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Abstract Estimation of soil sorptivity (S) and hydraulic conductivity (K) is fundamental to model the water infiltration into the soil. This process can be affected by soil water repellency, which is defined as a reduction in soil wettability due to coating of soil particles by hydrophobic substances. Unlike to wettable soils, this phenomenon can generate infiltration curves with double-slope shape: a transient infiltration curve followed by a steady-state section. Because the topsoil final volumetric water content (θ 1) of the transient phase of the double-slope curve is not a measurable data, in principle, the standard model based on the Haverkamp et al. (1994) model cannot be used to estimate S and K. This work presents two different approaches based on the Haverkamp et al. (1994) equation, which allow estimating S and K from the first phase of a double-slope infiltration curve, when θ 1 data are not available. The methods, which are based on the analysis of both short-medium time transient infiltration curve (Tr) and the combination of both short-medium transient and steady-state infiltration steps (Mx), were applied on 20 soils affected by different degrees of water repellency. The Haverkamp et al. (1994) model was also valid for infiltration curves measured on hydrophobic soils, and the final volumetric water content was not an essential data to estimate K and S. Although the steady-state infiltration rate (q 1) calculated with Mx was about 26% larger than that estimated with Tr , comparable K and S values were obtained with both methods. Overall, a large dispersion on the estimate of θ 1 was observed with both methods. The gravimetric time, t grav , estimated in the studied soils was low, <500 s. While the Mx method required simpler numerical calculus, Tr looked like to be more robust and less subjective. Highlights • This work analyzes the first part of a bi-slope infiltration curve affected by SWR. • A first method (Tr) estimates K and S from the transient infiltration curve. • The second one (Mx) combines short-transient and steady-state infiltration analysis. • The methods were applied on 20 soils affected by SWR. • Mx requires less numerical calculus, but Tr was more robust and less subjective. [ABSTRACT FROM AUTHOR]

• A new method to simultaneously estimate soil hydraulic properties is presented. • K s , α and n are estimated from inverse analysis of an upward infiltration curve. • The method is evaluated on different synthetic and experimental soils. • Accurate estimates of K s , α and n are obtained in the theoretical curves. • The method allows accurate estimates of K s and n in all experimental soils. This paper presents a new laboratory method to simultaneously estimate K s and α and n parameters of the van Genuchten (1980) θ (h) from the inverse analysis of an upward infiltration curve measured in a 5-cm high soil column. The method was evaluated on synthetic 1D infiltration curves generated for a theoretical loamy sand, loam and clay soil. The influence of the soil initial condition on the inverse analysis was also studied. Next, an optimization method was presented and tested on eight theoretical soils (from loamy sand to clay). The method was subsequently applied to experimental curves measured on five sieved soils (from sand to clay) packed in 5-cm high and diameter cylinders. The K s , α and n values estimated from the inverse analysis of the experimental curves were compared to those measured by Darcy and the pressure cell method (PC). The initial soil tension, h i , which had an important influence on the optimization, was fixed to −6.0·105 cm. The optimization method resulted robust and allowed accurate estimates of the actual hydraulic parameters. A close to one relationship (R2 = 0.99) was observed between the theoretical K s , α and n and the corresponding values obtained with the inverse analysis. Regarding to the experimental soils, significant relationships close to one were obtained between K s and n (R2 > 0.98) estimated from inverse analysis and those measured with Darcy and PC. A non-significant relationship with slope away from one was found for α. [ABSTRACT FROM AUTHOR]

The soil sorptivity, S , which is defined as a measure of the capacity of a porous medium to absorb or desorb liquid by capillarity, is commonly estimated under laboratory conditions from upward infiltration measurements. The objective of this work is to compare different methods to estimate S from a single upward infiltration curve obtained from both theoretical and experimental soils. An additional analysis of the influence of synthetic infiltration noise on the estimation of S was also performed on the theoretical soils. Five different methods were compared: Short Time model for horizontal infiltration (ST), the Cumulative Linearization method (CL) and the Differentiated Linearization (DL) linear regressions models, Short-time (SIM) methods that use the simplified Haverkamp et al. (1994) model, and Complete-time (CIM) upward infiltration method that uses the quasi-analytical Haverkamp et al. (1994) function. Since finite soil columns were considered, the saturated hydraulic conductivity needed to estimate S with the Haverkamp et al. (1994) model was calculated from an overpressure step at the end of the water absorption process, using the Darcy's law. The methods were contrasted on four theoretical and six sieved experimental soils, ranging from sand to clay textures. Although all methods showed acceptable estimates of S on clean theoretical upward infiltration curves, the ST, SIM and CIM were the methods that gave significant ( p < 0.001) regression analysis on noisied infiltration curves, and only SIM and CIM presented a relative error < 1%. From these results we can conclude that although acceptable approaches of S were obtained with the simplest ST method, the CIM procedure was the most accurate method to estimate S in both clean and noised theoretical and experimental upward infiltration curves. [ABSTRACT FROM AUTHOR]

Determination of saturated hydraulic conductivity,Ks, and the van Genuchten water retention curveθ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimateKs,αandnfrom numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces,Ks–n, α–nandKs–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h+ Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils. [ABSTRACT FROM PUBLISHER]

The water retention curve ( θ ( h )), which defines the relationship between the volumetric water content ( θ ) and the matric potential ( h ), is of paramount importance to characterize the hydraulic behaviour of soils. Because current methods to estimate θ ( h ) are, in general, tedious and time consuming, alternative procedures to determine θ ( h ) are needed. Using an upward infiltration curve, the main objective of this work is to present a method to determine the parameters of the van Genuchten (1980) water retention curve ( α and n ) from the sorptivity ( S ) and the β parameter defined in the 1D infiltration equation proposed by Haverkamp et al. (1994). The first specific objective is to present an equation, based on the Haverkamp et al. (1994) analysis, which allows describing an upward infiltration process. Secondary, assuming a known saturated hydraulic conductivity, K s , calculated on a finite soil column by the Darcy’s law, a numerical procedure to calculate S and β by the inverse analysis of an exfiltration curve is presented. Finally, the α and n values are numerically calculated from K s , S and β . To accomplish the first specific objective, cumulative upward infiltration curves simulated with HYDRUS-1D for sand, loam, silt and clay soils were compared to those calculated with the proposed equation, after applying the corresponding β and S calculated from the theoretical K s , α and n . The same curves were used to: (i) study the influence of the exfiltration time on S and β estimations, (ii) evaluate the limits of the inverse analysis, and (iii) validate the feasibility of the method to estimate α and n . Next, the θ ( h ) parameters estimated with the numerical method on experimental soils were compared to those obtained with pressure cells. The results showed that the upward infiltration curve could be correctly described by the modified Haverkamp et al. (1994) equation. While S was only affected by early-time exfiltration data, the β parameter had a significant influence on the long-time exfiltration curve, which accuracy increased with time. The 1D infiltration model was only suitable for β < 1.7 (sand, loam and silt). After omitting the clay soil, an excellent relationship (R 2 = 0.99, p < 0.005) was observed between the theoretical α and n values of the synthetic soils and those estimated from the inverse analysis. Consistent results, with a significant relationship (p < 0.001) between the n values estimated with the pressure cell and the upward infiltration analysis, were also obtained on the experimental soils. [ABSTRACT FROM AUTHOR]

• This method estimated K s , θ s , n and α dr of a soil column by inverse analysis. • 1D infiltration followed by successive steady-states drainages were measured. • The drainage curves are generated by a differential h between the top and the bottom. • The method was tested on 2.5 cm high synthetic and experimental soil columns. • Accurate estimates of θ s , K s , α dr and n were obtained. Determination of the saturated hydraulic conductivity, K s , and the water retention curve, θ(h) , is of paramount importance to characterize the hydraulic behavior of the vadose zone. Given the van Genuchten hydraulic model, defined by the residual, θ r , and saturated, θ s , volumetric water content and the α and n parameters, this work presents a new laboratory procedure to estimate K s , θ s , n and α for a drainage process, α dr , from the inverse analysis of successive drainage steady-states curves generated by a tension-gradient between the surface and the base of a soil column. To this end, a double disc system, one connected a bubbling tower and placed at the soil surface and the second one placed under the soil core, was employed. The second disc was connected to an air-vacuum system. The experiment presented two parts: a first 1D downward infiltration at saturation on a dry soil column, followed by successive drainage steps. During the drainage process, the tension of the upper and lower discs varied between 0 and −5 cm, and from −5 to −100 cm, respectively. The soil sorptivity, S , and θ s were calculated from the 1D transient infiltration measure, K s was calculated by Darcy's law, α dr and n were optimized from the inverse analysis of the steady-state curves under tension-gradient and α for a wetting process, α w , was calculated from previously obtained S , θ s , K s and n. Once K s estimated, α dr and n were optimized by minimizing the Q = h b - h n objective function, where h b and h n are the experimental and calculated tensions at the base of the soil core. Given a α dr value, the optimimum n was computed as the value that provides a minimum Q. By repeating this process for a sequence of α dr , different Q -isolines were obtained, one for each h b value, which crossing-point corresponded to the actual α dr and n values. The method was tested on 2.5 cm high columns of four different synthetic soils. Next, it was applied on an experimental sand column of 5 cm height and on 2.5 cm high columns filled with sieved loam, clay loam and clay soil. The estimated α dr and n were compared with corresponding values measured in the same soils with the pressure plate technique and α w was contrasted with the corresponding value calculated with an empirical hysteresis model. The method, which was fast (from 1 to 2 h) and easy to implement for small-scale experiments, was successfully applied to soil samples 2.5 cm high and allowed to explore a range of soil tensions from 0 to −100 cm. Overall, accurate estimates of θ s , K s , α dr and n were obtained in both synthetic and experimental soils. A significant relationship was also obtained between α w estimated from S and the corresponding value calculated from the hysteresis model. [ABSTRACT FROM AUTHOR]

Determination of saturated hydraulic conductivity, Ks, and the shape parameters α and n of the water retention curve, θ(h), is of paramount importance to characterize the water flow in the vadose zone. This work presents a modified upward infiltration method to estimate Ks, α and n from numerical inverse analysis of the measured cumulative upward infiltration (CUI) at multiple constant tension lower boundary conditions. Using the HYDRUS-2D software, a theoretical analysis on a synthetic loam soil under different soil tensions (0, 0-10, 0-50 and 0-100 cm), with and without an overpressure step of 10 cm high from the top boundary condition at the end of the upward infiltration process, was performed to check the uniqueness and the accuracy of the solutions. Using a tension sorptivimeter device, the method was validated in a laboratory experiment on five different soils: a coarse and a fine sand, and a 1-mm sieved loam, clay loam and silt-gypseous soils. The estimated α and n parameters were compared to the corresponding values measured with the TDR-pressure cell method. The theoretical analysis demonstrates that Ks and θ(h) can be simultaneously estimated from measured upward cumulative infiltration when high (>50 cm) soil tensions are initially applied at the lower boundary. Alternatively, satisfactory results can be also obtained when medium tensions (<50 cm) and the Ks calculated from the overpressure step at the end of the experiment are considered. A consistent relationship was found between the α ( R2 = 0.86, p < 0.02) and n ( R2 = 0.97, p < 0.001) values measured with the TDR-pressure cell and the corresponding values estimated with the tension sorptivimeter. The error between the α (in logarithm scale) and n values estimated with the inverse analysis and the corresponding values measured with pressure chamber were 3.1 and 6.1%, respectively. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• This work presents an upward infiltration method to estimate K PF = K T - K s. • K s and K T are measured from the transient infiltration and an overpressure step. • It was satisfactorily validated on packed soil with and artificial PF channel. • It was applied on soil cores collected from a grazing and tillage experiment. • 5, 35 and 60% of soil cores presented significant, moderate and negligible PF. Soil water preferential flow, PF, is the phenomenon where water moves along certain pathways, while bypassing a fraction of the porous matrix. This work presents a laboratory procedure to estimate the hydraulic conductivity of the soil water preferential flow, K PF. Using an upward infiltration curve followed by an over-pressure step, K PF is calculated as the difference between the total hydraulic conductivity, K T , measured with the constant head method, and the soil matrix hydraulic conductivity, K s , calculated from the inverse analysis of the transient upward infiltration curve. Previous to this analysis, a new approach to detect and remove the effect of possible overpressures due to the soil core placement on the sorptivimeter on the hydraulic properties estimate was presented. This consisted on searching the best fitting between the experimental infiltration curve after removing successive early time steps and the corresponding simulated function. The method to estimate K PF was validated on four different 5-cm height soil columns packed with 2-mm sieved clay loam and loam soils traversed longitudinally by a closed/opened pipe of 1.5 mm and 2.5 mm internal diameter, respectively. This same experiment was also repeated on the same soils without artificial preferential channel. Next, the method was applied on 20 undisturbed soil cores collected from two fields with different grazing intensity and soil tillage management (conventional, CT, reduced, RT and no-tillage, NT, practices). Results showed that correction made to remove the infiltration curve jump due to an overpressure step allowed more accurate and realistic estimates of the soil matrix hydraulic properties. On the other hand, both K T and K s , which could be satisfactorily calculated from a single upward infiltration curve followed by an overpressure step, where satisfactorily employed to quantify K PF. While no significant effect of grazing intensity on K PF was observed, the CT K PF was significantly larger than those obtained in RT and NT. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a new method (NSQE) to estimate soil hydraulic properties (sorptivity, S, and hydraulic conductivity, K) from full-time cumulative infiltration curves. The technique relies on an inverse procedure involving the quasi-exact equation of Haverkamp et al. (1994). The numerical resolution is described and the sensitivity of the method is theoretically evaluated, showing that the accuracy of the estimates depends on the measured infiltration time. A new procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve is also given. The method was subsequently compared to the differentiated linearization procedure (DL), which calculate K and S from the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. A total of 264 infiltration measurements performed with a 10cm diameter disc under different soil conditions were used. Compared to the DL procedure, field measurements showed that the NSQE method allowed better estimates of soil hydraulic properties, independently on the infiltration noise and the presence of contact sand layer. Overall, although comparable S values were estimated with both methods, the longer infiltration times allowed by the proposed method made this procedure more accurate estimations of K. In conclusion, the NSQE method have shown to be a significant advance to accurate estimate of the soil hydraulic properties form the transient water flow. [Copyright &y& Elsevier]

Abstract: Pasture productivity depends on soil hydro-physical properties, which in turn are deeply affected by livestock grazing. However, the comparative response of different soil types, and particularly gypseous soil types, to grazing has hardly been studied before. This paper compares the effect of grazing on the soil hydro-physical properties of silty gypseous (Gy) and non-gypseous (NGy) soils located in a semi-arid region (Middle Ebro Valley, NE, Spain). Two different soil managements were selected: ungrazed natural shrubland (N) and grazed shrubland (GR) soils. The gypsum, CaCO3 and organic matter content (OM), soil texture, soil bulk density (ρ b ), penetration resistance (PR), saturated sorptivity (S), hydraulic conductivity (K), and the water retention curve (WRC) for undisturbed soil samples from 1 to 10cm depth soil layer were measured. The ρ b and PR in NGy soils were significantly higher than those observed in the Gy ones. Soil compaction due to grazing treatment tended to increase ρ b and decrease the K and S values. While no differences in PR were observed in the Gy soils between grazing treatments, the PR measured in the NGy soils under GR was significantly higher than the corresponding values observed under N. Differences in K and S between GR and N treatments were only significant (p <0.05) in NGy soils, where K and S values under the N treatment were almost four times greater than the corresponding values measured under GR. Overall, no differences in the WRCs were observed between soil types and grazing treatments. While the WRCs of NGy soils were not significantly affected by the grazing treatment, Gy soils under N treatment present a significantly higher level of soil macropores than under GR treatment. The hydro-physical features of Gy soils tended to be less affected by grazing than those of the NGy soils. These results suggest that livestock grazing, in both Gy and NGy soils, has a negative effect on the physical soil properties, which should be taken into account by land managers of these semi-arid regions where silty gypseous and non-gypseous areas coexist. [Copyright &y& Elsevier]

• Effect of grazing on soil hydraulic properties of gypseous soils were studied. • Three grazing intensities, High, Medium and Low, were compared. • Soil surface S and K c and subsurface ρ b , K s , θ s , α and n were measured. • H presented the highest ρ b and the lowest K c values. • In semiarid gypseous soils M did not have a negative effect of soil properties. Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (S c) and hydraulic conductivity (K c) of the soil surface layer and the soil bulk density (ρ b), saturated hydraulic conductivity (K s), saturated volumetric water content, θ s , and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρ b , a significant influence of grazing on ρ b was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content. [ABSTRACT FROM AUTHOR]

• This work analyzes the influence of layered soils on K s and S estimates. • The Sequential Infiltration Analysis (SIA) method was proposed. • SAI was tested on synthetic and laboratory columns and experimental soils. • Estimates of K s and S improved when the SIA method was applied. • Method also allowed determining the thickness of the upper soil layer. The soil sorptivity, S , and saturated hydraulic conductivity, K s , can be estimated from the inverse analysis of a cumulative infiltration curve using the quasi-exact implicit (QEI) formulation or its corresponding 4-Terms (4T) approximation. Although these models consider the soil as homogeneous media, there is no information about how heterogeneous profiles can affect the inferred soil properties. This work analyzes the influence of layered soils on K s and S estimates using QEI and 4T models, and designs a new procedure for treating infiltration curves measured on layered soil profiles. The Sequential Infiltration Analysis (SIA) method considers a sequence of increasing time series from the cumulative infiltration data to estimate K s and S , and its corresponding RMSE as a function of the number of samples used. A procedure to estimate the thickness of the upper uniform soil layer from the estimated wetting front advance (WFA) is also reported. The SIA method was applied on: (i) synthetic homogeneous profiles of loam soil and six layered profiles involving a 1, 2 and 3 cm thickness loam layer over silty or sandy loam soils, respectively, (ii) stratified laboratory soil columns, and (iii) 20 experimental infiltrations performed in a semiarid region of North-Eastern Spain. Similar results were found between QEI and 4T models for all cases. Erroneous estimates of K s and S were observed when the total infiltration time series was considered for the analysis, regardless of the presence of soil layering. In opposite, estimates improved when the SIA method was applied to the layered systems. The SIA method exploits the fact that the RMSE increases when the wetting front reaches the interface between the soil layers. Such increase allows: (i) detection of the soil heterogeneity, (ii) determination of the infiltration time, t o , required for the wetting front to reach the lower layer, and, (iii) accurate estimates of the upper layer K s and S along with its thickness. Laboratory experiments on layered soils and field measurements demonstrated that the SIA method could be satisfactorily applied on different curves with contrasting shapes and magnitudes. Although soil layering encountered on most field samplings restricted the treatment of the observed infiltrations to short-medium times, the SIA method allowed robust estimates of K s and S. These results indicate that the proposed method is a promising tool for characterizing the hydraulic properties of layered and heterogeneous soil profiles. [ABSTRACT FROM AUTHOR]

• A method to estimate θ s , α , n and K s from an upward infiltration is presented. • The influence of θ s, θ r and h i , on the α , n and K s optimization was studied. • It was applied to 50 mm high undisturbed cores under different soil management. • θ s and h i affected α , n and K s , and h i should be located the d θ dh ≈ 0 region. • It was sensible to different texture and structure due to the soil management. Estimation of the α and n van Genuchten (1980) parameters and the saturated hydraulic conductivity, K s , of undisturbed soil samples is critical for realistic water flow simulations in the vadose zone. Given the Latorre and Moret-Fernández (2019) method, which allows estimating K s , α and n from the inverse analysis of a single upward infiltration, the objective of this work is to advance on the theoretical understanding of this method and to apply it on undisturbed soil cores. To this end, the influence of the saturated, θ s , and residual, θ r , water content and initial soil tension, h i , on the α , n and K s optimization was first studied on synthetic soils. A procedure to simultaneously estimate θ s , α , n and K s , which consisted on optimizing α , n and K s for a range of θ s values, was proposed. To this end, α , n and K s were optimized leaving each θ s as a fixed value. The method was next applied to experimental curves measured from sieved and undisturbed soil cores of 50 mm high and diameter, sampled the last ones from three fields with different management: bare vs. under plant soil; agricultural soil under conservation vs. conventional tillage; and overburden soil from mine vs. topsoil formed by the original soil. Results showed that θ s had an important effect on α , n and K s optimization, where the minimum error within the selected θ s interval corresponded to the theoretical θ s. An important effect of h i on the optimization was also observed. However, this influence was omitted by using a h i value located in the θ r region, where d θ dh ≈ 0. Under this assumption, θ r only affected the θ s optimization, which value varied with θ r. A robust relationship (R2 = 0.99; p < 0.0001) was found between theoretical and optimized θ s , K s and α and n calculated for the synthetic soils. Thus, the method allowed estimating four of the five van Genuchten (1980) parameters. An absolute minimum was also observed when the method was applied on experimental infiltration curves. The θ s measured gravimetrically on the undisturbed samples was, on average, 8.1% higher than the optimized one. Overall, the method allowed detecting significant differences (p < 0.05) in hydraulic properties between bare and under plant soils and among tillage treatments. The large variability found in the mine's soils prevented to find significant differences within this scenario. [ABSTRACT FROM AUTHOR]

Summary Based on the analysis of Haverkamp et al. (1994), this paper presents a new technique to estimate the soil hydraulic properties (sorptivity, S , and hydraulic conductivity, K ) from the full-time cumulative infiltration curves. The proposed method, which will be named as the Numerical Solution of the Haverkamp equation (NSH), was validated on 12 synthetic soils simulated with HYDRUS-3D. The K values used to simulate the synthetic curves were compared to those estimated with the NSH method. A procedure to detect and remove the effect of the contact sand layer on the cumulative infiltration curve was also developed. A sensitivity analysis was performed using the water level measurement as uncertainty source and the procedure was evaluated considering different infiltration times and data noise (e.g. air-bubbling in the infiltrometer). The good correlation between the K used in HYDRUS-3D to model the infiltration curves and those obtained by the NSH method ( R 2 = 0.98) indicates this technique is robust enough to estimate the soil hydraulic conductivity from complete infiltration curves. The numerical procedure to detect and remove the influence of the contact sand layer on the K and S estimates resulted to be robust and efficient. A negative effect of the curve infiltration noise on the K estimate was observed. The results showed that infiltration time was an important factor to estimate K . Smaller values of K or lower uncertainty required longer infiltration times. In a second step, the technique was tested in field conditions on 266 different soils at saturation conditions, using a 10 cm diameter disc infiltrometer. The NSH method was compared to the standard differentiated linearization procedure (DL), which estimates the hydraulic parameters using the simplified Haverkamp et al. (1994) equation, valid only for short to medium times. Compared to DL, NSH was considerably less affected by the infiltration bubbling and the contact sand layer, and allowed more robust estimates of K and S . Although comparable S values were obtained with both methods, the NSH technique, which is not limited to short times, resulted in more accurate and robust estimates for K . This paper demonstrates the NSH method is a significant advance to estimate of the soil hydraulic properties from the transient water flow. [ABSTRACT FROM AUTHOR]