Explicit infiltration function for boreholes under constant head conditions (original) (raw)
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The borehole permeameter technique can produce erratic saturated hydraulic conductivity (K,J in soils with macropores and abrupt layers because operating theory assumes homogeneous and isotropic conditions. Dye application during an infiltration test demonstrated water movement in macropores and erratic K M or matric flux potential ( m )-To evaluate the effects of macropores, cracks, and layered soil on K, a and <A m , a finite element solution of the Richards equation was used to simulate infiltration from a borehole (0.03-m radius and 0.50 m deep) with a constant head (H) of 0.05 or 0.10 m. Borehole infiltration (for 2 h) was simulated for a Rozetta silt loam (fine-silty, mixed, mesic Typic Hapludalf) with four configurations: homogeneous, layered, a cylindrical macropore centered at the borehole base, and a crack intersecting the borehole wall. Simulated flow rates were increased by 29% (with H = 0.05 m) and 21% (with H = 0.10 m) when a cylindrical macropore (4 mm by 0.10 m) was located at the borehole base. Respective increases were 25% (H = 0.05 m) and 20% (H = 0.10 m) when a crack extending 0.1 m laterally intersected the borehole wall. Three methods were tested for calculating K M . The simultaneous-equations approach (SEA) using either the Guelph or the Philip model for a homogeneously configured borehole estimated K M within a factor of 2 from input K M , but the Laplace analysis method overestimated input K,, t by a factor of 5 to 12. The fixed a value (a = K a JJ method with either the Guelph or Philip model estimated K M close to input K M when a proper a value was chosen, but the proper a value differed by soil and model. A negative K M was computed using the SEA with the Guelph model when macropores intersected the base of a borehole; negative K,, t or m were produced when cylindrical macropores laterally intersected the borehole wall, depending on the vertical locations of the macropores. Soil with layered hydraulic properties also produced unrealistic K M .
Applied Engineering in Agriculture, 2006
Field-saturated hydraulic conductivity (K fs) is considered the most important parameter for water flow and chemical transport phenomena in soils. The Richards' and Laplace's solutions of the Guelph Permeameter (GP) and the Glover's solution of the Compact Constant Head Permeameter (CCHP) for calculating K fs were compared. Steady-state flow rates of water into soil at a single constant head infiltration (H = 20 cm) from a borehole measured with the Guelph permeameter method were used to estimate K fs values using these solutions. The geometric mean values of K fs calculated using Richards', Laplace's, and Glover's solutions were 0.112, 0.185, and 0.224 cm h −1 , respectively, for a Duffield silt loam soil. The Glover's and Laplace's solutions, neither of which takes into account the effect of unsaturated capillary flow, produce K fs values approximately 1.5 to 2 times larger than the K fs values calculated using Richards' solution. While the Glover's solution gives K fs values nearly 1.4 times larger than those estimated by the Laplace's solution. The student t-test showed that the mean difference (M d) among Richards', Laplace's, and Glover's solutions were significantly different from zero at p < 0.01. Thus, statistical analyses indicated that the three analytical methods result in dissimilar estimates of K fs values. Negative K fs values are often obtained using simultaneous equations of Richards' solution approach in heterogeneous soils and the Richards' solution can only be used at one constant water depth when an a value must be estimated or assigned based on the soil texture and structure. Both Glover's and Laplace's solutions can be used in coarse textured soils where the capillarity effect is minimal and initial water content in the soil is near the field capacity level. This indicates that the variability in K fs estimates depend not only on soil structure, texture, and other soil characteristics, but also on the method of estimation imposed by the borehole analytical solution.
Modelling infiltration: A measurable parameter approach
Journal of Agricultural Engineering Research, 1981
Development of a 2-stage, measured parameter, infiltration model is reviewed. The model has been verified against finite difference solutions of the unsaturated flow equation, by laboratory tests and has been evaluated under field conditions. Progress of recent research utilizing this model is discussed. Results of recent research indicate that the effects of air entrapment on hydraulic conductivity must be taken into account. A reasonable approach to this problem is to evaluate relative conductivity as a function of relative moisture content and use this relationship to evaluate hydraulic conductivity at field saturation. Additional factors which have been investigated include air viscous effects and the effects of tillage and surface sealing. While significant progress has been made toward including these effects in the model, additional research is required. An attractive attribute of the model is that all parameters utilized in the model are measurable and thus no parameter fitting is required. The paper discusses how parameters may be evaluated and how the model operates, and presents some examples of model predictions under different conditions of soil composition and rainfall pattern.
Procedia Environmental Sciences, 2013
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.
Parameter estimation using the falling head infiltration model: Simulation and field experiment
Water Resources Research, 2005
Soil hydraulic parameters have high spatial variability. A large number of measurements are needed to characterize these parameters in a field. Therefore there is a need to develop quicker and cheaper methods to determine soil hydraulic parameters. The objective of this study was to examine the uniqueness of the K fs (field saturated hydraulic conductivity) and a (inverse macroscopic capillary length scale) parameters obtained through inverting the falling head infiltration model. Five simulated scenarios were imposed on the cumulative infiltration data [L(t)] during the inverse procedure. The uniqueness of the K fs and a estimates under each scenario was studied. In situ infiltration data were used to verify the scenario that provided unique parameter estimates. It appears that the falling head infiltration model can be used to simultaneously estimate the K fs and a parameters when estimates (or published values) of the a parameter for the site are available.
Prediction of infiltration from soil hydraulic properties
EURASIAN JOURNAL OF SOIL SCIENCE (EJSS), 2018
Field and laboratory infiltration measurements using infiltrometers have been the only methods of effectively determining the infiltration rates of soils. Infiltration is mainly controlled by soil hydraulic properties, especially the hydraulic conductivity. Due to the ease with which the saturated hydraulic conductivity can be determined, it is often preferred to the unsaturated hydraulic conductivity in hydrological studies. It is well known that, at saturation the steady state infiltrability controls the infiltration process. Thus, it is very clear that the saturated hydraulic conductivity and steady state infiltrability may be closely related in one way or the other, as suggested in some few studies, wherein functions have been developed to relate these two parameters. However, these functions are often site specific and do not always carry out accurately all the time. Determination of can be tedious and time consuming, whereas can be easily determined in the laboratory. The present study aimed to assess the predictability of a modified Philip's equation by substituting for. In this study, field infiltration measurements were conducted in two soil types under three different land use systems with a single ring infiltrometer. Field and laboratory hydraulic and hydrologic experiments were conducted on soils in a turf grass, an arable land and a pastureland in the
Evaluation of some infiltration models and hydraulic parameters
Spanish Journal of Agricultural Research, 2010
The evaluation of infiltration characteristics and some parameters of infiltration models such as sorptivity and final steady infiltration rate in soils are important in agriculture. The aim of this study was to evaluate some of the most common models used to estimate final soil infiltration rate. The equality of final infiltration rate with saturated hydraulic conductivity (K s ) was also tested. Moreover, values of the estimated sorptivity from the Philip's model were compared to estimates by selected pedotransfer functions (PTFs). The infiltration experiments used the doublering method on soils with two different land uses in the Taleghan watershed of Tehran province, Iran, from September to October, 2007. The infiltration models of Kostiakov-Lewis, Philip two-term and Horton were fitted to observed infiltration data. Some parameters of the models and the coefficient of determination goodness of fit were estimated using MATLAB software. The results showed that, based on comparing measured and model-estimated infiltration rate using root mean squared error (RMSE), Horton's model gave the best prediction of final infiltration rate in the experimental area. Laboratory measured K s values gave significant differences and higher values than estimated final infiltration rates from the selected models. The estimated final infiltration rate was not equal to laboratory measured K s values in the study area. Moreover, the estimated sorptivity factor by Philip's model was significantly different to those estimated by selected PTFs. It is suggested that the applicability of PTFs is limited to specific, similar conditions.
Measuring infiltration rate and hydraulic conductivity in a dry well in a thin overburden
2016
IInfiltration rate and hydraulic conductivity are immensely important parameters for evaluating the hydrology of subsurface environments. Specifically, in disposal wells schemes and in artificial recharge plans both properties must be correctly assessed to better analyze the performance of these installations. In a new research, tanker water and rainfall runoff were injected into a 22.5 m deep well dug in a 15 m thick dry overburden and the underlying impermeable marl bedrock (7.5 m) to evaluate the feasibility of using the well to store winter runoff in the overburden for recovery in the summer. Rates of rise and fall in the hydraulic head were measured, and infiltration rate in various depths were calculated. Also, hydraulic conductivity of the overburden was calculated using particle distribution curves of the overburden samples. Infiltration rate showed close correlation with the hydraulic conductivity. Maximum infiltration rate occurs at depths of 10-11 m; depth of 10 m is the ...
Breakdown pressures due to infiltration and exclusion in finite length boreholes
Journal of Petroleum Science and Engineering, 2015
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Field Estimates of Hydraulic Conductivity from Unconfined Infiltration Measurements
Field-Scale Water and Solute Flux in Soils, 1990
Soil water infiltration exhibits spatial variability due to both intrinsic soil properties and management effects (e.g. wheel traffic and tillage). The description or prediction of field scale water and solute movement, therefore, requires that the spatial distribution of hydraulic properties be known. Practical measurement of hydraulic properties of unsaturated soil requires both a rapid field technique to sample the necessary number of sites and a straightforward analytical technique for interpreting data. We have designed precision automated tension infiltrometers that enable rapid determination of soil water infiltration. Tension infiltrometers were used to obtain unsaturated infiltration data for chisel-plow, no-till, wheel-trafficked, and non-wheel trafficked management zones. This paper reports means and coefficients of variation for hydraulic conductivities at multiple tensions derived from unconfined infiltration measurements. Mean hydraulic conductivities decreased as tension increased. Trafficked sites had lower values of hydraulic conductivity than non-trafficked sites. The tension infiltrometer is a useful tool for obtaining spatial measurements of field infiltration and unsaturated hydraulic conductivities.