BOULDER, Colo.—Erosion of rocks and mud could damage buildings, roads and reservoirs in an area blackened by a wildfire west of Boulder in September, federal researchers said Tuesday.
A report by the U.S. Geological Survey said computer modeling showed the possibility of substantial damage from a slurry created when rain mixes with dirt and rocks in areas where trees and other vegetation burned.
The fire started Sept. 6 and went on to blacken about 6,200 acres, or nearly 10 square miles. It destroyed at least 166 homes and caused an estimated $217 million in damage, making it the costliest wildfire in state history.
The USGS report said the probability of debris flows is above 60 percent in some areas if 0.9 inch of rain falls in an hour. It also said the volume of debris from high-risk areas could range from 1,600 to more than 12,000 cubic yards.
Damage could occur both in the burn area and in downstream areas that didn’t burn, the report said.
The computer models were based on the consequences of recent fires elsewhere in the West.
Investigators said the wildfire probably spread from a fire pit at the home of a volunteer firefighter. The firefighter told authorities he took steps to extinguish the pit fire and thought it was out.
Prosecutors declined to file charges, saying they couldn’t prove the firefighter knowingly or recklessly started the blaze.
———
Online:
USGS erosion report:
