Measurement Of Field-saturated Hydraulic Conductivity Research Articles

Digital interface device for field soil hydraulic conductivity measurement

Accurate and reliable measurements of field-saturated hydraulic conductivity (Kfs) are essential for accurate determinations of soil and solution water fluxes. Kfs is a crucial parameter to design drainage, irrigation systems and many other environmental, agricultural and industrial installations Reynolds et al. (1983). There is a high demand for Kfs data. Its evaluation is preferable to be done in situ. A popular device to measure the Kfs is the head well permeameter such as the Guelph Permeameter. However, it is an analog equipment based on a Mariotte’s bottle that requires full attention and training to be manually operated, where the reading of the flux values (Q, in cm3/min) is time-consuming and costly. In this paper, we describe a device, with a digital readout, to measure the steady state rate of water level change Rs, in order to obtain Qs and Kfs. The method is based on the monitoring of the vacuum variation of the Mariotte’s bottle. Our results show no statistical differences between the measurements values of manual and automatic recording using paired t-test. In addition, our device identifies measurement artifacts due to the variation of the ambient temperature during measurements. The necessary accuracy for the digitalization method becomes feasible due to the availability of accurate piezoelectric transducers (Micro-Electro-Mechanical System – MEMS). Automating and digitizing these processes will reduce time, costs and increase the accuracy and availability of data. The device can be directly adapted to commercially available head well permeameters as shown in our experimental results. The more widespread use and understanding of this parameter can improve the rational use of water for irrigation and use in risk models for forecasting available soil water and therefore crop productivity.

Sensitivity of Percolation Estimates to Modeling Methodology: A Case Study at an Unlined Tailings Facility with Limited Monitoring Data

Calculation of water budgets is critical to developing long-term management and remediation plans for legacy mine waste facilities. The effects of several modeling decisions commonly made by practitioners constructing numerical hydrologic models can significantly alter estimates of percolation and resultant management strategies. We investigated the effects of variations in several common modeling decisions for an unlined legacy tailings emplacement in Lincoln County, Nevada using predictions from HYDRUS 1D and 2D simulations. Modeling decisions investigated include choice of hydraulic property model, hydraulic properties, numerical mesh discretization, boundary condition representation, dimensionality, and geometry. Hydrologic parameterization was informed by measurement of field-saturated hydraulic conductivity, in-situ density, field moisture content, bulk (dry) density, and water retention curve by hanging column, pressure plate, and chilled mirror hygrometer. Numerical hydrologic models resulted in percolation estimates from 0 to 24 mm/year through the tailings. Choice of hydraulic properties and temporal resolution of boundary condition data contributed the most to variations in percolation estimates. For comparison, percolation was predicted with a simple water balance model (HELP), resulting in a percolation rate of 51 mm/year. Such a wide range of percolation rate predictions demonstrates the potential for significant variability in model output within a range of defensible modeling decisions, assumptions, and parameterization methods. To appropriately bound this uncertainty, several model assumptions and iterations should be considered.

A generalized variable-head borehole permeameter analysis for saturated, unsaturated, rigid or deformable porous media

The variable-head borehole permeameter (VHBP) method is a long-standing international standard for in-situ measurement of field-saturated hydraulic conductivity, KFS, in natural and engineered porous media. Its applicability is restricted, however, because traditional VHBP theory does not apply for unsaturated or deformable porous media, and because precise knowledge of the boundary condition on the interface of the borehole outlet (screen) is required for accurate KFS determination. This study extends the traditional VHBP theory to include saturated, unsaturated, rigid and deformable porous media, and also clarifies the boundary condition at the screen interface. Using a recent VHBP analysis developed for rigid, unsaturated porous media, it is shown (via flow conservation and the total increment theorem) that change in porous medium water content, ∆θ, can be extended to include change in porosity (deformation) as well as change in degree of saturation. It is also shown that the appropriate boundary condition on the borehole screen is antecedent pore water pressure head, Ha, for saturated porous media, but effective wetting front pressure head, ψf (or sorptive number, α*), for unsaturated porous media. The KFS, ∆θ, Ha, and ψf (or α*) parameters can be determined using numerical optimization (e.g. “Solver” in the Excel spreadsheet) to curve-fit the extended VHBP analysis directly to borehole head versus time measurements; however, fitting to the velocity graph (borehole head plotted against change in head with time) is generally less problematic. In a cursory assessment of the extended VHBP analysis, KFS was determined with ≤7% error, ∆θ with ≤15% error, Ha with ≤1.4% error, and ψf with ≤0.5% error, which is more than sufficient accuracy for most applications. It was concluded that the VHBP method was successfully extended for application to saturated, unsaturated, rigid and deformable porous media.

An assessment of borehole infiltration analyses for measuring field-saturated hydraulic conductivity in the vadose zone

Single-borehole infiltration tests are widely used for in-situ measurement of field-saturated hydraulic conductivity, Kfs, in the vadose or unsaturated zone. United States Bureau of Reclamation (USBR) methods are used extensively in geologic and water management engineering to analyse single-borehole infiltration data, while borehole permeameter (BP) methods are preferred in the environmental and agricultural sciences. Little is known about how well the USBR and BP analyses correspond; hence, the objectives of this study were to compare and provide usage recommendations for some of the most common constant head and falling head USBR and BP analyses in terms of range of validity and accuracy for Kfs determination. HYDRUS-2D numerical simulations of variably saturated, axisymmetric flow for a range of specified Kfs values, porous media capillarities (as represented by sorptive number, α*, and change in water content, ∆θ) and outflow geometries (as represented by length, L, and radius, a, of borehole discharge zone) were used to generate perturbation-free borehole test data for use in the USBR and BP analyses. The numerically generated test data consisted of steady borehole discharge rate, QS, versus steady ponded head, H, for the constant head borehole tests, and ponded head, Ht, versus time, t, for the falling head borehole tests. The constant head USBR estimates of Kfs were generally accurate (≤25% error) when H/a≥10, α*≥12m−1, a≥10cm and L/a≥10, but could overestimate or underestimate by more than an order of magnitude when the above parameters were outside those ranges. The falling head USBR analysis appeared to always overestimate or underestimate Kfs (>25% error), and the overestimates could be more than an order of magnitude when early-time Ht vs. t data were used. The constant head and falling head BP analyses, on the other hand, provided accurate Kfs estimates (≤26% error) for all test scenarios. The BP analyses were therefore recommended for all tested borehole configurations and porous medium characteristics, while the USBR analyses were recommended only for constant head tests when H/a≥10, L/a≥10, α*≥12m−1, and a≥10cm.

Morphological, physical and pedogenetic attributes related to water yield in small watersheds in Guarapari/ES, Brazil

Soil characteristics related to the genesis, land use and management are important factors in water dynamics in watersheds. This study evaluated physical, morphological and pedogenetic attributes related to water yield potential in small watersheds in Guarapari, ES, Brazil. The following representative profiles were selected, morphologically described and sampled in area of Atlantic Forest domain: Lithic Udifolists, Oxyaquic Udifluventes, Typic Paleudults, Typic Hapludults, Typic Hapludox, Oxic Dystrudepts and Typic Endoaquents. Samples were collected in the soil profiles for physical analysis. Measurements of field-saturated hydraulic conductivity and soil penetration resistance were perfomed in some profiles, which were under different uses. The Endoaquents of Limão Creek can be considered efficient as temporary water reservoirs. However, the use of artificial drainage tends to reduce this effect. Differential erosion was detected by the sand texture on the surface of the Typic Paleudults due to the low degree of clay flocculation, slope, high resistance to the penetration and low hydraulic conductivity of the Bt horizon, making it necessary to adopt soil management practices to increase the water infiltration. Under pasture, mainly in the cattle trails where the trampling is more intense, there was high resistance to penetration in the superficial layers of the Typic Hapludults. The Typic Hapludox have the greatest potential for water yield in the small watersheds because of its greater extent in the headwaters and their morphological and physical characteristics, which can result in increased aquifer recharge.

Measurement of field-saturated hydraulic conductivity on fractured rock outcrops near Altamura (Southern Italy) with an adjustable large ring infiltrometer

Up to now, field studies set up to measure field-saturated hydraulic conductivity to evaluate contamination risks, have employed small cylinders that may not be representative of the scale of measurements in heterogeneous media. In this study, a large adjustable ring infiltrometer was designed to be installed on-site directly on rock to measure its field-saturated hydraulic conductivity. The proposed device is inexpensive and simple to implement, yet also very versatile, due to its large adjustable diameter that can be fixed on-site. It thus allows an improved representation of the natural system’s heterogeneity, while also taking into consideration irregularities in the soil/rock surface. The new apparatus was tested on an outcrop of karstic fractured limestone overlying the deep Murge aquifer in the South of Italy, which has recently been affected by untreated sludge disposal, derived from municipal and industrial wastewater treatment plants. The quasi-steady vertical flow into the unsaturated fractures was investigated by measuring water levels during infiltrometer tests. Simultaneously, subsurface electrical resistivity measurements were used to visualize the infiltration of water in the subsoil, due to unsaturated water flow in the fractures. The proposed experimental apparatus works well on rock outcrops, and allows the repetition of infiltration tests at many locations in order to reduce model uncertainties in heterogeneous media.

The well-shape factor for the measurement of soil hydraulic properties using the Guelph Permeameter

The Guelph Permeameter method is one of the most frequently used field methods to measure soil hydraulic properties in situ. The well-shape factor which is necessary in the calculation must be obtained visually from a chart. We provide three empirical formulae which can almost perfectly describe the shape factor calculated numerically by Reynolds (see, e.g., Reynolds, 1986. The Guelph Permeameter method for in situ measurement of field-saturated hydraulic conductivity and matric flux potential. Ph.D. Dissertation. University of Guelph, Guelph, Ont.). We conclude that the three empirical formulae can replace the three shape factor curves in the Operating Instructions of Model 2800K1 Guelph Permeameter ( Soil Moisture Corp., 1987).

Measurement of Field-Saturated Hydraulic Conductivity by Using Guelph and Velocity Permeameters

ABSTRACT Field experiments were conducted to evaluate the performance of two recently developed in situ techniques to measure saturated hydraulic conductivity (K). These two techniques are (1) the constant-head well permeameter method using the Guelph permeameter, and (2) the falling-head permeameter method using the velocity permeameter. K was measured on a silt loam soil at eight sites and for four different depths (150, 300, 450, 600 mm) at each site by using these two techniques. K determinations were also made in the laboratory by using a constant-head permeameter on undisturbed soil columns collected from all test sites and depths. Measurements of K for the selected test sites and conditions indicate that Guelph and velocity permeameters provided reasonably similar values. Both methods are simple to use and easily portable, and both produce results in a relatively short time (usually 15 min to 20 min for the velocity permeameter and 60 min to 90 min for the Guelph permeameter for a single measurement). Field-measured K values tended to be much lower than laboratory values.