They've survived 126 years of periodic flooding on the Mississippi River in Minneapolis, but it looks like the end for twin piers that held up the first bridge at Franklin Avenue.

The U.S. Coast Guard is ordering removal of the piers as part of a rehabilitation of the existing bridge, a decision that sparked a brief effort to keep them as historic artifacts.

Two Minneapolis political leaders, Park Board Commissioner Scott Vreeland and City Council Member Cam Gordon, lamented the loss of the historical artifacts in online postings. Hennepin County is overseeing the bridge rehab and County Commissioner Peter McLaughlin responded by asking project staff about the feasibility of sparing the redundant stacks of limestone blocks.

But after being floated on a barge under the bridge with McLaughlin and others this week, even Vreeland conceded that the piers need to go.

"If they have to come down, they have to come down," he said. "We've done everything we could to look at the possibilities."

Keeping the deteriorating piers emerged as a potentially attractive option when McLaughlin and others hoped it would help the county save some money on a project that has ballooned to more than twice an earlier cost estimate.

County officials were advised that leaving the piers in place would drive up the costs of the Franklin Avenue bridge rehab project.

But county project engineer Paul Backer used the barge trip to demonstrate how leaving the piers in place would complicate construction and actually drive up costs. And that's without doing any work to stabilize them, with the west pier in particular listing badly and eroded on the side that's less visible from shore.

"I'm always wary of adding costs to someone else's project," Vreeland said.

The piers were once much taller and held up the two-lane Franklin bridge that opened in 1889. But that bridge was inadequate and reopened in 1923 as a wider span with room for streetcars, featuring the longest concrete arch in the world at that time. That bridge was rehabbed in 1971.

The piers were supposed to be removed when the old bridge came down. That was a condition of a 1919 permit for the new bridge issued by the U.S. Army Corps of Engineers. That's according to Eric Washburn, bridge administrator for western waters for the Coast Guard, which inherited bridge duties from the corps.

There is nothing in the bridge file indicating why the piers weren't removed, Washburn said. But the issue arose during the 1970s, and again when the permit file was reviewed for the current work.

Washburn said concerns about liability and navigation are the main reasons that old piers are typically required to be removed. But a spokesman for the St. Paul district of the corps said it doesn't have navigational concerns about the long-standing piers. Barge traffic in Minneapolis is ceasing with the end of lock operations at St. Anthony Falls, but crew teams, sightseeing boats and recreational craft still use the river gorge in Minneapolis.

Backer said the presence of the old piers would complicate the installation of coffer dams for rehab work on the piers of the current bridge, and that vibrations from installing sheet piling for the dams would likely damage them. He said that they'd also make using a crane more complicated when slabs of bridge deck being cast at Bohemian Flats Park and floated by barge to the bridge are hoisted high above the river for installation.

Those issues would add roughly $500,000 to $700,000 to the project. Although that's not a big part of a $50 million bridge project, the county is scraping for any cost savings, given that the project was estimated to cost $20 million back in 2010. The final construction bid was $43.1 million, compared to an earlier estimate of $27.9 million.

Inflation played a role, according to County Engineer Jim Grube, but an estimated $11.3 million of increased cost is attributable to a concrete shortage in the region. Construction of the Minnesota Vikings stadium and oil train traffic are contributing to that shortage, he said.

The county began renovating the substructure of the bridge this year, temporarily narrowing the roadway. It plans to replace the bridge deck next year, closing the span in 2016 during school summer vacation. That's much shorter than in the last renovation, which closed the bridge for about a year, but used rehab techniques that didn't conflict with the old piers. Besides the pier, arch and deck work, the project will rebuild railings, install different lighting and widen the bridge, accommodating a protected bike lane and walkways.

The county is planning to have its contractor stack any blocks of limestone salvaged from the piers at Bohemian Flats Park. That will give the Park Board time to figure out whether they can be used in a planned rehab of that park or elsewhere after construction crews vacate their staging area under the Washington Avenue Bridge. Still, some will lament their eviction.

"I like them and I will miss them if they are removed," Gordon posted online. He lives just off the bridge's west end. "I think future residents will miss the chance to see and think about our city's history when they are gone."

Steve Brandt • 612-673-4438

Twitter: @brandtstrib