The Journal of Research ANGRAU

SREEDEVI et. al.
the pilot area is paddy followed by paddy with a fallow period of two months. The pilot area
receives irrigation water from Kalipatnam main channel of Godavari Western Delta with an
average EC of 0.4 dS m -1 . Flooding method of irrigation is adopted and water is allowed to
flow from field to field. The water from the fields is drained to Upputeru through a separate
drain called Magaleru drain. The ground water quality is poor with EC 4.8 to 43 dS m -1. .The
water table of pilot area is at the surface during crop period and decline up to 0.9 m during
summer. Hence waterlogging conditions exist in the pilot area.
For the design of subsurface drainage system, it is essential to estimate drain
discharge i.e the amount of leaching water required to reduce the soil salinity to a desired
level. Hence drain discharge is calculated based on salt water balance equation.
The leaching requirement of the soils of pilot area was calculated using the formula
(Ritzema, 1994)
Eci
L.R = (E-P)
f(2Ece-Eci)
Where,
L.R. = Leaching requirement, mm
E
P
f
= Evapotranspiration, mm
= Effective Precipitation, mm
= Leaching efficiency coefficient
Eci = mean salinity of irrigation water, dS m -1
Ece = desired salinity of soil saturation water, dS m -1
Assuming the flow of groundwater to the drains under steady state, Hooghout’s equation
was used to design the lateral drain spacing (Ritzema, 1994).
R = q =
8kd e
h + 4kh 2
L 2
Where,
R = Recharge rate per unit surface area , m day -1
q= Drain discharge rate per unit surface area , m day -1
k= Hydraulic conductivity , m day -1
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