Cooper, Bredehoeft, Papadopulos Type Curve
Cooper, Bredehoeft, Papadopulos
(fully penetrating wells)
See Also:
The Cooper, Bredehoeft, Papadopulos method requires the matching of the time and drawdown data to a type curve. After a match is selected, a value of the logarithm of alpha is estimated by the user. The results will be displayed and the user will have the option of creating a file of the results, or returning to the type curve.
The Calculations
The method is developed for use in confined aquifers that are fully penetrated by the well screen.
A series of type curves is plotted semi-logarithmically, with F(alpha, beta) plotted arithmetically on the vertical axis, and beta plotted logarithmically on the horizontal axis. A different curve is plotted for each selected value of alpha.
Time and Head Ratio values are plotted semi-logarithmically to the same scale as the type curves. Head Ratio is plotted arithmetically on the vertical scale, and log of time is plotted on the horizontal scale. The data is fit to a type curve, and a value of alpha is estimated.
When the match is indicated, Super Slug determines the match point of F(alpha, beta) and beta for the value of time = 0.1 days and head ratio = 0.5. These match points will be indicated with the results of the calculations.
Using Equation 1 below, aquifer transmissivity is determined from the values of t = 0.1 and the beta value calculated from the match.
Equation 1
Using Equation 2 below, storativity is calculated from the value of alpha estimated by the user.
Equation 2
Because of the similar shape of the type curves, it may be difficult to obtain a unique match for one type curve, especially as alpha becomes small. Papadopulos et al. (1973) state that for alpha < 10e-5, if the error in the chosen alpha is within two orders of magnitude of its actual value, the error in the determined transmissivity would be less than 30 percent.