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Show much of the past, especially records of unusual and extreme avalanches. But it is just these slides that are most important for avalanche zone planning. It is regretable that not much progress has been made in compiling a Swiss avalanche cadaster, but some cantons and many communities have not yet been included in the project. Summaries of avalanches which have caused accidents and damage, are published since 1936/ 37 by the SLF Institute in yearly winter reports. These reports can also be used as a source of information. On- site inspection of the terrain offers one an opportunity of asking those who live and work there what they have observed about avalanches. Information given by laymen has to be accepted with caution. However, farmers who live in mountain areas often recollect clearly damage done to land, forests, living quarters and farm buildings remarkably far in the past. Such knowledge is often the only criterion regarding past avalanche occurrence. Avalanche events have also been recorded as part of history. While most pertinent information must be collected laboriously from old calendars, palaeographs, community records, local magazines and local history, some towns and communities have maintained an avalanche chronicle of their own. Yet the historian was mostly interested in how many people were killed, and how many homes were damaged, than in giving information on the actual extent of the avalanche itself. But summary information in a chronicle can often yield valuable contributions. For example: one would have been much better advised in preparing the avalanche zoning map for the area of Egga Boden in Davos, if more weight had been given to information found in a chronicle dealing with the avalanche on 3 March 1609, rather than to recently observed avalanches. Avalanche control structures in areas of avalanche zone planning must be examined to determine their effectiveness. Most supporting structures built in the starting zone of avalanches do not provide the necessary protection that was expected of them when installed. Opinions concerning the effectiveness of such structures are frequently too optimistic, but optimists are often desired in the realm of human relations. False optimism used in engineering these structures can have fatal consequences, for which several examples could be cited. Somewhat more caution and maybe more factual knowledge- good examples excepted-- would be useful in building avalanche control structures. Proof of the effectiveness of supporting structures can often be obtained by simply looking at the state of the reforestation below them. If no success is observed with it, the control structures must be considered inadequate for that area. For many people, this is a bitter pill to swallow, but it must be strongly emphasized here to prevent future failures. IV. Legal Aspects of Avalanche Zone Planning It was pointed out in the chapter dealing with the historical aspect of avalanche zone planning that the tremendous construction developments in some tourist resorts have created new problems for the building commissions. An example is the protection of the population against avalanche danger. Under the pressure of necessity, certain communities established avalanche 14 |
