Drainage of Agricultural Lands - Practices of Irrigation and On-farm Water Management - page 376

secondary drain would have to carry 15 of tertiary, and the main drain to carry
discharge of 4 secondary drain (of similar flow). It is required to maintain the
water table not lower than 1.0 m from the soil surface. The soil is uniform in
texture and other hydraulic properties. The value of K is 6 mm/d. A relatively
impervious layer exists at 1.8 m depth from the surface. Determine:

(a) drain spacing at tertiary level
(b) size of secondary and main drain pipe to carry the generated outflow
Assume standard value of any missing data.

(35) It is proposed to design a subsurface drainage system to leach water through
the root zone in an area where surface irrigation will be practiced with poor
quality water. Parallel perforated GI pipe drains are to be laid to a slope of 3 in
1,000, so that the drains could discharge freely into the main collector ditch.
Hydraulic conductivity of the soil is 10 mm/d. Calculate the drain spacing
required to meet the requirements given below.
Irrigation water EC = 0.15 dS/m

Salt tolerance level 1.8 dS/m

Maximum crop rooting depth

=

=

0.8 m

=

4.0 mm/d
Assume standard value of any missing data.

Mean ET rate

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