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A procedure is proposed for calculating the spatial and temporal variation of drawdown due to pumping a well tapping two aquifers separated by an aquitard, using convolution and MODFLOW. It can take into account the unsteady pumping discharge and cross flow through the intervening aquitard. A discrete pulse kernel method based on superposition/convolution is used to account for the unsteady pumping discharge. The discrete pulse kernels are calculated using MODFLOW. The contributions of the aquifers to the pumped discharge are accounted implicitly and not required to be specified explicitly. Available numerical models (e.g., MODFLOW) require the aquifer contributions that are implicitly controlled, to be specified explicitly. The use of the suggested procedure is illustrated using examples. The contributions of the aquifers are found not in proportion to their transmissivities but vary with time, when the diffusivities of the aquifers are not equal. Applying the new procedure, the numerical models, such as MODFLOW can be used to correctly model the transient pumping from two aquifers with cross flow: thus, it opens up the possibility of numerically accounting for the aquifer heterogeneity while dealing with the flow to a well tapping two aquifers under a transient pumping, which would be otherwise difficult to account for analytically. DOI: 10.1061/(ASCE)IR.1943-4774.0000162 CE Database subject headings: Aquifers; Wells; Pumps; Drawdown; Groundwater; Unsteady flow; Numerical models; Heterogeneity. Author keywords: Aquifers; Wells; Pumping; Drawdowns, Multiaquifer well; Groundwater; Aquitard; Unsteady flow; Numerical modeling; Aquifer heterogeneity.

Analytical solutions for groundwater head in the presence of subsurface drains are important in assessing the effectiveness of an existing drainage system under a probable extreme variation in the rate of recharge and designing a new drainage system. Generalized analytical solutions for groundwater head in inclined aquifers in the presence of parallel subsurface drains are obtained considering the transient rate of recharge as a power series (polynomial) function and depth-dependent rate of evapotranspiration. An appropriate function, new to analytical drainage studies, is used for correctly representing the depth-dependent rate of evapotranspiration. The solutions are obtained considering the practical situation of drains placed at shallow depth in a considerable depth of aquifer. Two conditions of large and small saturated thicknesses in comparison to the increase in groundwater head are considered. A mathematical criterion is proposed to distinguish between large and small saturated thicknesses. The analytical equations for discharge to drains for different cases considered are also obtained. The discharge equations used by prior investigators are found inappropriate. DOI: 10.1061/(ASCE)IR.1943-4774.0000150 CE Database subject headings: Agriculture; Drainage; Subsurface drainage; Groundwater; Analytical techniques; Evapotranspiration; Unsteady flow; Aquifers; Transient flow. Author keywords: Agricultural drainage; Subsurface drains; Analytical solutions; Transient recharge; Evapotranspiration; Unsteady flow; Inclined aquifer; Groundwater head; Transient flow.

Simple method and explicit equations are proposed for estimating the parameters of leaky aquifers from drawdown at an observation well, which avoid the curve matching or initial estimate of the parameter. The proposed method is computationally simple and the calculations can be performed even on a handheld calculator. The application of the methods is illustrated, using published data sets. The new method yields quick and accurate estimates of the leaky-aquifer parameters, if observed drawdowns do not contain large errors. The proposed method can also analyze the early drawdowns for accurate characteristics/parameters of a confined aquifer, if the conductance of the aquitard is assigned a zero value. It is hoped that the proposed method would be of help to field engineers and practitioners. DOI: 10.1061/(ASCE)IR.1943-4774.0000131 CE Database subject headings: Drawdown; Aquifers; Pumping tests; Parameters; Groundwater; Estimation; Wells; Leakage. Author keywords: Drawdowns; Aquifers; Pumping test; Aquifer parameters; Groundwater; Estimation of parameters; Wells; Leaky aquifer.

Two sets of unimodal diagnostic curves, one set assumes no aquitard storage and the other set assumes aquitard storage, are developed for identifying the parameter of leaky aquifers from early drawdowns, which yields accurate estimates of the parameters and lessens the subjectivity due to personal errors. The proposed diagnostic curve method is simple, easy to apply, and is based on matching of the diagnostically plotted observed drawdowns to an appropriate diagnostic curve. The new method is simple, easy to apply, does not require either the initial guess for the parameter values or repetitive evaluation of the leaky aquifer well function, and outperforms the conventional curve-matching, optimization, extended Kalman filter, and artificial neural network methods. The proposed set of diagnostic curves has a good diagnostic property and is able to easily identify nonideal conditions. The new method suggests a shorter duration pumping test, which would save time, money, and water. It is hoped that the proposed method would be useful to the field engineers and practitioners. DOI: 10.1061/(ASCE)IR.1943-4774.0000116 CE Database subject headings: Groundwater management; Aquifers; Drawdowns; Pumps; Parameters; Estimation; Leakage. Author keywords: Groundwater; Aquifers; Aquitard; Drawdowns; Pumping test; Aquifer parameters; Simple method; Parameter estimation.

Analytical but approximate invertible equations for time base of gamma unit hydrographs or unit kernel hydrograph (UKH), which are applicable to all catchments, are derived in terms of the parameters of the unit hydrograph. The time base has been linked to the time to peak and lag time for the gamma UKH. The gamma UKH is redefined taking the time base and time to peak as parameters, as these parameters are physically more conceivable than the conventional parameters. The widely used National Resource Conservation Service empirical equations for the time base are found not applicable to all catchments. The proposed equations can also be used for determining the conventional parameters from the known values of the time base and time to peak or lag time. Using the proposed equations for time to peak and time base, the gamma UKH is fitted to few published storm events considering the time base as a parameter. DOI: 10.1061/(ASCE)IR.1943-4774.0000105 CE Database subject headings: Hydrographs; Runoff; Rainfall; Parameters.

Analytical solutions for rate and volume of flow depletion induced by pumping a well from a stream that intersects an impermeable or a recharge boundary at right angles are derived using the basic flow depletion factor defined earlier by the author. A new concept of directly obtaining stream flow depletion using the method of images is proposed. The solutions are derived for five different management cases of a stream and boundary intersecting at right-angles, assuming the aquifer to be confined with semi-infinite areal extent. A computationally simple function is proposed for accurately approximating the error function. The existing analytical solution in the case of a right-angle bend of stream given by Hantush was obtained for unconfined aquifers using a linearization of the governing partial differential equation. The solution for this case obtained using the proposed method for confined aquifer is the same as obtained by Hantush for unconfined aquifers, which shows that the linearization adopted by Hantush does not actually solve this problem for unconfined aquifers. DOI: 10.1061/(ASCE)IR. 1943-4774.0000095 CE Database subject headings: Groundwater; Pumps; Streamflow; Aquifers; Analytical techniques; Transient flow.

The approach by the author for modeling the large-diameter wells using MODFLOW is extended to the partially penetrating large-diameter wells. The temporal variation of drawdown due to a steady pumping is presented in the form of diagnostic curves for different penetration. These diagnostic curves can also be used to estimate the aquifer parameters from the observed drawdowns in a partially penetrating large-diameter well. DOI: 10.1061/(ASCE)IR.1943-4774.0000066 CE Database subject headings: Aquifers; Wells; Numerical model; Transient flow; Drawdowns; Partial penetration; Large diameter well; Groundwater modeling.

Generalized analytical solutions for groundwater head in horizontal aquifers in the presence of parallel subsurface drains are obtained considering a transient rate of recharge as a power series (polynomial) function and depth-dependent rate of evapotranspiration. A function, new to analytical drainage studies, is proposed for correctly representing the depth-dependent rate of evapotranspiration. The solutions are obtained considering the practical situation of drains placed at a shallow depth in a considerable depth of aquifer. Two conditions of large and small saturated thicknesses in comparison to the changes in groundwater head are considered. A mathematical criterion is proposed to distinguish between large and small saturated thicknesses. DOI: 10.1061/(ASCE)IR.1943-4774.0000069 CE Database subject headings: Agriculture; Drainage; Evapotranspiration; Unsteady flow; Aquifers; Groundwater.

A kernel method is proposed for calculating transient rate and cumulative volume of well discharge under constant drawdown. The new method can also be used for obtaining the drawdown (in pressure head) in the aquifer at some distance away from the well. Employing the new method, an optimization method is used to estimate the aquifer parameters from transient well discharge or drawdown in the aquifer pressure head. The proposed method can also be used to model the recovery of drawdown (in aquifer pressure head) after the plug-in of the well. CE Database subject headings: Groundwater management; Wells; Aquifers; Parameters; Unsteady flow; Estimation.

A ramp kernel method is proposed for accurately calculating the drawdown due to any temporal variation in pumping discharge. The use of the ramp kernels assumes the linear variation between the two consecutive measured pumping discharges. The prior studies assume a rectangular variation between the two consecutive measured pumping discharges. In the rectangular variation, a uniform pumping rate is assumed during a time span. An analytical equation for calculating the ramp kernel is derived. An optimization method is used with the proposed ramp kernels for inversely estimating the aquifer parameters from drawdown due to an arbitrary unsteady pumping discharge. Unlike the prior methods, the proposed method accurately identifies the parameters even when the sampling interval for the drawdown and pumping discharge is longer than that needed for assuming a linear variation. The proposed method outperforms the prior method. Application of the proposed method is illustrated using examples. CE Database subject headings: Aquifers; Drawdowns; Pumps; Discharge; Storage; Coefficient; Parameters; Estimation.

A computationally simple semianalytical model is proposed for calculating the drawdown due to pumping a well tapping two aquifers separated by an aquiclude with no cross flow. The new model can take into account the transient pumping discharge. Equations are proposed for calculating the transient contributions of the aquifers to the pumped discharge and drawdowns in aquifers. The residual drawdowns in the aquifers and the aquifer contributions during recovery period can also be obtained using the proposed model. Based upon a similar principle, another model is also developed that can consider the effect of the well storage. The proposed models can be used to calculate drawdowns neglecting or considering the well storage, in the case of transient pumping from two aquifers having different values of transmissivity and storage coefficient. It is hoped that the new models would be of help to the field engineers and practitioners. DOI: 10.1061/(ASCE)0733-9437(2009)135:1(102) CE Database subject headings: Pumps; Aquifers; Drawdown; Groundwater management; Transient flow.

The existing equation for leaky aquifers is transformed into a nondimensional form using new parameters and a scaled well function for leaky aquifers is proposed. A computationally simple function is developed for accurately approximating the scaled well function for the practical range of the parameters. Utilizing this function (approximation), an optimization method is proposed for identifying the leaky-aquifer parameters from observed drawdowns. The new function has an enhanced utility when a repetitive numerical evaluation of the well function for leaky aquifers is needed, e.g., while estimating the aquifer parameters using optimization or Kalman filter or artificial neural network methods. The application of the proposed method is illustrated using a few sets of published data. The proposed method outperforms the extended Kalman filter method, based on the reported results in the literature. DOI: 10.1061/(ASCE)0733-9437(2008)134:6(864) CE Database subject headings: Groundwater management; Aquifers; Leakage; Drawdown; Pumping test; Parameters; Optimization; Water storage; Coefficients; Wells.

The modified advection dispersion equation (MADE) model is compared to the transient storage model (TSM) and fractional advection dispersion equation (FRADE) model for modeling riverine transport. The comparisons are illustrated using field examples. The parameter F of the FRADE model is found to be inconsistent to its physical meaning and is unrelated to dead zone fraction. Also, the estimated parameters of TSM are found to be inconsistent to their physical meaning. On the contrary, the parameters of MADE are consistent and related to the dead zone fraction. It is observed that the MADE model is easy to use and yields reliable and consistent results. DOI: 10.1061/(ASCE)0733-9437(2008)134:6(853) CE Database subject headings: Solutes; Parameters; Estimation; Rivers; Analytical techniques; Models.

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. DOI: 10.1061/(ASCE)0733-9437(2008)134:4(515) CE Database subject headings: Aquifers; Parameters; Drawdown; Ground water; Optimization; Pumps; Water storage; Coefficients.

Abstract: The existing equation applicable for large diameter wells in confined aquifers is transformed into a convenient form and a set of semilogarithmic diagnostic curves is developed for identifying the aquifer parameters (storage coefficient and transmissivity) from early drawdowns in large diameter wells. A scaled well function is proposed for the diagnostic curves. The aquifer parameters are estimated by matching the diagnostically plotted drawdowns to one of the diagnostic curves by a parallel shift of only one axis. The substantial curvature of the diagnostic curves and shifting of only one axis facilitate matching and reduce subjectivity. The proposed method is an improvement over the existing matching methods. The new method can reliably identify the aquifer parameters from only early drawdowns and would result in a 100-fold saving in time and money. It is hoped that this method would be helpful to field engineers and practitioners. DOI: 10.1061/(ASCE)0733-9437(2008)134:3(409) CE Database subject headings: Ground-water management; Wells; Drawdown; Parameters; Pumping test; Water storage; Water supply.

A simple semianalytical model is proposed for calculating the drawdown due to pumping a well tapping two aquifers. The new model can take into account the transient pumping discharge and cross flow between the aquifers. The transient contributions of the aquifers to the pumped discharge can also be implicitly obtained using the model. DOI: 10.1061/(ASCE)0733-9437(2008)134:2(228) CE Database subject headings: Pumps; Aquifers; Drawdown; Reservoirs; Groundwater; Transient flow; Cross flow.

A method is proposed for identifying the head loss from the early drawdowns at the pumped well and an observation well. The new method is computationally simple and the calculations can be performed even on a hand-held calculator. The previously proposed methods for identifying the head loss requires a long duration pumping test, while the new method requires only a short duration pumping test. The use of the proposed method would save time and money and would be of help to field and practicing engineers. A nondimensional coefficient of head loss is also proposed, which permits a meaningful comparison of the efficiency conditions of different wells. DOI: 10.1061/(ASCE)0733-9437(2008)134:1(107) CE Database subject headings: Aquifers; Pumping tests; Drawdowns; Head loss; Parameters; Optimization.

A simple procedure is proposed, using a linear transform, for obtaining a single representative effective rainfall hyetograph (ERH) and the corresponding direct runoff hydrograph (DRH) by processing multistorm data. Using these representative ERH and DRH, the representative parameters of the two-parameter gamma distribution instantaneous unit hydrograph (IUH) is determined by either the proposed optimization method or the conventional method of moments. The optimization method is found superior to the method of moments and yields reliable IUH. However, the method of moments is easier to apply and yields acceptable results. A two-parameter gamma distribution is used for the parametric representation of the IUH, which yields a smooth shape of the IUH. A linear programming or a least-squares approach does not yield a IUH and the UH it identifies does not have a smooth shape (oscillations are observed in the tail of the UH). The new method yields a reliable representative IUH. The use of the methods is illustrated using the published data sets. DOI: 10.1061/(ASCE)0733-9437(2007) 133:6(602) CE Database subject headings: Rainfall; Runoff; Hydrographs; Optimization; Gamma function; Nonlinear analysis; Parameters.

An objective method and a diagnostic curve method are developed for estimating the aquifer parameters (storage coefficient and transmissivity) from shig test data oil a fully penetrating well. In the objective method, explicit equations are developed for estimating the aquifer parameters. In the diagnostic curve method, a set of unimodal diagnostic curves is developed along with a guiding straight line. The rise or fall in water level of the well is plotted diagnostically on a double logarithmic graph and matched to one of the diagnostic curves plotted on the same scale with a parallel shift of axes. to estimate the aquifer parameters from the dual coordinates of a selected point on the matched portion of the graphs. The unimodal shape of the diagnostic curves and the guiding straight line facilitate the matching and limit the subjectivity. The proposed methods can easily identify a nonideal condition. The estimates of the aquifer parameters obtained using the proposed methods are more accurate than those obtained using the prior curve matching methods. The proposed methods are also able to identify nonideal conditions. It is hoped that the new methods will be of help to field and practicing engineers. DOI: 10.1061/(ASCE)0733-9437(2007)133:3(272) CE Database subject headings: Water storage: Coefficients: Estimation: Parameters: Wells: Ground water management: Aquifers: Water levels.

A simple approximation of the well function for a constant drawdown is developed. This approximation is used to estimate the storage coefficient and transmissivity of the aquifer from observed unsteady discharge under a constant drawdown condition, using an optimization method. Another simple approximation for calculating the total production volume during a time span is also developed. The developed approximations for the well function and production function are accurate within a maximum error of 0.7% for the practical range of the argument. DOI: 10.1061/(ASCE)0733-9437(2007)133:3(282) CE Database subject headings: Drawdown: Aquifers: Water storage: Coefficient: Parameters: Estimation: Ground water; Wells: Unsteady flow: Water discharge.

A semianalytical model is developed for computing drawdowns in and around a partially penetrating large diameter well. The new model can take into account an unsteady pumping discharge and thus drawdowns during recovery can be computed. This model can also yield the unsteady contributions from well and aquifer storages to the pumped discharge. While developing the model, the flow from the bottom of the well is also accounted. DOI: 10.1061/(ASCE)0733-9437(2007) 133:2(155) CE Database subject headings: Drawdowns; Wells; Pumps; Unsteady flow; Analytical techniques.

A head loss concept, new to the stream-aquifer interaction, is introduced for modeling laboratory observations. Using this concept, the equation applicable to fully penetrating streams is modified to account for the head loss at the entrance. The modified model is able to explain and fit the observed laboratory data correctly. Equations are proposed to calculate the hydraulic diffusivity of aquifer and head loss at the entrance from the estimate of diffusivity obtained without considering the head loss. An optimization approach is also proposed to estimate the hydraulic diffusivity of the aquifer and head loss from the observed groundwater heads at different sections. DOI: 10.1061/(ASCE)0733-9437(2007)133:1(79) CE Database subject headings: Aquifers; Diffusivity; Head loss; Parameters; Optimization; Ground water.

A procedure for calculating the flow depletion from a finite length of a stream induced by a pumping well in an adjacent aquifer is developed. Four management cases of finite length of the stream including a basic case are considered. A 'basic flow depletion factor' is defined, in terms of which the flow depletion factors for all cases are expressed. The basic flow depletion factor is twice the Hantush M function. A computationally simple and accurate practical approximation of the basic flow depletion factor is presented that encompasses the full practical range of the solutions. Using this approximation, an optimization method is proposed for the estimation of the aquifer hydraulic diffusivity and effective distance from the pumping well to the line of recharge from the measured temporal variation of stream flow depletion between two sections. During optimization, repeated computation of stream flow depletion is required; use of the proposed approximation simplifies the computation. DOI: 10.1061/(ASCE)0733-9437(2006)132:5(508) CE Database subject headings: Ground-water management; Pumps; Transient flow; Streamflow; Wells; Optimization.

Analytical expressions for rate and volume of flow depletion of semipervious streams due to sinusoidal variation in pumping rate are obtained. An analytical but approximate method is developed for obtaining the rate and volume of stream flow depletion due to arbitrary unsteady pumping discharge. The method uses the ramp kernel and convolution. The use of ramp kernels permits linear interpolation between two consecutive discretized discharge values. The analytical equations for the ramp kernels for the rate and volume of stream flow depletion are derived. The proposed method is applicable for homogeneous and isotropic aquifers that are hydraulically connected to streams. CE Database subject headings: Streams; Pumps; Aquifers; Surface water; Ground water; Unsteady flow; Streamflow.

An optimization method for estimating an optimal smooth instantaneous unit hydrograph (IUH) from multistorm data taken simultaneously is proposed. A gamma IUH is used for representing the analytical IUH. The parameters of the analytical IUH are optimized. The method avoids oscillations in the tail end of IUH. It automatically takes care of the volume and nonnegativity constraints. The application of the method is illustrated through examples. The new method reliably estimates the optimal IUH. DOI: 10.1061/(ASCE)0733-9437(2006)132:3(298) CE Database subject headings: Rainfall; Runoff; Hydrographs; Nonlinear analysis; Optimization; Parameters; Estimation; Data analysis.

Analytical but approximate methods are developed for obtaining pumping induced rate and volume of stream flow depletion, which can account for unsteady (any variation) pumping discharge and are also applicable for intermittent pumping and recovery. Exact analytical solutions for a sinusoidal variation in the pumping discharge are proposed; the proposed methods are verified using these solutions. The proposed methods use ramp kernels that give results superior to the conventional convolution. These ramp kernels assume the linear variation in pumping discharge between the two consecutive discretized points as opposed to the uniform variation assumed in the conventional convolution. The proposed solutions are applicable for homogeneous and isotropic aquifers hydraulically connected to streams. DOI: 10.1061/(ASCE)0733-9437(2005)131:6(539) CE Database subject headings: Aquifers; Ground water; Pumps; Streams; Streamflow; Transient flow; Flow rates.

Analytical expressions for ramp kernels (new kernels) for an improved convolution for obtaining aquifer responses, viz, groundwater head, rate, and cumulative volume of groundwater flow, to an arbitrary stage, are obtained. The use of the ramp kernels gives accurate aquifer responses and is superior to the conventional convolution in which numerical integration or pulse kernels are used. The extent of improvement in the results with the use of the ramp kernels is discussed and quantified for three examples, where the results are compared to analytical solutions. For the comparisons, the analytical solutions for linear and sinusoidal stream stages are derived. The use of the ramp kernels reproduces accurately the analytical solutions. The concept of ramp kernels can also be used for obtaining an accurate solution of convolution integrals observed in other fields. CE Database subject headings: Aquifers: Analytical techniques; Ground-water flow: Floods: Streamflow: Ramps.

Expressions for the rate and volume of flow depletion of semipervious streams due to pumping are presented in computationally simple forms. Analytical expressions have been proposed to take into account both partial penetration and semipervious bed and banks of the stream. Graphs suitable for engineering applications are presented for siting wells, and the effect of an intermittent pumping cycle on the rate and volume of stream flow depletion has also been discussed. The exclusive volume of flow depletion during a cycle is shown to vary with the selection of the end of the cycle. DOI: 10.1061/(ASCE)0733-9437(2003)129:6(449) CE Database subject headings: Pumps; Aquifers; Streams; Wells; Water shortage.

An efficient method that uses discrete ramp kernel is proposed for obtaining the piezometric head in an aquifer due to an arbitrary variation in stream stage considering stream resistance. The method assumes straight line variation between two consecutive points in representing the arbitrary stream stage variation. Expression for the ramp kernel is derived for homogeneous and isotropic aquifer conditions. Using the method, the stream resistance and hydraulic diffusivity of the aquifer are estimated for a set of published data. It is observed that the hydraulic diffusivity should be estimated along with the stream resistance for a better estimation of aquifer diffusivity. CE Database keywords: Streams; Aquifers; Diffusivity; Resistance; Penetration.

Early drawdown data, for which the argument u of the well function is >0.01, have often been considered unimportant in evaluating aquifer parameters. This paper shows that these early drawdown data, especially in the neighborhood of u = 0.43, can yield accurate values of aquifer parameters. A simple method has been presented for explicit determination of aquifer parameters using early drawdown data. The method does not require curve matching, initial guess of the parameters, or special care to check for u < 0.01, and the computations involved can be performed on a calculator. Application of the method on published data sets shows that the estimates of the aquifer parameters using only a few initial drawdowns are as good as those obtained by Theis curve matching when all data, including the late drawdowns (u < 0.01), are used. The new method converges with the Cooper-Jacob method when the late drawdown data are considered. Thus, the late drawdown data also can be analyzed using the new method.

A computationally simple approximation of the Hantush M function is proposed. Using this approximation, an optimization method is proposed for identifying the aquifer parameters from early drawdowns around partially penetrating wells. The aquifer parameters are hydraulic conductivity and specific storage. The application of the method is illustrated using a field example. The proposed method results in a 120-fold saving in time when compared to the prior method. It is hoped that the proposed approximation and method will be of help to the field engineers and practitioners. DOI: 10.1061/(ASCE)0733-9437(2008)134:6(861) CE Database subject headings: Aquifers; Parameters; Wells; Drawdown; Hydraulic conductivity; Water storage; Estimation; Groundwater management.

Abstract: An approach for incorporating large-diameter wells into MODFLOW is presented. A transformation of transmissivity in the flow field is devised to simulate the well function for a large-diameter wells. Transformations for accounting for the well radius and well storage are also developed. Using these transformations, MODFLOW is used to obtain the drawdowns. It is observed that the flow to a large diameter well can be accurately modeled using the proposed transformations and MODFLOW. DOI: 10.1061/(ASCE)0733-9437(2008)134:3(414) CE Database subject headings: Aquifers; Wells; Numerical models; Transient flow; Drawdown; Water storage.

A new accurate approximation for the well function for instantaneous charge of water for large diameter wells is proposed. Using this approximation with an optimization method, storage coefficient and transmissivity are estimated from slug test data on large diameter wells. The proposed method is void of the subjectivity of curve matching procedure. CE Database subject headings: Storage coefficient; Wells; Ground-water management; Parameters; Optimization; Aquifers.

A computationally simple and accurate algebraic approximation of the well function for large diameter wells is proposed. This approximation can be used to calculate drawdown in a large diameter well due to steady pumping. Using this approximation, a method is proposed for calculating drawdowns in large diameter wells due to unsteady pumping discharge. The proposed method is also applicable for calculating residual drawdowns in large diameter wells. In principle, the proposed method that uses the approximation of the well function should yield more accurate results than the previously proposed kernel methods. DOI: 10.1061/(ASCE)0733-9437(2007)133:4(414) CE Database subject headings: Pumping; Storage coefficient; Approximation; Drawdown; Large diameter wells; Unsteady flow; Transmissivity; Well function; Classification description; Ground water.

An optimization method is proposed for estimating the storage coefficient and transmissivity of an aquifer from drawdowns in large diameter wells consequent to an unsteady pumping. The concept of an optimal time step size is propagated in the proposed method. The estimate of the aquifer parameters corresponding to the optimal time step size is termed final estimate. The estimates for any other time step size are not reliable. The proposed method can also take into account the residual drawdowns. The application of the method is illustrated using an example. DOI: 10.1061/(ASCE)0733-9437(2007)133:4(411) CE Database subject headings: Drawdowns; Optimization; Large diameter well; Residual drawdown; Storage coefficient; Transmissivity; Classification description; Ground water.

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. DOI: 10.1061/(ASCE)0733-9437(2007)133:3(279) CE Database subject headings: Water storage: Coefficients: Wells: Aquifers; Ground water; Pumps; Unsteady flow; Estimation.

A diagnostic curve is developed for identification of dispersivity and injected mass in case of homogeneous and isotropic soil. The exit concentration from a soil column experiment is diagnostically plotted and matched to the diagnostic curve to yield the estimates of dispersivity and injected mass. A changed value of dispersivity can be identified during increasing versus decreasing concentrations. The new method is applicable for any value of the Peclet number or specific dispersivity. An estimate of the injected mass would be helpful in assessing the pollutant load from a point source. Thus, the new method would be useful for field application. DOI: 10.1061/(ASCE)0733-9437(2006)132:3(281) CE Database subject headings: Isotropic materials; Soil pollution; Mass; Injection.

A computationally simple kernel method is proposed for obtaining drawdowns due to unsteady pumping of large diameter wells. The kernels can be worked out even on a hand-held calculator. The new method can also be used to obtain residual drawdowns. The new method yields results as good as those obtained using earlier methods. CE Database subject headings: Aquifers; Pumps; Drawdown; Wells; India; Developing countries.

The two analytical solutions researched by Theis, and also Glover and Balmer, for the rate of stream depletion are shown to be the same in the mathematical sense by solving the integral appearing in the Theis solution. Expressions for the volume of stream depletion expressed as a fraction of total volume pumped relative to the rate of depletion are obtained for pumping and recovery. The optimum location of a well near the stream and the time to reach equilibrium are suggested.