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The longest historical closure of shipping lanes on the Columbia and Snake rivers is about to be five days longer – at least for waterways around The Dalles Dam.

A problem that arose early on in the manufacturing process of the dam’s new gate led to a decision by the U.S. Army Corps of Engineers Monday to extend the shutdown until March 23, rather than March 18, said Scott Clemans, a spokesman.

“We ran into difficulties and slipped behind schedule by a couple of weeks,” Clemans said. “We’ve been making up time since then, but at this point we just don’t think we can safely make up those last five days.”

The corps shut down shipping on the two rivers on Dec. 10 so that the agency could replace navigation lock gates on the John Day, The Dalles and Lower Monumental dams.

The manufacturing problem was a learning experience for both the corps and its contractors – because the gate is made of huge pieces of metal that can be difficult to weld, Clemans said.

“There were some problems with distortion of the metal as we were heating it,” he said. “In addition, there was a contract requirement that was unclear. We had to specify more complex penetration welds, and we had to ask the contractor to do more than they were originally asked to do.”

Dix Corp. of Spokane, Wash., is the general contractor and Thompson Metal Fab Inc. of Vancouver, Wash., is the subcontractor that built the gates for The Dalles. But the problem was not their fault, said Pat Duyck, project manager for the corps.

“It was kind of the perfect storm of events,” Duyck said. “We had to add larger welds to the gate bottoms and the welding codes we had to use were more geared toward bridges. We were already on a compressed schedule, and those stringent requirements accelerated that.”

After the gates were built, the corps did significant ultrasonic testing to make sure the welds were clean, he added.

“If you have a rejected weld, you lose about three days per weld,” Duyck said.

The corps also altered the design of the gates fairly late in the process in order to make them sturdier, Clemans added.

“It’s a more robust design that we think is going to last a lot longer, and it has some adjustability,” Clemans said. “Also, design standards have changed over the years – good design; it’s just an evolving art.”

The extension of the outage will affect areas only near The Dalles Dam; other waterways for the two other gates should open by March 18, he added.