Environmental Engineering Reference
In-Depth Information
10000
1000
H
Dry
Unavailable
31
Hygroscopic
coefficient
0·001
15
Wilting point
0·002
C
Moist
Available
0·33
Field capacity
0·01
Wet
0·05
0·06
G
0·001
Saturated
Unavailable
transient
Notes
: H, hygroscopic; C, capillary; G, gravitational.
anaerobic conditions. It is therefore often necessary to provide artificial drainage to
remove excess water from the soil. A variety of methods are available, including open
drains or ditches, tile or plastic drainpipes in the subsoil, mole drains or subsoil
ploughing. Investment in artificial drainage has been the largest area of capital
investment in British agriculture during the twentieth century. Figure 18.5 illustrates how
a poorly drained soil may be improved by a combination of tile drainage and mole
drainage, installed at 90° to each other.
In order that water can be stored in soil, it is first necessary for it to enter downwards
from the surface. The rate at which a soil can absorb water, defined as the volume of
water passing into a unit area of soil per unit time, is the
