Correct Answer - Option 2 : S
y + S
r = porosity
Explanation:
1) Porosity (n):
Porosity is the measure of storage property of an aquifer
\({\rm{n}} = \frac{{{{\rm{V}}_{\rm{v}}}}}{{\rm{V}}}\)
n > 25 % → Sufficient amount of groundwater present
5 % < n > 25 % → Moderate amount of groundwater
n < 5 % → Less amount of groundwater
2) Specific yield (Sy):
It is the ratio of the volume of water that is extracted from a saturated rock (due to gravity) to the total volume of the rock.
\({{\rm{S}}_{\rm{y}}} = \frac{{{\rm{Volume\;of\;water\;extracted}}}}{{{\rm{Volume\;of\;aquifer}}}}\)
3) Specific Retention (Sr):
Specific retention of a rock or soil is the ratio of the volume of water a rock can retain against gravity to the total volume of the rock.
Therefore, the total porosity(n) is equal to the volume of water that a rock will yield by gravity drainage (Sy) and the volume held by surface tension (Sr) and is given as:
\({S_y} + {S_r} = n\)
