Debris Flow in Ada County, Idaho

Heavy rainfall rates on the recent Valley Fire burn scar created a debris flow that ran down the entire length of Highland Valley, half of which flowed into the Boise River and the other half into a canal. The slurry heavily impacted a community along Warm Springs, running water/slurry could have been anywhere from 3 to 8 ft in height, swept a truck into a fence, only being caught by other debris. Lawns were covered in debris and a white picket fence would have been submerged in the flow. This came from a storm with a peak rain rate of 7 inches per hour that remained over Lucky Peak for an extended period of time.

Monsoonal moisture surged into the region over a three day period, the most intense of which was the 26th. High atmospheric moisture content combined with weak flow in a monsoonal pattern to produce very moist storms moving very slowly. Additionally, as terrain served as the main trigger for convection, storms would train over the same spots for much longer than normal. Precipitable water was at near record levels around 1.2 inches.