Case Study of Debris Flow

A debris flow is defined as soil with entrained water and air that moves readily as a fluid on low slopes. A case history of a debris flow adjacent to the Pauma Indian Reservation is described. Two contributing factors in the debris flow were the cutting down of trees and the construction of haul roads. The debris flow travelled a long way (370 m) in the depositional area before striking a house. Fortunately, by the time the debris flow reached the house, the energy was nearly spent and there was no damage to the structural frame. The material involved in the debris flow was classified as silty sand. Results of laboratory tests indicate that this type of soil is susceptible to debris flow. There is a range of coefficient of permeability from about 10⁻² to 10⁻⁶ cm/s that corresponds to soils that have an optimum soil permeability for long‐distance flow in the depositional area. Based on the historical method, it is probable that there will be future debris flow in this area.