After a two-year long public enquiry, a new set of rules for risk prevention in the Chamonix valley has finally been passed, though local planning authorities had been using the “unofficial” version of the document in anticipation for the last two years. So-called “natural risks” are a very sensitive issue in Chamonix, especially since the 1999 Montroc avalanche in which 12 people died and a large part of the hamlet was flattened by a giant snow slide. There are in total 110 avalanches couloirs all around Chamonix.
The novelty is the creation of “yellow” areas in addition to the traditional white/blue/red zones. Presently there are 900 buildings in blue or red areas where special dispositions apply, either in terms of building regulations (e.g. new constructions of reconstruction of existing houses is not allowed in red zones) or for the possible evacuation of inhabitants in the event of a threat of natural disaster. The white/blue/red system was based on the likelyhood of natural catastrophes which had historically occured at least once in a hundred years, known as “risque centenaire”, for events such as avalanches, landslides or flash floods.
Yellow zones cover areas where there is a suspicion of very ancient avalanches, up to 300 years ago. No special building regulations have been designed for these areas of Chamonix but authorities are required to put in place evacuation plans, should the risk materialise. In all, 1,700 constructions (chalets, farms etc.) are located in such areas.
