Design Storms
Design Storms
(OP)
The following is a policy stated in a County regulation--
Detention facility storage volume shall be adequate to attenuate the post-development peak discharge rates to pre development discharge rates for the 2,10 and 100 year storms.
Detention facility outlet structure release rates shall be less than the pre-development peak runoff rates for the 2,10 and 100 year storm events.
The total combined post-development peak flow rate from a development cannot exceed the total pre-development peak flow rate for the 2,10 and 100-year storms.
Question:
Why are the 2 and 10 year storms considered if the 100-year storm generates more peak flow (More precipitation)?
Detention facility storage volume shall be adequate to attenuate the post-development peak discharge rates to pre development discharge rates for the 2,10 and 100 year storms.
Detention facility outlet structure release rates shall be less than the pre-development peak runoff rates for the 2,10 and 100 year storm events.
The total combined post-development peak flow rate from a development cannot exceed the total pre-development peak flow rate for the 2,10 and 100-year storms.
Question:
Why are the 2 and 10 year storms considered if the 100-year storm generates more peak flow (More precipitation)?





RE: Design Storms
This is the reason for the multi-stage outlet controls used on many ponds. The usual procedure is to start with the smallest event, designing the appropriate storage and outlet controls, and then work up through larger events, adding storage and outlet capability as required to handle the peak flow.
RE: Design Storms
24 hr precip with a Type II distribution?
6 hr precip with a Type II distribution?
24 hr precip with a 6 hour specified distribution?
6 hr precip with a 6 hr specified distribtuion?
24 hr precip with a 2 hour specified distribution?
6 hr precip with a 2 hr specified distribtuion?
All of the above, selecting the storm with the greatest
peak?
RE: Design Storms
Hopefully the regulating body has guidlines on the parameters to be used of the design storms.
Here, in Delaware, we use the NRCS Type II 24 hour storm with the Delmarva Unit Hydrograph. The 2 & 10 year events are regulated to pre-development rates and the 100 year rate is regulated in a certain geographic area (not in the coastal plain).
RE: Design Storms
Thank you in advance.
RE: Design Storms
Please start a new thread rather than posting under an unrelated topic.