>100-yr floods in Tennessee 1

[francesca]

Parts of Nashville, TN had >10" of rain in 24 hours with the storm lasting 36 hours or more. (100-yr/24-hr rainfall depth for Nashville is 7.53 in.) There is widespread flooding and a state of emergency has been declared.

Not all of the flooding is unexpected. One of the worst-affected areas, the intersection of I-24 and Bell Road where Mill Creek and Sorghum Branch have their confluence, is under the 100-yr flood on the FIRM. Yesterday it looked like this:

http://www.youtube.com/watch?v=wkQ1gWB0avk

The debris you see is a building from the Lighthouse Christian School.

The facebook group has some spectacular photos, and there are plenty of videos on YouTube. Sadly the DOT cameras at the most interesting places are offline. Not sure if that's a PR move or if the cameras are malfunctioning. (They're solar powered and elevated.)

http://www.facebook.com/#!/pages/I-...e-Monsoon-of-May-1st/103465826364244?v=photos

 

[SMIAH]

Looking at photos and videos I just can't imagine:

The 24-hr recorded maximum of 74 inches (Cialos, La Réunion I)
or the 48-hr recorded maximum of 66 inches (Taiwan)

And nearly half of Americans (48%) now believe the threat of global warming has been exaggerated...

 

[SMIAH]

For general information:

Duration,Précipitation (inches),Location

1 min 1.23 Unionville, MD
15 min 7.8 Jamaica
42 min 12 Holt, Missouri
130 min 19 Rockport, WV
15 hr 34.5 Smethport, PA
24 hr 74 Cilaos, La Réunion I
48 hr 65.79 Taiwan
5 days 152 Cilaos, La Réunion I
1 month 366 Cherrapunji, India
1 year 1042 India
2 years 1605 India

Taken from Hydrologic Analysis and Design, McCuen, 2004

 

[cvg]

I'm not sure the threat of globabl warming is exaggerated, only that reducing our carbon footprint could have any measurable effect on reducing it. But that is a topic for another thread - try this one thread730-270583

By the way, accurate precipitation records in the US have only been maintained perhaps for the last 100-years. Couple that with long term drought and wet cycle trends and it is easy to see that our estimates of 100-year rainfall depths are woefully inaccurate.

 

[francesca]

Update from the USACE Nashville commander regarding flood control initiatives.

https://eportal.usace.army.mil/sites/LRN_Blog/default.aspx

The worst-affected cities are Nashville and Clarksville. Nashville's downtown is flooded, and is seeing the highest water levels since the construction of flood control dams in the 1930s.

Clarksville is at a record high. This is because the majority of the rainfall was downstream of Nashville's flood control structures (Old Hickory Dam, J Percy Priest and dams upstream) and the primary flood control structure for Clarksville is the Cheatham Lock & Dam in Ashland City, which is in free-flow.

Flood hydrographs visible here:

http://water.weather.gov/ahps/index.php?stage=6

 

[cvg]

Interesting that the Cumberland has exceeded the 51 foot flood stage three times in the 20th century and at least 8 times in the 19th century. Thats 11 times for an average of once every 18 years. It seems that the term "100-year flood" might be an exaggeration in this case. I know, "100-year flood" doesn't mean it happens just once in 100 years, but still something seems a bit fishy here...

http://water.weather.gov/ahps2/crests.php?wfo=ohx&gage=nast1

 

[francesca]

True... Except that in the 1930s flood control structures were built so the levels you're seeing now are with flood control in place versus previous floods were without. Also, these were 100-year, 24-hour storms, but the Cumberland River time of concentration is on the order of days, so prolonged storms with lower daily rainfall depths would have the same result.