Drainage of Agricultural Lands - Practices of Irrigation and On-farm Water Management - page 339

Fig. 9.7 Schematic of water
balance of ( a ) artificial
drained ( upper one )and
( b ) natural drained soil

ET

Precipitation

Surface
runoff, R

WT

Drainage,
D

Deep percolation

(a)

ET

Precipitation

Surface
runoff, R

Deep percolation

(b)

P + IR − R − ET − DP = S (9.3)

If the deep percolation continues, there is an opportunity for the water table to
rise. It is evident from the water balance that the amount of deep percolation depends
on the extent to which the precipitation and/or irrigation input to the soil is reduced
by R , ET , and S .
In case of artificially drained soil profile, similar water balance equation holds
true. However, the drainage flow becomes a major component of the water leaving
the system. The water balance equation can be written as

P + IR = R + ET + DP + S + D (9.4)

As in case of natural drainage, the amount of drainage is dependent on how much
precipitation is lost to R , ET , and the drainage capacity itself. In artificial drained