Avalanche hazard mapping in Nesa -Gachsar road using geomorphologic and climatic data

Nowadays¡ hazard mitigation strategies in avalanche prone areas¡ rely both on practical experience and avalanche models that predict snow avalanche path¡ run out distance and impact pressure. Increasing the reliability and accuracy of avalanche zoning methods is of primary importance in heavily populated areas. Avalanche hazard zones are defined by the frequency and impact pressure of a potential avalanche event. Potential avalanche is the biggest avalanche that an avalanche path can release and is related to snow supply and path geometry. Therefore it is necessary to accurately estimate the release frequency and release areas for a specific avalanche track. Avalanche frequency can be calculated by analyzing avalanche records. But in the case of lacking data it can be estimated by climatic data. In this research¡ Voellmy-Salm model is used for computing run out distances and velocities for extreme avalanches. Geomorphologic parameters like elevation¡ slope and aspect were derived from DEM¡ or aerial photos interpreting. Then potential avalanche release areas are defined and impact pressure and avalanche volume are calculated for a potential avalanche by dynamic models. Consequently¡ run out distances are defined with respect to avalanche speed that will be zero in run out zone. Finally avalanche hazard zones are defined by impact pressure and avalanche frequency. In this paper we analyzed Karaj road (between Nesa and Gachsar) and provide avalanche hazard map. It can be fined that this area is avalanche prone by analyzing topographic parameters. Steep slopes without dense forests are the most important factor in avalanche releasing. High mountains and climatic parameters can supply instable snow pack that can release. The results show that the road is in red and blue zones.