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Show under way is a tremendous force, which only the most solid structures, more substantial than those for holding snow in place, are capable of resisting. Tree planting, digging horizontal plots ( terracing), ditching, construction of retaining walls, snow guards, fences and nets, and setting up posts in checkerboard pattern, these are the several methods of holding snow in place. At Kirovsk three experimental snow guards, made of timber supported on rail uprights were installed in a cirque on Mount Ukspor. Results demonstrated that where sufficient snow had accumulated at the retainer guards, snow slides could overrun these barriers; and there was one instance where the great accumulation of snow behind a guard resulted in an avalanche, while nearby, on an unguarded portion of slope, no avalanching occurred. Metal nets, since they do not allow ( undue) snow accumulation, are more practical than snow guards or walls. On slopes with thick snowcover, terrace construction is ineffective because the resultant heavy snow accumulation smooths over the breaks in grade thus created. Where local conditions permit, it is a relatively simple procedure to detour or deflect the moving avalanche from the place needing protection. At the beginning of 1935, on the advice of A. H. Hrgian, our station built directing ( deflecting) snow walls 2- 3 m high at an angle of 30° to the avalanche direction as a protection for the railroad line across the slope of Mount Ukspor. Since the strength of these walls was doubtful, we intended to ice them by watering, but had no chance to do so before the avalanche that took place the night following construction. The avalanche partly overran one wall, but the main snow bulk was turned aside. Following this, snow deflection walls or fences were used extensively. Built at six danger spots, they deflected nearly 100 avalanches from the ( RR) right of way during six winters. Their effectiveness can be gauged from the fact that a properly constructed ( deflection) wall diverted a 10,000 m3 avalanche at a site where a 3,000 m3 slide had blocked the railroad line just before construction of the walls. Aside from this positive aspect, and despite the speed of construction and the insignificant expense as compared with other defensive measures, these deflection walls or fences have a number of serious drawbacks. First of all, the construction of such walls is dangerous for the workers and can be carried out under only the most favorable weather and snow conditions on the slope, often necessitating a wait of several weeks. They can be built only where there is available a sufficient amount of dense snow, which is ordinarily formed during mid winter when much avalanching may have already occurred. Also, though such a snow wall can withstand, on the average, a force of 30 tons per m2 of wall surface, gaining in strength with melting ( and freezing), a large- scale avalanche can overrun these walls easily, flattening them and decreasing their effective height. A project of the Tbilissy Construction Institute was the erection of solid deflection walls of rock by a work brigade on the slope of Mount Aykuayventchorr opposite " December 22" cirque, where a flat- iron dump was left by an avalanche in 1936. These deflection structures consisted of two rock walls each, aligned to cut up and across the slide slope to join in the middle at an angle of 46° and divert the avalanche laterally in two directions. No avalanches have taken place here since construction of the walls, and so no data on their effectiveness are available. One drawback of deflection walls of snow or rock is a consequence of - 61- |