EXAMPLE $2\mathrm{.}6$

For the precipitation data arranged for different durations in Table $2\mathrm{.}6,$ prepare intensity$-$

duration$-$frequency curves for $20-$year and $10-$year frequencies.

Solution

For each duration, the precipitation depths are arranged in descending order. The high$-$

est value has been assigned a rank of $1$ and the lowest a rank of $22.$ The return periods

are obtained in column $8$ of Table $2\mathrm{.}6.$

The depths of different duration corresponding to $20-$year frequency are interpolated

from the values for $23-$ and $11\mathrm{.}5-$year frequencies and converted to intensities in Table $2\mathrm{.}7.$

Similar calculations are done for $10-$year frequency. These are plotted in Figure $2\mathrm{.}6.$

Table $2\mathrm{.}6$ Frequency Analysis of Different Duration of Precipitation Depths

$(2)$

$(3)$

$(4)$

$(5)$

$(6)$

$(7)$

$(8)$