5. Porosity
The ratio of volume of voids to the
volume of formation multiplied by 100.
Proportion of void space: pore space,
cracks, vesicles
• Gravel : 25-45% (1K - 10K), clay: 45-55%(<.01)
• Sandstone: 5-30% (0.3 - 3), granite: <1 to
5%(.003 to .00003)
Higher porosity in well rounded,
equigranular, coarse grained rocks.
7. Specific Yield
The specific yield is the actual amount of water that will drain out of saturated
soil and rock by gravity flow.
It is also called EFFECTIVE POROSITY. 𝑆 𝑦 =
𝑉𝑦
𝑉 𝑓
× 100
8. Permeability
Measure of how readily fluid
passes through a material.
Depends on the size of the pores
and how well they are
interconnected.
Clay has high porosity but low
permeability.
9. Hydraulic Conductivity
In Darcy law,
or
K is the hydraulic conductivity or permeability constant.
It depends on
• soil matrix ( porosity, pore size distribution, tortuosity of soil pores )
• Water properties ( viscosity, density )
𝑄 𝛼 𝐼𝐴 𝑄 = 𝐾𝐼𝐴
10.
11. Ground Water In
Hydrological Cycle
Ground water constitutes one portion of hydrological cycle.
Formations of ground water
Recharge of ground water
• Natural ( like precipitation, lake, stream flow)
• Artificial ( like irrigation, seepage from canal)
Discharge of ground water
• Natural ( like oceans, lakes, streams)
• Artificial ( like pumpage from wells)