Question

Furrows of 150 m long and 2 m apart, have longitudinal slope of 0.5 percent are initially irrigated by non-erosive stream for 100 minutes. The stream size is reduced to 50% and continued for another 40 minutes. Determine the average depth of irrigation.

(a) 50.34 mm

(b) 43.56 mm

(c) 47.58 mm

(d) 43.84 mm

I have been asked this question in a job interview.

My question is based upon Techniques of Water Distribution in the Farms topic in portion Water Requirements of Crops of Irrigation Engineering

Answer 1

The correct answer is (d) 43.84 mm

Explanation: Given L = 150 m and W = 2 m and s = 0.5%

Now we have qm = 0.6/s = 0.6/0.5 = 1.2 lps

Now q = 0.4qm = 0.4×1.2 = 0.48 lps

Average depth of water applied

= (2 x 100 x 60 + 0.48 x 40 x 60) / 1000 x (1 / 300) x 1000

= (12+1.152) / 300 x 1000

= 43.84 mm.