3
$\begingroup$

The 100-year flood line runs through my property (Midwest - United States). I am always curious when I see flooding how close to a 100-year flood it might be. Is there any way to know? Does any official service/site post data that rates how significant a flood was? The National Weather Service issues flood warnings. After a significant rainfall, is there a way to know how the flood was rated?

$\endgroup$
3
  • $\begingroup$ flooding is hydrology not meteorology. $\endgroup$ Commented Apr 16 at 4:47
  • $\begingroup$ I assume because you mention the National Weather Service that you're interested in the US specifically, or are you interested in other countries? $\endgroup$
    – Deditos
    Commented Apr 16 at 8:15
  • 1
    $\begingroup$ I am interested in the US only. $\endgroup$
    – JWess
    Commented Apr 18 at 6:43

1 Answer 1

3
$\begingroup$

I'm not sure whether anyone officially evaluates it (consistently), but here are a few ideas for checking it yourself (for the US, since you mentioned the NWS):

  • On the precipitation end, you could compare the reported precipitation and duration to the Precipitation Frequency Data Server (PFDS). For example, during Colorado's 2013 floods, a site in Boulder, CO recorded about 15" of rainfall. That figure was for 7 days, but the description says most of it fell in 30 hours, so we'll say two days. The PFDS, selecting that point (estimated: 40.0156° N, -105.2800° E), says that 15" is more than the 1000-year return interval precipitation for a 2-day (or, for that matter, a 7-day) storm. A 1000-year, 2-day storm would be 9.4". Therefore, we can say that, in that area, the actual rainfall exceeded a 1000-year storm.
  • For streamflow, USGS StreamStats can estimate peak flow statistics for a site if you go through the steps for the delineation and report tool, selecting "peak flow statistics", and if you select a gage on the map you can view the "StreamStats Gage Page" with observed flow data (under the "Gage Analysis Plots" tab). For example, USGS gage 06730200 (on Boulder Creek) had a peak discharge of 8400 cfs during the September 2013 flood. For estimated floods, StreamStats only goes up to 0.2% (500-year), but that figure is 7420 cfs (generating a report for peak flow statistics). Thus, the flood was more than a 500-year flood. Those are estimated values only, but it provides some reference point.
$\endgroup$
1
  • 1
    $\begingroup$ I think streamflow data is probably the only way you can make a direct estimate. Here's another streamflow gauge data link: water.weather.gov/ahps/index.php $\endgroup$
    – f.thorpe
    Commented Apr 18 at 16:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.