Determination of hydraulic parameters in a fractured rock aquifer

Abstract

The following equation is derived to determine the vertical hydraulic conductivity Kz of an artesian fractured rock aquifer: Kₒ[(Kz/Kr) ½ πr/b] = 2B csc(πd/b) where Kₒ, Kr, b, d, and B are respectively the zero-order modified Bessel function of the second kind, the radial hydraulic conductivity, the aquifer thickness, the depth of penetration of the pumped well, and a function of Kr, h, d, discharge Q, drawdown s, and the well function W(u). An estimate of Kr is obtained using the Theis equation or the double slope method. A drawdown prediction equation is also formulated: S = (Q/4πKrb)/{W(u)+(2b/πd) Kₒ[(Kz/Kr) ½πr/b]sin(πd/b). Data from two aquifer tests in a fractured volcanic tuff aquifer were analyzed using these equations to determine Kz. In test 1 it was not possible to obtain realistic values for Kz. In test 2, a value for Kz obtained that was both realistic and consistent with a value obtained by another method. The Theis equation is easier to use than the double slope method. However, both techniques neglect Kz when they are used to estimate Kr. Neglect of observation well partial penetration may have introduced some error. Methods presented in this study are also applicable to artesian nonfractured rock aquifers.