SENSITIVITY AND APPROPRIATENESS OF DEBRIS FLOW RUNUP AND SUPERELEVATION EQUATIONS

Predictions of debris flow runup and superelevation are important for the sizing of control structures. Runup refers to the elevation gain of a debris flow head as it encounters an adverse slope, such as a barrier at the distal end of a debris flow basin. Superelevation refers to the banking of a channelized debris flow surface as it travels around a bend. The general consensus in the literature is that the leading-edge model can most accurately predict debris flow runup, provided that appropriate estimates can be made for velocity and the apparent friction angle. The forced vortex equation is commonly used to predict superelevation around bends. This method includes uncertainties due to the predicted velocity, measurement of the radius of curvature, and a correction factor applied for viscosity and vertical sorting. Most previous formulations and runup experiments assume that the debris flow will have an approach angle normal to the barrier, with no allowance for oblique impact onto dikes. It should be expected that as the angle of impact with the barrier deviates farther from normal, the debris will experience more superelevation and less pure runup. This paper uses existing data to compare the sensitivity of runup and superelevation equations, the accuracy with which the abovementioned uncertainties can be estimated, and identification of limiting field criteria to differentiate between the appropriateness of runup or superelevation estimations.