A Field Method to Determine Unsaturated Hydraulic Conductivity Using Flow Nets (original) (raw)
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ESTIMATION OF SATURATED HYDRAULIC CONDUCTIVITY: A REVIEW
Hydraulic conductivity plays a key role in water resources development, planning and management as well as environmental protection. Saturated hydraulic conductivity is one of the most important physical features of soil that has wide usage in soil and water science. It can be measured above and below water table level. Constant head, falling head, auger hole method, pipe cavity test method, inversed auger hole method (Porchet method), shallow well pump in test method, and Guelph Permeameter are the different methods used to measure saturated hydraulic conductivity have been discussed in this chapter. Various factors including physical and chemical properties of soil, soil aggregate stability, climate, tillage, land use, root dynamics, and activity of soil organisms have effect on saturated hydraulic conductivity. Effects of those factors in different methods of saturated hydraulic conductivity measurement have also been discussed. It is expected that the article will help hydraulic and environmental engineers, agriculture and soil scientists as well as others working in related fields to enrich their
In situ estimation of hydraulic conductivity using simplified methods
Water Resources Research, 1984
Five simplified methods of estimating the relationship between hydraulic conductivity K and water content 0 were compared in this study. Redistribution of water following constant rate infiltration (steady state) was monitored for a 10-day period at 100 locations and seven depths at each location within a 5000-m 2 fallow sandy loam field. All the methods assumed a unit hydraulic gradient during redistribution and an exponential relationship between K and 0 of the form K(O) = K o exp [/•(0 -0o) ]. The five methods were the 0, flux, and CGA methods (Libardi et al., 1980) and two methods based on a Lax solution of the Richards' equation (Sisson et al., 1980). Water content data were used to calculate Ko and /• by each method at each depth and location. Soil water flux was estimated for selected depths using appropriate mean and variance values of K o and/• for the field. Relative differences between the methods are briefly discussed.
Estimation of Saturated Hydraulic Conductivity on the Basis of Drainage Porosity
2007
A large single-ring infiltrometer test was performed in order to characterize the saturated hydraulic conductivity below an infiltration basin in the well field of Lyon (France). Two kinds of data are recorded during the experiment: the volume of water infiltrated over time and the extension of the moisture stain around the ring. Then numerical analysis was performed to determine the saturated hydraulic conductivity of the soil by calibration. Considering an isotropic hydraulic conductivity, the saturated hydraulic conductivity of the alluvial deposits is estimated at 3.8 10-6 m s-1. However, with this assumption, we are not able to represent accurately the extension of the moisture stain around the ring. When anisotropy of hydraulic conductivity is introduced, experimental data and simulation results are in good agreement, both for the volume of water infiltrated over time and the extension of the moisture stain. The vertical saturated hydraulic conductivity in the anisotropic configuration is 4.75 times smaller than in the isotropic configuration (8.0 10-7 m s-1), and the horizontal saturated hydraulic conductivity is 125 times higher than the vertical saturated hydraulic conductivity (1.0 10-4 m s-1).
A Comparison of Three Field Methods for Measuring Saturated Hydraulic Conductivity
Canadian Journal of Soil Science, 1985
The saturated hydraulic conductivity, Ks, was measured on a loamy sand, a fine sandy loam, a silt loam and a clay at four 100-m2-area sites in southern Ontario. Twenty measurements of Ks were obtained by each of three different measurement techniques at each of the four sites. The techniques included: (1) the air-entry permeameter method; (2) the constant head well permeameter method using the Guelph Permeameter; and (3) the falling-head permeameter method applied to small soil cores. The Ks data were found to be better described by the log-normal frequency distribution than by the normal frequency distribution. Statistical comparison of the mean Ks values [Formula: see text] indicated significant differences between some or all of the methods within each site. This site-method interaction was interpreted in terms of the influence of macropores and air entrapment on each of the measurement techniques. The measured Ks values ranged over an order of magnitude on the sand, one to two o...
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1996
The estimation of hydraulic conductivity and concentration profiles is important for groundwater quality studies and for planning remediation action. A simple and economical way is to use existing wells, provided that appropriate sampling techniques are available. The reliability of some new techniques (Separation Pumping (SEP), Packer-Baffle Systems (PBS), Multi-Port Sock Sampler (MLPS or BMS)) is studied in this paper by using numerical models to simulate flow and mass transport to the sampling device. The results of testing the methods in different hydrogeological environments as well as in the laboratory were analysed in order to understand-from a hydraulic point of view-the reasons, why these techniques succeed or fail to give reliable results. Important factors influencing the flow and transport in the system are identified and discussed. The investigation showed that SEP which can be used to estimate hydraulic conductivity as well as concentration profiles, gives reliable results. In order to obtain reliable results by means of PBS the hydraulic conductivity must be known and the sampling rate must be adjusted to it. However, experience showed that further problems can arise in the field. Multi-Port Sock Samplers give reliable results if the concentration profile around the borehole is not disturbed owing to vertical flow in the gravel pack or owing to the installation of the device.
COMPARISON OF EMPIRICAL MODELS AND LABORATORY SATURATED HYDRAULIC CONDUCTIVITY MEASUREMENTS
Numerous methods for estimating soil saturated hydraulic conductivity exist, which range from direct measurement in the laboratory to models that use only basic soil properties. A study was conducted to compare laboratory saturated hydraulic conductivity (K sat) measurement and that estimated from empirical models. Soil samples for the study were collected from four sites at varying depths (15cm, 30cm, 45cm and 60cm) at the Faculty of Agriculture Teaching and Research Farm, University of Maiduguri. The K sat value for each sample was determined in the laboratory using the falling head permeameter method. Soil physical properties (bulk density, porosity, gravimetric water content, % sand and % silt) required by the models were also determined. A refined Kozeny-Carman model and model developed from multiple regression analysis were used to predict K sat which were compared with the results obtained from laboratory measurement. The developed model predicted values of 0.0065, 0.0010, 0.0965 and 0.0048cm/s at 15cm, 30cm, 45cm and 60cm, respectively, that is closer to the value of K sat measured in the laboratory (0.0061, 0.0054, 0.0050 and 0.0048cm/s at 15cm, 30cm, 45cm and 60cm, respectively) while Kozeny-Carman model predicted a value of 0.2208, 0.2161, 0.2020 and 0.1974cm/s at 15cm, 30cm, 45cm and 60cm, respectively, that is far above the one measured in the laboratory. Therefore, K sat estimating models could not fit for all locations very well.
Variability of Hydraulic Conductivity Due to Multiple Factors
American Journal of Environmental Sciences, 2012
Soil properties are greatly influenced by intrinsic factors of soil formation as well as extrinsic factors associated with land use and management and vary both in time and space. Intrinsic variability is caused by the pedogenesis and usually takes place at large time scales. The variability caused by extrinsic factors could take effect relatively quickly and could not be treated as regionalized. Saturated hydraulic conductivity is one of the most important soil properties for soil-water-plant interactions, water and contaminant movement and retention through the soil profile. It is a critically important parameter for estimation of various other soil hydrological parameters necessary for modeling flow through the naturally unsaturated vadose zone. Among different soil hydrological properties, saturated hydraulic conductivity is reported to have the greatest statistical variability, which is associated with soil types, land uses, positions on landscape, depths, instruments and methods of measurement and experimental errors. The variability of saturated hydraulic conductivity has a profound influence on the overall hydrology of the soil system. Therefore, focus of this review is centered on the variability of saturated/unsaturated hydraulic conductivity due to a large number of factors. This study reviews recent experimental and field studies addressing the measurements and variability of hydraulic conductivity. A synthesis of a large amount of data available in literature is presented and the possible sources of the variability and its implications are discussed. The variability of a soil hydraulic conductivity can be expressed by range, interquartile range, variance and standard deviation, coefficient of variation, skewness and kurtosis. The spatial and temporal variability of hydraulic conductivity and the influences of sample support, measurement devices/methods, soils, land uses and agricultural management on hydraulic conductivity are evaluated. Methods of measurements strongly impact variability, for example, saturated hydraulic conductivity measured using a single ring may produce significantly different mean and standard errors than those measured using a double ring. The sample support can also influence the variability, for example, increasing or decreasing the size of the infiltrometer rings can change the mean and variability of the saturated hydraulic conductivity. Similarly, hydraulic conductivity measured in the field could show a much larger variability than those measured in the laboratory. The spatial and temporal variations of hydraulic conductivity and interactions among soil characteristics, land uses, agricultural management, climatic and environmental conditions and measurement methods are rather complex, which should take into account multiple factors discussed in this review. Decisions and choices made by investigators during sampling, sampling designs, availability of resources, number of investigators involved in sampling and analysis, skill level of investigators, type and quality of tools and equipments used to collect samples and analyses, scale of the domain, availability of time, accessibility of sites, criteria of success and assumptions made for the sampling and analysis have profound influence on the variability of hydraulic conductivity.
Improved Prediction of Unsaturated Hydraulic Conductivity with the Mualem‐van Genuchten Model
Soil Science Society of America Journal, 2000
In many vadose zone hydrological studies, it is imperative that the al., 1998). Far fewer alternatives exist for unsaturated soil's unsaturated hydraulic conductivity is known. Frequently, the Mualem-van Genuchten model (MVG) is used for this purpose be-hydraulic conductivity. Although some pedotransfer cause it allows prediction of unsaturated hydraulic conductivity from functions are available (Saxton et al., 1986; Schuh and water retention parameters. For this and similar equations, it is often Bauder, 1986; Vereecken et al., 1990), pore-size distriassumed that a measured saturated hydraulic conductivity (K s) can bution models by Burdine (1953) and Mualem (1976), be used as a matching point (K o) while a factor S L e is used to account among others, are more popular. for pore connectivity and tortuosity (where S e is the relative saturation Generally speaking, the Burdine and Mualem models and L ϭ 0.5). We used a data set of 235 soil samples with retention infer the pore-size distribution of a soil from its water and unsaturated hydraulic conductivity data to test and improve preretention characteristic. By making assumptions about dictions with the MVG equation. The standard practice of using K o ϭ continuity and connectivity of pores, integral expres-K s and L ϭ 0.5 resulted in a root mean square error for log(K) sions can be derived that describe unsaturated conduc-(RMSE K) of 1.31. Optimization of the matching point (K o) and L to the hydraulic conductivity data yielded a RMSE K of 0.41. The fitted tivity in terms of water content or pressure head. A K o were, on average, about one order of magnitude smaller than general expression can be given as (after Hoffmannmeasured K s. Furthermore, L was predominantly negative, casting Riem et al., 1999): doubt that the MVG can be interpreted in a physical way. Spearman rank correlations showed that both K o and L were related to van