The relations for confined aquifers are also applicable to unconfined aquifers as long as the drawdown is small in comparison with the aquifer thickness (Driscoll, 1986). If t is large, dR/dt is close to zero, i.e., R varies very slowly and it seems as if a steady-state has been achieved (De Marsily, 1986). (1) is time-dependent and, for confined aquifers, it may be represented through the Cooper-Jacob approximation of the Theis solution for an infinite uniform aquifer (Van Tonder et al., 2001).Īs a matter of fact, comparing the Cooper-Jacob approximation of Theis solution with the Dupuit's formula, if the aquifer is infinite and not recharged, one finds that the radius R of influence of the well scales as with time, and its time-derivative dR/dt scales as. Instead, under unsteady-state (transient) conditions, the coefficient B in Eq. (1) is constant with time and it can be directly derived from Dupuit's formula. Under steady-state conditions, for confined aquifers, and following Dupuit's assumption, the coefficient B in Eq. Jacob (1947), deriving his equation, made the analogy between the drawdown s w of a well and the voltage drop Δ V through a resistor, and between the discharge Q and the electric current I. He proposed the following equation:ī is a numerical parameter which takes into account linear head losses of the aquiferĬ is the analogous parameter for non-linear (quadratic) head losses, mainly imputable to the construction characteristics of the well (Driscoll, 1986) Step-drawdown tests were introduced by Jacob (1947) in order to study how the discharge Q affects the drawdown s wof a well drilled in confined aquifers. There are various reasons why they are performed: in the case of exploration wells, they enable determination of the proper discharge rate for the subsequent aquifer test in the case of exploitation wells they can be used to develop an understanding of the behaviour of the well during pumping, in order to determine the optimum production capacity and to analyse the well's performance over time (Boonstra and Kselik, 2001). Step-drawdown tests are currently quite popular they are the most frequently performed tests in the case of single wells (Kawecki, 1995). Keywords: characteristic curve, pumping test, equipment/field techniques, hydraulic testing Moreover, it was observed that for the well in question the ratio Q/s w remains almost constant within each step. It also enables one monitor the approaching of the equilibrium between Q and s w, using both the variation of Q and s w with time. This approach, in this unique case, made possible an understanding of how the discharge Q varies as a function of the drawdown s w. This technique has been experimentally applied to a well and a description of the operations and results are presented in detail. The new approach presented in this paper is based on the idea of keeping the value of r/min fixed at every step of the test, instead of keeping constant the value of the discharge. Current technology allows one to let the submerged electric pumps work at a specific revolution per minute (r/min) and to suitably modify the rotation velocity at every step. Step-drawdown tests known to date are performed strictly keeping the value of the pumping rates constant through all the steps of the test. In this paper a new approach to perform step-drawdown tests is presented. Monticchio Bagni, 85028 Rionero in Vulture (Potenza), Italy
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