Editor’s note: An earlier version of this article should have reported council voted 6-3 to advance flood mitigation plan Variant 1, and that all of the flood plan options were designed to prevent overtopping of U.S. 36 in the event of a 100- or 500-year storm. The article below has been corrected.

Boulder City Council on Tuesday night voted to move forward with a flood mitigation plan that ignored expert advice, objections from a key project partner, and the preferences of the public and a city advisory board.

The 6-3 vote to advance the plan known as Variant 1, taken around 11:30 p.m., was to a mostly empty chamber: Residents of Frasier Meadows retirement community left earlier after a failed vote for the Variant 2 plan, which received the most support during a public feedback process, best met the nine identified project criteria, was preferred by the University of Colorado (the property owner) and the Water Resources Advisory Board and is the most easily adaptable for larger storms brought about by climate change.

Council deliberations Tuesday night were punctuated with hisses, boos and calls for a vote from the orange shirt-clad audience members from Frasier Meadows. Mayor Suzanne Jones issued multiple admonitions from the dais.

The five members of council who voted for Variant 1 cited a planned flow restriction at U.S. 36 as their primary concern. Though all options presented were designed to, at a minimum, prevent overtopping of the highway during a FEMA-designated 100- or 500-year flood event, several members feared that potential debris would block the restriction in the event of a larger storm, causing water to back up over the roadway.

Consultants and flood experts testified that the restriction did not increase the risk of blockage above the risk already present due to the bridge structure, which will remain in place. But a majority of council was not swayed.

“I do appreciate the opinion of the experts, but I don’t know how it would prevent over-topping of 36 if blocked,” said Councilman Sam Weaver.

Councilwoman Lisa Morzel added that the plan “gives people downstream a false sense of security.”

Council members in the minority pushed back. “We just spent an hour and a half listening to experts tell us it’s not an issue,” said Councilwoman Jill Adler Grano. “We’re not experts.”

Grano and councilmen Aaron Brockett and Bob Yates, who dissented to the vote moving Variant 1 forward, said choosing an option that CU doesn’t support ignored the project criteria of cooperation and would prevent the process from moving forward.

“I do think there would be, at minimum, a significant delay and possibly a large one if we pick Variant 1,” Brockett said. “We would lose that time and lose that money. I also feel that if CU said four of these six proposals in front of you are good, choose one of those, picking one of the two that aren’t (acceptable) doesn’t meet our guiding principles.”

Echoed Grano: “We’re talking about risk. I don’t know how much riskier we can get than moving into prelim design than a concept the property owner has already said no to.”

Citizen groups, including Frasier Meadows residents and workers, have criticized the process as too slow, with delays endangering the lives of more than 3,000 downstream residents. They also have accused council and other boards from listening too much to a small group of residents whose real aim, they allege, is to limit what CU can build on the roughly 308-acre property.

Variant 1 places a greater amount of water onto land CU hopes to develop. That option and the upstream concept, which council directed staff to look at were pushed by a group of engaged residents, including members of an ad hoc working group. While some of those individuals have maintained their greatest desire is for safety, others have openly stated that CU should not build on the land, and called for the city to exercise eminent domain to seize the property from CU.

Nearly every City Council member expressed hope that CU will be open to working with them on adjustments to Variant 1. A condition of approval was that solutions be found to reduce the amount of inundation on buildable land, and suggestions were made that land-use designations be changed to compensate for 36 acres that would currently be lost to flood detention.

A representative for CU also was asked if the resident-proposed upstream storage concept would be acceptable. Frances Draper, vice chancellor for strategic relations, said she did not have enough information to make a determination.

Staff and consultants have warned that upstream water storage might not pass muster of federal regulators due to impacts to cattail wetland protected under the Clean Water Act, as well as disturbances to Preble’s jumping mouse habitat. Council directed staff to more thoroughly analyze the plan as flood work moves into the next stage: annexation of CU’s land into the city.

The annexation process will go before Planning Board on Sept. 6 and back to council — along with an update on design options — on Sept. 20.

Shay Castle: 303-473-1626, castles@dailycamera.com or twitter.com/shayshinecastle