Question

A water course commands an irrigated area of 1000 hectares. The intensity of irrigation of rice in this area is 45%. The transplantation of rice takes 15 days and the total depth of water required by the crop is 45 cm on the field during the transplantation period. During the transplantation period, the useful rainfall on the field is 10 cm. The discharge required at the head of the water course, if losses of water is to be 20% in the water course, is _________ cumec.

• A. 1.52

Answer 1

The correct option is A 1.52
As we know the relation,
$\Delta =8.64\times \frac{B}{D}$

Here,
$B=15\text{days}$
$\Delta =45-10=35cm=0.35m$
$D=\text{Duty of irrigation water in hectares/cumec}$

$D=8.64\frac{B}{\Delta }=8.64\times \frac{15}{0.35}=370.29\text{hectare/cumec}$

Since , the losses in the water course are 20%
Hence, the duty of water at the head of the water course,
$=370.29\times 0.8=296.232\text{hectares/cumec}$

Now, total area under rice plantation,
$=1000\times 0.45=450\text{hectares}$

So, discharge at the head of water course,
$=\frac{450}{296.232}=1.52cumec$