Ten years ago this week, a cold front settled over the Front Range, fueling a thousand-year rainstorm that dropped more than 18 inches of rain on Boulder in under a week. More than half fell on Sept. 12, 2013 alone, almost doubling the previous single-day record for the area.
Though the thousand-year rainstorm didn’t result in thousand-year flooding, many areas of Boulder did experience 100- to 200-year flooding that killed four people, destroyed upwards of 300 homes, wiped out roads and bridges, and stranded mountain communities west of Boulder. The devastation served as a stark reminder that the city has the highest risk of flooding of any municipality in Colorado.
Now, 10 years later, how much better prepared is Boulder for a flood like 2013? This matters because we likely don’t have 100 to 200 years before the next flood. Climate change is expected to bring more infrequent but more ferocious precipitation, potentially changing 100-year floods to 50-year or even 10-year events.
The answer is that Boulder is not much better prepared — at least, not yet. Seven years ago, the city outlined a 30-year journey for 37 flood mitigation projects costing more than $300 million. While some are in the design stage, most of the creeks putting Boulderites at risk are still years or even decades away from project completion. The South Boulder Creek project, closest to construction, would safeguard over 1,100 homes in case of a repeat of the 2013 flood. Another top priority, the Upper Goose Creek project, is set to begin construction in 2026. (See the city’s list of projects, by priority.)
Some of this wait is due to necessary engineering and bureaucratic steps that take years to fund and complete. Yet objection of residents sometimes contributes to the sluggish progress. Joe Taddeucci, Boulder’s utilities director, suggested the extended timeline of projects, which puts them further and further from memories of 2013, can lead to complacency.
“There can be a false sense of security, when we’re not experiencing a dramatic flood event right now, that we’ve got time to continue to debate and debate and debate,” Taddeucci said after this year’s fierce spring storms. “Finding a way to have good processes but getting these critical life-safety projects done expeditiously is the challenge we have as city staff.”
A flood conundrum with a long legacy and many warnings
Of all the cities in Colorado, Boulder ranks first for flood risk due to 16 drainages flowing through the city. Until federal floodplain regulations were adopted in the late 1960s, Boulderites built their homes and public buildings on the banks of the plethora of creeks.
Now, 16% of the city sits in the 100-year floodplain, meaning these structures have a 1% chance of flooding in a given year based on historical data, more when climate change is factored in.
It’s not like there weren’t warnings. In the late 1950s, for instance, when Boulder was deciding on a location for its new public library, Gilbert White, then a professor of the University of Chicago who later moved to the University of Colorado and founded its Natural Hazards Center, cautioned against the spot on Arapahoe Avenue. The city ignored this warning and now the main library sits in a high-hazard flood zone.
“Floods are acts of God,” said White, according to a Natural Hazards Center video about his life. “But flood losses are largely acts of man.”
Even before he spoke against the library, White, sometimes referred to as the father of modern floodplain management, warned Boulderites of their town’s unique risk of flooding. That blue flood marker along Boulder Creek near Central Park showing the heights of different flood risks? That’s a memorial for White.
“Instead of moving water away from people, [White] argued we should move people away from water,” according to the video.
The problem is reconciling White’s recommendation with Boulder’s current reality.
With some 2,600 structures in the 100-year floodplain — and more in the 500-year floodplain that are at risk of shallow flooding in 100-year floods — it isn’t possible to move people away from water, at least not all of them right away.
The City of Boulder is buying some high-risk properties as they come available and then deconstructing or relocating them. An historic public housing community next to the main library is being sold and the residents are being relocated because of its flood risk. But much of Boulder will remain at risk unless some dams and levees, and channels and flood piping are built.
CU South and the removal of a controversial levee
The most imminent city flood mitigation project also holds an opportunity to incorporate at least some of White’s perspective. The South Boulder Creek project is one of few the city will undertake that can reclaim some of its historic floodplain, according to Brandon Coleman, a city stormwater engineer managing the project.
The property sitting to the south of the confluence of US 36 and Foothills Parkway is where the University of Colorado wants to build a swath of new housing and academic buildings. Last year Boulderites voted, once again, to make the property — known as CU South — part of the city, giving CU access to city utilities and allowing construction to theoretically move forward on the property.
It’s not just CU that will be building. In negotiations to annex the property, the city received a chunk of land to use for flood mitigation on South Boulder Creek for a project that would take 1,100 homes out of the 100-year floodplain. In the 2013 flood, almost $30 million in damages was caused by an overflowing South Boulder Creek, the costliest drainage in the flood only behind Boulder Creek.
The reason South Boulder Creek’s floodwaters didn’t flow as they should have during that fateful storm was due partly to a levee built as a berm during the property’s gravel mining in the 1980s. This levee shielded the mining site from the creek to prevent periodic flooding.
The original reclamation plan for the CU South property — which outlines how to restore the land after mining — required the immediate removal of the levee once mining stopped. But after the City of Boulder missed its chance to purchase the property in the 1990s and CU bought it instead, the university kept the levee, and bolstered it to the chagrin of the then-Boulder City Council.
Read: Decades of ‘what-ifs’: The history of CU South leaves many wondering what could have been
CU not only fortified the levee but flattened the land it encircled and nixed much of the original reclamation plan. That plan envisioned more than 40 acres of lakes. There are now about four acres of ponds on the property.
A comparison between a floodplain map from 1981 and Boulder’s current floodplain webpage shows that the levee currently redirects most floodwater around the CU South property to the detriment of those downstream.
Soon though, as part of the South Boulder Creek mitigation project, city staff said, the levee will be removed, allowing floodwaters to partially return to their natural flow. Some of the originally intended wildlife habitat mecca might even be realized, albeit to a lesser extent.
Taddeucci said the small ponds and wetlands currently outside the levee provide an insight into what might be after the mitigation project is complete.
“When that floodplain is reconnected and that levee removed, some of those same features or better are planned to be on the inside of the levee,” he said.
Why the South Boulder Creek project is top priority and where it stands
The South Boulder Creek project is the city’s top priority largely because of its cost efficiency, according to city staff. At $63 million, it’s more cost-effective in terms of homes protected compared to other projects. This efficiency standard is now being applied to other flood mitigation projects, although it’s unlikely they will be as cost effective, according to city staff.
For instance, the Upper Goose Creek flood mitigation project would cost over $80,000 per home to remove from the 100-year floodplain, according to a city memo. Compare that to the South Boulder Creek project that protects each home for under $60,000.
During a recent city council meeting, Coleman, the city stormwater engineer, said the South Boulder Creek project’s cost-effectiveness is due to its detention capabilities, made possible by available open space. “Because of [Boulder’s] drainage basins, we don’t have a lot of large open areas where we can do detention,” Coleman said. “But [detention] is a very cost-effective approach.”
So far, the South Boulder Creek mitigation project is progressing according to schedule, city staff said. Construction is still slated to begin in late 2024. After presenting preliminary designs to city council in April 2022, the next milestone is the 60% design update expected in October.
“Between 30 and 60% we get a lot of the larger design details figured out, like the final location of the flood wall, major grading and layout of the key design elements,” said Coleman. “How it gets built is determined between 60 and 90% percent.”
Coleman said a year will separate the 60% and 90% design phases. The final 10% primarily involves addressing issues raised about the design. After that, the city will solicit bids for the project, and construction can begin.
Public opposition looms over open space disposal hearing
The public, however, could still pose a potential hurdle, this time through the open space disposal process. Approximately five acres of the South Boulder Creek project will be developed on land that Boulder previously designated as open space. To allow flood mitigation on this property, a hearing is required, involving both the Open Space Board of Trustees and city council. Public input will be sought during this disposal process, and given the strong opposition to construction on the CU South property, it’s likely the hearing will face at least some pushback.
Margaret LeCompte and Steven Telleen of Save South Boulder, a group opposing the South Boulder Creek flood project as well as CU’s construction vision, said their group plans to oppose the open space disposal process. They said their organization will keep a close eye on the permitting process for the project and will gear up for a legal battle should it find an opening.
Save South Boulder is closely echoing the arguments made by those who put forth the ballot measure to reject the CU South annexation last year. Their concerns include the belief that the current flood plan doesn’t adequately address the real flood risk, and they question CU’s purchase of the property in the first place. They advocate for the use of a 500-year flood model instead of the current 100-year model. They refer to White’s work as evidence supporting the need for a 500-year mitigation plan. White’s ideal was avoiding construction in the 500-year floodplain whenever possible.
“This project is only built to contain a 100-year flood, and we are already being forecast to have 500-year floods on a regular basis,” LeCompte said. Another major flood, Le Compte said, could “overtop” even the new flood protections.
Coleman, of the city, suggested public pushback will always be a part of flood mitigation.
“The storm flood utility is really unique in the amount of impacts we have with the projects we do and also the visibility of them,” he said. “Outreach for our utility in particular is a huge component.”
As for who bears the brunt of the critique, Coleman said he silos himself to a certain extent, as he’s just concerned with finding answers to established problems.
“I can only recommend the technical solutions,” he said. “It’s up to the community what projects we pursue.”
The city has been hyper-focused on flooding, but the Marshall Fire and NCAR Fire have shown that the city needs to pay much more attention to wildfire. The “evacuation” from the NCAR Fire was a disaster-in-making. Taking an hour to get from Greenbriar to Table Mesa along Broadway is disturbing. Are there any posted wildfire evacuation routes, signage or Boulder web pages?
I sense a story, BRL.