOIST SOIL

That thermal gradients cause moisture transport in soil has been well known for at least 50 years. It is, however, surprising that so little attention has been paid to this phenomenon, since soil in its natural environment is continuously subject to changing temperatures. In 1957 Philip and de Vries (14) published a theoretical article in which they attempted to reconcile the few existing experimental data. Since then, alternative approaches have been suggested by Derjaguin and Melnikova (5), Matthes and Bowen (12), and Taylor and Cary (16). The experimental observations available are, however, insufficient to make a fair test of any of the proposed theories. As a general statement, about all that can be said is: A thermal gradient in soil will cause water to move from a warm to a cooler area in both the liquid and vapor phases, and the rate of transfer is greater than can be predicted with Lick's law and the diffusion coefficient for water vapor into air. The experiment reported in this article was designed to yield data defining the relative importance of thermal gradients in transporting soil moisture and to probe the mechanisms of transfer.