Agriculture Reference
In-Depth Information
ET
I
f
×
=
−
LF
1
(8.14)
t
i
The above relationship is applicable when no drainage limitation exists.
Case 2: Internal drainage is limiting
Assume that internal drainage is limiting for the prevailing field condition.
Now, if the average drainage rate is
R
d
(cm/d) for the irrigation cycle
t
c
(days), LF can be expressed as
D
d
D
i
=
R
d
t
c
LF
=
(8.15)
ET
+
R
d
t
c
where ET is the evapotranspiration for the irrigation cycle (cm)
(B) Drainage
Where the subsoils are permeable, natural drainage may be sufficient. Otherwise,
drainage system may be needed. Various types of drainage are used throughout
the world, such as surface drainage, subsurface drainage, mole drainage, vertical
drainage.
Surface drainage
: Ditches are provided on the surface so that excess water will
run off before it enters the soil.
Subsurface drainage
: For the control of groundwater table to a certain depth
(safe position for the crop), deep open ditches or tile drains or perforated
plastic pipes are installed below ground level.
Mole drainage
: Shallow channels left to a bullet-shaped device are pulled
throughout the soil. This acts as a supplementary drainage system connected
to the main drainage system.
Vertical drainage
: pumping out excess water from tubewells when the deep
horizons have an adequate hydraulic conductivity.
The depth and spacing of the drainage system should be based on soil type
(subsoil strata) and local economic considerations.
Artificial Recharge of Rainwater to Aquifer Through Recharge Well
Through recharge tubewells, excess rainwater can be conveyed to aquifer. Large
amount of water can be recharged through recharge well. As a result, the salinity
of the aquifer water will be lower due to dilution and become within acceptable
range. In flat topography, where aquifer with good transmissibility exists at shallow
depth (in the first aquifer of 20-60 m depth), recharge structures with tubewells
Search WWH ::
Custom Search