Post Fire Flooding on the Front Range

Here’s a link to a story from the Denver Post, and below is an excerpt.

Typical monsoon-season rainfall in the High Park area for the month ranges from 2 to 2½ inches, but this year, the amount more than doubled to nearly 6 inches in some spots, bringing an increased chance of mud, ash and debris
Piles of mud, rocks and other debris washed across U.S. 24 near Cascade on Tuesday after heavy rain Monday. The highway was closed for several hours. (Mark Reis, Colorado Springs Gazette)
slides.

“July and August typically have thunderstorm activity, so it would not have been a total fluke to have some locally heavy rains,” said Nolan Doesken, the state climatologist based at Colorado State University’s Department of Atmospheric Science. “But 5 inches in one month in Colorado’s dry climate is a lot.”

Most of the rain fell July 6-9, washing ash into the Cache la Poudre Canyon and coating many of the river banks with black sludge. Although much of the ash had cleared by the next week, erosion and mudslides continue to be a concern.

The area near Colorado Springs, where the Waldo Canyon fire ripped through 18,247 acres and destroyed 346 homes, is experiencing similar conditions, with 10 flood advisories issued for the month of July already.

“We hardly ever issue flood advisories up there, probably just one or two,” said Tom Magnuson, warning coordination meteorologist for the weather center’s Pueblo office. “Typically they don’t get big rainfalls up there, and they don’t do much.”

Five of the 10 advisories were issued Monday night, Magnuson said, with heavy rains causing gravel to slide from the burn area onto U.S. 24 west of Cascade.

“I went out there this morning to take pictures, and the pile of granite, just the pebble size, was probably 8 feet deep to the side of the road and 5 feet deep in the middle of the road,” he said.

Emergency management and U.S. Forest Service officials began creating barriers of sandbags last week around homes that survived the Waldo Canyon blaze and were able to prevent floodwater from reaching them.