Experts say unusual amount of precipitation should have little impact on rivers, streams
Jan 21, 2013 at 8:52 AM
For residents living in Washington County, the weather over the last week or so has been a tad unconventional.
Following a spell of 70-degree weather, Jan. 13 started the deluge of rain across the region that brought flooding problems to area communities.
To shake things up a bit more, by Thursday afternoon a mix of freezing rain, which later turned into quarter-size snowflakes, dumped approximately 3 to 5 inches in Johnson City and throughout Washington County.
According to Meteorologist Derek Eisentrout with the National Weather Service in Morristown, in a five-day period starting last Sunday, residents in the city and county saw around 7.07 inches of rainfall.
He said the amount of precipitation the area received was highly unusual, saying the normal precipitation for January is around 3.37 inches and for February it’s around 3.45 inches.
“We had over two months worth of precipitation in a week,” Eisentrout said.
And with the rain and snow that had already started to melt Friday morning and on into the evening, snow runoff and even more flooding in area streams and rivers was a concern, but Eisentrout said the amount of both wouldn’t turn out to be very much.
“When we’re looking at either rainfall or snowfall we’re also looking (at) how much precipitation is involved in that. With rainfall, you know exactly how much that is, but ... snow a lot of times will fall at a 10 to 1 ratio, which means if you get an inch of snow, if you’d melt that down you’d get a tenth of an inch of water,” he said. “If we follow that 10 to 1 rule, then 3 to 4 inches would be somewhere between 3 to 4 tenths of an inch.”
He said Friday that runoff had already been happening and would continue to happen for a while, but doesn’t believe it will have a harsh impact on area streams.
Jim Habera, cold water fisheries biologist with Tennessee Wildlife Resources Agency, said streams like the Nolichucky River got high because of the influx of precipitation, but it’s nothing that area streams couldn’t handle.
“We’ve had flows like that in the past plenty of times ... so as far as record-setting conditions or anything like that, no. We didn’t have that,” he said. “Wintertime is when we have our higher flows during the year. They’re normally up a little bit this time of year anyway, but we’ll see them drop back down to what would be normal for this time of year I would think within a week or so. It always takes longer for them to drop down, than it does to come up.”
Habera said the flooding that occurred prior to the snow could have a negative effect on brown brook trout, which fall spawn in mountain streams.
“Their eggs would already be in the gravel and when you have a high flow, a flushing flow like this, you move the gravel around,” he said. “There’s going to be some loss of those eggs. I would expect when I sample the trout streams this summer I may see lower numbers of young ... trout in a lot of streams, but ... they won’t be absent.”
Habera said the rain and snow event would not effect other wildlife because it built up gradually and gave them time to get to higher ground.
Tennessee Valley Authority representative Travis Brickey said that lakes in the region, such as South Holston and Watauga, have been slowly accumulating water and that full turbine capacity at the local tributary dams were released this weekend.
Brickey said Friday the reason TVA keeps lakes in the Tri-Cities so low after Labor Day each year is that when the winter season hits those lakes more or less become storage tanks for the excess water.
“In the wintertime, the lakes are drawn down really low. We do that for a reason ... because we get most of our rain runoff this time of the year and this rain event was a perfect example of that and, of course, then we had snow packed on top of that,” he said.
Brickey said the water was being held in the tributaries to prevent flooding parts along the Tennessee River, which resulted in higher lake levels for those in the Tri-Cities.
“We can’t put the water that’s in the tributaries on top of the high water that’s on the Tennessee, then we’d have a flooding condition,” he said. “Basically, (TVA is) trying to move that water out of the Tennessee River to make room for the water that’s sitting in lakes in the Tri-Cities.”
He said Friday that South Holston Lake levels were around 1,719.8 feet and that Watauga Lake levels were around 1,960.5 feet.
At capacity, South Holston can generate 44 megawatts of hydropower and Watauga can generate 66 megawatts, but power totals had not yet been calculated from the weekend’s release of water through the turbines.