Aquifer and Pump Test Analysis Software Slug test analysis and Step drawdown test analysis Analytical groundwater flow modelling and pumping test simulations Confined Aquifer, Unconfined Aquifer, Leaky Aquifer (original) (raw)
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Transient well flow in vertically heterogeneous aquifers
Journal of Hydrology, 1999
A solution for the general problem of computing well flow in vertically heterogeneous aquifers is found by an integration of both analytical and numerical techniques. The radial component of flow is treated analytically; the drawdown is a continuous function of the distance to the well. The finite-difference technique is used for the vertical flow component only. The aquifer is discretized in the vertical dimension and the heterogeneous aquifer is considered to be a layered (stratified) formation with a finite number of homogeneous sublayers, where each sublayer may have different properties. The transient part of the differential equation is solved with Stehfest's algorithm, a numerical inversion technique of the Laplace transform. The well is of constant discharge and penetrates one or more of the sublayers. The effect of wellbore storage on early drawdown data is taken into account. In this way drawdowns are found for a finite number of sublayers as a continuous function of radial distance to the well and of time since the pumping started.
Simple Equations for Aquifer Parameters from Drawdowns in Large-Diameter Wells
Journal of Irrigation and Drainage Engineering-asce, 2007
Simple equations are proposed for estimating storage coefficient and transmissivity of an aquifer from drawdowns in largediameter wells. The proposed method requires determination of the peak and time to peak of a unimodal curve. Using these values and utilizing the provided set of equations, the aquifer parameters are estimated through an iterative procedure. The proposed method is void of subjectivity involved in the previously proposed curve matching methods. Also, the new method can be used when the conventional curve matching methods cannot be applied to estimate the aquifer parameters. The new method can be used to estimate the aquifer parameters from the drawdown data observed only up to a time so that the peak could be determined.
Diagnostic Curve for Confined Aquifer Parameters from Early Drawdowns
Journal of Irrigation and Drainage Engineering-asce, 2008
A diagnostic curve of unimodal shape is developed for identifying the confined aquifer parameters from early drawdowns. A scaled well function is proposed for the diagnostic curve and computationally simple functions are developed for its accurate approximation. The diagnostic curve may be viewed as an alteration of the Theis' curve or as the generalization of a previous approach proposed by the writer. Plotting the pumping test data in a convenient form and matching it to the diagnostic curve with a parallel shift of axes identify the aquifer parameters. The unimodal shape of the diagnostic curve facilitates matching and reduces the personal errors. The proposed method is simple, easy to apply, and yields accurate estimates of aquifer parameters from only early drawdowns, which would save considerable time and money involved in conducting a long-duration pumping test. The estimates obtained using the new method are as good as those obtained from much more complex methods. The new method does not require either the initial guess for the parameter values or repetitive evaluation of the well function.
A simple procedure for the identification of aquifer parameters based on steady-state pumping tests
IAHS-AISH publication, 2006
Résumé/Abstract Three-dimensional steady flow towards a fully penetrating well of radius rw, in a confined aquifer, is studied by means of a finite-volume numerical scheme. The hydraulic conductivity K is modelled as an axisymmetric, stationary random space function mimicking hydraulic property variations at the local scale. We develop a new methodology for the identification of the geostatistical model of variability from a steady-state pumping test involving a few wells. A constant water discharge is extracted from each well in sequence ...
A revisit of drawdown behavior during pumping in unconfined aquifers
Water Resources Research, 2011
1] In this study, the S-shaped log-log drawdown-time curve typical of pumping tests in unconfined aquifers is reinvestigated via numerical experiments. Like previous investigations, this study attributes the departure of the S shape from the drawdown-time behavior of the confined aquifer to the presence of an "additional" source of water. Unlike previous studies, this source of water is reinvestigated by examining the temporal and spatial evolution of the rate of change in storage in an unconfined aquifer during pumping. This evolution is then related to the transition of water release mechanisms from the expansion of water and compaction of the porous medium to the drainage of water from the unsaturated zone above the initial water table and initially saturated pores as the water table falls during the pumping of the aquifer. Afterward, the 1-D vertical drainage process in a soil column is simulated. Results of the simulation show that the transition of the water release mechanisms in the 1-D vertical flow without an initial unsaturated zone can also yield the S-shaped drawdown-time curve as in an unconfined aquifer. We therefore conclude that the transition of the water release mechanisms and vertical flow in the aquifer are the cause of the S-shaped drawdown-time curve observed during pumping in an unconfined aquifer. We also find that the moisture retention characteristics of the aquifer material have greater impact than its relative permeability characteristics on the drawdown-time curve. Furthermore, influences of the spatial variability of saturated hydraulic conductivity, specific storage, and saturated moisture content on the drawdown curve in the saturated zone are found to be more significant than those of other unsaturated properties. Finally, a cross-correlation analysis reveals that the drawdown at a location in a heterogeneous unconfined aquifer is mainly affected by local heterogeneity near the pumping and observation wells. Applications of a model assuming homogeneity to the estimation of aquifer parameters as such may require a large number of observation wells to obtain representative parameter values. In conclusion, we advocate that the governing equation for variably saturated flow through heterogeneous media is a more appropriate and realistic model that explains the S-shaped drawdown-time curves observed in the field. (2011), A revisit of drawdown behavior during pumping in unconfined aquifers, Water Resour. Res., 47, W05502,
An evaluation of analytical solutions to estimate drawdowns and stream depletions by wells
Water Resources Research, 1991
Analytical solutions for computing drawdowns and streamflow depletion rates often neglect conditions that exist in typical stream-aquifer systems. These conditions can include (I) partial penetration of the aquifer by the stream, (2) presence of a streambed clogging layer, (3) aquifer storage available to the pumping well from areas beyond the stream, and (4) hydraulic disconnection between the stream and the well. A methodology is presented for estimating extended flow lengths and other parameters used to approximate the increased head losses created by partially penetrating streams and clogging layer resistance effects. The computed stream depletion rates and drawdown distributions from several analytical solutions were compared to those obtained using a two-dimensional groundwater flow model. The stream geometry was approximated as a semicircle. Numerical simulation results indicate that, because of the use of simplifying assumptions, the analytical solutions can misrepresent aquifer drawdown distributions and overestimate stream depletion rates. Assuming that a correct simulation of the stream depletion phenomenon is provided by the numerical model, the error associated with each of the simplifying assumptions was determined. At a time of 58.5 days after pumping began, errors in computed stream depletion rates due to neglect of partial penetration were 20%, those due to neglect of clogging layer resistance were 45%, and those due to neglect of storage in areas beyond the stream were 21%. Neglecting hydraulic disconnection had only a minor effect (i.e., an error of 1% only at a time of 58.5 days after pumping began) on computed stream depletion rates and a noticeable effect on aquifer drawdown distributions. groundwater withdrawals near a stream, the water table can be lowered below the streambed elevation, thereby severing the saturated exchange between the stream and the aquifer, creating disconnection, and forming an unsaturated zone Copyright 1991 by the American Geophysical Union. Paper number 91WR00001. 0043-1397/91/91WR-00001 $05.00 below the streambed (Figure 1 c). Under these conditions, as long as the water level in the stream does not change, a further drawdown of the water table due to pumping does not significantly affect the seepage rate from the stream. Several analytical solutions are available for computing drawdowns and stream depletions caused by pumping near a stream [e.g., Theis, 1941; Glover and Balmer, 1954; Jacob, 1950; Hantush, 1965]. These solutions typically incorporate image well theory to predict the rate at which a pumping well depletes flow in a nearby stream. The solutions are based on simplifying assumptions, e.g., (1) the stream fully penetrates the aquifer, (2) the stream and the aquifer are hydraulically connected, (3) the streambed is unclogged, (4) the stream is infinitely long and straight, and (5) the aquifer underlying the stream is isotropic, semi-infinite in extent, of constant transmissivity, and that only horizontal flow (i.e., Dupuit flow) occurs in the aquifer. To account for the effects of vertical seepage from streams that only partially penetrate the full aquifer thickness and whose beds and banks are much less permeable than the aquifer, the method of additional seepage resistances [e.g., Streltsova, 1974] has often been applied [Hantush, 1965]. This technique extends the actual distance between the stream and the pumping well by an additional length, horizontal flow through which results in head losses equivalent to the additional losses created by partial penetration and clogging layer effects. Extended flow lengths based on the Hahtush [1965] solution are, however, smaller than those based on the Jacob [1950] solution. The new "effective distance" replaces the actual distance between the stream and the well as used in the Theis [1941] solution.
A New Method for the Interpretation of Pumping Tests in Leaky Aquifers
Ground Water, 2007
A novel methodology for the interpretation of pumping tests in leaky aquifer systems, referred to as the double inflection point (DIP) method, is presented. The method is based on the analysis of the first and second derivatives of the drawdown with respect to log time for the estimation of the flow parameters. Like commonly used analysis procedures, such as the type-curve approach developed by Walton (1962) and the inflection point method developed by Hantush (1956), the mathematical development of the DIP method is based on the assumption of homogeneity of the leaky aquifer layers. However, contrary to the two methods developed by Hantush and Walton, the new method does not need any fitting process. In homogeneous media, the two classic methods and the one proposed here provide exact results for transmissivity, storativity, and leakage factor when aquifer storage is neglected and the recharging aquifer is unperturbed. The real advantage of the DIP method comes when applying all methods independently to a test in a heterogeneous aquifer, where each method yields parameter values that are weighted differently, and thus each method provides different information about the heterogeneity distribution. Therefore, the methods are complementary and not competitive. In particular, the combination of the DIP method and Hantush method is shown to lead to the identification of contrasts between the local transmissivity in the vicinity of the well and the equivalent transmissivity of the perturbed aquifer volume.
Sequential aquifer tests at a well field, Montalto Uffugo Scalo, Italy
Water Resources Research, 2007
This paper investigates our ability to characterize an aquifer using a sequential aquifer test in a well field that consists of six wells. During the test, we pumped water out from the aquifer at one well and monitored the water level changes at the rest of the wells to obtain a set of five well hydrographs. By pumping at another of the six wells, we obtained another set of five hydrographs. This procedure was repeated until each of the six wells was pumped. We then analyzed the six sets of hydrographs using the classical drawdown-time, the drawdown-distance, and the drawdown-distance/time methods. Results of the analysis confirm recent findings that the transmissivity estimates vary significantly at early time and stabilize at late time. At late time, the estimated values from all hydrographs are similar overall but vary slightly according to the locations of the pumping and observation wells. In contrast, storage coefficient estimates stabilized rapidly to distinct values associated with the well locations. We subsequently used a hydraulic tomography approach to include all hydrographs from the sequential aquifer test to estimate the spatially varying transmissivity and storage coefficient fields. The estimated fields appear to be realistic: They reflect the geologic setting and the behaviors of the well hydrographs, although more definitive confirmation is needed.
Arabian Journal of Geosciences, 2013
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