Praying for rain is common when your state is beset by record-setting blazes, but as always, be careful what you wish for. Heavy downpours create their own hazards. The irony was highlighted for me two weeks ago when the city of Colorado Springs found itself simultaneously under a “red flag” fire warning and a flash flood warning.
The good news is that monsoon rains in Colorado over the last week helped firefighters bring an end to the High Park Fire in the foothills above Fort Collins, as well as Colorado Springs’s Waldo Canyon fire, which was declared 100 percent contained Tuesday night. Between them, the two most destructive wildfires in Colorado history burned nearly 600 homes, so no one was sad to see them quenched.
But before the firefighters had even finished scratching their firelines around the blazes, residents were facing new threats -- including floods fed by runoff from the burnt land, along with mudslides, debris flows, and contaminated water supplies, all a result of the heavy downpours that fell over the weekend.
Like wildfires, powerful afternoon thunderstorms are a regular part of Colorado’s summer. (The National Weather Service reported that one area between Denver and Colorado Springs received 2.5 inches of rain in an hour last Friday afternoon.) But when fires and floods mix, bad things happen: a mudslide from the High Park burn zone covered the highway with ash, branches, and black mud up to a foot deep; volunteers filled thousands of sandbags to protect their neighbors’ homes and used snowplows to clear ash and mud; and the Cache la Poudre River turned as black and turbid as India ink when inundated with the ash and cinders from fire runoff.
Post-wildfire debris flows can destroy houses, bury or wash out roads, contaminate reservoirs, block drainages and water pipes, and threaten lives. Some flows are strong enough to carry boulders, automobiles, and parts of houses. Debris flows that followed Southern California wildfires in 2003 killed 16 people on Christmas Day that year. In 1994, after the South Canyon fire killed 14 firefighters near Glenwood Springs, Colorado, debris flows crossed Interstate 70, overrunning Jersey barriers, burying 30 cars, and pushing some of them into the Colorado River. Miraculously, there were no fatalities.
But the threat from the combination of fire and water can last for years, or decades. Initially the grasses, shrubs, and small trees that would hold soil in place are burned away. Larger trees that are killed by fire leave their roots in the ground, and as those decay or give way during the coming years, they perpetuate the risk of debris flows. Flows from 2002’s Hayman fire, Colorado’s largest on record, destroyed homes and washed out a highway four years after the fire.
But the longest-term threat in Colorado is to the water itself. Denver Water, the public agency that provides 1.3 million people with water in the Denver metro area, has spent more than $26 million restoring land, repairing water-system infrastructure, and dredging reservoirs since the Hayman fire and the 1996 Buffalo Creek fire. “It’s hundreds of years for something like this to recover,” said Denver Water spokesperson Travis Thompson.
Residents of Greeley, Colorado, were warned that their drinking water might smell smoky after this year’s High Park fire, and since the weekend’s floods, both Greeley and Fort Collins have ceased taking water from the Poudre River, which normally provides much of those cities’ supplies.
In the meantime, Burned Area Emergency Response teams are looking for ways to reduce the flooding and water pollution expected in the wake of the massive High Park and Waldo Canyon fires. In the coming months, the teams’ soil scientists, hydrologists, and biologists will try to minimize further damage to homes, water supplies, and the mountain landscape through methods that include stabilizing eroding slopes with mulch, and holding back or redirecting floods with straw dams, catchment basins and deflecting walls.
Nothing all that sexy sounding, but they work. Then it will be time to plant thousands of seedlings to help restore the burned forests.
Still, there’s only so much humans can do to staunch the damage from massive forest fires, which -- even once they’re put out -- will continue trickling down on, and sometimes flooding, Colorado for decades.
This is part of an occasional series on Western wildfires and climate change. Read related stories here.
Image: High Park fire/Michael Kodas