"The damage caused by avalanches can be summarized as follows: the dislodgement of stones and soil; damage to pastures and forests, to buildings and communication routes, and finally danger to mankind and to animals."
This sentence, written about a century ago by one of the pioneers in the subject matter, Coaz, is still valid. The fundamental causes of this damage must be sought in topographical and climatic conditions.
It is clear that illegal deforestation at the upper forest limit and uncontrolled grazing (in so far as Crazing damages the forest) have also contributed to increasing the danger.
A more recent factor is the advent of mass tourism which is at the root of the often undisciplined development of buildings and sport complexes in avalancheswept areas. Naturally this last development cannot simply be rejected; rather, some order must be imposed and the appropriate precautions must be taken.
The aim of this manual, which is primarily addressed to those actively engaged in forestry, is to offer these people a choice of practical measures which can be taken. These measures are of two types. As far as buildings, communication routes and pre-existing forests are concerned, there are a number of active methods of combatting the problem:
1. The first is to place isolated buildings of scarce importance away from the path of avalanches. This will not be discussed further, even if in certain cases it is undoubtedly the best solution.
The three other possibilities where use is made of special techniques are:
2. Deviate, contain or brake the avalanches.
3. Anchor the snow in the starting zone.
4. Make use of the effects of wind continually to drive snow away from areas where its accumulation would be dangerous, and thereby cause its settlement in a safe place.
For the future development of a region, passive control can be achieved by good pre-emptive planning in the danger areas. The importance of this cannot be overstressed, for active safety measures are generally extremely expensive.
Finally, one chapter is dedicated to temporary measures which can be taken before a permanent solution is found. Various such solutions can be envisaged, ranging from the evacuation of certain buildings (or the utilization of shelters similar to air-raid shelters if evacuation is impossible), to the closure of approaches to the temporarily dangerous area, or to the more active artificial release of avalanches. The latter is most frequently used to ensure the safety of particular ski runs, or even of roads.
Naturally all solutions must be carefully considered for each particular case. Only the best and cheapest method will be used, although generally this will consist of a combination of various techniques.
This manual is the fruit of a team effort and we must thank especially the members of the FAO group for watershed management who have provided their invaluable collaboration, particularly Professor Benini; Yr. de Crecy, Chief Engineer of GREF and author of Chapters III and IV; Dr. Kronfellner-Kraus; Dr. A. Kravogel; Professor Poncet; Professor Seyberth; the administrative council of "Bundnerwald" in the person of its president, Mir. Bavier; Messrs. W. Bauer, K. Breu, E. Campbell, H. Donni, H. In der Gand, H. Oppliger, F. Pfister, C. Ragaz, B. Rageth, B. Salm, W. Schwarz, A. Sialm and E. Sommerhalder, who all authorized us to use essential extracts from their contributions to "Beiheft 9 zum Bundnerwald" The technical cooperation of FAO in Rome was provided by Messrs. T. Eren and S.H. Kunkle.
Our gratitude extends equally to the Swiss Federal Institute for Snow and Avalanche Research at Weissfluhjoch above Davos, and to its Director, Professor M. de Quervain. The Institute's "Guidelines" of 1968 have been intellectually "plundered". Our gratitude must also, of course, extend to the pioneers at the Institute of the previous generation, who provided the groundwork, in particular Professor Haefeli, and Messrs. E. Bucher and A. Roch; their Austrian colleagues who were pioneers in the techniques of avalanche braking, use of wind, etc: Professor Aulitzki, the Ing. Brugger, E. Hanausek, W. Hassenteufel, J. Hopf and Schilcher, as well as their French colleagues who have already been mentioned above. Also of great importance was the contribution of the Federal Forestry Inspectorate of Berne and its Director, Mr. de Coulon, and the Chief of the Technical Service, Mr. P. Nipkow, who presides over the Swiss group for avalanche defence works; the founder of this group, Mr. A. Janett, and finally of all those experts who have collaborated from far and near in the struggle against avalanches.
One further comment on the "Guidelines" of the Weissfluhjoch Institute: they have been divided up among the relevant chapters with the remainder of the chapters in question being in the nature of a commentary. Furthermore we must remember that the "Guidelines" were prepared by Messrs. de Quervain, the Institute's Director, and B. Salm, engineer, with the assistance of Professor Haefeli of the Federal Laboratory for Materials Testing at Dubendorf, Switzerland, and the Laboratory of Soil Mechanics and Hydraulics of EPFZ in Zurich, Switzerland, and taking into account the practical experience of experts and of industrial enterprises concerned with the problem.
It is important to remember when using these guidelines that the technology of avalanche control cannot be compared to that of civil engineering, for in the latter, the forces at work on a structure are reasonably well known and its behaviour can be predicted with considerable precision; whereas in the realm of avalanche-control technology we often find unknown factors which require special observations, and possibly measurements of natural phenomena on site.
The photographs without credits are from two sources: the early ones are from the archives of the Federal Forestry Inspectorate of Berne and particularly from the collection of Dr. Hess, whereas the more recent photographs are by J.-P. Graf.
Information on the DIN or SIA standards mentioned in the text can be obtained from the following addresses:
DIN: Deutscher Normenauschuss
Burggrafenstrasse 4-7
Postfach
D-1000 Berlin 30
SIA: Secretariat general de la Société suisse des Ingénieurs et des architectes
Selnaustrasse 16, Case postale
CH-8039 Zurich
