The relationship among specific yield (S_y), specific retention (S_r) and porosity (n) of an aquifer is

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This question was previously asked in

BPSC AE Paper 6 (Civil) 11 Nov 2022 Official Paper

Answer 1

Following are the properties of aquifer

1) Porosity (n):

Porosity is measure of storage property of 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.

The relation between porosity (n), specific yield (Sy) and surface retention (Sr)

n = Sy + Sr