Ground water specific Yield:
Specific Yield = (Volume of water obtained by gravity drainage/ Total volume of sub-soil) *100
Specific Retention =(Volume of water held against gravity drainage/ Total volume)*100
Porosity= Specific Yield + Specific Retention
Formula for ground water velocity:
(1) Slichter's formula:
V= (k.SD^2)/U
V = velocity of ground water in m/day
k = constant (approx. 400)
S = Slope of hydraulic gradient line
D = Effective size of the particle in aquifer (in mm)
U = Dynamic Viscosity
(2) Hazen's Formula:
V = [K.SD^2(1.8T+42)]/60
K = constant approx. 1000,
T = Temperature in degrees Celcius.
Specific Yield = (Volume of water obtained by gravity drainage/ Total volume of sub-soil) *100
Specific Retention =(Volume of water held against gravity drainage/ Total volume)*100
Porosity= Specific Yield + Specific Retention
Formula for ground water velocity:
(1) Slichter's formula:
V= (k.SD^2)/U
V = velocity of ground water in m/day
k = constant (approx. 400)
S = Slope of hydraulic gradient line
D = Effective size of the particle in aquifer (in mm)
U = Dynamic Viscosity
(2) Hazen's Formula:
V = [K.SD^2(1.8T+42)]/60
K = constant approx. 1000,
T = Temperature in degrees Celcius.
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