Unconfined AquifersUnconfined Aquifers

Unconfined aquiferUnconfined aquifer --Steady State & Non Steady StateSteady State & Non Steady State--

q=2 Л r kh dh/dr

r/dr= (2 Л k/q) h dh

Integrating the above equation between limits r1 and r2 and h1 and h2

2 Л k/q) hdh

= ln (r2/r1)= (2Лk/2q)(h2^2-h1^2)

= ln (r2/r1) = (Лk/q)(h2^2-h1^2)

q= (Лk)(h2^2-h1^2)ln (r2/r1)

H

Theim equation for Steady StateTheim equation for Steady State

Unconfined aquiferUnconfined aquifer--Steady StateSteady State-- Theim Theim equationequation

•The Theis equation has

been derived assuming that

the water is released

instantaneously from

storage and the aquifer

thickness does not vary with

pumping

•But in unconfined

conditions both H will vary

and also water is released

slowly Called delayed yield.

Unconfined aquiferUnconfined aquifer--NonNon--Steady StateSteady State--

Boulton equationBoulton equation

t in days

Boulton initial curveBoulton initial curve Boulton latter partBoulton latter part

First Part

III rd part

SA= Initial Sp.y

Sy=Final Sp.y

Twt is the time where delayed yield does not effect drawdown and behave as unconfined aquifer

1/ =Delayed

Index

Minimum Pumping hours (twt)

Aquifer

material

Minimum

Pumping time

(twt) hrs

Medium to

coars sand

4

Fine sand 30

Silt and clay 170

Delayed index (1/Alpha)-

minutes

Corse sand 10

Medium sand 60

Find sand 200

Very find Sand 1000

Silt 2000