A new equation for the soil water retention curve (original) (raw)
Related papers
A model for soil relative hydraulic conductivity based on the water retention characteristic curve
Water Resources Research, 2001
A simple model is proposed which predicts the relative unsaturated hydraulic conductivity function of nonswelling soils by using the first two moments of their water retention curve (WRC). The model is based on the statistical approach but uses less restrictive assumptions concerning the pore configuration than Mualem's [1976] model. The result is that the relative hydraulic conductivity (RHC) is a power function of the relative contribution of the pores filled with water. It is shown that the power value is related to the coefficient of variation characterizing the retention curve, expressed in terms of the WRC model ofAssouline et al. [1998]. Therefore a relationship is established between the RHC and the soil structure and texture, as reflected by the measured WRC. The model is calibrated on data from eight soils and tested on data from five soils, representing a wide range of soil textures, from sand to silt. The performances of the model are compared to those resulting from the application of Mualem's [1976] model to the analytical expressions of Brooks and Corey [1964] and Assouline et al. [1998] for the WRC. In most of the cases the proposed model improves the fit of the predicted RHC to the measured data, although its performance in the case of loam soils seems to be weak.
A closed form equation for predicting the hydraulic conductivity of unsaturated soils
1980
A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, K r , when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for K r (h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity.
A Model to Predict the Unsaturated Hydraulic Conductivity from Basic Soil Properties
The relative hydraulic conductivity kr of unsaturated soils is typically obtained from their water retention curve (WRC). In this paper, the modified Kovács (MK) model developed to predict the WRC is combined with the Mualem model to predict the kr function using basic geotechnical properties of granular soils. The ensuing equations, which have been implemented into MATLAB, have been validated against existing solutions and against testing data. It is shown here that the predictive results show a good agreement with the experimental results obtained from tests performed by the Authors and taken from the literature. The applicability of the proposed approach is briefly discussed. RÉSUMÉ
Field-Obtained Soil Water Characteristic Curves and Hydraulic Conductivity Functions
Journal of Irrigation and Drainage Engineering, 2018
A compacted clay liner (test pad) was constructed and instrumented with volumetric water content and soil matric potential sensors to determine soil water characteristic curves (SWCC) and hydraulic conductivity (k) functions. Specifically, the compacted clay liner was subjected to an infiltration cycle during a sealed double ring infiltrometer (SDRI) test followed by a drying cycle. After the drying cycle, Shelby tube samples were collected from the compacted clay liner and flexible wall permeability (FWP) tests were conducted on sub-samples to determine the saturated hydraulic conductivity. Moreover, two computer programs (RETC and UNSAT-H) were utilized to model the SWCCs and k-functions of the soil based on obtained measurements including the volumetric water content ( v), the soil matric potential (), and the saturated hudraulic conductivity (k s). Results obtained from the RETC program (θ s , θ r , α, n and k s) were ingested into UNSAT-I would like to express the deepest appreciation to my thesis director, Dr. Richard A. Coffman for giving me the opportunity to conduct this research and guiding me along the way. Without his guidance, mentorship and persistent help this thesis would not have been possible. I would also like to thank my committee members, Dr. Norman D. Dennis and Dr. Michelle Bernhardt for being extraordinary committee members who showed me the road and helped to get me started on the path to this degree. I would also like to thank Cyrus Garner for assisting me to collect and reduce data for the research presented in this document. Also, a special thanks goes out to the students:
Derivation of Soil Moisture Retention Characteristics from Saturated Hydraulic Conductivity
Knowledge of the physics of soil water movement is crucial to the solution of many problems in watershed hydrology, for example, the prediction of runoff and infiltration following precipitation, the subsequent distribution of infiltrated water by drainage and evaporation, and estimation of the contribution of various parts of a watershed to the ground water storage. Mathematical models of hydrologic and agricultural systems require knowledge of the relationships between soil moisture content (θ), soil water pressure (h) and unsaturated hydraulic conductivity (K).
Predicting unsaturated hydraulic conductivity of soil based on some basic soil properties
Soil and Tillage Research, 2001
Soil hydraulic conductivity is a crucial parameter in modeling¯ow process in soils and deciding water management. In this study, by combining the non-similar media concept (NSMC) to the one-parameter model of Brooks and Corey, a new NSMCbased model for estimating unsaturated hydraulic conductivity of various soils was presented. The main inputs are soil bulk density, particle-size distribution, soil water retention characteristic and saturated hydraulic conductivity of soil. The results indicated that the NSMC-based model could generally more accurately predict unsaturated hydraulic conductivity of soils, as compared to four one-parameter models and van Genuchten±Mualem model. This study, by introducing NSMC, provided a new way to incorporate soil physical heterogeneity into soil hydraulic simulation, and hence NSMC-based approach is expected to improve ef®ciency of the existing models in the simulation of soil water¯ow.
Journal of Hydrology, 1984
A simple algorithm is presented that estimates the parameters contained in the Van Genuchten analytical soil-moisture characteristic curves. No graphical estimations are involved and convergence is rapid. The values obtained from the simple algorithm are introduced as starting values in a Newton-Raphson minimization procedure which yields more accurate evaluations of the parameters. The very good approximation offered by the simple algorithm is responsible for the small number of subsequent Newton-Raphson iterations. Based on the final results of the minimization scheme an analytical sensitivity analysis is carried out with respect to changes induced in the basic parameter "residual water content". Soils with a wide range of hydraulic properties were subjected to the above analysis. It is demonstrated that for lower water contents the sensitivity of the hydraulic conductivity becomes by 2-5 orders of magnitude larger than it is for higher ones.
Journal of Hydrology, 2015
Soil water retention curve (SWRC) and saturated hydraulic conductivity (SHC) are key hydraulic properties for unsaturated zone hydrology and groundwater. In particular, SWRC provides useful information on entry pore-size distribution, and SHC is required for flow and transport modeling in the hydrologic cycle. Not only the SWRC and SHC measurements are time-consuming, but also scale dependent. This means as soil column volume increases, variability of the SWRC and SHC decreases. Although prediction of the SWRC and SHC from available parameters, such as textural data, organic matter, and bulk density have been under investigation for decades, up to now no research has focused on the effect of measurement scale on the soil hydraulic properties pedotransfer functions development. In the literature, several data mining approaches have been applied, such as multiple linear regression, artificial neural networks, group method of 2 data handling. However, in this study we develop pedotransfer functions using a novel approach called contrast pattern aided regression (CPXR) and compare it with the multiple linear regression method. For this purpose, two databases including 210 and 213 soil samples are collected to develop and evaluate pedotransfer functions for the SWRC and SHC, respectively, from the UNSODA database. The 10-fold cross-validation method is applied to evaluate the accuracy and reliability of the proposed regressionbased models. Our results show that including measurement scale parameters, such as sample internal diameter and length could substantially improve the accuracy of the SWRC and SHC pedotransfer functions developed using the CPXR method, while this is not the case when MLR is used. Moreover, the CPXR method yields remarkably more accurate soil water retention curve and saturated hydraulic conductivity predictions than the MLR approach.
Comparison of Six Methods To Determine Unsaturated Soil Hydraulic Conductivity
Soil Science Society of America Journal, 1994
Knowledge of soil hydraulic properties is required for soil-water flow models. Although many studies of individual methods exist, comparisons of methods are uncommon. Therefore, we compared application ranges and results for six laboratory methods for determining hydraulic conductivity or diffusivity on eolian sand, eolian silt loam, marine sandy loam, and fluviatile silt loam. The methods, hot air, sorptivity, crust, drip inflltrometer, Wind's evaporation, and one-step outflow, fall into three groups: (i) those that only yield a conductivity curve; (ii) those that yield a simultaneous estimate of conductivity, diffusivity, water content, and pressure head; and (iii) those that yield a diffusivity curve. Diffusivities were converted to conductivities with a water retention curve. One main difference between the methods was the pressure head-water content range. Despite the large differences between the methods, the results for the first two groups tended to be similar. The results of the third group did not match well with those of the first two. It proved difficult to compare these methods correctly due to hysteresis.