1. Boundaries and Superposition
Groundwater Hydraulics
Daene C. McKinney

2. Introduction Review Superposition Two Wells in an Aquifer Image Well
Continuity in Aquifers
Steady flow to a well in confined aquifer
Superposition
Two Wells in an Aquifer
Image Well
for an Impermeable Boundary
for a Constant Head Boundary
Multiple Wells in an Aquifer

3. Continuity in Aquifers
Confined aquifer
Unconfined aquifer
Linear equations
If h1 and h2 both satisfy a linear equation
Then another solution is
h3 = Ah1 + Bh2
where A and B are constants
(For unconfined aquifer, everything is in terms of h2)

4. Steady Flow to a Well in a Confined Aquifer
2rw
Ground surface
Bedrock
Confined aquifer Q h0
Pre-pumping
head
Confining Layer b r1 r2 h2 h1 hw
Observation wells
Drawdown curve
Pumping well
Point of interest (x,y)
Well at = (xw,yw)

5. Superposition (2 wells pumping)

6. Superposition (n Wells pumping)

7. Steady Flow to a Well in an Unconfined Aquifer
2rw
Ground surface
Bedrock
Unconfined aquifer Q h0
Pre-pumping
Water level r1 r2 h2 h1 hw
Observation wells
Water Table
Pumping well

8. Example x y

9. Example Q = 2x10-2 m3/s, T = 5x10-3 m2/s, Ho = 25 m, rw = 0.25 m y x

10. Example How much does the pumping in well 2 affect the head in well 1?
With both wells pumping
With only Well 1 pumping
Difference = 1.54 m x

11. Superposition (n Wells pumping)

12. Image Well to Simulate Impermeable Boundaryx y

13. Drawdown Near Impermeable Boundary

14. Image Well to Simulate Constant Head Boundaryx y
Todd, 1980.

15. Example - Constant Head Boundary

16. Example – Impermeable Boundary

17. Multiple Well Systems

18. Summary Review Superposition Two Wells in an Aquifer Image Well
Continuity in Aquifers
Steady flow to a well in confined aquifer
Superposition
Two Wells in an Aquifer
Image Well
for an Impermeable Boundary
for a Constant Head Boundary
Multiple Wells in an Aquifer

19. Well 1
pumping alone
Well 2
Both wells
pumping together