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