Increased flows from the Garrison Dam, meant to lessen the impact of drought on Lake Oahe, are making construction of the new Liberty Memorial Bridge more difficult.

The Army Corps of Engineers increased the flows from 21,000 cubic feet per second to 24,000 last Wednesday, in hopes of slowing the decline of Oahe. At the same time Lunda Construction was putting the final touches on the cofferdam for pier 7 of the bridge.

Having cut off the sheet piling surrounding the pier site, Lunda poured cement into the cofferdam to create a seal at the bottom, allowing for dewatering of the cofferdam. Water was pumped out of the dam on Tuesday in preparations of constructing footing for the pier, according to Department of Transportation spokesman Mike Kopp.

Lunda area manager Joe Larson said the river has risen about a foot and a half since last week, though it had dropped off slightly Tuesday. The current also has become substantially swifter in his estimation.

"It came within about a inch of over-topping the number 7 cofferdam," Larson said. "It's not where we want to be, but the situation is what it is."

Corps spokesman Paul Johnston said the flows will continue at 24,000 cfs until about mid-September. Johnston estimated the additional flow made the river come up about a half-foot and should have had little effect on the current.

"I don't think the current has changed at all," Johnston said. "There is just additional volume, it's not coming down any faster."

The cofferdam being built for pier 8 remains in good shape and should be unaffected by the increased flow, Larson said. Crews continue to remove river bottom from the dam and then will pour cement to the bottom to create a seal to allow water to be removed. About 3,500 cubic feet of soil are being removed from the cofferdam at the rate of about 50 yards per crane load.

"We take the soil put it on a barge and then to shore. It's a slow process, but the only one feasible," Larson said.

Larson estimated it will be a couple of more months before pier 7 is out of the water, depending on the water level remaining constant. If it overtopped the cofferdam, crews would move on to other projects until such time they could return.

Construction of piers 12, 13 and 14 for the east approach continues.

Toni Erhardt, of the corps regulatory office in Bismarck, said he has been in contact with the bridge contractors and has relayed their information to the corps' reservoir management people. She said there is little her office can do other than provide for an exchange of information. The Bismarck office has nothing to do with the operation of the reservoir.

The flows also have impacted the buoys being used to direct traffic on the river, according to Kopp. They will be replaced with buoys more suited for the situation.

(Reach reporter Gordon Weixel at 250-8255 or gordon.weixel@;bismarcktribune.com.)