UNIT HYDROGRAPH QUESTION.

A storm drain is being designed for an urban catchment of $A=5km2.$ The design requirement is the $5\%$ AEP flood.

Continuous records are unavailable at this location. However, data from a single event was analysed to develop a unit hydrograph for this catchment. The ordinates of this UH are shown in the table below and graph.

The design requires the $36$minI$20$ design rainfall which is $80$ mm$/$hr$.$ The areal reduction factor for this location, catchment size, duration and AEP is $0\mathrm{.}95.$

The temporal pattern to be simulated is $10\%$ of rainfall in the first $9-$minute period, $30\%$ of rainfall in the second $9-$minute period, $40\%$ of rainfall in the third $9-$minute period, and $20\%$ of rainfall in the fourth $9-$minute period.

Rainfall loss for this location can be neglected $($ie$,$ assume incident rainfall $=$ effective rainfall$).$

Using the information, obtain the direct runoff hydrograph at this location for the abovementioned rainfall pattern.