Porosity, Specific Retention And Specific yield

(i) porosity

• It is a measure of the void spaces in a material.
• Porosity is defined as the ratio of the volume of pores to the volume of bulk rock and is usually expressed as a percentage.
• Porosity (%) = (Volume of Voids / Total Volume) x 100
• n (%) = (V_v/V) x 100

(ii) specific retention

• It is the ratio of the volume of water a rock can retain (against gravity) to the total volume of the rock.
• S_r = (volume of water retained / volume of aquifer)

(iii) specific yield

• 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.
• S_y = (volume of water extracted / volume of aquifer)

The relation between porosity, specific retention and specific yield is

• n = S_r + S_y