Hidden behind homes on the south side of Central Boulder’s Edgewood Drive is a largely untouched landscape. And the residents of Edgewood like it that way. It’s almost a private oasis for them and for wildlife.
But now this oasis could become less so, as a plan to provide flood protection in the Goose Creek and Twomile drainages moves forward. And while the project is in its early stages, the area behind the Edgewood homes seems destined to be altered.
Sixteen canyons drain into the City of Boulder. If the city were being built today, careful analysis would prevent any construction in areas that held the possibility of flooding. But Boulder isn’t being built today, and many homes and businesses lie in harm’s way.
“Most of the city was built out through all these drainages,” said Gordon McCurry, a hydrologist and the chair of the city’s Water Resources Advisory Board, which recently voted to recommend approval of the mitigation plan. “We saw very painfully in 2013 what the ramification was of all these neighborhoods being built right up to, and over, all these drainages.”
McCurry said the catastrophic 2013 flood that killed four people in Boulder and destroyed more than 300 homes was a wake-up call to the city that had until then been lackluster on flood mitigation. Having opened its eyes to flooding risks, the city is now “playing catch-up” to prevent similar damage that affected so many 10 years ago, he said.
Yet just as floodwaters affect many, projects to fortify against floods are often remedies with unwelcome side effects. In the case of Edgewood, the plans could alter a beloved asset: a pathway for local wildlife.
Nancy Trigg has lived in her house on Edgewood Drive for 13 years. “I walked into the backyard and said, ‘This is where I’m going to live,’” she said.
Trigg’s backyard borders “Reach 6” of the flood mitigation plan being proposed. The plan is broken into various stretches called “reaches,” and the reach behind Trigg’s home is seen as an essential piece of the flood mitigation puzzle, according to city staff. To Trigg and some of her neighbors, however, it’s a wildlife corridor that should be left alone.
“We have great-horned owls nesting, we’ve had mountain lions hunting back here,” Trigg said. “It’s like nothing I’ve ever seen.”
The plan for Reach 6 is to widen the channel to allow it to better handle high flows. This is needed, city staff says, because the channel is a natural confluence for floodwaters coming from both Upper Goose Creek and Twomile Creek. According to an interactive city flood map, Twomile Creek’s floodplain flows southeast across town towards Edgewood from its origins above Linden. Goose Creek, meanwhile, begins near the base of Dakota Ridge and flows past North Boulder Park.
To allow the stream to handle 100-year floodwaters from both these creeks — 100-year meaning each year there’s a 1% chance of this level of destructive flooding happening — the city will have to take out many of the trees Edgewood residents hold dear. It would also need to cut into the hill that rises away from Edgewood towards homes on Balsam Drive.
“It just feels like it was a given from day one that they were going to demolish this area,” Trigg said. “And no matter what any of us said, it was like white noise.”
Trigg said she is not opposed to flood mitigation, but rather wanted the city to explore different options for this particular reach. Residents along Edgewood have pushed for water from the Twomile drainage to join Goose Creek downstream from their homes rather than upstream, with the understanding that this would mean far less would need to be done to the stream they, and wildlife, enjoy.
In an interview, Joe Taddeucci, director of utilities for the City of Boulder, said he believes no such alternative exists.
“My understanding from working through this with our project technical team is there’s really no alternative that exists that would eliminate the need for channel improvements behind Edgewood,” Taddeucci said. “Unless we did nothing and left it at a 10-year flood level.”
Tadeucci added that framing the situation as an either/or scenario — having either a wildlife corridor or a flood mitigation stream — neglects a broader range of possibilities that could be explored.
By using “natural design features” — like manufactured wetlands and carefully chosen vegetation — “you can have both,” Taddeucci said. He acknowledged that construction would effect the area for a year or so, but after its completion, vegetation would start to recover and wildlife would return.
“The way we’ve done projects across the city, there are lots of engineered structures that look really natural that people would have no idea that’s an engineered structure,” he said.
When asked if the city has had a wildlife ecologist visit Reach 6 to determine the possible impact on the animals Edgewood residents are so protective of, Taddeucci said he was unsure. But as the project moves forward, the city will have to prove to federal agencies that the option chosen is the least environmentally damaging of those available.
McCurry of the Water Resources Advisory Board said he understands the frustration of those living along Reach 6. He has visited the site and remarked on its beauty. But he also pointed out that 759 structures lie in the two drainages the city is working to protect from floods, part of its new Comprehensive Flood and Stormwater Master Plan designed to slow and divert floodwaters amid worsening climate change.
“I would like to think that those residents in Reach 6 could take a slightly bigger perspective,” McCurry said. “Yes, the drainage they look out over is going to be impacted by flood mitigation improvements, but it’s to the benefit of hundreds and hundreds of neighbors upstream.”
On Thursday, May 17, city staff from the Utilities Department will present Boulder City Council with its plan for flood mitigation in the Goose Creek and Twomile drainages. If council approves the plan, city staff will move forward from a conceptual level to begin engineering details.