![]() They obtained the Laplace domain solution for the residual drawdown. Later, Yeh and Wang developed a mathematical model for describing the residual drawdown by taking into consideration the pumping drawdown distribution in addition to the effects of well radius and wellbore storage. Mishra and Chachadi obtained the recovery type curves for large-diameter pumping wells by discrete kernel approach while Şen presented an analytical solution and a set of type curves for the drawdown distribution in a large-diameter well recovery. Ramey presented the type curves for drawdown during the pumping and recovery periods, where the recovery times are plotted as large times. Through a simple transformation of the data from a recovery test, Agarwal method allows one to apply the same diagnostic principles and type curves used for drawdown analysis in the interpretation of recovery data. Agarwal developed a method for recovery test analysis which is widely used by petroleum engineers. ![]() developed convenient equations in the forms of a series based on the Theis recovery equation using the residual drawdown data. The recovery analysis is also investigated by many researchers. In this formulation corresponds to the antilogarithm as. Later, USDI gave an alternative method for determining the storage coefficient ( ) as follows: where is the transmissivity, is pumping period drawdown projected to time at any radial distance,, is residual drawdown at time, is recovery at time, and is slope of the time-recovery graph. The method depends on the extension of the time-drawdown pumping test data, which can also be applied to the time-recovery graph. On the other hand, Jacob observed that the storage coefficient estimation is generally greater during the pumping period than the recovery period.īruin and Hudson proposed the time-recovery drawdown graph to find the time of zero recovery. This plot on the semilogarithmic graph paper passes below the origin (, ) giving the value of for a zero residual drawdown and that is the reason why different storage coefficient estimations are valid for the pumping and recovery periods. Theis observed that a straight-line through the residual drawdowns ( ) versus plot ( indicates the total time since pump start while is the time since pump shut). The Theis recovery method considers the late-time residual drawdowns with the Cooper and Jacob formulations and it estimates the transmissivity and the ratio of storativity values during pumping and recovery periods. However, in cases of measurements from the observation wells there will not be such restrictive effects. With the Theis recovery method, the transmissivity can be estimated easily using pumping well recovery data, but the storage coefficient cannot be calculated due to wellbore storage effects, unknown effective radius, and difficulty in finding the time of zero recovery as needed for the application of Cooper and Jacob method. The recovery drawdown is known as the difference between the total drawdown at the end of pumping and the residual drawdown. The residual drawdown measurement at any time during the recovery period is the difference between the observed water level and the prepumping static water level. The parameters’ estimations from both tests are practically equal to each other if the Theis assumptions are satisfied. The recovery method serves as a check and alternative to the pumping test. This is referred to as the recovery test which starts just after the pump shut. One of the practical ways to estimate the aquifer parameter is to measure the water level rise by time in the production or observation wells after the pumping test stoppage. It presents a strength methodology for the parameters decision making from the residual data in the groundwater field of civil engineering. The method can be applied reliably to extensive and homogeneous confined aquifers resulting in different storage coefficients during the pumping and recovery periods. It is based on the expansion series of the Theis well function by consideration of three terms, and this approach is valid for the dimensionless time factor. The proposed method of this paper depends on a straight-line through the field data and it helps to calculate the parameters quickly without any need for long-term pumping data. ![]() For this purpose, the residual drawdowns have been in use to estimate the aquifer parameters by the classical Theis recovery method. Determination of the hydraulic parameters (transmissivity and storage coefficients) of a confined aquifer is important for effective groundwater resources.
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