Deflecting structures are used to change the direction of avalanche flow. Impact with the structure causes the avalanche depth to increase which adds to the frictional forces at the base of the flow and enables the momentum to decrease. The impact wall is most effective in slowing the avalanche when it is vertical relative to the downhill slope. Many structures are reinforced with earthen backfill.
The increase in depth when the avalanche impacts the structure is a function of velocity (V), deflecting angle (*), and the acceleration of gravity (g). The design height (H) of the structure is the sum of the climbing height (h), flow height (h'), and the snowpack depth (h"). The design height of the structure can then be described by the following equation:
The climbing height (h), or the expected height to which the avalanche flow will move up the impact wall is described by the following equation:
therefore the design height equation becomes:
From this equation it is apparent that with increasing velocity and deflecting angle it is neccessary to increase the design height of the structure to maximize the slowing of the avalanche.
Straight deflecting walls are also used to separate one avalanche flow into two components. This can be accomplished by creating a wedge shaped structure in the center of the flow field area. The avalanche impacts the point of the wedge and is split into the two components thereby contributing some portion of the avalanche to each side of the defense structure which in turn decreases the climbing height.