The risk of erosion from the Plateau Fire’s burn scar into McPhee Reservoir is considered low, according to a recent hydrology report.
Burn specialists and hydrologists flew over the fire area Saturday, focusing on Plateau and Beaver drainages. Monsoonal rains could push some sediment into channels that feed McPhee Reservoir, but it will not be a significant amount, said San Juan National Forest hydrologist Shauna Jensen.
The limited amount of ash on the mesa tops will likely stay there and will not wash into canyons, the report said. Also, the low-intensity fire and unburned areas in the Plateau and Beaver Creek drainages might help filter the sediment.
“This is significant, as it will buffer any sediment that comes from the hill slopes,” Jensen said.
The slopes are mainly a mix of unburned areas and low- and moderate-intensity burns, with isolated areas of high-intensity burns, the report states. Unburned areas and low-intensity burns dominate the area, and moderate-intensity areas make up about one-third of the canyon areas.
The mesa tops surrounding Plateau and Beaver Creek drainages will not contribute a significant amount of sediment to Plateau Creek or Beaver Creek because they have little or no slope, the report states.
A summary states that both Plateau Creek and Beaver Creek drainages are low-gradient streams that are not prone to debris flows.
“There may be some microscale debris flows on the sides of Plateau Creek and Beaver Creek, but there will not be debris flows exiting the mouth of either creek,” Jensen stated.