University of Colorado officials and Boulder City Council came close to getting on the same page Tuesday for the long-studied flood mitigation project set to be built on the school’s planned south campus.

With flood mitigation needed for future South Boulder Creek flows, and CU planning to develop 129 acres out of the 308 it owns near U.S. 36 and Table Mesa Drive, officials from the city and school have been at odds in the past on the best way to proceed.

But the school has given up pushing for a flood mitigation design known as Variant 2, which the city has killed, and City Council pushed forward a project design meant to protect against a 100-year flood, as opposed to a 500-year flood or an event between those levels. The chosen option would least impact the property out of the options still under consideration.

But CU once preferred that Variant 2 design because a flood wall would have been built more alongside U.S. 36, rather than along Table Mesa, as the project concepts currently propose.

CU remains wary of the current designs — all versions of a concept known as Variant 1 — potentially cutting off access from Table Mesa to the school’s property with the proposed flood structure locations. Last month the school wrote a letter to the city warning new housing for upper-division students and faculty may not be feasible under any scenario with such infrastructure in place at any level of flood protection.

But CU has since shown flexibility on that stance, saying it would be OK with the flood structure going in place as long as the city agrees to create multiple entries into the property from Colo. 93 and adjacent neighborhoods.

“We are committed to working with them on that,” CU Senior Strategic Advisor Frances Draper said. “It’s do-able. … What (the compromise) won’t do is cater to one group.”

Some residents opposed to the area’s development have urged the city to consider a land swap with CU, with the city providing the school land it could build on and the city taking control of the CU South parcel and gaining flexibility to erect flood mitigation structures.

But CU does not want to go that route. City Council this year directed staff to analyze possibly trading publicly owned land in the city’s planning reserve north of municipal boundaries.

It could take years, though, for the reserved land to be prepared for annexation and development, delays CU wants to avoid and that could also slow the city being able to build South Boulder Creek flood infrastructure, since the school would retain its land until it could annex the planning reserve land. The city would have to perform potentially lengthy studies to determine if it could provide municipal services to the planning reserve land.

“It’s not something we recommend the city look at seriously,” Draper said of a land swap.

Draper said CU officials could not agree to allow flood mitigation work to move forward without a south campus annexation agreement in place, so downstream residents would be protected and the school could consider using planning reserve land for development.

“I feel like we’re making real progress,” Councilman Aaron Brockett said.

City officials are hesitant to continue pushing forward a 500-year flood protection design because it could be harder to receive permitting from state and federal agencies, they said, with the Colorado Department of Transportation a potential hurdle to such a project.

At a 100-year design level, the project would not disturb wetlands in the area and habitat for Ute-ladies’-tresses orchid and Preble’s jumping mouse, officials said. The CDOT last year declined to allow a flood wall in the U.S. 36 right-of-way, meaning it will need to be constructed on Boulder Open Space and Mountain Parks land and require that city agency to dispose of some land.

“We are waiting for city of Boulder to provide an engineering analysis to resolve outstanding questions about the functional viability of their proposed detention facility, or provide us with enough background information to run our calculations to find answers ourselves,” CDOT spokesman Jared Fiel said in an email. “CDOT has been waiting for some design detail, background studies or any calculations they can provide to prove they can actually detain 20 feet of unconstrained flow without any engineering feature on the ground.”

The city has estimated a $66 million cost for the 100-year flood mitigation design it will continue working on, with $41 million for flood detention work, $10 million to fill soil on the land to keep CU’s property able to be developed and $15 million in impact to CU South, though the latter amount could be negotiated with the school.

The 500-year flood design concept is estimated at $96 million, with $47 million for flood infrastructure and $34 million for earth fill.

Mayor Pro Tem Bob Yates asked city staff to develop some estimates of the cost impact on resident utility bills to underlie the bonds that would likely be sold to fund either project.

“We may make a decision for reasons other than economics, but it would be nice to know what the difference is” in resident costs between the 100-year and 500-year flood protection designs, Yates said.

Council will meet in May to make an official decision on a flood mitigation project for South Boulder Creek that officials will move forward through several state and federal permitting processes as the design becomes complete. Council is set to discuss terms of the CU South annexation later this year.

“The annexation piece has to get settled before we can move forward” with flood work, Boulder Director of Public Works for Utilities Joe Taddeucci said.