HYDROGEOLOGY

HYDROGEOLOGY

هیدروژئولوژی - مدل سازی و مدیریت آب زیرزمینی
HYDROGEOLOGY

HYDROGEOLOGY

هیدروژئولوژی - مدل سازی و مدیریت آب زیرزمینی

SAVE WATER

Of all the water in the world, only 3% is fresh. Less than one third of 1% of this fresh water is available for human use. The rest is frozen in glaciers or polar ice caps, or is deep within the earth, beyond our reach.To put it another way, if 100 litres represents the world's water, about half a tablespoon of it is fresh water available for our use.

Specific yield

Specific yield, also known as the drainable porosity, is a ratio, less than or equal to the effective porosity, indicating the volumetric fraction of the bulk aquifer volume that a given aquifer will yield when all the water is allowed to drain out of it under the forces of gravity:
S_y = \frac{V_{wd}}{V_T}

where

Vwd is the volume of water drained, and
VT is the total rock or material volume


Specific Yield (%)

Material

Maximum

Minimum

Average

coarse gravel

26

12

22

medium gravel

26

13

23

fine gravel

35

21

25

gravelly sand

35

20

25

coarse sand

35

20

27

medium sand

32

15

26

fine sand

28

10

21

silt

19

3

18

sandy clay

12

3

7

clay

5

0

2

(Johnson (1967) as quoted by C.W. Fetter)