Question

Consider the following statements:
1. A 100 year flood discharge is greater thana 50 year flood discharge.
2. 90% dependable flow is greater than 50% dependable flow.
3. Evaporation from salt-water surface is less than that from fresh-water surface.
Which of the statements are correct?

• A. 1 and 2
• B. 2 and 3
• C. 1 and 3
• D. 1, 2 and 3

Answer 1

The correct option is C 1 and 3

For a return period T, the magnitude of flood is given by equation of hydrologic frequency analysis as
$x_T=\overline{x}+k\sigma$
The value of k increases with higher return period. So flood magnitude for 100 year return period is more than that of 50 year return period.
% dependable flow means number of times the given discharge is equalled or exceeded.
$\%\text{Dependability}=\frac{100}{\text{Return period}}$
90% dependable flow has lesser return period while, 50% dependable flow has higher return period. So, 90% dependable flow is less than 50% dependable flow.
When a solute is dissolved in water, the vapour pressure is less than that of pure water and hence causes a reduction in the rate of evaporation.