1. Chapter 11 Large-Diameter Wells
Stephanie Fulton
February 27, 2014

2. Large-Diameter Wells Difference from other methods Two methods
Well storage previously assumed negligible
Must be taken into account
When is “large” diameter large?
Two methods
Fully penetrating well in a confined aquifer
Partially penetrating well in an unconfined anisotropic aquifer

3. Papadopulos’s (1967) Curve Fitting Method
Assumptions
Confined aquifer
Unsteady-state flow
Fully penetrating
large-diameter well so storage cannot be neglected

4. Papadopulos’s (1967) Curve Fitting Method (cont)
Similar to other methods (Theis equation) except for the well function
Well function F(u,α, r/rew) accounts for the size of the well

5. Papadopulos Type Curves
For 1/u and α = (10-1, 10-2, 10-3), select a value for r/rew using look-up tables in Annex 11.1
α is a function of well radius and storativity
For long pumping times, F(u,α, r/rew) can be approximated with the Theis equation well function W(u) (Equation 3.5)

6. Remarks Early drawdown data yields unreliable results
Data curve can be readily matched with more than one type curve but estimated S values differ by an order of magnitude
Transmissivity (KD) is less sensitive to the choice of type curve
Large-diameter wells are often partially penetrating, in which case another solution is needed.
Drawdown reaches a max when t > DS/2K
Drawdown can be estimated using an equation analogous to Equation 10.7:

7. Boulton-Streltsova’s Curve Fitting Method
Unconfined, unsteady-state flow
Homogeneous, anisotropic, uniform thickness
Partially penetrating large-diameter well
Well diameter is not small so well storage cannot be neglected
SY/SA > 10

8. Boulton-Streltsova’s Curve Fitting Method (cont)
Type A curves
Early-time drawdown
Boulton and Streltsova (1976) developed a well function describing the first segment of the S-curve typical of unsteady-state flow in an unconfined aquifer

9. Streltsova Type Curves

10. Boulton-Streltsova’s Curve Fitting Method (cont)
Type B curves
Late-time drawdown
Curves result from Streltsova’s equation for a small diameter, partially penetrating well in an unconfined aquifer
Applicable for long pumping times when the effect of well storage is negligible
Modifed form of the Dagan solution (1967):