Tree Debris Dam Formation and Breach

Approximately 711 yd (650 m) upstream of Highway 1, two contributing streams to Rat Creek merge. This is also the location of a large tree and debris dam that was identified by the reconnaissance team. Breach of this dam was likely rapid, and the released water gained significant energy descending the about 1,969 ft (600 m) in elevation from the dam to the exit point of Rat Creek at Highway 1. The area upstream of the dam was completely unvegetated compared to low green vegetation on the side slopes because it was likely submerged by the debris dam. Just below the debris dam, two stream channels were scoured owing to the presence of a large redwood tree in the middle. The main breach location of the tree debris dam must have breached with high intensity and a significant volume of water because of the amount of damage and scour observed in the breach section.