Question

A field was supplied with water from an irrigation tank at a rate of 120 lit/sec to irrigate an area of 2.5 hectares. The duration of irrigation is 8 hours. It was found that the actual delivery at the field, which is about 4 km from the tank, was 100 lit/sec. The runoff loss in the field was estimated as 800 $m^3$. The application efficiency in this situation is

• A. 62%
• B. 72%
• C. 76%
• D. 80%

Answer 1

The correct option is B 72%

Water application efficiency is the ratio of the quantity of water stored into the root zone of the crops to the quantity of water actually delivered into the field.

Actual discharge in field,
$Q=100lit/sec$

Duration of irrigation,
$T=8hours$

Runoff loss,
$L=800m^3$

$\therefore \text{Water stored in root zone depth,}$

$V=\frac{100\times 8\times {60}^2}{{10}^3}-800=2080m^3$

$\therefore \text{Water application efficiency,}$

${\eta }_a=\frac{V}{Q\times T}=\frac{2080}{\frac{100\times 8\times {60}^2}{{10}^3}}$

= 0.72 = 72 %