Study examines impacts of the Riverside Fire
The Riverside Fire south of Estacada was big and dangerous, but it didn't impact all areas it touched equally.
A study found that of the 137,792 acre Riverside Fire, which began in the Mt. Hood National Forest last month, 18,192 acres (13%) remained unburned; 47,548 acres (35%) experienced a low amount of burn; 55,118 acres (40%) were moderately burned; and 16,934 acres (12%) experienced a high amount of burn.
As of Wednesday, Oct. 28, the Riverside Fire is 72% contained.
The information was released in a burn severity study published by the U.S. Forest Service earlier this month. Burned Area Emergency Response specialists used satellite images to prioritize locations on the ground to assess soil burn severity and collected information on ground cover, ash color, soil depth and structure, intact roots and water repellency.
The information from the study will help determine areas in need of potential emergency stabilization work because of increased soil erosion, accelerated surface water run-off and debris flows.
According to a document published by the U.S. Department of Agriculture, soil with a low burn severity has surface layers that are not completely burned and roots are typically unaffected. In moderately burned soil, up to 80% of the ground has been affected; some roots may be scorched, but they are not typically completely consumed and the soil structure is generally unchanged. With soil experiencing a high amount of burn, all organic matter is usually consumed, soil and ash are susceptible to erosion, and sometimes large tree roots are entirely burned.
Typical characteristics of burned soil include: loss of effective ground cover; color change because of char, ash cover and oxidation; loss of structure; consumption of fine roots; and formation of water repellent layers that reduce infiltration.
"The Soil Burn Severity map isn't an erosion-risk map but does help define areas where potential increases in the rates of erosion and run-off are expected from steep hillslopes with high and moderate soil burn severity. Areas located downstream from moderate and high soil burn severity may experience increased rates of erosion, debris flows, and surface run-off due to cumulative effects," a website for the study states.
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