159 research outputs found
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On the use of the Boussinesq equation for interpreting recession hydrographs from sloping aquifers
The method of recession analysis proposed by Brutsaert and Nieber (1977) remains one of the few analytical tools for estimating aquifer hydraulic parameters at the field scale and beyond. In the method, the recession hydrograph is examined as −dQ/dt = f(Q), where Q is aquifer discharge and f is an arbitrary function. The observed function f is parameterized through analytical solutions to the one-dimensional Boussinesq equation for unconfined flow in a homogeneous and horizontal aquifer. While attractive in its simplicity, as originally presented it is not applicable to settings where slope is an important driver of flow, or where hydraulic parameters vary greatly with depth. We compare analytical solutions to the linearized one-dimensional Boussinesq equation for a sloping aquifer to numerical solutions of the full nonlinear equation. The behavior of the nonlinear Boussinesq equation is also assessed when the aquifer is heterogeneous wherein the lateral saturated hydraulic conductivity k varies as a power law with height z above the impermeable layer (k ∼ z[superscript n] , n constant ≥ 0). All of the analytical solutions differ in key aspects from the nonlinear solution when plotted as −dQ/dt = f(Q) and thus are inappropriate for a Brutsaert and Nieber-type analysis. However, new analytical solutions for a sloping aquifer are derived “empirically” from the numerical simulations that are applicable during the late period of recession when the recession curve converges to −dQ/dt = aQ[superscript b] , where b = (2n + 1)/(n + 1) and a is a function of the dimensions and hydraulic properties of the aquifer.Keywords: Boussinesq, Recession analysis, Slopin
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Development and Testing of Single-Parameter Precipitation Distributions
Distributed temperature data are used as input and
as calibration data for an energy based temperature model
of a first order stream in Luxembourg. A DTS (Distributed
Temperature Sensing) system with a fiber optic cable of
1500m was used to measure stream water temperature with
1m resolution each 2 min. Four groundwater inflows were
identified and quantified (both temperature and relative discharge).
The temperature model calculates the total energy
balance including solar radiation (with shading effects),
longwave radiation, latent heat, sensible heat and river bed
conduction. The simulated temperature is compared with the
observed temperature at all points along the stream. Knowledge
of the lateral inflow appears to be crucial to simulate the
temperature distribution and conversely, that stream temperature
can be used successfully to identify sources of lateral
inflow. The DTS fiber optic is an excellent tool to provide
this knowledge
Heat Transfer in the Environment: Development and Use of Fiber-Optic Distributed Temperature Sensing
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Evaluation of hydrodynamic scaling in porous media using finger dimensions
The use of dimensionless scaling is ubiquitous to hydrodynamic analysis, providing a powerful method of extending limited experimetnal results and generalizing theories. Miller and Miller [1956] contributed a scaling framework for immiscible fluid flow through porous media that relied on consistency of the contact angle between systems to be compared. It is common to assume that the effective contact angle will be zero in clean sand material where water is the wetting liquid. The well-documented unstable wetting process of fingered flow is used here as a diagnostic tool for the scaling relationships for infiltration into sandy media. Through comparison of finger cross sections produced using three liquids as well as various concentrations of anionic surfactant, it is shown that the zero contact angle assumption is very poor even for laboratory cleaned silica sand: Experimental results demonstrate effective contact angles approaching 60°. Scaling was effective for a given liquid between sands of differing particle size. These results suggest that caution should be exercised when applying scaling theory to initial wetting of porous media by liquids of differing gas-liquid interfacial tensions
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A glass always half full: Reconsideration of the Wales apparatus to apply constant head boundary conditions
A new apparatus is presented that is capable of applying a constant fluid pressure at inflow and outflow boundaries. The apparatus can be refilled during operation and does not rely on an overflow mechanism. The device is constructed of two vessels, one that contains the delivered fluid and the other that contains a less dense fluid. By matching the fluid densities and the areas of the vessels the absolute elevation of the delivered fluid is maintained as the fluid is added to or removed from the system. The history of the development of the device, the underlying physical principles, and two demonstrations of the operation of a prototype device are shown
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Pesticides in southern Willamette Valley groundwater
The region’s high winter rainfall provides aquifers
that are often within 50 feet of the land surface. In
many parts of the United States and in other countries
where groundwater is this close to the surface, pesticide
contamination has been observed. Thus, with our
high population, significant applications of pesticides,
and a water table close to the surface, it is natural to
wonder whether our aquifers are contaminated. This
publication reviews the findings of recent studies.Published May 2003. Reviewed March 2016. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo
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Methods for colloid transport visualization in pore networks
Prediction of colloid transport in the subsurface is relevant to researchers in a variety of fields such as contaminant transport, wastewater treatment, and bioremediation. Investigations have traditionally relied on column studies whereby mechanistic inferences must be drawn on the basis of colloid behavior at the outlet. Over the past decade, development of noninvasive visualization techniques based on visible light, magnetic resonance, and X rays have provided insight into a number of colloid transport mechanisms by enabling direct observation of individual colloids at the pore scale and colloid concentrations at longer length scales. As research focus shifts from transport of ideal colloids in ideal media such as glass beads to natural colloids in natural porous media, these noninvasive techniques will become increasingly useful for studying the collection of mechanisms at work in heterogeneous pore systems. It is useful at this juncture to review recent progress in colloid transport visualization as a starting point for further development of visualization tools to support investigation of colloids in natural systems. We briefly discuss characteristics of visualization systems currently used to study colloid transport in porous media and review representative microscale and mesoscale visualization studies conducted over the past decade, with additional attention given to two optical visualization systems being developed by the authors.Keywords: Review, Methods, Colloids, Visualization, Porous medi
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Green and Ampt infiltration into soils of variable pore size with depth
Most expressions for infiltration rely upon the assumption of vertical uniformity in soil texture and hydraulic properties. We present an extension of the results of Beven [1982, 1984] for infiltration and lateral flow in soils with decreasing permeability with depth. Unlike Beven, we base the derivations upon joint changes in soil properties based on an overall change in characteristic pore size via Miller scaling. A set of very simple expressions for the time rate of infiltration are obtained using a Green and Ampt approach for soils with permeability that decreases with depth following linear, power law, and exponential relationships.Keywords: Hydrology: Soil moisture, Hydrology: Unsaturated zoneKeywords: Hydrology: Soil moisture, Hydrology: Unsaturated zon
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Frequency distribution of water and solute transport properties derived from Pan sampler data
Modeling of water and solute movement requires knowledge of the nature of the spatial distribution of transport parameters. Only a few of the field experiments reported in the literature contained enough measurements to discriminate statistically between lognormal and normal distributions. To obtain statistically significant data sets, six field experiments at four different sites were performed. Different degrees of macropore and matrix flow occurred at each site. In each experiment a solute pulse was added followed by artificial or natural rainfall. Sixteen thousand spatial distributed fluxes and solute concentrations were collected with wick and gravity samplers. Spatial distributions of solute velocity, dispersion coefficient, water flux, and solute concentration were determined over different timescales ranging from 1 hour to the duration of the experiment. A chi-square test was used to discriminate between the type of frequency distributions. The spatially distributed water and solute transport parameters when averaged over the experimental period were found to fit the lognormal distribution when macropore flow dominates. Otherwise, when only matrix flow occurs a normal distribution fitted the data better. Under no-till cultivation, hourly concentration and water flux are lognormally distributed, while tillage makes the tracer concentration to be normally distributed. Spatial frequency distributions of daily solute concentration change in time: Concentrations were normally distributed when the bulk of the solute broke through with the highest concentrations and lognormally distributed in the beginning and end of the experiment. Daily water flux was found to be lognormally distributed throughout the experiment, but the distribution varied between water applications: Shortly after water application, when wick and gravity pan samplers collected water predominantly from macropores and normally distributed at later times when mostly matrix pores were sampled with wick pan samplers.Keywords: Hydrology: Evapotranspiration, Hydrology: Soil moistur
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Water vapor transport in the vicinity of imbibing saline plumes: Homogeneous and layered unsaturated porous media
Water vapor transport in the vicinity of imbibing saline solutions was investigated in two-dimensional (2-D) chambers using a light transmission technique. Concentrated NaNO3 solutions (brines) were applied as point sources to the surface of homogenous packs of prewetted silica sand for four different sand grades. The same solutions were applied to layered systems, where two horizontal fine layers were embedded within a coarser matrix, mimicking stratified sedimentary deposits. Water vapor transport from the residually saturated sand into the imbibing brine was observed in all sand grades and geometries. Pure water applied to sand prewetted with brine migrated into the surrounding residual brine. Water vapor stripping was found to enhance the lateral transport of brine in layered sand, where capillary barrier effects play a major role. Our observations suggest that osmotic potential and vapor density lowering in saline solutions, often neglected in predictive models, should be taken into account when predicting the transport of brines in the vadose zone.Keywords: saline solution, layered porous media, brine, osmotic potential, vapor transport, unsaturated zoneKeywords: saline solution, layered porous media, brine, osmotic potential, vapor transport, unsaturated zon
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