We had an unusually large amount of rainfall in a very short period of time on Wednesday in Beulah.
I received several Facebook messages, phone calls and emails about flooding throughout the area. One neighborhood's storm retention pond was inundated and residents were in fear that it would
overflow from the top and flood the houses in the neighborhood.
I also received calls and photographs indicating that the red clay and dirt being utilized by several developments throughout the area was washing through silt fences and over roadways and into private ponds.
Beulah road at one point was covered in as much as 2 inches of water at some locations north of Mobile Hwy. according to one resident.
Staff, to their credit, immediately went out to Beulah to check conditions at the Navy Oaks ponds. I drove the area after work at around 5:30PM----and thankfully the water had receded from the roadways I traveled (Helms,Beulah, Mobile Hwy, Klondike, 9-Mile Road).
So how did this happen--what was the cause?
According to a local engineer, Tom Hammond from Hammond Engineering, this event was actually greater than a 100-year flood event for a short duration of time. He sent staff and the commissioners the chart and weather station data, above, showing that in just 2 1/2 hours--we were hit with a 5.29 inches of rain--which exceeds the intensity of a 100-year flood event according to Hammond.
"The rainfall event yesterday in Beulah was 5.29 inches in 2.5 hours which far exceeded a 100 year rainfall event. The weather station is at the Beulah Nursery. It is likely rainfall exceeded the 100 year event in other parts of the county as well. Please see attached. Figured this documentation may help with responses to citizen concerns." stated Hammond in an email to the county.
11 comments:
Thank you for the information. Your blog is informative. No one else does this. Please keep it going.
This is incorrect. This was closer to a 25 yr storm. Learn how to use the curve.
Check out the SWAT https://myescambia.com/docs/default-source/sharepoint-public-works/final-swat-paper-7-28-2015.pdf
Anonymous 9:22--The analysis was provided by an engineer to the county and the commissioners unsolicited. You claim his analysis and conclusions were wrong? I'm not a meteorologist, but it seems that 5.29 inches of rain in 2 and 1/2 hours equals 2.116 inches per hour. Now, a couple of years back we had 25 inches of rain over 24 hours and that equated to 1.04 inches per hour and that did catastrophic damage in and around our entire community. That was considered a 500 year storm by the media. So if we took Wednesday afternoon's event (which thankfully only lasted 2 1/2 hours) and and had that intensity of rain per hour (2.116 inches per hour) and multiplied that by 24 hours--that would have equated to more than 50 inches in 24 hours--double what we had in 2014. So yes, thankfully this only lasted a couple of hours, but that amount of rain in a couple of hours seems to me based upon the facts alone, to be more than simply a "25" year event. But if the engineer who sent this was wrong, by all means anonymous--please illuminate how he was wrong specifically. I'd like to know, because I'm not a meteorologist.
You don extrapolate it out to 24 hours at the same intensity. That's why the are shorter time periods on the curve. Ask any other engineer besides Tom Hammond.
https://youtu.be/yBpW2F_fOXA
Please look at the top left corner of the IDF curve provided as an example
Well I'm no meteorologist or engineer but I think Hammond is a developer perhaps and was trying to explain away the red clay run off, via mis information.
So... if the chart says PER HOUR and they draw the line for what happened TOTAL over the entire event -- then that's a mistake. Draw the line with the 2.16 inches..not the 5.29
It will intersect the 25 year for THAT drainage basin..chart, but has that drainage basin changed?? perhaps added more impervious structures as in houses , roads..etc..
Don't let them buffalo you.
Anonymous 7:16--thanks for linking that video. That clears up the mystery and the engineer was wrong. It appears that it was a 25 year event; he took the total number of inches and made that the "per hour" part of the graph and it should have been the 2.16" per hour--which would have intersected at about the 25 year storm level. Thanks for the fact check and the video.
I’m glad you have the blog. I learn a lot. The type of storm flood event discussion is very illuminating.
Thanks for making this a priority! Best wishes!
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