500 year flood data
500 year flood data
(OP)
I have a detention pond which I have sized for the 100 year flood + freeboard + water quality according to the city standards. The city has commented that they want to know how large the pond would have to be to hold the 500 year flood. I have no data on a 500 year flood, and haven't been able to find any. Does anyone know where I can find anything regarding a 500 year storm, or any storm greater than 100 year?





RE: 500 year flood data
(I'm guessing it's you.)
I have never seen information published with that info. The few times I have seen it referenced in reports it was extrapolated.
I do have a couple of ideas though. You may try your state department of natural resources. Also, FEMA has a flood insurance program and produces maps that show 500-year floodplains. Here that info is based purely off stream flow, but your area might have rainfall data. There should be a local entity with that data, here it is the County Engineer's Office.
Rik D.
RE: 500 year flood data
My project is in Denver, and there is no data from the City and County or Urban Drainage for anything greater than the 100 year storm (that I can find). And I've checked the firm maps and it's not in the 500 year floodplain. I don't know why the City is insisting on wanting 500 year flood conditions.
RE: 500 year flood data
http://www.wrcc.sage.dri.edu/pcpnfreq.html
However there is not a listing for the 500-year.
How the 500-year is typically found is by plotting
the other frequency flows onto probability paper and
drawing a line to the 0.002 probability line.
Also if the stream is a studied stream, then the 500-year
flow should be listed in the city's FEMA FIS Volume 1.
RE: 500 year flood data
I would report the pond size for the 500 year storm without any pond freeboard and with limited parking lot/local road flooding. Basically, I would toss all safety factors to the winds and concentrate on not flooding any habitable structures and not excessively flooding any arterial roadways.
Clifford H Laubstein
FL Certified PE #58662
RE: 500 year flood data
I'm good, I'll e-mail you with more.
I would go with gibfrog's method. Excel will also do the math, in addition to producing a nice graph for the report.
Personally, I think designing for the 500-year event is overkill in most cases.
RE: 500 year flood data
RE: 500 year flood data
rmw
RE: 500 year flood data
Good luck
RE: 500 year flood data
RE: 500 year flood data
RE: 500 year flood data
The simple extrapolation method suggested by others should be the easiest, and reasonably accurate, way to arrive at this.
Good luck
RE: 500 year flood data
RE: 500 year flood data
TTFN
RE: 500 year flood data