Tuesday, March 10, 2015

What is Flood Stage?

I was  watching some very young lady on The Weather Channel this morning in Louisville going absolutely goofy about the Ohio River rising over “Flood Stage”, and  I began to wonder…”does she knows what that means?”   Years ago, the NWS arbitrarily assigned flood stage numbers that described flooding that would occur WITHOUT LEVEES.   We all know, all major rivers are contained by levees including the Ohio.   As TWC Lady asked the local Louisville manager of flood control about getting over flood stage, he CALMLY said…”happens every year with the Spring snow melt.  We’re protected by the levees for another 10-12 feet!”   Yet she still persisted saying about this 1-2 feet of snow melt that was causing the rise.   The usual ration of snow to water content is 10 to one meaning 10” of snowfall would be like having one inch of rainfall.  Melting all of the 2 feet of snow is like having a rain storm dropping 2-3 inches of rain.   Clearly this is not enough to cause any major flood problems.   As I have mentioned before, it’s the heavy Spring rainfall ON TOP OF the snow melt that can cause high water problems. 


Last week the River at Cairo, IL was 12 feet below flood stage (flood stage being no big deal).  Today the river had risen 12 feet in one week!  That’s quite a rise but  nowhere near the 50’+ that caused major flood several years ago.   That crest will take about 2-3 weeks to reach us and will probably get the Carrollton gage up to 12 feet (roughly 7’ today).  Any concern here?   Only IF more heavy rains fall over the Ohio River between now and May.   We’re protected to 17’ and if that value is predicted by the River Forecast center in Slidell, the Corps of Engineers will open the Bonne Carre Spillway to divert some of the flow into Lake P.   Will we have high river water here?  Yep, happens every Spring.


Our current wet pattern shows little signs of breaking before Friday.  Hopefully the rainfall will be spread out over many hours so not to create any street flooding like what happened this afternoon in Kenner when nearly 2” fell in 90 minutes.   Time to pay attention next 2-3 days.  Stay tuned!

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