Barometric Efficiency Research Articles

A new theoretical solution of the effect of atmospheric pressure on water level

Based on the partial differential equation governing the effect of atmospheric pressure on water level of confined well, deriving the boundary condition and considering the seepage water between well and aquifer, the author obtained the analytical solution of water level change in time domain under the action of an atmospheric pressure history with the Laplace transform method. This solution is composed of two terms:stable and retarded terms. The stable term is the multiplication of barometric efficiency and simultaneous atmospheric pressure, and it implies the value of water level after infinite time when the atmospheric pressure is a constant from the time in question. The retarded term is the transient process due to the time lag of water exchange between well and aquifer. From the solution, it is obtained that the interference of atmospheric pressure on water level is the integral superimposition of the contribution of all atmospheric pressure changes before the time in question. So that, we further found out the response function of pulsive atmospheric pressure history. Calculation shows: (1) The pulsive response function starts from zero and tends to a steady value, which is proportional to the barometric efficiency, when the time tends to infinity; (2) The retarded time depends on the mechanical property of aquifer and the radius of well. The larger the seepage coefficient, the smaller the radius of well and the thicker the aquifer, then the shorter the retarded time gets. This solution can be used as the theoretical basis for further analysis of the atmospheric effect and practical correcting method in the future.

Sedimentologic and Diagenetic Controls on Aquifer Properties, Lower Cretaceous Edwards Carbonate Aquifer, Texas: Implications for Aquifer Management: ABSTRACT

ABSTRACT The distribution of water in the Edwards aquifer was assessed using a core and log-based study. Porosity distribution reflects both depositional fabric and subsequent diagenesis. Vertical facies stacking patterns influence the depositional porosity as well as dolomitization and diagenetic porosity modification. Subtidal facies deposited during sea-level highstands are generally undolomitized and exhibit low porosity (5 to 10 percent); platform grainstones commonly have high depositional porosity and significant solution enhancement (20- to 42-percent porosity). Dolomitized subtidal facies in tidal-flat-capped cycles have very high porosity (20 to 40 percent) because of selective dolomite dissolution in the fresh-water aquifer. Porosity in former evaporite beds is high in some areas because of dissolution and collapse, but it is low where gypsum was replaced by calcite cement. Low-energy subtidal and evaporitic units in the Maverick Basin have porosities that are generally less than 15 percent. The overlying basinal packstones and grainstones have solution-enhanced porosities of 25 to 35 percent. Mapped average porosity also shows nonstratigraphically controlled variations. Diagenesis associated with fluctuations in water chemistry near the saline/fresh-water interface may be one cause. Other complex patterns of high and low porosity are attributed to structurally and hydrologically controlled porosity enhancement and cementation. Three-dimensional mapping of porosity trends provides data for improved aquifer management. Only about 3 percent of the water stored in the aquifer during a year of average water level lies above the water table at which natural spring flow is diminished. An average specific yield of 42 percent in the unconfined aquifer is determined from total porosity, changes in the water-table elevation, and changes in estimated recharge and discharge. Average storativity of 2.6 10-4 in the confined Edwards is estimated using average porosity and barometric efficiency calculated from comparing water-level hydrographs and atmospheric-pressure changes.

A comparison of linear regression with Clark's Method for estimating barometric efficiency of confined aquifers

An estimate of barometric efficiency, often necessary for aquifer pump test interpretation, is difficult to obtain when there is a trend in water levels over time. Ordinary least squares (OLS) regression methods can be used to determine both the barometric efficiency and a trend function when the form of the trend is known. Clark's (1967) procedure, which does not require specification of the trend functional form, is shown to provide an unbiased and consistent estimate of barometric efficiency. OLS is only advantageous for a short data record providing the form of the trend is known. Clark's method may still be used with short data records with a linear trend when augmented by a recursive correction procedure. Both methods work best with constant barometric efficiency and rapid aquifer‐borehole water level equilibration.

Estimation des caractéristiques physiques d'aquifères profonds à partir de l'incidence barométrique et des marées terrestres

Time series analyses are used to investigate the relationship between barometric efficiency, earth tides, and water level fluctuations in a confined aquifer. Applied to a limestone confined aquifer in France, this method allowed the estimation of porosity, storage coefficient and aquifer thickness. This case study shows that the method is easily used, particularly in the case of limestone confined aquifers, where pumping test analyses are difficult and require numerous assumptions.

Determination of Specific Storage by Measurement of Aquifer Compression Near a Pumping Well

AbstractAquifer tests of confined aquifers in deep formations can yield inaccurate specific–storage and storage‐coefficient estimates if the distance between the pumped and observation wells is imprecisely known. The distance between the wells can be uncertain because small deviations in the vertical alignment of deep wells can markedly change the distance between the perforated intervals of the wells. Uncertain distance between wells may seriously degrade the accuracy of specific‐storage or storage–coefficient values calculated from aquifer–test data obtained from closely spaced wells.A method is proposed whereby compression of the aquifer matrix can be measured during an aquifer test and used to calculate specific‐storage and storage–coefficient values without knowledge of the distance between the pumped and observation wells. In a field trial of the method, specific–storage and storage‐coefficient values calculated from aquifercompression data were 8.16 × 10 ‐7 and 3.04 × 10 ‐4, which is nearly identical to values (8.04 × 10 ‐7 and 2.99 × 10 ‐4) obtained from longer–term monitoring of aquifer barometric efficiency. Additional comparison with results of a Theis analysis of drawdown data indicates that the aquifer compression data may provide a more accurate determination of specific–storage and storage–coefficient values than would be possible even if the vertical alignment of the pumped and observation wells had been surveyed.

Determination of Bulk Rock Properties From Ground-water Level Fluctuations

The response of ground-water levels to tides and changes in barometric pressure provides an in-situ measure of the response of the rock-water system to changes in stress. Tidal and barometric efficiencies can thus be expressed in terms of drained and undrained moduli. In addition, if the various moduli are known from laboratory measurements, the laboratory equivalents of both tidal and barometric efficiency can provide an estimate of the specific storage. The method is demonstrated to provide reasonable and consistent results when applied to various rock types of differing rigidity.

Determination of aquifer parameters from well tides

An equation for the specific storage of an inland artesian aquifer of infinite extent is developed from a consideration of the tidal dilatation of an idealized well‐aquifer system. It was found that for a particular tidal frequency the specific storage Ss is related to tidal water level and barometric pressure fluctuations according to the relationship Ss = −0.5 W2 cos Φe/{ag [dhw cos Φw + B dhb cos Φb]}, where W2, dhw, dhb are the amplitudes of the periodic tidegenerating potential, the water level fluctuations in the well, and the barometric pressure fluctuations; Φe, Φw, and Φb are the phase angles between the tide‐generating potential and the earth tide dilatation, the water level fluctuation in the well, and the barometric pressure fluctuations; B is the barometric efficiency; a is the radius of the earth; and g is the acceleration of gravity. The earth tide dilatation phase angle Φe ≈ 0.0 can be assumed. Two arbitrary numerical methods are devised for estimating barometric efficiency from aperiodic water level and barometric pressure fluctuations. If the specific storage and barometric efficiency are known, in situ values of porosity n and the matrix bulk modulus Em can be calculated by the following expressions: n = {1 ± [1 ‐ (4 Ss Ew [B‐B2]/ρg)]½}/2(1‐B) and Em = ρg {1 ± [1 ‐ (4 Ss Ew [B‐B2]/ρg)]½}/2 Ss (1‐B) where Ew is the bulk modulus of water and ρ is the density of water. Tidal water level fluctuations were recorded in three observation wells in Montgomery County, Virginia. Physically reasonable values of specific storage, barometric efficiency, porosity, and matrix bulk modulus were calculated, but the accuracy of these values is limited by the imprecise measurements of water level and barometric pressure and the possibility of leakage from imperfectly confined aquifers.

Fluctuations in the Waterlevel in Wells Due to Variations in Atmospheric Pressure

Deviations from the classical theory of the barometric efficiency (Jacob 1940) is shown in some examples. A model with a semipermeable bed overlying the aquifer is proposed, and equations for the flow in this model, generated by changes in the total load, for instance changes in air pressure, are presented. Solutions are given for specified variations in the total load, and some data from nature are compared with one of these solutions. The data presented are from the archives of the Geological Survey of Denmark, Hydrogeological Department (DGU, HA).

A Contribution to the Analysis of Recovery Data for the Determination of the HydrauIic Properties of an Aquifer

The purpose of this paper is to present a more reliable calculation of hydraulic properties (T) and (S) utilizing recovery data instead of residual drawdown data. A useful formula for the computation of the recovery from the extrapolated drawdown is recommended. Practical data for this paper has been obtained from a pumping test in an artesian aquifer at Hvinningdal, Silkeborg, Denmark. The calculations are made by means of the nonequilibrium formulas of Theis and Jacob. In addition, the paper provides procedure and examples of adjustments of water-level data for barometric efficiency.

Nye metoder for prøvepumpning af boringer og grundvandsreservoirer

The purpose of this paper is to introduce the practical application of selected quantitative and analytical methods for testing wells and evaluation of aquifers to engineers and geologists within the field of groundwater hydrology in the Nordic countries. This abstract, a list of symbols and units and text of figures and tables in English may possibly provide understanding of the used formulas and methods for readers not familiar with Danish.The increasing demand for ground water and the need for optimal utilization of aquifers accelerate the use of quantitative methods for predictions of available quantities of ground water and aquifer response on withdrawal.The first part of this paper gives a short introduction into the developed theory for analysing drawdown data from pumping tests and a number of selected formulas in their developed form for determining the hydraulic properties of wells (B, C and n), aquifers, (T and S) and confining bed (P'). Selected hydrogeological terms are defined. The procedure of pumping and the frequency of waterlevel observations in space and time is briefly mentioned both for step-drawdown test and pumping test with constant capacity.Formulas for adjustments of drawdown- and recovery data for barometric efficiency and decrease of saturated thickness are described. Examples of logarithmic and semilogarithmic plots of data are given together with type curves for leaky artesian and watertable conditions.Principles and formulas for prediction of the future drawdown in pumped wells and aquifers are outlined.The second part of the paper gives the practical application of the selected analytical methods and formulas. Illustrative examples with actual field data collected by the Hydrogeological Department, Geological Survey of Denmark, are presented for each method discussed. Basic data as well drawdown as recovery from 4 pumping tests and their numerical and graphical analysis a represented in 27 figures and 16 tables.

PUMPING TESTS AND HYDROGEOLOGICAL INVESTIGATIONS OF AN ARTESIAN AQUIFER NEAR HORSENS, DENMARK

In the Egebjerg area, near Horsens, several aquifers consisting of glacial outwash material deposited in a glacial eroded buried valley in the Tertiary formation have been encountered. The lowest of these, which is the main productive aquifer, and which has leaky artesian conditions, has been investigated. The thickness of this aquifer varies from 10-40 m. The lower confining bed consists of boulder clay or meltwater clay underlain by boulder clay. The upper confining bed, where leakage occurs, consists of meltwater clay with thickness from 0 to 5 m. The upper meltwater deposits include a sequence of interglacial lake deposits and several layers or laminae of clay, which separate this water-bearing material into more aquifers with watertable or artesian conditions. In the eastern part of the area boulder clay deposits are found at the top of the sequence. The Theis modified non-equilibrium equation and its derived formula for the non-steady-state leaky artesian case have been used to determine aquifer properties from pumping test data. By means of Jacob's method and a logarithmic method, well characteristics are determined graphically. Barometric efficiency, reverse fluctuations, and boundary conditions are recorded and discussed.

A rigid plate model of the barometric effect

The proposed “rigid plate model” envisages a plate lying between the atmosphere and the water table which prevents the complete transfer of increased pressure loads to the groundwater mass. The barometric efficiency of a well is dependent not only on the properties of the aquifer, but also on the properties of the rigid plate. Jacob's equation is a special case of the general model. The soil moisture zone is one possible rigid plate. Measurements of barometric efficiency, air temperature and precipitation at Delta, Manitoba confirm the validity of the model.

Water Level Fluctuation in Evapotranspirometers

Eleven plastic lined evapotranspirometer tanks were constructed near Buckeye, Arizona. The levels of the artificially maintained ground water in these instruments show distinct diurnal fluctuations. On bare tanks or on vegetated tanks that are not transpiring, this fluctuation is highly correlated with diurnal and semidiurnal atmospheric fluctuations. Two possible reasons for such response are discussed: There might be air bubbles in the saturated zone, or it might be caused by the flexible plastic lining of the tank. The barometric efficiency is about 40%. On vegetated tanks that are transpiring the water level and barometric curves are out of phase, but if the water levels are corrected for atmospheric pressure fluctuations a curve appears that represents the hourly rate of water use. The results may be important in the interpretation of transpiration well data.

Computing the Barometric Efficiency of a Well

The barometric efficiency of a well may be determined from the slope of a graph of ∑ΔB against ∑ΔW, in which ∑ΔB is the arithmetical summation of the incremental changes, ΔB, of the atmospheric pressure and ∑ΔW is the summation of the incremental changes, ΔW, of the water level in the well, summed according to certain rules. The summing according to these rules eliminates the incremental components in the water level caused by influences other than changes in atmospheric pressure. The method provides a means for determining the barometric efficiency of a well more precisely.