We have taken return period of 2,5,10,25,50,100yr. and my question is to how we can select storm duration for design rainfall using Intensity-duration-frequency (IDF) curves.
Dear Bhupesh
If you are designing a storm water system then you need to estimate the “critical storm duration” for each storm water catchment. The "critical storm duration" is the storm duration of a specific return period storm event (e.g., 2, 5, 10, 25, 50, 100 years) which generates the highest flow in the storm water drainage system.
The critical storm duration is related to the catchment characteristics. Generally the larger the catchment area the longer the critical storm duration, although other factors such as the slope and impervious area of the catchment also have an effect.
In some regions of the world drainage authorities have formulae which define a first estimate of the critical storm duration. In some cases "trial and error" methods are used, for example, a rainfall-runoff model will be run with a number of different storm durations and the storm duration that generates the largest flow for the catchment draining to the discharge point into the storm water network will be deemed to be the "critical storm duration".
I hope that this is of help.
Best regards
Darren
Duration of the storm depends on watershed properties. Longer watersheds should consider longer duration storms. Google the Kirpich equation. Return period depends on risk. A sort of run of them, of only loss of a low value structure, like a terrace, 2 y; if high value structure, 5-25 y, if urban area, 100 y, if loss of life, greater than 100 years, depending on what the budget will allow.
Hi Bhuphesh,
I use design storm variations in time depending on slope angle (A) of the catchment area and the percentage of impermeable surfaces (IS) to plan storm water drainage systems.
Storm duration is 15 min (A50%)
Storm duration is 10 min (all other cases)
source: DWA A 118
Return periods depend on potential damage. Regarding EN 752 the minimum design storm return period has to be 1 year in rural areas up to 10 years for underground transportation.
However, these values are recommendations for storm water drainage system valid for Central Europe.
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