Engineers watching rising levels at Wappapello Lake

WAPPAPELLO LAKE, Mo. -- As of Friday morning Wappapello Lake was anticipated to crest at 397 feet on Sunday, about one and a half feet below a level which would force officials to increase its outflow above its already unusually high amount.

Levels were at 396.71 feet at 8:30 a.m. Friday, higher than the lake's second highest recorded amount ever.

Residents in Greenville spent Thursday constructing a dirt levee to protect the town's main entrance from flooding, while communities below the dam were waiting to see what affect the final crest will have on their water levels.

The lake was releasing 10,000 cubic feet per second Friday morning, or about 75,000 gallons of water, to accommodate that pool.

The U.S. Army Corps of Engineers considered the of release very rare. Outflow is typically between 2,000 and 500 cubic feet per second for the summer pool, which averages 359 feet.

"A water control plan based on the elevation of the lake requires us to release certain volumes of water," Col. Thomas O'Hara explained Thursday from the visitor's center above the lake's spillway.

If the level reaches 398.5 feet, the Corps will be required to release 17,000 cubic feet of water per second, he said. That would be about 127,500 gallons per second.

This is entirely dependent on future rainfall.

"There is obviously the potential of additional rain as we move forward," O'Hara said.

An increase in outflow could cause an average rise in water levels below the dam of 3 to 7 feet above what residents see at the current release, said Park Ranger John Daves.

"It's done to maintain storage, capacity and the structural capacity of the dam," O'Hara stated. "All changes are based on the elevation of the lake. It would be a gradual change."

Wappapello Lake can drop by an average .4 feet per day if the weather remains dry, he said.

The current crest is already more than the 394.74 feet the Overflow Spillway alone can hold back.

Gravel was poured Thursday on top of a temporary dike constructed behind the 750 foot long spillway to prevent the water from flowing onto Route T. It will prevent flooding on the highway until the lake reaches 398.5 feet.

"Its only purpose will be to protect Highway T," O'Hara said.

Infrastructure contained in the highway and utilities buried beneath it is valued at $18 million, he said.

A wall of sandbags has also been constructed on top of the spillway. This was done to prevent water from spilling onto Route T before the dike was complete, O'Hara said.

"That sandbag wall was constructed with 250 volunteers from the community. We very much appreciate their help," he said, adding volunteers worked until 11 p.m. Wednesday. "We couldn't have made our timeline without each and every person who came out."

The highway in front of the dam was closed Wednesday and is expected to remain closed until water recedes to the height of the spillway, according to O'Hara.

"Since the water is above the spillway, there would not be adequate reaction time if there was some type of failure," O'Hara said, adding later, "One point I would like to make is that this structure is not going to result in higher water levels in the lake."

The dike will not be built any higher because it would cause flooding not related to rainfall in areas behind the lake, according to officials. If water tops the spillway, the outflow will be adjusted to reflect that amount.

"Greenville has already got water," O'Hara said. "Our requirement is to try to balance upper and down river (needs) and maintain the structural integrity of the dam."

At summer levels, the lake covers about 8,400 acres. At current flood levels it has reached about 24,000 acres.

Officials at Greenville blame its high level for flooding around the town's two entrances from U.S. 67. Water covered the entrance near Route D Thursday morning and had begun to creep over the main entrance on Front Street. If those roads become impassable, residents' only remaining exit would be along a stretch of Route E prone to flash flooding.

The Front Street water was stopped by an earthen levee completed by officials and volunteers who worked from early morning to night Thursday. Corps engineers evaluated the work and indicated they believed it was the best way to prevent low-lying areas near Front Street from flooding.

City officials planned to pump the water near the entrance to the other side of the levee as soon as it was complete.

They were concerned about how the changed shape of the land around Greenville, with lanes added to U.S. 67, could impact flooding.

Pertinent address:

Wappapello Lake, MO

Greenville, MO