Flood control dams protected downstream towns

Thanks to a series of flood control dams built in the wake of hurricanes in the 1930s and ’40s, many Vermont towns downstream of the dams were spared even worse flooding.

http://www.rutlandherald.com/article/20110904/NEWS02/709049910

Published September 4, 2011 in the Rutland Herald

Flood control dams protected downstream towns

By SUSAN SMALLHEER

Staff Writer

NORTH SPRINGFIELD — It could have been worse.

Thanks to a series of flood control dams built in the wake of hurricanes in the 1930s and ’40s, many Vermont towns downstream of the dams were spared even worse flooding.

“I like to think our dams prevented a lot of damage,” said Mike Curran, operations manager for the Upper Connecticut River Basin for the U.S. Army Corps of Engineers. “Springfield would have been inundated,” he said, noting the heavy damage upstream on the Black River to the towns of Ludlow and Cavendish and roads in Weathersfield.

Curran oversees the operation of five flood control dams in Vermont and two in neighboring New Hampshire near Keene, N.H.

While towns along the West River such as Newfane and Jamaica were hard hit, it would have been even worse without the dams, he said.

In Vermont, the dams are holding back almost record levels of water, while in New Hampshire, the dams are about 20 percent above normal, Curran said Thursday.

Surprisingly, the levels at the dams in Vermont were not setting records, Curran said. Those record levels were set in the early spring of 1987, when a combination of warm weather, record snowfall and two rainfalls set records at North Springfield, Ball Mountain in Jamaica and Townshend Dam.

Those dams used their spillways in 1987 to avoid topping off the dams.

The two other dams in the network, at Hartland and Post Mills, set records back in 1973 or 1969, he said.

Hartland, which is located on the Ottauchequee River, was at 122.8 feet, while the normal level is 35 feet, or 57 percent capacity. Townshend Dam peaked at 86.5 feet, at 78 percent capacity.

Union Village dam, which is located on the Ompompanoosuc River in Thetford, was built in the 1940s, he said.

Once the Connecticut River crested, the flood control dams started “dumping” water, Curran said, and the reservoirs have already dropped several feet since Tuesday night, when releases began.

“We started opening up, essentially dumping water, on Tuesday,” Curran said. “Until it crests, we hold water, until the Connecticut River starts to recede.”

In general, he said, the Vermont dams are 65 to 70 percent full.

Springfield received 7.5 inches, he said. Ball Mountain got between 6.5 and 7.5 inches, and Townshend about the same. Union Village received 4 inches, as did Hartland, he said.

Curran said that the North Springfield dam reached 80.5 feet, and was 71 percent full. It hit 95 feet in 1987, he said, consulting his records.

Ball Mountain, which is in a narrower valley, is at 160 feet, while the normal elevation is 60 feet, he said. Ball Mountain dam peaked at 177.5 feet on Tuesday, while the spillway is at 211 feet.

“We have 100 feet of additional water there,” he said, taking up 71 percent of the dam’s capacity.

All the dams, he said,are designed to hold almost 6 inches of storm runoff.

While it rained more than 6 inches, Curran said some of the rain was absorbed by the soil, and since it is still the growing season, trees and other vegetation absorb a lot of moisture.

The 1987 floods came while the ground was still frozen and there were no leaves on the trees to draw up moisture.

“It will be a good week and a half to get down to normal,” said Curran, and a full two weeks for the Surry Mountain and Otter Brook dams in New Hampshire, because the downstream channels are not as large.

He said there is a lot of debris in the reservoirs, mostly trees.

“I hope we don’t have any houses,” said Curran, noting the wood would be removed from the reservoir, piled up and eventually burned. Its value as firewood is not great because it is covered with silt, he said.

Curran said that the trees that are underwater should survive the 10-day bath, but that any grassy areas will have to be reseeded.

He said that three flood control dams had been built on the Winooski River on the western side of the state, including the Waterbury dam and reservoir. They have been turned over to the state, he said.

He said it would be several weeks before the Army Corps does any calculations on water flow to determine what effects the dams helped prevent.