Question

For a station Q, the recorded annual maximum 24-hour rainfall magnitudes are given in the table:
$\begin{array}{cccccccc}\text{Year}& 1999& 2000& 2001& 2002& 2003& 2004& 2005\\ \text{Rainfall (cm)}& 13& 12.7& 15& 14.1& 11& 13.8& 11.3\end{array}$

Using Hazen's formula, the rainfall with a return period of 2 years is ______ cm.

• A. 13

Answer 1

The correct option is A 13
iven: T = 2 years
$\therefore P=\frac{1}{T}=\frac{1}{2}$

$P=\frac{M-0.5}{N}=\frac{1}{2}$

$\text{Here,}N=7$

$\therefore M=\frac{7}{2}+0.5=4\text{(order number)}$

Arranging the given data in descending order
$\begin{array}{cccccccc}\text{Rainfall(cm)}& 15& 14.1& 13.8& 13& 12.7& 11.3& 11\\ \text{Order number (m)}& 1& 2& 3& 4& 5& 6& 7\end{array}$

$\therefore ForM=4,$

$\text{Rainfall}=13cm$