Evaluating Soil Water Matric Pressure and Sorptivity Relationship as Affected by some Properties of a Clay Soil

Sorptivity (S) is the fundamental variable controlling the early infiltration process. Besides soil properties, soil initial water content (θi) and/or matric pressure (hi) are key factors determining extent of S. Assessment of interrelationship among S, hi and soil properties can provide a considerable insight into understanding the behaviour of dry soils to rainfall or irrigation water. This study was conducted to evaluate relationship between S and some selected soil parametric and morphometric properties within a range of hi. Sixteen undisturbed soil samples (5 cm id, 5 cm length) were taken from the topsoil (0-15 cm) of a paddy soil with clay texture. Sorptivity was measured with a mini-disc infiltrometer (MDI) on the samples equilibrated at h, ranging from -20 to -1500 kPa. A parameter (η), representing the relationship between S and hi, was introduced. Correlation analysis was conducted between η and selected soil morphometric and parametric properties. Soil structure and clay content appeared the most important soil attributes influencing S-hi relation between -200 and -1500 kPa. The results provided a fundamental understanding on S-hi-soil properties interrelations in a clay soil. The methodology developed in this study can be used to evaluate S-hi relationship across different soils and scales.

Analysis of 3D infiltration curves measured with disc infiltrometer in heterogeneous soil profiles: Sequential analysis of infiltration data and estimate of β

<p>The 3-D Haverkamp et al. (1994) model for disc infiltrometer measures on homogeneous media involves the following parameters: the soil sorptivity, S, the saturated hydraulic conductivity, Ks, the β parameter and the A= (γ S<sup>2</sup>)/(r<sub>d</sub>*Δθ) term, where r<sub>d</sub> is the disc radius, Δθ is the soil water increase and γ is proportionality constant. Fixed β and A values are commonly used in most cases. S, and Ks can be estimated from the inverse analysis of a cumulative infiltration curve by fitting it the Haverkamp model. For practical reasons, Haverkamp implicit model is replaced by its 4-term (4T) approximate expansion for the transient state. The first part of this work analyzes the influence of layered soils on Ks and S estimates, and designs a new procedure, sequential Analysis of Infiltration curve (SAI), for treating infiltration curves impacted by soil layering. The SAI method analyzes a sequence of increasing dataset for a given infiltration curve and fits to the 4T expansions to estimate Ks, S. Then estimates and RMSE are reported as a function of the number of data points used for the fit. The method was applied on synthetic profiles with homogeneous loam soil, six layered profiles involving a 1, 2 and 3 cm thickness loam layer over silty or sandy loam soils, respectively. Erroneous estimates of Ks and S were obtained when the total infiltration curves were considered for the analysis, regardless of the presence of soil layering. In opposite, estimates were improved using the SAI method for the layered systems. The SAI method relies on the fact that the RMSE increases when the wetting front reaches the interface between the upper layer and the lower layer. Such increase allows (i) the detection of the soil heterogeneity, (ii) the determination of the optimum infiltration time, t<sub>o</sub>, that corresponds to the minimum value of RMSE, and, (iii) accurate estimation the upper layer Ks and S.</p><p>Taking use of the SIA procedure, the second part of this communication studied the relationship between β and A, and proposed a new procedure to improve the estimate of Ks and S and approach β. The analysis was applied on synthetic infiltration curves simulated on homogneneous and layered columns. The results showed that different combinations of β and A resulted in similar Ks. Overall, optimization of Ks, S and A for different β values showed that β had an important effect on A and Ks, but not on S and RMSE.  We propose approaching the optimum β as the β for which is closer to zero, where A and A<sub>exp</sub> are the optimized and measurable parameter, respectively. While the optimum β is calculated, Ks and S are computed by applying the optimum β to the respective quadratic β(Ks) and β(S) relationships. This methodology allowed improving the estimate of Ks giving good approaches of β (36% error) and omitting the erroneous praxis of using constant β and A values.</p><p>Haverkamp, R., et al. 1994. 3. Water Resources Research 30, 2931–2935.</p>

Investigational methods for the modeling of infiltration process in the soil and the estimating the soil hydrodynamic parameters

Unsaturated zone in the soil generally plays an important role in the transfer of water and pollutants in the underground environment. In this context, the determination of the hydrodynamic parameters constitutes an essential step for any study of transfers of water and solutes in the unsaturated zone. The purpose of this article is the estimation the soil hydrodynamic parameters by the direct method and the inverse method, from the infiltration data by using the disc infiltrometer in the soil the basin Loukkos located in northern Morocco. Our results the numerical modeling reproduced correctly the experimental measurements. These results show that the inverse method remains a robust and accurate method for determining the soil hydrodynamic parameters compared to other conventional methods.

A Note on One- and Three-Dimensional Infiltration Analysis from a Mini Disc Infiltrometer

Disc infiltrometers are used to characterize soil hydraulic properties. The purpose of this study was to determine the difference between three- and one-dimensional infiltration and to calculate the infiltration shape parameter γ from a proposed analytical infiltration equation. One- and three-dimensional infiltration tests were done on three repacked soils (loam, sandy loam, and silty clay loam) for two negative pressure heads. A mini disc infiltrometer of a radius of 22.5 mm with suction that ranged from −5 mm to −70 mm was used. The difference between experimental three- and one-dimensional cumulative infiltration was linear with time, which confirmed the proposed equation. In this study, the shape parameter γ seems not to be seriously affected by the soil type and acquires values from 0.561 to 0.615, i.e., smaller than the value γ = 0.75, which is widely used. With these values, the criteria proposed for calculating hydraulic conductivity using three-dimensional infiltration data may be fulfilled in most soils.

Investigation of the Relationship between Three- and One-Dimensional Infiltration Using a Mini Disc Infiltrometer

Disc infiltrometer experiments were conducted in the laboratory on two disturbed soils, a loam and a silty clay loam soil, in order to investigate the relationship between three- and one-dimensional infiltration using the proposed equation of Smettem et al. A mini disc infiltrometer of a radius of 45 mm with suction ranged from −5 mm to −70 mm was used. Three- and one-dimensional infiltration tests were performed on repacked cores by applying pressure heads −70, −40 and −10 mm for loam soil, and −30 and −10 mm for silty clay loam soil. Analysis of the results showed that the difference between the three- and one-dimensional infiltration is linear with time confirming the equation of Smettem et al. [1]. Also, this difference is used to calculate the value of an additional infiltration parameter.

Analysis of Saturation Risk in Sprinkler Irrigation: Case of Cherfech Irrigation Perimeter in Tunisia

This study is targeted to the assessment of the saturation risk in sprinkler irrigation. For this purpose, in situ field trials were carried out to infer the saturated hydraulic conductivity (Ks) and sorptivity (S) using the disc infiltrometer method. Since the measured values of Ks are very close to prescribed application rate, caution is required. In a first step, the pressure head at the wetting front (hf) and the useful porosity (θs – θi) are assumed to be constant. Thus, the logarithmic derivation of the sorptivity provides a relation between relative variations of S and Ks. The ponding time (Ts) is estimated from Green and Ampt (1911) and Philip (1957b) infiltration equations. The risk of saturation is deemed to be inexistent inasmuch as simulated values of Ts are greater than the irrigation times practiced in the zone. In a second step, the values of the pressure head at the wetting front and saturated water content were assumed to be variable with soil texture. Simulations of the ponding time were carried out based on Rawls and al. (1981) data. For the recommended sprinkler spacing in the Cherfech perimeter (12 m × 12 m), the simulations show a good agreement between Ts values generated from Green and Ampt and Philip equations for Ks ranging from 1.5 to 6 mm/h. Moreover, it was established that saturation risk due to a gradual texture variation is virtually inexistent in the conditions prevailing in Cherfech perimeter.