Superelevation of flowing avalanches around curved channel bends

Abstract

Flowing avalanches are those with a dense core of flowing granular material at the base, which dominates the dynamics causing friction. Sometimes when avalanches descend, they encounter curved channel bends, which cause the flowing material to superelevate or climb up on the wall of the channel bend so that the level of the flowing snow is higher on the outside of the bend than at the center of the channel. This can provide important information about avalanche speeds. The conventional approach for estimating speeds is mathematically equivalent to one developed from equations based on fluid mechanics with a balance between fluid pressure force and centrifugal force to yield a simple expression which relates channel radius, avalanche speed, and superelevation geometry. In this paper, the conventional theory is replaced by one which relates avalanche speed to basal friction (as appropriate for flowing snow), passive snow pressure (accounting for friction between snow particles), channel radius, and superelevation geometry. It is shown that the conventional theory is physically unrealistic for flowing snow modeled as a frictional material. Also, the conventional theory will result in lower speed estimates than the new formulation for the same amount of superelevation.