Drainage of Agricultural Lands - Practices of Irrigation and On-farm Water Management - page 346

9.3.5 Functional Form of Water-Table Position During Flow
into Drain

Position of water table during flow into drain (steady or unsteady) can be described
by the following functional form:

( I , K , d , S , D , ..)

WT = (9.14)

where

=

WT water-table depth (or position)

=

function

I = recharge from rainfall or irrigation

K hydraulic conductivity of soil (vertical and horizontal direction, both

upper and lower layer of drain)

=

d = depth of drain from the soil surface

S = drain spacing

D = depth to impervious layer from the drain

9.3.6 Theory of Groundwater Flow Toward Drain

9.3.6.1 Steady State Problems

The steady-state drainage situation is one where a constant uniform accretion rate,
I , is recharging the water table and the drain tubes are simultaneously draining
the soil profile. After some time, a state of equilibrium will be established in
which the water table does not change shape, and the drain discharge is constant
(Fig. 9.11 ) .

q (mm /hr)

Fig. 9.11 Schematic of
Dupuit-Forcheimer
assumptions