Soil Moisture Transfer Research Articles

Boundary Value Problems for a Model Hyperbolic Equation of the Third Order with Non-local Conditions of the First Kind

Considers nonlocal problems of the first kind for a model third-order hyperbolic equation. The main goal of the article is to prove the solvability of nonlocal problems of the first kind for a model third-order hyperbolic equation. Using the Riemann function method, the problem is reduced to Volterra integral equations of the second kind. Using the method of integral equations, the existence of a unique solution to nonlocal problems of the first kind is proven. The resulting solution to nonlocal problems of the first kind makes it possible to describe the process of moisture transfer in soils, heat transfer in a heterogeneous medium, and fluid filtration in porous media.

An Analogue of the Darboux Problem for Hyperbolic Equations of the Third Order in a Rectangular Triangular Domain

The article considers the Darboux problem for a third-order hyperbolic equation in a rectangular triangular domain. The main purpose of the article is to prove the solvability of the Darboux problem. Using the Riemann function method, the problem is reduced to Volterra integral equations of the second kind. The existence of a unique solution to the Darboux problem is proved by the method of integral equations. The obtained solution of the Darboux problem allows us to describe the process of moisture transfer in soils, heat transfer in a heterogeneous medium, and liquid filtration in porous media.

Разностная схема повышенного порядка аппроксимации для уравнения Аллера с переменными коэффициентами

The initial boundary value problem for the one-dimensional Aller’s equation with variable coefficients and boundary conditions of the first kind is studied. The problem under study describes the processes of heat transfer in a heterogeneous environment, moisture transfer in soils, and fluid filtration in fractured porous media. To numerically solve the problem posed, a difference scheme of high order of accuracy was constructed - fourth order of accuracy in h and second order of accuracy in τ. Using the method of energy inequalities, an a priori estimate of the solution in a difference treatment is obtained. From this estimate it follows that the solution is unique and stable with respect to the right-hand side and initial data. Under the assumption of the existence of an exact solution to the original differential problem in the class of sufficiently smooth functions, and also due to the linearity of the problem under consideration, the obtained a priori estimate implies that the solution of the constructed difference problem converges to the solution of the original differential problem at a rate equal to the order of approximation of the difference scheme. The goal and scientific novelty of the work is to obtain a new numerical scheme of a higher order of approximation when solving the Dirichlet problem for the Aller’s equation with variable coefficients.

Numerical analysis on liquid seepage - Diffusion coupled with heat in soil of low - Pressure buried pipelines leakage

The incident of buried pipeline leakage has become one of the main concerns since the consequences of social economy and soil environment. The main objective in this study is to develop a numerical model for the low - pressure buried water pipeline leakage by CFD (Computational Fluid Dynamics). In this model, the process inside and outside of the pipeline is connected through the orifice, and the heat transfer is coupled during the leakage water seepage - diffusion in soil. In this way, the degree and diffusion range of buried pipeline leakage by considering soil as porous medium are investigated. Comparison of the numerical and experimental results demonstrated that the model has a higher precision in predicting accident severity and influencing range. Further, the effects of inlet water temperature, pipe pressure, orifice's diameter, orifice's position and soil porosity are systematically researched. Some acquired results are as follows: temperature can promote soil moisture transfer and the two are positively correlated. The degree and diffusion range increase with the increasing pipe pressure, orifice's diameter and soil porosity. Orifice's position only affects diffusion direction, not diffusion range. The conclusions will provide theoretical foundation for soil environment remediation.

Soil moisture transfer at the boundary area of soil water retention zone: A case study

Plant growth monitoring techniques are of great interest to agricultural engineering. The interaction between root and soil water is one important plant response to environmental variations. This paper aims to develop a new method to estimate plant biological response using root-soil water interaction. It provides a case study on moisture transfer at the boundary area of a soil water retention zone (SWRZ). We produced a SWRZ around growing roots of a cultivated tomato plant in homogenous dried soil using water-saving drip irrigation. The irrigation was designed to supply moisture only in the root zone to meet the minimum need of plant growth. High-resolution soil moisture sensors were used to detect moisture transfer at the boundary area of the SWRZ. We applied frequency analysis to the acquired vibration spectrum using filtering and Fast Fourier Transform (FFT) in order to investigate the frequency content at each sensor location. Distinct frequencies of moisture vibration were identified at the boundary area of the SWRZ which indicated water transfer to the roots caused by plant water absorption. A mechanical vibration model was proposed to describe this phenomenon. The pinpoint irrigation to the root zone in the water-saving cultivation method enabled a well-structured spherical root system to form via hydrotropism. This enabled a simple method to analyze moisture transfer based on a mechanical vibration model. The results suggest a new method to estimate plant biological response by studying root-soil water interaction.

A whole-process simulation for energy piles in unsaturated soils considering the coupled heat and moisture transfer

Compared with traditional borehole heat exchangers, energy geostructures are more common to be embedded in unsaturated soils. The coupled heat and moisture transfer in unsaturated soils makes the thermal performance of energy geostructures more complicated. In this study, a three-dimensional heat-water–vapor mathematical model has been developed through theoretical derivation, considering the changes in thermodynamic properties. The spatially and temporally varying moisture and temperature profiles were generated with a finite element method. Then, a comprehensive simulation of the whole operation process for energy piles was carried out by coupling the validated mathematical model with the non-isothermal pipe flow and solid heat transfer physical fields. The results showed that after operation at constant power for one month, the liquid content of the unsaturated soil surrounding the pile decreased by 16.9 %, and the thermal conductivity dropped from 1.4 W∙m−1∙K−1 to 1.31 W∙m−1∙K−1. In addition, after three months of operation at a given inlet temperature, the heat exchange rate of the fully-coupled model was 9.6 % lower than that of the model considering heat transfer only. The intermittent operation mode could effectively reduce the heat accumulation and alleviate the decrease of liquid content, helping improve the long-term heat transfer performance. During a three-year operation period, the cooling power generally presented a downward trend while the heating power was the opposite. Therefore, it can be concluded that the application of energy piles in unsaturated soil areas requires more accurate evaluations and long-term monitoring.

A method for leak detection in buried pipelines based on soil heat and moisture

Leakages in urban heating pipeline networks are mostly caused by underground corrosion, external environment interference and construction. The fluid leaking from pipes accumulates in surrounding soil for a long time, resulting in changes in soil machinery and hydraulic structure, and potential accidents threaten people's daily life and property safety. A preliminary judgment was made to determine whether the pipeline failed according to the infrared images of underground heating pipeline taken from the actual engineering. By comparing the soil moisture around the faulty pipe, we subsequently proposed a fault detection method for buried pipelines which coupled infrared thermography and the variation characteristics of surrounding soil moisture. In order to verify the effectiveness of this method, the numerical simulation was carried out on a leaking buried pipe, and the variation characteristics of soil heat and moisture in the direction of the failure point and its driving mechanism were analyzed. The results showed that the difference between the internal and external pressures at the failure point of the leaking buried pipeline enhanced the effect of soil pressure potential, resulting in significant heat and moisture transfer in soil, which contributed to detecting the buried pipeline failure and identifying the failure types of buried pipelines.

Experimental study on coupled heat and moisture transfer in soils during heat absorption and release processes

Heat and mass migration during the process of heat absorption and release in soil, as a randomly distributed porous medium, is different. The main objective of this work was to comparatively analyze the difference in heat and moisture transfer during the process of heat absorption and release in different soil. In this paper, an experimental study on heat and moisture migration in soils (coarse sand, gravel, and loam) was carried out, during heat absorption and release processes under the same excess temperature. Results showed that moisture migration nonlinearly increases with the excess temperature and initial moisture content, temperature variation linearly increases with the excess temperature, and hardly changes with the initial moisture content. There would be obvious deviation in temperature distribution during the process of heat absorption and release in gravel, loam and coarse sand with an initial moisture content of 15.4%, 20.4%\\23.3% and 23.3%, under the excess temperature of ±20 °C. The temperature variation and moisture migration during heat absorption process are all greater than those during heat release process. The final temperature distribution deviation of loam is the largest, reaches 15.7%, the final moisture migration difference of gravel is the largest, reaches 31.7%, and the moisture migration difference increases with soil porosity.

КАЧЕСТВО ВОСПРОИЗВЕДЕНИЯ СОСТОЯНИЯ ПОЧВЫ МОДЕЛЬЮ ДЕЯТЕЛЬНОГО СЛОЯ СУШИ ИВМ РАН - МГУ В СОСТАВЕ МОДЕЛИ ПРОГНОЗА ПОГОДЫ ПЛАВ

In situ soil moisture and temperature observations are used to evaluate soil moisture and temperature analysis of the global atmospheric model SL-AV for the summer season of 2014 across Western Europe. It is shown that the seasonal temperature analysis trends are reproduced better than the seasonal trends of soil moisture. Numerical experiments with the offline land surface scheme demonstrated that the implementation of the Mualem-van Genuchten water retention curve has the advantage for describing the processes of soil moisture transfer in comparison with Brooks-Corey parameterization. The last one is used in the basic version of the model. The Mualem-van Genuchten function provides better computational stability of the soil model in case of soils with high coarse grain content. An important contribution to the soil moisture error in the analysis and forecast is caused by specifying an inaccurate profile of the soil granulometric composition. It indicates a need to involve state-of-the-art databases for soil characteristics

Estimation of Groundwater Recharge from Rainfall for Arid Coastal Plain of Ninh Thuan Province, Vietnams

Estimation of groundwater recharge from rainfall is a key factor for determining groundwater resources in water development and management for supporting sustainable socio-economic development, especially for arid areas. The paper presents finite element modeling in the simulation of moisture transfer in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability and soil-moisture dispersivity. Those parameters required for soil moisture transfer are derived from the soil-water characteristic curve functions. Element sizes and time steps used in the modelling have been selected based on a detailed analysis of numerical simulation errors. The methodology had been applied to arid coastal plain area of Ninh Thuan province, Vietnam. Five subsurface soil types in the study area have been collected and analyzed, for saturated permeability, porosity, saturated soil water content, field moisture content, etc. Hourly rainfall data of the years 2014–2018 have been analyzed and grouped into different-duration rainfall events (1-hour, 2-hour, 3-hour and so on). The different rainfall durations and depths of rainfall events and temporal infiltration determined by the moisture transfer modelling have allowed determining the groundwater recharge from the rainfall data. The results show that during the rainy months from May to December 2014–2018, the groundwater recharge from the rainfall is very varying through the modeled soil profiles, from 0.280 m (silty clay) to 0.470 m (sandy silt), which is equivalent to 33.3%—55.2% of the rainfall depth during May—December. Lower infiltration in silty clay is due to low permeability and in the sand is due to low suction, and higher infiltration in silt and sandy silt is thanks to their higher moisture dispersivity. On average, in terms of annual rainfall and soil properties, the average infiltration during May—December is 0.380 m which is equivalent to 44.9% of the rainfall depth, which is about 289 106 m3 of rainwater infiltrated into the Quaternary aquifer over 760 km2 of the coastal plain of Ninh Thuan province. The results would be very useful for effective water resources development and management in a given specific hydrogeological condition for such a severe drought area where water is extremely essential.

THERMOPHYSICAL CHARACTERISTICS OF THE HEAT AND MASS TRANSFER EQUATION IN SOIL

The paper presents the coefficient inverse problem of heat and mass transfer. It is known that the process of moisture and heat transfer in soil is described by a system of partial differential equations. The inverse coefficient problem is solved for finding the thermophysical characteristics of the heat and mass transfer equations. The initial-boundary conditions for the heat and mass transfer system are set. To solve the problem, the measured values of temperature and moisture are additionally set at the accessible boundary of the considered area. To solve the inverse problem, the Dufort- Frankel scheme and Matlab Optimization Toolbox are used. The Jacobian is used to reduce the number of iterations. The results of numerical calculations with and without Jacobian are presented.

TO CONSTRUCTING AN ADAPTIVE COVER MODEL

A mathematical model for optimizing the growth and development of plant cover is investigated. For constant environmental parameters (humidity, soil and plant temperature), a balanced optimal distribution of photosynthetic assimilates was found by the choice of growth functions and the ratio of leaf and root biomass in explicit general terms, maximizing its reproductive biomass at the end of 3 phases of growth and development of plant cover. The expressions obtained are meaningfully interpreted and can be considered as the basis for an adaptive model of plant productivity and moisture transfer in soil in a constant or slowly changing environment.

Simulated or measured soil moisture: which one is adding more value to regional landslide early warning?

Abstract. The inclusion of soil wetness information in empirical landslide prediction models was shown to improve the forecast goodness of regional landslide early warning systems (LEWSs). However, it is still unclear which source of information – numerical models or in situ measurements – is of higher value for this purpose. In this study, soil moisture dynamics at 133 grassland sites in Switzerland were simulated for the period of 1981 to 2019, using a physically based 1D soil moisture transfer model. A common parameterization set was defined for all sites, except for site-specific soil hydrological properties, and the model performance was assessed at a subset of 14 sites where in situ soil moisture measurements were available on the same plot. A previously developed statistical framework was applied to fit an empirical landslide forecast model, and receiver operating characteristic analysis (ROC) was used to assess the forecast goodness. To assess the sensitivity of the landslide forecasts, the statistical framework was applied to different model parameterizations, to various distances between simulation sites and landslides and to measured soil moisture from a subset of 35 sites for comparison with a measurement-based forecast model. We found that (i) simulated soil moisture is a skilful predictor for regional landslide activity, (ii) that it is sensitive to the formulation of the upper and lower boundary conditions, and (iii) that the information content is strongly distance dependent. Compared to a measurement-based landslide forecast model, the model-based forecast performs better as the homogenization of hydrological processes, and the site representation can lead to a better representation of triggering event conditions. However, it is limited in reproducing critical antecedent saturation conditions due to an inadequate representation of the long-term water storage.

MATHEMATICAL MODELS OF DISCRETE IRRIGATION TECHNOLOGIES FOR AGRICULTURAL CROPS IN FURROWS

The article discusses mathematical modeling of discrete technology of irrigation of crops by furrows, based on joint consideration of the system of Saint-Venan equations and equations of moisture and heat transfer in soils. The boundary conditions are described in detail in accordance with the technologies of irrigation by furrows at discrete water supply.

Integrated modeling of canopy photosynthesis, fluorescence, and the transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum (STEMMUS–SCOPE v1.0.0)

Abstract. Root water uptake by plants is a vital process that influences terrestrial energy, water, and carbon exchanges. At the soil, vegetation, and atmosphere interfaces, root water uptake and solar radiation predominantly regulate the dynamics and health of vegetation growth, which can be remotely monitored by satellites, using the soil–plant relationship proxy – solar-induced chlorophyll fluorescence. However, most current canopy photosynthesis and fluorescence models do not account for root water uptake, which compromises their applications under water-stressed conditions. To address this limitation, this study integrated photosynthesis, fluorescence emission, and transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum system, via a simplified 1D root growth model and a resistance scheme linking soil, roots, leaves, and the atmosphere. The coupled model was evaluated with field measurements of maize and grass canopies. The results indicated that the simulation of land surface fluxes was significantly improved by the coupled model, especially when the canopy experienced moderate water stress. This finding highlights the importance of enhanced soil heat and moisture transfer, as well as dynamic root growth, on simulating ecosystem functioning.

Moisture Transfer Finite Element Modeling with Soil-Water Characteristic Curve-Based Parameters and its Application to Nhan Co Red Mud Basin Slope

Since the year of 2017 landslides at the red mud basins in Nhan Co alumina factory, Dak Nong province have been occurring during the rainy seasons. The change of the soil physical and mechanical parameters due to rainwater infiltration has been considered as the main factor of the slope instability. The soil cohesion and angle of internal friction depend very much on the soil moisture: soil with a lower moisture content has a higher shearing strength than that with higher moisture content. The finite element modeling of moisture transfer in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability and soil-moisture dispersivity is capable of accurately predicting the wetting front development. The element sizes and time steps have been selected based on detailed analysis of analytical error estimation and on the numerical simulations with different element sizes numerical simulation errors. Soil samples had been taken and the soil different suctions and corresponding soil moisture values have been determined in the laboratory. The soil water characteristic curve (SWCC) parameters (a, n and m) have been determined by the best fitting using the least squared error method. The hydraulic conductivity of the saturated soil, one of the key input parameters was also determined. The results of the application to the study area's slope has shown that the wetting front depth can be up to 8 meters for 90 days of moisture transfer due to the rainwater infiltration The wetting front depth and the length of the intermediate part of the moisture distribution curve have increased with the infiltration time. The soil moisture distribution with a depth is an essential information to have soil strength parameters for the slope stability analyses. The slope stability analysis with the soil shear strength parameters which are strictly corresponding with the moisture change would provide the most accurate and reliable slope stability results and provide more reliable slope stabilization solutions.

Влияние климатических изменений на вертикальный влагообмен в почвах (на примере бассейна реки Волги)

The effect of climatic changes on surface and underground runoff cannot be explained without studying such changes on such processes of moisture transfer in soils as infiltration, evaporation, migration of moisture to the frost front. These processes are components of moisture exchange in soils and almost completely determine the mechanisms of runoff formation and its climatic interconformity. The paper discloses the main links of vertical moisture exchange in soils with environmental factors such as temperature, precipitation, wind speed and water vapor pressure. On the example of the Volga basin, changes in moisture flows in soils over the past decades are considered. Methods. To reveal the patterns of moisture exchange, a physically sound mathematical model of vertical heat-moisture transfer in soils and snow cover was used. Numerical experiments were carried out to assess the impact of all the main weather factors that cause long-term changes in vertical moisture flows in soils for the period 1952-2019. Results. Calculations showed that in the 1970s there were significant changes in soil moisture flows. There was a preferential increase in downstream flows and a decrease in upstream flows, which under certain weather conditions led to an increase in the level of groundwater. In recent decades, the growth of descending soil moisture flows in the river basin. Volga and, accordingly, groundwater levels have slowed down.

Experimental Study on Soil Heat and Moisture Transfer with a Flow Heat Source

Experimental Study on Soil Heat and Moisture Transfer with a Flow Heat Source

EVALUATING PREDICTIONS OF THE SOIL MOISTURE MODEL WITH DATA ASSIMILATION BY THE TRIPLE COLLOCATION METHOD

For a long time, ground measurements are considered the most accurate method of regular monitoring of soil moisture. However, ground stations are expensive, require local calibration and thus often not practical to use. Other, more affordable means of soil moisture monitoring can be developed with the recent advancement of Earth remote sensing technologies. In this paper, we describe a nonlinear problem of soil moisture transfer problem with addition of satellite soil moisture measurements. The mathematical model is based on the Richards equation for soil moisture transport, and solved with the finite difference method on implicit iterative scheme. Satellite moisture retrievals are acquired by combining active and passive sensors data with the decomposition algorithm. The satellite data are incorporated into the model with the data assimilation algorithm called Newtonian nudging. This method adds a special ‘nudging’ term into the model governing equation. This assures that the model is corrected by satellite measurements without affecting the process physics. Moreover, we look into the nudging factor problem, and propose a simple empirical relation based on the soil properties for more universally stable work of the method. For validation purpose, we conduct a massive numerical experiments over all registered ground stations in the USA. Evaluation is done by the use of triple collocation method, which allows assessing the errors of three independent data sources. The data sources used for evaluation are the model results, ground station measurements and ERA5 satellite observations. The results demonstrate that the presented model is capable of producing results with close accuracy to the ground station measurements.

Modeling the temperature and humidity conditions of mineral soils in an active layer model taking into account in depth changes in the thermodynamic properties of the soil

The thermal regimes of peat and mineral soils differ significantly. Peat soils are characterized by the presence of a surface peat horizon, which is replaced by organogenic rock. The total thickness of the peat layer can reach several meters. The peat strata is a complex organomineral system with specific properties: high water content and porosity, the content of a large amount of little decomposed organic. For the correct modeling of this type of soil, a transition was made from the approach of modeling heat and moisture transfer in a porous medium with averaged thermodynamic characteristics (porosity, density, hydraulic conductivity …), to modeling heat and moisture transfer for each of the identified soil types with individual properties. In addition, in the modified model, all constants describing the thermodynamic properties of the soil are functions of depth. This made it possible to model soils with a complex soil profile, for example, bog ecosystems (peat deposit and a layer of mineral soil under it). To calculate the thermophysical characteristics of soils, the measured volumetric content of organic matter, mineral particles of different sizes, and soil porosity at all depths were used. Calculations based on the model of the active layer showed that within the framework of the approach used it is possible to correctly reproduce heat and moisture transfer in both mineral and organic soils without adding any runoff-related parameterizations, but using relevant thermophysical characteristics of the soil.