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The HYDRUS-1D Software Package for Simulating the One-Dimensional Movement of Water, Heat, and Multiple Solutes in Variably-Saturated Media
... completely saturated porous media (Šimůnek et al., 2009). The model numerically solves Richards' equation to predict water flow and, advection-dispersion and diffusion equations to simulate solute transport in the liquid and gaseous phase, respectively, (Šimůnek et al., 2009;Kanzari et al., 2018). The water flow equation can be considered of single porosity (such as van Genuchten-Mualem), dual-porosity or dual-permeability type flow, with or without hysteresis. ...
... The model is driven by meteorological data, soil hydraulic parameters and geometry information in a selected timestep. Meteorological data include time series of precipitation, ET and air temperature, soil hydraulic parameters include the van Genuchten-Mualem parameters (θ r , θ s , a, n, K s, and l) and geometry information include length units, soil depth and a number of soil materials and layers (Šimůnek et al., 2009;Saeidi et al., 2023). ...
Climate change, food and water security and ecosystem sustainable management are tightly interlinked and require holistic approaches to achieve solutions that do not impact adversely one-another. The objective of this work was to conduct studies, collect data and assess the Water-Ecosystem-Food (WEF) nexus in avocado plantations in the Mediterranean region systematically to minimize the environmental footprint while maximizing the benefits for the farmer and the environment. The study includes two distinct experiments; the first addresses the impact of soil organic amendments addition to optimize the WEF nexus and the second monitors experimentally crop water needs and thus illustrates how irrigation practices aided by technology can reduce substantially water consumption. The results showed that organic amendments addition improves fertility, nutrient sequestration and structure but only had a weak effect on biodiversity by increasing the number of unique species. For the development of an efficient irrigation system it is necessary to determine the radius around the tree, the depth of the roots and the time required for the water to reach the active root zone to determine the amount and duration of irrigation. In this way sufficient water will be added to replenish the soil moisture deficit created due to the evapotranspiration. HYDRUS-1D model was used to simulate soil moisture and the hydrologic budget of an avocado tree located in Koiliaris river basin and confirm the percolation losses to groundwater. The results of this study showed that the actual irrigation needs of avocados in the Mediterranean is less than 2,000 m ³ /ha which is 75% less than what is recommended and could become the primary measure for the mitigation of climate change impacts especially in semi-arid regions such as the Mediterranean.
... Assume that the immobile moisture content is redundant in water flow researches and the soil moisture at permanent wilting point is redundant in root water uptake. The hydraulic parameter of Van-genuchten n, m, and α could be estimated if SSI is known (reverse solution) or from HYDRUS 1D [6]. ...
... Conceptual physical nonequilibrium models for water flow and solute transport. In the plots, θ is the water content, m is mobile phase, im is immobile phase, M is soil matrix, and f is soil fracture respectively; c is concentrations of corresponding regions, with subscripts having the same meaning as for water contents, while S is the total solute content of the liquid phase [6]. ...
... We employed the HYDRUS-1D software (version 4) [32] for simulating the process of capillary water. Based on the experimental work, a numerical model was established using the Richards's equation. ...
Capillary water, serving as a crucial intermediary between groundwater and crop root layer moisture, is important for both soil retention and crop utilization. To investigate the effect of mulched drip irrigation (MDI) on upward capillary water in cotton fields with different application years (0, 10, 14, 18, 20, and 24 years) in the saline–sodic region of Northwest China, an indoor soil column test (one-dimensional capillary water rise experiment) was conducted. The results showed that the wetting front transport law, capillary water recharge, and wetting front transport rate over time exhibited an increasing trend in the early stages of MDI application (10 and 14 years), peaking at 18 years of application, followed by a decreasing trend. The relationship between the capillary water recharge and rising height was fitted based on the Green–Ampt model, and their slopes reveal that 14 and 18 years of MDI application required the largest amount of water per unit distance, indicating an excellent water-holding capacity beneficial for plant growth. Conversely, 0 years required the smallest amount of water per unit distance. Based on the movement characteristics of upper capillary water, we confirmed that the MDI application years (0–18 years) improves soil infiltration capacity, while the long-term application years (18–24 years) reduces groundwater replenishment to the soil. Furthermore, the HYDRUS-1D model was employed to simulate the capillary water rise process and soil moisture distribution under different MDl application years. The results showed an excellent consistency with the soil column experiments, confirming the accuracy of HYDRUS-1D in simulating the capillary water dynamics in saline–sodic areas. The results would provide suggestions to achieve the sustainable development of long-term drip-irrigated cotton fields.
This study aims to present a comprehensive study on the risks associated with the residual presence and transport of Escherichia coli (E. coli) in soil following the application of livestock manure in Chinese farmlands by integrating machine learning algorithms with mechanism-based models (Phydrus). We initially review 28 published papers to gather data on E. coli's die-off and attachment characteristics in soil. Machine learning models, including deep learning and gradient boosting machine, are employed to predict key parameters such as the die-off rate of E. coli and first-order attachment coefficient in soil. Then, Phydrus was used to simulate E. coli transport and survival in 23692 subregions in China. The model considered regional differences in E. coli residual risk and transport, influenced by soil properties, soil depths, precipitation, seasonal variations, and regional disparities. The findings indicate higher residual risks in regions such as the Northeast China, Eastern Qinghai-Tibet Plateau, and pronounced transport risks in the fringe of the Sichuan Basin fringe, the Loess Plateau, the North China Plain, the Northeast Plain, the Shigatse Basin, and the Shangri-La region. The study also demonstrates a significant reduction in both residual and transport risks one month after manure application, highlighting the importance of timing manure application and implementing region-specific standards. This research contributes to the broader understanding of pathogen behavior in agricultural soils and offers practical guidelines for managing the risks associated with manure use. This study's comprehensive method offers a potentially valuable tool for evaluating microbial contaminants in agricultural soils across the globe.
In the previous version of the computer program SWATRE calculations of the soil motsture distrihution and the waterbalsnee stoppad when the water table was rising close to the soil surface. This restrietion was caused by the way of computation of the height of the groundwater level. In practice, situalfons may occur in which the groundwater table is rlsing up to or even beyond the soil surface. This paper presents an extension of SWATRE, which is capable to deal with this type of situation, including the ponding phenomenum.
Introduction: This report describes the computer program for the computation of chemical equilibria in aqueous systems, MINEQL. The purpose of the report is to present the program in sufficient detail that the reader not only can use the program exactly as it is written, but also can modify it to suit whatever his particular needs may be. The evolution of the program, examples of its use, and general approach to the chemical equilibrium problem are described in Part I of the report. Part II presents a "MINEQL-1 User's Manual". A detailed mathematical description of the solution to the chemical equilibrium problem used in MINEQL appears in Appendix 1. It was felt that the solution could best be presented by an abstract description of the mathematical problem (without any reference to its chemical analog), followed by a very simple example of a chemical problem (which is given in Appendix 2). This avoids the intermingling of chemical and mathematical concepts which is sometimes confusing. Appendix 3 gives a description of the program itself. The three appendices are related in that they present the same concepts - the actual theory and its application in MINEQL - from three different viewpoints: mathematical, chemical, and computational. They should be read in conjunction with one another. First the concepts involved in the basic chemical equilibrium problem, (i.e., where there are no solid phases present) should be mastered, and then the extension to the consideration of solid phases, which is somewhat more complicated, should be undertaken. This report contains a complete description of all of the concepts employed in the program MINEQL. However, a working knowledge of the program is obtainable without attention to all of the details. It is hoped that this roadmap through MINEQL will enable the reader to maximize his use of the program without becoming bogged down in the details of the report.
An approach is presented to infiltration and drainage of one square pulse of water into and from porous media containing large pores, applying kinematic wave theory. The governing flow equation is a two-parameter power function. The approach is applied to infiltration-drainage experiments performed on a water saturated block of polyester consolidated sand containing large pores. The derivation of the two parameters of the flow equation is demonstrated.
Research and concepts related to the response of crops to limited oxygen and carbon dioxide transfer in the soil profile, produced by excess soil water conditions, and the mechanisms for gaseous transfer are reviewed and evaluated. The conceptual framework for a physically-based model capable of defining the dynamic status of water, air, oxygen, and carbon dioxide in the root zone in proposed.
The understanding of the processes of dissolution, volatilization, and gas-liquid partitioning in porous media is very limited. The few models which attempt to characterize the transport of volatile organics in variably saturated media all assume that mass transfer processes are at equilibrium. In addition, gas phase advection is neglected by assuming that gas phase pressures are uniformly atmospheric and that density gradients are negligible. In this study a model was developed to solve for water phase flow and transport and density dependent gas phase flow and transport. Simple expressions for dissolution, volatilization, and gas-liquid partitioning, employing the concept of an overall mass transfer coefficient, were incorporated into the model. The transport of trichloroethylene in a variably saturated vertical cross section, under a variety of conditions, was simulated. Results of the simulations appeared qualitatively correct. The importance of gas phase processes in increasing subsurface contamination from volatile organics, and in dissipating residual amounts of these substances, was demonstrated. The lack of similar analytical and/or numerical models, or suitable experimental studies, excluded the possibility of validating, or verifying, the model.
A hysteretic model for two-phase permeability (k)-saturation (S)-pressure (P) relations is outlined that accounts for effects of nonwetting fluid entrapment. The model can be employed in unsaturated fluid flow computer codes to predict temporal and spatial fluid distributions. Consideration is given to hysteresis in S-P relations caused by contact angle, irregular pore geometry, and nonwetting fluid entrapment effects and to hysteresis in k-S relations caused by nonwetting fluid entrapment effects. An air-water flow experiment is conducted with a 72-cm vertical soil column where the water table is fluctuated to generate scanning S-P paths. Water contents are measured via a gamma radiation system, and water pressures are measured via pressure transducers connected to ceramic tensiometers inserted in the soil column. Computer simulations of the experiment employing the hysteretic k-S-P model and a nonhysteretic k-S-P are compared with measured water contents and pressures. Close agreement is found between experimental water contents and those predicted by a numerical code employing the hysteretic k-S-P relations. When nonhysteretic k-S-P constitutive relations are utilized, there is poor agreement between measured and predicted water saturations of the scanning paths. Only one more parameter is needed to model two-phase hysteretic fluid behavior than to model nonhysteretic behavior. Results of this study suggest that consideration should be given to effects of hysteresis in k-S-P relations to accurately predict fluid distributions.
The UNSAT-H model was developed at Pacific Northwest National Laboratory (PNNL) to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. To achieve the above goals for assessing water dynamics and estimating recharge rates, the UNSAT-H addresses soil water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow. The UNSAT-H model simulates liquid water flow using the Richards equation, water vapor diffusion using Fick's law, and sensible heat flow using the Fourier equation. This report documents UNSAT-H Version 3.0. The report includes the bases for the conceptual model and its numerical implementation, benchmark test cases, example simulations involving layered soils and plants, and the code manual. Version 3.0 is an enhanced-capability update of UNSAT-H Version 2.0 (Fayer Jones 1990). New features include hysteresis, an iterative solution of head and temperature, an energy balance check, the modified Picard solution technique, additional hydraulic functions, multiple year simulation capability, and general enhancements. This report includes eight example problems. The first four are verification tests of UNSAT-H capabilities. The second four example problems are demonstrations of real-world situations.
Fixed gradient models result when the gradient term in the soil moisture
equation is assumed to vary only with depth (remains invariant in time).
The fixed gradient assumption results in a first-order partial
differential equation that is transformable to a mathematical form
identical to that for a uniform soil. When the transformation was
applied to field data, all water content data were found to plot along a
single curve. Assuming a fixed gradient and an exponential form for
K(Θ) resulted in a fitted curve with an r2 = 0.847
(d.f. = 405) when data from three sites and seven depths were used.
Assuming a power function for K(Θ) resulted in a similar
r2. Prior to applying the transform, hydraulic conductivity
required 42, 42, and 63 parameters to fit data obtained at the 21
spatial points sampled, assuming a Davidson, Watson or Brooks and Corey
function, respectively. With the transform 23, 23, and 24 parameters
were required for the three K(Θ) functions, respectively.
Data obtained from careful water balance studies on water uptake by the roots of red cabbage are compared with results obtained from a modified numerical model of Nimah and Hanks. In the modified model the air dry moisture content at the soil surface may vary with time depending on meteorological conditions. The maximum possible rate of evapotranspiration is calculated by considering both meteorological conditions and crop properties. Data are quoted to suggest that the coefficient of the root sink may sometimes vary exponentially with depth. A period of 7 weeks was simulated, and the calculated weekly moisture profiles did not agree completely with those measured in the field. On the other hand, the calculated cumulative rates of evaporation and transpiration were in excellent agreement with the field data. When the original model was used without the suggested modifications, the agreement of these rates with the field data was not as good, an indication that some of these modifications actually improve the predictive capabilities of the model.