What exactly is a 2- year storm event? 5

[dhot]

I am trying to justify running my spare pump and need to know what is a 2- Year 24 Hour storm event. I know its a propability of it accuring is 50% every year. What is it in terms of inches per hour or an equivalent? Does anyone know a website that catagorizes the storms into these events?

 

[francesca]

It varies from region to region. Your state's DOT most likely has a drainage manual that details the 2-year storm (and others) for your nearest city. Your city/county government likely also has a drainage manual that details it.

 

[tsgrue]

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Precipitation Frequency Data Server

NOAA National Weather Service
Office of Hydrologic Development
Hydrologic Data Systems Branch
Hydrometeorological Design Studies Center

http://hdsc.nws.noaa.gov/hdsc/pfds/orb/nc_pfds.html

.


tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com

 

[elev8848]

Lets say it has been established (by somebody who performed statistical calculations of years of rainfall record) that for Neverland, 2yr 24 hour storm is 2.75 inches.

It means:
if you leave a cylindrical cup outside, there is an annual exceedence probability of 0.50 that the cup will fill at least up to 2.75 inches depth in a maximum 24 hour duration.

It also means that the average rainfall rate is 0.1146 inches per hour for that 24 hour duration. Because 2.74inches/24 hours = 0.1146 inches per hour.

It does not, however, mean that the peak rainfall rate for this rain storm period is 0.1146 inches. Peak intensity will be higher because the rainfall intensity varies within that 24 hours.

How it varies is summarized by the four SCS curves depending upon the location.

Compare with:
If you drive a car from LA to San Francisco in 24 hours, the distance covered is 800 miles. Same as total rainfall depth of 2.75 inches.

The average speed is 33.33 miles/hour. Same as 0.1146 inches/hour.

Highest speed is unknown without knowing how you drove.

 

[msquared48]

It's about 690 days more than what Noah experienced.

Mike McCann
McCann Engineering