Dougherty-Babu Solution for Step-Drawdown Tests in Confined Aquifers
Description
A mathematical solution by Dougherty and Babu (1984) is useful for determining the hydraulic properties (transmissivity, storativity and hydraulic conductivity anisotropy ratio) of nonleaky confined aquifers. Analysis involves matching the solution to drawdown data collected during a pumping test. The Dougherty-Babu solution accounts for wellbore storage effects in a finite-diameter, partially penetrating well with wellbore skin. Moench (1988) extended the method to account for anisotropic conditions. The Dougherty-Babu step test solution also includes linear and nonlinear well losses for the pumping well (Jacob 1947; Rorabaugh 1953; Ramey 1982).
AQTESOLV provides visual and automatic methods for matching the Dougherty and Babu solution to step-drawdown test data. This easy-to-use and intuitive software promotes rapid and accurate determination of aquifer properties.
Assumptions
The following assumptions apply to the use of the Dougherty and Babu solution step tests:
- aquifer has infinite areal extent
- aquifer is homogeneous, anisotropic and of uniform thickness
- pumping well is fully or partially penetrating
- flow to control well is horizontal when the control well is fully penetrating
- aquifer is nonleaky confined
- flow is unsteady
- water is released instantaneously from storage with decline of hydraulic head
Solution Options
AQTESOLV provides the following options for the Dougherty and Babu step-drawdown test solution:
- large-diameter pumping wells
- variable pumping rates
- multiple pumping wells
- multiple observation wells
- partially penetrating wells
- boundaries
References
Dougherty, D.E and D.K. Babu, 1984. Flow to a partially penetrating well in a double-porosity reservoir, Water Resources Research, vol. 20, no. 8, pp. 1116-1122.
Moench, A.F., 1988. The response of partially penetrating wells to pumpage from double-porosity aquifers, Proceedings of the International Conference on Fluid Flow in Fractured Rocks, Atlanta, GA, May 16-18, 1988.
Jacob, C.E., 1947. Drawdown test to determine effective radius of artesian well, Trans. Amer. Soc. of Civil Engrs., vol. 112, paper 2321, pp. 1047-1064.
Ramey, H.J., 1982. Well-loss function and the skin effect: A review. In: Narasimhan, T.N. (ed.) Recent trends in hydrogeology, Geol. Soc. Am., special paper 189, pp. 265-271.
Rorabaugh, M.J., 1953. Graphical and theoretical analysis of step-drawdown test of artesian well, Proc. Amer. Soc. Civil Engrs., vol. 79, separate no. 362, 23 pp.
Bear, J., 1979. Hydraulics of Groundwater, McGraw-Hill, New York, 569p.
See also: solution methods, pumping tests