Question

Determine the discharge required at the head of the distributary in a canal where Kharif area to be irrigated is 2400 hectares and Rabi area to be irrigated is 1800 hectares, for fulfilling maximum crop requirement. Assume suitable values for kor depth and kor period.

(a) 2.08 cumec

(b) 2 cumec

(c) 2.1 cumec

(d) 2.2 cumec

This question was posed to me in class test.

My doubt is from Design Capacity for an Irrigation Canal in division Sediment Transport and Irrigation Channels Design of Irrigation Engineering

Answer 1

Correct choice is (a) 2.08 cumec

Easy explanation: Now let us assume kor period of 4 weeks for Rabi and 3 weeks for Kharif crop. Also, assume kor depth of 12.5 cm for Rabi and 21 cm for Kharif crop.

Outlet factor for rabi = (864B/∆) = 864 x 4 x 7 / 12.5 = 1935.36 hectares/cumec

Outlet factor for kharif = (864B/∆) = 864 x 3 x 7 / 21 = 864 hectares/cumec

Area to be irrigated for Rabi season = 2400 hectares

Area to be irrigated for Kharif season = 1800 hectares

Water required for Kharif season at the distributary = 1800 / 864 = 2.08 cumec

Water required for Rabi season at the distributary = 2400 / 1935.36 = 1.24 cumec

Therefore, the canal capacity at the head of the distributary is the maximum of the two, 2.08 cumec.