3 Well Hydraulics geology geology hut.ppt

Hydraulics

1. Well Hydraulics
The principle objective of groundwater studies is to
determine how much groundwater can be safely
withdrawn perennially from the aquifers in the area
under study. This determination involves:

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2. By conducting aquifer or pumping tests, to evaluate
groundwater aquifers and pumping wells, and also to
determine the following groundwater hydraulics such as:
1 -Transmissivity (T) and Storage coefficient(S) of aquifers
2 -The hydraulic nature of aquifer boundaries.
3 -Effect of recharge and discharge and vertical leakage if any.
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3. •Most of the above information can be obtained by
conducting aquifer or pumping tests. In these
studies tow different flow conditions are assumed.
a) a steady state condition: When the flow is steady
and the water levels stopped to decline.
b) a non- steady state condition: when the rate of
flow through the aquifer is changing and the water
levels are declining.
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4. Transmissivity (T):
the rate at which water is transmitted through a
unit width of aquifer under a unit of hydraulic
gradient
T = K*b m
2
/day
K = hydraulic conductivity m/day
b = saturated thickness of the aquifer m
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5. Storage coefficient or Storativity (S)
It is the volume of water released from storage
or taken into storage per unit of surface area of
the aquifer per unit change in head
Values of S = 0.01 ~ 0.35 for unconfined aquifer
= 10
-3
~ 10
-5
for confined aquifer
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6. METHODS OF ANALYZING PUMPING TEST DATA
A) Steady state flow in confined aquifer
1- Thiem’s method (from two observed wells)
p.153 (Todd)
2- Thiem’s method (from three observed wells)
using distance-drawdown graph.
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7. 1- Thiem’s method (from two observed wells) p.153 (Todd)

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8. 2- Thiem’s method (from three observed wells) using distance-drawdown graph.
T= KD =
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9. Where;
Q = Pumping rate m
3
/day
T = Transmissivity m
2
/day
K = Hydraulic Conductivity (m/day)
b OR D = Confined aquifer thickness (m)
r
1
= Distance from pumping well to observation well 1(m)

r
2
= Distance from pumping well to observation well 2(m)
s
1 = drawdown in meter in observation well 1(m)
s
2
= drawdown in meter in observation well 2(m)
Δs = drawdown difference per log cycle
h
0=saturated thickness in unconfined aquifer
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10. Radial flow to a well penetrating an unconfined aquifer. (Todd p.157)
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11. B) Unsteady state flow in a confined aquifer
1- Theis’s method. (Todd p.164)
2- Cooper-Jacob method. (Todd p.167)
3- Chow method. (Todd p.169)
4- Recovery test. (Todd p. 170)
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15. 1- Theis’s method. (Todd p.167)

and
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16. Where;
Q = Pumping rate m
3
/day
T = Transmissivity m
2
/day
S = Storage Coefficient
r = Distance from pumping well to observation well (m)

t = time in minutes
s = drawdown in meter (static water level – dynamic water level)
Δs = drawdown difference per log cycle
W(u) & u are well functions
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17. 2 -Cooper-Jacob method. (Todd p.168)

&
to=time when drawdown (s =0) in the taken observation well
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18. 3- Chow method. (Todd p.170)

&
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20. 4 -Recovery test. (Todd p. 171)
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