Design of snow avalanche deflecting dams

Abstract

Extensive effort has been put into improved understanding of avalanche deflection over the last two years. This paper discusses construction of deflecting dams in steep terrain, and gives an in-depth description of the recent design of two deflecting dams in western Norway. The design is based on a computationallempirical approach convenient for practitioners. Trajectories and preliminary run-up heights on the deflecting dam are fIrst calculated using a centre-of-mass model based on the Voellmy-Perla equation. To compensate for the limitations of a centre-of-mass consideration, the run-up heights are subsequently calibrated utilising observations of six full-scale avalanches in terrain formations acting as "natural deflecting dams". The functionality of the two dams is demonstrated by comparisons between the design criteria and the observations of four major avalanches impacting the two darns shortly after completion. The validity of the method is further demonstrated by comparison of calculated and observed run-up heights for avalanches impacting the deflection dam in Flateyri, Iceland. The observations on the constructed dams are fmally used to update the calibration procedure.