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Slide 1
Hooghoudt's Equation Application for Drainage
Dr. M. Anwar Baig
2nd April 2013
The objectives of agricultural drainage systems are to:
reclaim and conserve land for agriculture,
to increase crop yields,
to permit the cultivation of more valuable crops,
to allow the cultivation of more than one crop a year,
and/or to reduce the costs of crop production in otherwise waterlogged land.
Other benefits:
- A reduction in the average amount of water stored on or in the soil, inducing drier soil conditions and reducing water logging;
A discharge of water through the system.
The direct effects trigger a series of indirect effects. These are determined by climate, soil, crop, agricultural practices, and the social, economic, and environmental conditions.
Hooghoudt's equation can be written as:.[3]
Q L2 = 8 Kb d (Di - Dd) (Dd - Dw) + 4 Ka (Dd - Dw)2 where:
Q = steady state drainage discharge rate (m/day)
Ka = hydraulic conductivity of the soil above drain level (m/day)
Kb = hydraulic conductivity of the soil below drain level (m/day)
Di = depth of the impermeable layer below drain level (m)
Dd = depth of the drains (m)
Dw = steady state depth of the watertable midway between the drains (m)
L = spacing between the drains (m)
d = equivalent depth, a function of L, (Di-Dd), and r
r = drain radius (m)
The equivalent depth De depends on the depth D of the impermeable layer below the drains as follows:
If D