Hydraulics of Solving Unsteady Debris Flow

This report describes methods for determining the depths, velocities, and flow rates of debris flows. As used herein debris flow consists of water rand solid particles sot that the density of the mixture is roughly twice as large as water, and due to the accumulation of large solid particles the viscosity of the mixture is large enough for the flow to exhibit typical laminar flow properties in which adjacent layers slide with respect to each other rather than intermix as occurs in turbulent flows of water for example. A previous report from this project proposed a basic equation for estimating the friction slope in a steady-state debris flow. This report extends the solution capabilities to unsteady open channel debris flows. The assumption is made that the debris flow is separated from the previous water flow by leading surge of debris flow so that downstream there from steady-state, but gradually varied water flow exists. Time varying debris flow exists from this surge back to the beginning of the channel. The channel containing this combination of upstream debris flow and downstream water flow may be non-prismatic, with the slope of its bottom, its bottom width, and side slopes varying with position as given by input data. Examples illustrate the results obtained from the solution methods