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Weekend storms pose flood threat below 416 Fire burn areas

Ash-covered ground won’t hold moisture, sending torrents of water and debris downstream

HERMOSA – Rainstorms forecast for this weekend could help quench the 416 Fire, but county officials warn it could also trigger flash floods and debris flows below the 33,000-acre burn area.

The National Weather Service in Grand Junction said the area could expect up to an inch of rain Saturday, with a majority of the storms occurring in the afternoon. Flooding in burn areas is a high risk, which is why the agency issued a flash-flood watch for from 9 a.m. Saturday to 12:01 a.m. Sunday.

Butch Knowlton, director for La Plata County Emergency Management, is concerned residents in the area are not aware of how a small amount of rain can lead to drastic flooding. It took only 0.33 inches of rain to cause widespread flooding and debris flows that washed over county roads and entered people’s homes during the first storm after the Missionary Ridge Fire in 2002, Knowlton said.

“We saw massive, massive debris movement,” Knowlton said. “If we get a half-inch of rain concentrated in a short period of time in one of these drainage’s up here, it’s going to be catastrophic.”

The 416 Fire has burned 32,959 acres and was 20 percent contained as of Friday night. The chance of moisture this weekend creates a lot of possibilities, said Bethany Urban, spokeswoman with the incident command team fighting the fire. Though rain could help calm the fire, officials are concerned dry lightning and increased gusts of winds could create new complications. Fire officials will monitor the impact of flooding when deciding where to place firefighters in the days ahead, said incident commander Todd Pechota.

Wildfires burn the soil along with the trees. When it rains, the water doesn’t seep directly into the ground. Instead, it runs down the canyons, collecting ash, dirt and other sediment along the way. The runoff flows until it reaches flatter land.

“When you introduce fire into a forest scenario, you completely alter the storm runoff characteristics of all the small basins and larger basins,” Knowlton said. “Very simply put, all of that ash, all of that material now that’s been exposed by the fire has to come down those canyons. All of those little ravines, all those little canyons, all that debris has to come down.”

Evacuation orders were lifted Friday for 761 residences and 94 businesses. Significant flooding could lead to new evacuations, Knowlton said.

“It’s just going to be too dangerous for people to stay in their homes, especially at night,” Knowlton said. “We’re probably going to be doing additional evacuations for people so they can get out.”

The 416 Fire torched trees and underbrush on both sides of the Hermosa Creek drainage. It also cooks the soil, stripping it of its ability to absorb rainfall, which can lead to flooding downstream.

The floods after the Missionary Ridge Fire were a lesson in what can occur. The county’s Road and Bridge Department can move equipment to help affected residents. The La Plata County Sheriff’s Office spent Friday preparing for the flood, and swiftwater rescues personnel will be on standby.

The Colorado Department of Transportation also is on standby because flooding will likely alter U.S. Highway 550 and county roads, Knowlton said. He is particularly concerned with two stretches of the highway – one north of Bakers Bridge and one north of Honeyville.

The 416 Fire consumed everything in its path in some areas north of Durango. The barren landscape covered in ash increases the chances for flash flooding during significant rain events, including the storm expected to arrive Saturday.

Officials have been communicating among themselves and with residents about how to respond to possible flooding. The county’s Office of Emergency Management is using the same weather resources used by the Type 1 Rocky Mountain Incident Management Team to predict precipitation levels, assess current drainage systems and locate homes at risk. Knowlton has also used the county’s geological hazard maps, which identify historical debris fans in the area.

“We’re watching very closely the density, the volume of precipitation that’s in those storms, and we’re going to do our best to predict where that precipitation is going to fall,” he said.

People’s homes that weren’t impacted by the fire can still be threatened by the debris flows, Knowlton said.

“Debris can flow far past the exterior boundary of the fire,” Knowlton said. “Sometimes, debris flows can reach out way past those perimeters and get into areas that we’ve never experienced water or debris before. People have got to understand that.”

Knowlton said officials know that homes in the path of the Hermosa drainage will be affected. There are also canyons on the southern portion of the fire that are at risk.

Houses that sit below burnt hillsides are susceptible to flooding and debris flows. This home sits above a drainage, which may keep it safe.

Most people in harm’s way attempt to mitigate the threat around their properties by using sandbags. But sandbags aren’t typically much of a match for the intensity and volume of floods because they don’t weigh enough, Knowlton said.

During the Missionary Ridge Fire, some residents dug ditches around their property so the debris moved around their homes. However, that can create problems for their neighbors.

Knowlton said the flooding won’t go away after the first storm.

“It’s going to be storm after storm after storm,” he said.

asemadeni@durangoherald.com


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