Question

The total irrigation depth of water required by a certain crop in its entire growing period (150 days) is 25.92 cm. The culturable command area for a distributary channel is 100,000 hectare. The distributary channel shall be designed for a discharge.

• A. less than 2 cumecs
• B. 2 cumecs
• C. 20 cumecs
• D. more than 20 cumecs

Answer 1

The correct option is D more than 20 cumecs

Depth of water required by crop,
h = 25.92 cm
= 0.2592 m

Growing period,
B = 150 days
= 150 × 86400 seconds

Area, A = 100000 hectare
$={10}^9{m}^2$

Water supplied by distributing = Water required by crop

Design discharge × B = A × h

$Q\times 150\times 86400={10}^9\times 0.2592$
$\therefore Q=20m^3/s.$

Demand of water is not uniform for the whole base period and the canal may also remain closed for some time for maintenance purposes, so the canal should be designed for discharge more than $20m^3$/s.