The Animas River in Durango ran black Monday as a result of rain over the weekend washing down ash from the 416 Fire burn area.
Since June 1, the 416 Fire has burned more than 34,000 acres, mostly in the San Juan National Forest. A tropical storm off the Pacific Coast brought the first moisture the area has seen since the fire broke out.
It was also the first chance for local officials to see the 416 Fire’s influence to both landslides and flash flooding, as well as impacts on waterways.
For starters, even small amounts of precipitation can cause landslides and flash flooding in burn areas because of the damage fires cause to the soils, which can no longer absorb moisture.
Butch Knowlton, director of the La Plata County Office of Emergency Management, said the storm over the weekend didn’t drop heavy amounts of rain in a short time period, the equation for significant flooding.
Instead, rain fell at a moderate pace over several hours, which Knowlton called the “perfect prescription” that allowed the region to get a healthy dose of rainfall while not creating additional hazards for residents.
Still, the threat of landslides and flash flooding will persist for years to come, Knowlton said, especially when monsoons arrive, which are known for intense but short-duration rainfall.
“We just have to be aware of the fact there’s a lot of material up there that can come down with a heavy rain,” Knowlton said. “That’s what we’re going to be watching.”
Scott Roberts, an aquatic biologist for Mountain Studies Institute, said samples were taken over the weekend from Hermosa Creek, and also from the Animas River above and below the confluence with the tributary stream.
The samples haven’t been analyzed yet, but research on rivers from other places that have experienced wildfires shows there is a potential for effects to water quality and aquatic life.
Because wildfire wipes out vegetation, more nutrients that would otherwise be consumed by plants get into waterways. An excess of nutrients in the water can cause algae to grow at greater levels and cut off oxygen to aquatic life.
John Alves, a senior aquatic biologist for Colorado Parks and Wildlife, said fires can also burn trees that provide shade over streams and rivers, and that allows for cooler temperatures preferred by fish.
But by far the largest danger that fires pose is the fact runoff with high amounts of ash can quickly and suddenly raise the pH of a waterway, causing fish to go into shock and die.
Alves said because of the closure of the San Juan National Forest, biologists have not been able to go out on Hermosa Creek or near its confluence with the Animas River to see if there has been fish kill.
Fish were placed in a cage at two locations on the Animas – one near the confluence with Junction Creek and the other at the fish hatchery at 16th Street and Main Avenue. Alves said no fish have died, but that’s likely because the river is highly diluted by that point downstream.
The 416 Fire has yet to reach a stretch of Hermosa Creek that is the target of an extensive native cutthroat trout reintroduction program.
Aquatic insects are also at risk, Roberts said. Ash can be deposited and blanket on river bottoms, thereby suffocating macroinvertebrates like mayflies, caddisflies and midges.
Sediment loading and increased turbidity also pose water-quality issues as a result of ash runoff, Roberts said.
“Basically, all the issues the Animas already has,” he said. “So it’s nothing new, but it could exacerbate the problem.”
Knowlton said landslides and flooding occurred regularly for at least five years after the Missionary Ridge Fire in 2002.
“Every time it rained we saw debris movement,” he said.
Issues in waterways as a result of wildfires usually last only a couple of years, however. Fish and other aquatic life tend to rebound quickly, Alves said.
After the West Fork Complex Fire in the Rio Grande National Forest in 2013, for instance, fish were able to survive ash flow runoff and actually thrive, Alves said.
“People reported some great fishing after the ash flows,” he said.
Anyone who sees fish kill is asked to report it to CPW.
Calls to the city of Durango were not returned Monday, so it’s unclear how, if at all, runoffs with high amounts of ash may affect the city’s municipal water.