Everything you wanted to know about flooding


By Frank Lewis - [email protected]



Flood waters threaten the Second Street Bridge in Portsmouth last year


If you want to know how much rain poured down on the area shortly after 4 p.m., Wednesday, you have to know the formula for figuring such things out.

Scioto County Emergency Management Agency Director Kim Carver said Wednesday afternoon’s rain event dropped about a half-inch of rain on the area in about five minutes, but the National Weather Services factors that amount into what would be the total if it fell at the same rate for one hour.

“Sometimes we’ve had rainfall rates at four to five to six inches per hour,” Carver said. “What that little piece of data means is that if it would rain for an hour there would be six inches of rain.”

There is a thing called a “flash flood threshold” that the National Weather Service looks at. It takes into account soil moisture and anticipated rainfall events. They combine those entities into a model based on how much rain has to fall in a certain period of time for the flash flood threshold to be met. Carver said those guidances are not anywhere close to being a threat at this time.

Just because there is a downpour does not mean flooding will follow.

“We have no flood watches up. We aren’t anticipating the threshold to reach where we would be approaching flash flooding at this point,” Carver said. “I know they got a significant amount of rainfall just south of the (Ohio) river in the two rounds of storms that came through Wednesday, and I know they had several water rescues in Kentucky and Tennessee Wednesday afternoon and night.”

According to Carver, if you look at a map of Scioto County flood plains, there is a large chunk of real estate that is in the flood plain. That means if all the little streams dump into the larger bodies of water, they can quickly go out of their banks and can do damage before they recede. She said the flash floods from the small streams often become river flood events.

Carver said there are rain gauges strategically located at five places in Scioto County that are part of what meteorologists look for as a part of real time rainfall that accumulates in the county, to make sure the county does not exceed the threshold that would call for a flood watch or warning.

How about the near future?

“We could have some heavy rainfall with storms that move through, but at this time, the National Weather Service is not considering a flash flood watch,” Carver said. “If they do think that there will be the possibility of flooding with some of these heavy thunderstorms that will move through the next couple of days, they’ll put up a watch to make sure that folks that live in the low-lying areas will kind of keep an eye on things if these storms move through and dump a couple of quick inches of rain.”

Flood waters threaten the Second Street Bridge in Portsmouth last year
http://portsmouth-dailytimes.com/wp-content/uploads/2016/07/web1_Flooding2.jpgFlood waters threaten the Second Street Bridge in Portsmouth last year

By Frank Lewis

[email protected]

Reach Frank Lewis at 740-353-3101, ext. 1928, or on Twitter @franklewis.

Reach Frank Lewis at 740-353-3101, ext. 1928, or on Twitter @franklewis.

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