Analysis: Upstream detention too costly, destructive for CU South flood control — #boulder beat

Photo courtesy of the City of Boulder via boulder beat

From boulder beat:

City council this week will again consider an alternative design for flood control on South Boulder Creek, one that’s been rejected twice before. This time, staff, the open space board and an advisory group of elected and appointed officials are recommending against the plan, pushed by residents opposed to University of Colorado plans for an eventual southern campus.

If city council agrees with that assessment, it will cap an effort to protect south Boulder from flooding — a process that, by the city’s own reckoning, started, nearly half a century ago. Winnowing potential options took two decades…

Council settled on a “final” detention, dam and flood wall design in June, but their vote came with a caveat: One more look at resident-proposed design to detain water further upstream on South Boulder Creek. The Open Space Board of Trustees requested further analysis once it was revealed that flood structures would be built on open space land rather than state right-of-way along U.S. 36.

Upstream detention, as the design is referred two, was ruled inadequate by project staff in 2015 and again in 2018. This time, a staff analysis showed that upstream detention would be more costly than the current plan for the same level of protection and would impact more sensitive habitat.

OSBT agreed on Dec. 16, as did an advisory group assembled by the city that included representatives from OSBT, Water Resources Advisory Board, Planning Board and city council.

“The advisory group concluded that although an upstream alternative could be feasible, it does not perform better than the Variant 1, 100-yr design when considering the June 2020 council comparison criteria, and substantial engineered structures would still be required on OSMP lands.”

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