SWRC fit - a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure (original) (raw)
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Evaluation of Different Models for Predicting Soil Water Retention from A Semiarid Region of Duhok
مجلة جامعة دهوك, 2022
A study was carried out to examine the capability of bi and uni-models to explore water retention data for two different textured soils from a semiarid region Duhok-Iraqi Kurdistan. A soil hydraulic model, can be used to derive the parameters of soil hydraulic properties for describing soil water movement. The program "SWRC Fit," which performs nonlinear fitting of soil water retention curves for the two examined soils using six models, was employed for this purpose. The six models are the Brooks Corey, van Genuchten, Kosugi, Fredlund and Xing model as uni models and Durner and Seki as a bimodal model used for this purpose. The program can be carried out straightly from a web page at http://purl.org/net/swrc/; The program was used for determining Fifteen parameters of soil hydraulic for two different textured soils. As related to Berderash sandy loam soil the LN uni-model revealed better performance than the FX, BC and VG models and at same time the FX, BC and VG models exhibit similar fitting precision on average. Whereas bi-models is shown that the Durner's bi-model (DB) revealed very well fitting performance than that of the bi-log-normal distribution model (BL) models, regarding to Zawita clay soil it revealed that the unimodels, of BC, VG, FX and LN revealed good fitting performance with similar fitting precision on average. Whereas in bi-models it was noticed that the log-normal distribution model (BL) gave very wellsuitable performance than that of the Durner's b-model (DB). After comparing between the uni-models and bi-models of the six mentioned soil hydraulic models from accuracy and coefficient determination (R 2), for two different textured soils under the study it can be illustrated: firstly, for fine texture soil (clay soil) the most precision fitting performance was found by model (BL), whereas for light texture soil (sandy loam soil) the most very well-fitting performance was noticed by (DB) model, and secondly the bi-models hydraulic were better than uni-models in fitting performance.
Modelling soil water retention to identify management influence on soil pore characteristics
Anais Da Academia Brasileira De Ciencias, 2022
The water retention curve is widely used in studies involving soil. The management systems directly infl uence soil structure by altering water retention dynamics. Several equations are used to adjust the retention of water in the soil, but most of the time, the choice of these models occurs in an arbitrary way. From this problem, it was proposed with the present study to relate the best mathematical model to water retention, taking into account the different management systems adopted, based on previously established adjustment criteria. For the accomplishment the study, a soil of caulinitic mineralogy and average texture was utilized. The treatments were area under native Cerrado (Savanna), eucalyptus plantation with six and twelve years of cultivation, pasture with two and six years of cultivation, conventional plantation with two and eight years of cultivation, no-till with three and six years of cultivation. From the adjustment criteria for non-linear models, it was found that the management infl uences the choice of the water retention model. It is possible to observe that the greatest divergences between the models occurred close to the soil saturation zone, and that the Fredlung-Xing model is more effi cient in adjusting the water retention curve under conservationist management systems.
A conceptual model of the soil water retention curve
Water Resources Research, 1998
A conceptual model based on the assumption that soil structure evolves from a uniform random fragmentation process is proposed to define the water retention function. The fragmentation process determines the particle size distribution of the soil. The transformation of particles volumes into pore volumes via a power function and the adoption of the capillarity equation lead to an expression for the water retention curve. This expression presents two fitting parameters only. The proposed model is tested on water retention data sets of 12 soils representing a wide range of soil textures, from sand to clay. The agreement between the fitted curves and the measured data is very good. The performances of the model are also compared with those of the two-parameter models of van Genuchten [1980] and Russo [1988] for the water retention function. In general, the proposed model exhibits increased flexibility and improves the fit at both the high and the low water contents range.
A new equation for the soil water retention curve
European Journal of Soil Science
The soil water retention curve is a fundamental characteristic of unsaturated zone flow and transport properties. Recent studies show that an air-entry value is needed in a soil water retention equation in order to provide a better prediction of relative hydraulic conductivity. A new equation considering the air-entry value is proposed to describe the soil water retention curve. The performance of the proposed equation is contrasted with a well-supported equation by comparing measured and calculated data for 14 soils, representing various soil textures, which range from sandstone to clay. Results show that the proposed equation provides adequate characterization of the soil water retention curves. The equation for predicting relative hydraulic conductivity is derived from the proposed soil water retention equation. An empirical equation for relative hydraulic conductivity is also used. Our results show that the agreement between the predicted and measured relative hydraulic conducti...
Comparing the Applicability of Soil Water Retention Models
2016
Recently, the public has become more aware of the environmental problems facing our planet today. Underground water pollution is one of these problems, and it requires serious attention. As a result, many studies have been performed to examine the movement of water within soil. These studies present many new models for determining soil water retention rates. It is essential that these models be investigated for accuracy and applicability. This study attempts to analyze three of these well-known water retention models: Campbell, Saxton, and Huston-Cass. To analyze these models, the pressure plate test (ASTM C199-09) was performed on soil samples with different soil textures and from different geographical locations within the country of Iran. Using these results, the general applicability of each model was measured using the 1:1 slope line correlation method. In addition, the accuracy and applicability of each model was measured by calculating the Root Mean Square Error (RMSE) and th...
Comparison of Unimodal Analytical Expressions for the Soil-Water Retention Curve
Soil Science Society of America Journal, 2005
dictive models. One of the most manifest examples is the use of the SWRC to indirectly determine the unsatu-This study was conducted to evaluate ten closed-form unimodal anarated hydraulic conductivity, using statistical pore-size lytical expressions to describe the soil-water retention curve, in terms distribution models (see e.g., Mualem, 1986, for a review), of their accuracy, linearity, Akaike Information Criterion (AIC), and prediction potential. The latter was evaluated by correlating the model which are well represented by the SWRC. Such SWRCs parameters to basic soil properties. Soil samples were taken in duplican be obtained by fitting closed-form analytical exprescate from 48 horizons of 24 soil series in Flanders, Belgium. All sample sions containing several parameters to discrete (, ) data locations were under forest and hence the samples had, besides their sets, which can be obtained through laboratory experidifference in texture, a high variety in bulk density ( b ) and organic matments or from pedotransfer functions (PTFs) that estiter content (OM). The van Genuchten model with m as a free parammate distinct SWRC data pairs. The most widely adopted eter showed the highest overall performance in terms of goodnessand best-performing PTFs enable, however, to directly of-fit. It had the highest accuracy, the highest degree of linearity, and predict the parameters of some closed-form analytical the lowest AIC value. However, it had a low prediction potential. expressions (Cornelis et al., 2001). Applications of closed-Imposing the constraint m ϭ 1 Ϫ 1/n and hence reducing the number form analytical expressions can also be attractive for other of model parameters by one, increased the prediction potential of the model significantly, without loosing much of the model's accuracy and W.M. Cornelis, M. Khlosi, R. Hartmann, and M. Van Meirvenne, does not pretend to be complete and focuses only on unimodal Dep. Soil Management and Soil Care, Ghent Univ., Coupure links expressions. One of the first expressions for the SWRC was 653, B-9000 Ghent, Belgium; and B. De Vos, Institute of Forestry the still widely used four-parameter power function presented and Game Management, Ministry of the Flemish Community, Gaverby Brooks and Corey (1964) (BC model): straat 4, B-9500 Geraardsbergen, Belgium. Mention of the company name is for the convenience of the reader and does not constitute Abbreviations: A1, Assouline et al. (1998) with five free parameters; any endorsement in whatever sense from the authors.
Soil and Tillage Research, 2004
The unsaturated soil hydraulic functions involving the soil-water retention curve (SWRC) and the hydraulic conductivity provide useful integrated indices of soil quality. Existing and newly devised methods were used to formulate pedotransfer functions (PTFs) that predict the SWRC from readily available soil data. The PTFs were calibrated using a large soils database from Hungary. The database contains measured soil-water retention data, the dry bulk density, sand, silt and clay percentages, and the organic matter content of 305 soil layers from some 80 soil profiles. A three-parameter van Genuchten type function was fitted to the measured retention data to obtain SWRC parameters for each soil sample in the database. Using a quasi-random procedure, the database was divided into ''evaluation'' (EVAL) and ''test'' (TEST) parts containing 225 and 80 soil samples, respectively. Linear PTFs for the SWRC parameters were calculated for the EVAL database. The PTFs used for this purpose particle-size percentages, dry bulk density, organic matter content, and the sand/silt ratio, as well as simple transforms (such as logarithms and products) of these independent variables. Of the various independent variables, the eight most significant were used to calculate the different PTFs. A nonlinear (NL) predictive method was obtained by substituting the linear PTFs directly into the SWRC equation, and subsequently adjusting the PTF parameters to all retention data of the EVAL database. The estimation error (SSQ) and efficiency (EE) were used to compare the effectiveness of the linear and nonlinearly adjusted PTFs. We found that EE of the EVAL and the TEST databases increased by 4 and 7%, respectively, using the second nonlinear optimization approach.
MATEC Web of Conferences, 2021
Soil-water retention curve (SWRC) has a wide application in geoenvironmental engineering from the predication of unsaturated shear strength to transient two-phase flow and stability analyses. Although various SWRC models have been proposed to take into account some influencing factors, less attention has been given to consider the effects of pore fluid osmotic potential. Therefore, the key objective of this study is to extend van Genchten's model so that osmotic potential is considered as an independent factor governing the SWRC behavior. The new model comprises only six variables, which can be calibrated through minimal experimental measurements. More importantly, most of the model parameters have physical meaning by correlating macroscopic volumetric behavior and general trends of SWRC to osmotic potential. The results of validation tests revealed that the new osmotic-dependent SWRC model can predict the retention data in terms of both total and matric suction for two differen...
Hydrology Research, 2015
This study investigated the impact of different input variables on the predictability of the water content using soil water retention curve (SWRC) models. The particle and aggregate size distribution model parameters were calculated by fitting the Perrier model to the related distributions for 75 soil samples. Nine SWRC models were fitted to the experimental data and their coefficients were obtained. The regression method was used to estimate the coefficients for nine SWRC models at three input levels. Cluster analysis classified the SWRC models into more homogeneous groups according to the accuracy of their predictions. The SWRC estimated using the Gardner model had the highest accuracy, but it was not an appropriate model for the soils because of its low fitting accuracy. Boltzman, Campbell, and Fermi models obtained the highest accuracy after the Gardner model. The Durner model yielded the lowest prediction accuracy due to the lack of correlation between the input variables and c...