never be greater than unity

be zero

take any value greater than zero

take values between 0 and 1 only

1.0 and 0.0

0.0 and 1.0

0.5 and 1.0

1.0 and 0.5

one phase system

two phase system with soil and air

two phase system with soil and water

three phase system

lD>0

ID>0

0 < lD < 1

0 < ID < 1

40%

60%

80%

100%