Effect of storm duration on Peak Flows

[salhu]

Hi there!

I wanted to know the difference in the effect of storm duration on the Peak flows. I am reading a report that has used 12 hour storm duration to do the culvert design. Catchment areas vary from less than one hectare to more than 1000 hectares. I think 12 hour storm would result in lower peak flows values than those resulting from 3 hour or 6 hour storms, and hence 12 hour storm does not represent the worst case scenario?

Thanks!

KH

 

[RWF7437]

In the US you can study the effect of rainfall- duration-frequency for any given geographic area. In general, peak flows will tend to be higher for short duration storms. However, the "worst case" depends on what you are trying to do. If you're trying to size a storm drain then the highest flow matters. But if you're trying to sizea detention basin the storm producing the greatest runoff volume is the "worst case". But the most important questions remain unanswered. What will this cost ? Can we afford it ? How much flooding can be tolerated ? Is there room to build this facility ?

Good luck

 

[salhu]

Thank you RWF for your reply. As it would appear that the drainage structures that i am dealing with are not volume sensitive. Therefore worst case scenario here would be the highest value of Peak flow. Design storm frequency i have is 50 years. So for this frequency, I wanted to know the impact that it would make if someone selected say 6 hour storm duration and 12 hour storm duration.

 

[cvg]

as previously stated, you need to review the IDF relation for your region. you may have to calc the runoffs for both storms and compare. For larger, more complex watersheds and larger storms, we typically do this. For example, on a current project, we are looking at 6-hour and 72-hour pmf runoff, 6-hour and 24-hour 100-year runoff and a 10-day storm runoff for the same area.