Hydrograph Query.

[ldavison10]

Hi,

In the UK, rainfall is calculated over a 2 minute storm duration period. The location of the project, plus the building use determines the specific rainfall rate. (say 200mm/hr intensity)

Say I have a downpipe discharging approx 70 litres per second. If I was to size an underground pipe to store water at 70 lps x 120 secs this would equate to a necessary capacity 8400 in the underground pipe.

However, what if the rainfall leading upto this 200mm/hr peak was 199mm/hr for 10 mins, this means the pipe could nearly be full even before the rain hits full intensity.

How is this considered / overcome?

If you need anything further, please let me know.

Thanks

Lee

 

[francesca]

Short duration storms are typically used to calculate peak flow rates. Long duration storms are typically used to calculate peak volumes. What you describe is typically used to calculate the size of pipes that convey flow, not store it. Look for a different methodology to calculate the storage volume. In the US it's typically a 24-hour storm.