Boulder’s stormwater infrastructure has been tested in recent weeks by an extra-wet spring. This May, for instance, got nearly double the average precipitation compared to the same month since 1971. Today’s severe hailstorm and significant flooding added more strain to already-high creeks and an overstretched system.
In less than an hour, 1.24 inches of rain plus hail — up to an inch in diameter — fell with vigor around mid-day.
“With the hail, we did think about — and start — preparing to deploy plow trucks,” said Scott Schlecht, the city’s transportation maintenance manager. “Had it continued hailing at that rate for another 20 minutes or so we probably would’ve needed to.”
Pictures of water washing over Pearl Street populated social media, and bike underpasses washed out with flows of ominous brown water. According to the city, Bear Canyon Creek, Skunk Creek, Goose Creek and South Boulder Creek breached their banks. The city is urging people to avoid all underpasses. The intersection at 9th St. and Balsam Ave. remains affected by flooding.
And yet, Joe Taddeucci, director of utilities for the city, said in an interview that Boulder is still in the realm of normal in terms of floodwaters moving through the city’s infrastructure — and not spilling into neighborhoods.
“I still think we’re okay and we can handle it,” he said. “But if it starts raining day after day after day like it did in 2013, that’s where I get concerned,” he added, referring to the catastrophic flooding that killed three people and damaged hundreds of homes a decade ago.
Taddeucci said flooded overpasses and multi-use paths are part of functioning stormwater infrastructure.
“For really minor events, like an everyday rainshower, ideally you want the [infrastructure] to be designed so the creek can handle that and the path can stay open,” he said. “But as the events get bigger and more intense, you do count on the paths being part of the system that can convey or store water.”
Taddeucci said in newer cities, in addition to paths and overpasses used to convey floodwaters, municipalities will situate recreational facilities, like a soccer field, as a place for floodwaters to pool.
Top left: The upstream side of the underpass on Bear Canyon Creek at Gilpin Drive. Top right: The downstream side of the Gilpin Drive overpass. Bottom: A different perspective of downstream of Gilpin Drive. Credit: Tim Drugan
Don’t go in the water
In floods, most people get themselves into trouble by trying to drive, walk or bike through floodwaters. Knowing this, safety personnel do their best to deter people from engaging in such activities. A Boulderite near 9th Street and Balsam Ave., however, took videos of cars and bikes pushing their way through deep floodwaters despite firefighters waving for them to stop. One car appeared to get stuck. Boulder Fire-Rescue said it rescued two people from being stranded in Boulder Creek.
The reason there was so much water at 9th and Balsam is because that’s the start of the Goose Creek floodplain, as seen on the city’s floodplain map. With Boulder’s flood risk, residents are encouraged to take a look at the floodplain map to see where water pools in flood situations so they can establish a plan to avoid future floodwaters and stay safe. A layer of the map is the “high-hazard zone,” which Taddeucci said are the areas most likely to cause injury and should be avoided.
The pooling at 9th and Balsam will one day be tempered by the Upper Goose Creek and Two Mile Creek flood mitigation project that was approved by Boulder City Council in mid-May to move into a more detailed design phase. If the plan stays as is, a new culvert on 9th Street would feed a flood conveyance channel that will flow along the south side of Balsam Ave.
“When we get a high-intensity thunderstorm, water tends to pond up there,” Taddeucci said. “That is exactly what those projects are intending to address.”
The flooding came a day after a nine-year-old tragically drowned in Boulder Creek after falling off his tube, prompting a reminder that water, especially when flowing at the rates seen today and recently, is a force of nature and should be treated with respect and wariness.
For today, the storm appeared short enough to avoid any major catastrophe. But the rain “can stop at any time as far as we’re concerned,” Taddeucci said.
This is a developing story and will be updated as needed.
Thanks Tim for the great reporting!