UDOT crews are working hard to clear debris and reestablish drainage in the area of the Seeley Fire where a flash flood stripped the area of trees, rocks and soil and shut down SR-31.
The flooding occurred during a rain storm on August 1 in the Manti-La Sal National Forest in southeastern Utah. The storm dropped about one and a quarter inch of rain in a half hour. Although similar storms are fairly common in the forest, this storm “was enhanced by the fire,” says Jim Chandler, UDOT Region Four Area Engineer.
“When fires go through the forest, they can make the soil hydrophobic,” explains Chandler. The temporary soil condition can occur when burned material takes up the empty pore spaces where water would normally seep in. In just a short space of time, the runoff “hit rocks and trees and brought them down the canyon,” says Chandler. “The fire just created the perfect condition to wash everything away.”
And much of the debris ended up on SR-31. Chandler says in one spot, rock, soil and trees were piled over 6 feet high. UDOT crews from the Huntington, Wellington, Colton, Emery, Mt. Pleasant and Gunnison Maintenance Stations “worked hard day after day moving a lot of material and trees,” says Chandler. Given that the road was open one week later, their effort was “quite amazing.”
The run-off that occurred during the flash flood also caused scour in stream beds and in other natural run-off areas, according to Darren Olsen, U.S. Forest Service District Ranger. Olsen says the USFS is planning some mitigation to prevent similar flash floods in the future.
Because of the volume of debris flow, the most challenging part of the erosion repair effort for UDOTis cleaning out and restoring culverts and cut ditches “so that the water that does reach the road can pass through with minimal damage to the road” says Daryl Friant, UDOT District Engineer. During a storm, runoff flows along the road in cut ditches and the under the road through culverts.
UDOT is also in the process of rebuilding the road in two areas where water flow washed out embankment and shoulder and one area where water flowed over the road and caused pavement to break up.
Work will continue through fall, according to Chandler. “They’ll be out there until the snow flies,” getting drainage established in order to make the area safe for the traveling public.