Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

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Chapter 4:
Well Hydraulics

SPECIFIC YIELD (Sy:
The specific yield of an unconfined aquifer is the ratio of volume of water which will flow under saturated condition due to gravity effects to the total volume of aquifer (V).Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where, VWY = Volume of water yielded under gravity effect and V = Total volume of water.

SPECIFIC RETENTION:
The specific retention of an unconfined aquifer is the ration of volume of water retained against gravity effect to the total volume of aquifer (V)

Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where Vwr =  Volume of water retained under gravity effect

Remember:- 
S+SR=n where, n = porostiy

COEFFICIENT OF TRANSMISSIBILITY:
T=kH
where,
H = Thickness
K = Coefficient of permeability

UNCONFINED AQUIFER:

 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

(a) Theims Theory

 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

Where,
q = Rate of flow in m3/s
h1 = Height of water table of 1st observation well
h2 = Height of water table of 2nd observation well
s1 = Drawdown of 1st test well
s2 = Drawdown of 2nd test well.
h1 + s1 = h+ s2
S1 = Drawdown of 1st test well
S2 = Drawdown of 2nd test well
r1 and r2 are radius of 1st and 2nd observation wells respectively.

(b) Dupits Theory:
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where, S = Drawdown in the well
K = Permeability coefficient in m/s.
R = Radius of influence in ‘m’
150m ≤ R ≤ 300m
r = Radius of test well in ‘m’.
Results of dupits theory are not accurate because ‘R’ is based on empirical relation.

CONFINED AQUIFER:

Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE) 

(i) Theims theory:
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
(ii) Dupits theory
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

SPHERICAL FLOW THROUGH WELL
qs=k2πrs, R = Radius of well
S = Drawdown
qs = Rate of flow through spherical well in m3/s
 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)

PUMPING-IN-TEST
(a) Open end test
 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where, r = radius of pipe, h = head of water above the base of pipe, it may include gravity head and pressure head.

(b) Tacker test
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where, L = Length of perforated section of pipe

Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
r = Radius of pipe
h = head of which water is added

 OPEN WELL (RCUPERATION TEST):
 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
where,
 Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)
Volume = A. H
A = Area of well
C/A = specific yield or specific Capacity of an open well.
T = Time in ‘sec’
h1 = Position of water table of t = 0
h2 = position of water table of t = T
Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE)


VALUES OF PERMEABILITY:

 SOILK (cm/sec)Degree of
 permeability
1. Coarse Gravel>1High
2. Fine gravel-Fine sand1 to 10-2medium
 
3. Silt-Sand admixtures,loose silts, rock flour and loess10- 2 to 10-4Low
4. Dense slit, clay silt
admixutures,non-homogenous clays
10-4 to 10-6Very low
5. Homogenous clays< 10-6Impervious
The document Well Hydraulics - Notes | Study Civil Engineering SSC JE (Technical) - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Civil Engineering SSC JE (Technical).
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