Warning Systems and Hazard Mapping Formation zone avalanche control scheme at D-IO avalanche site on National Highway, Jammu-Srinagar (India): A case study Vinay Chaudhary *, Praveen Mathur and Gurpreet Singh Snow and Avalanche Study Establishment, Chandigarh, India Abstract: The Pir Panjal range in the Indian Himalaya in Jammu and Kashmir state lies in the lower Himalayan region between latitude 33°10' and 34°40'N. This region experiences short winters (2-3 months) and moderately high snow precipitation having high moisture content, high temperatures and direct action avalanche activity. The area also experiences very high drift activity. Due to the above conditions which are typical to the lower Himalaya region, the conventional structures for control of avalanches in formation zone are relatively very expensive. Keeping this in view it is desirable to follow a composite scheme having combination of wind control structures, supporting structures, terrain modification and controlled release of avalanches using explosives. The above has been done at an experimental site located on a mountain ridge in Pir Panjal range of Himalayas under which 2.6 kID long tunnel joins the National Highway from south to north. Among 15 avalanche sites on this highway, D-I0 is one of the most important sites with very high frequency of avalanche triggering. The mouth of the tunnel gets blocked frequently due to D-l 0 avalanche. Since the catchment is very large and the snow accumulation pattern is quite different in various gullies, a composite scheme to use various types of formation zone control measures was worked out, both from the point of controlling the avalanches as well as understanding the efficacy of this scheme evolved for D-lO experimental site. This paper describes the composite avalanche control scheme, modification made in the design of Snow nets and the effectiveness of structures observed during last four winters from 1998-2002. Keywords: Avalanche defence, snow drifting, snow fence, snow load on structures, controlled release of avalanches 1. Introduction Indian Himalayan ranges, experience a wide diversity in climatic and precipitation patterns so that the snow properties and related avalanche activity assume a wide variation. The avalanche affected area in Indian Himalaya lies in Western Himalaya, Central Himalaya and North Eastern Himalaya. From climate and avalanche activity point of view, Sharma and Ganju (1999) have classified the Western Himalaya in three zones as, Lower Himalayan zone (LHZ) or subtropical zone, Middle Himalayan zone (MHZ) or Mid Latitudinal zone and Upper Himalayan zone (UHZ) or High latitudinal zone. D-I0 experimental site situated in Pir Panjal range in Jammu & Kashmir falls in the Lower Himalayan zone. Geological and climatic conditions of Pir Panjal range are entirely different from Alpine ranges. The LHZ could be classified as the zone of warm temperature, high precipitation and short winter period. The precipitation is generally concentrated between December and March with the periods before and after experiencing wet snow precipitation * Corresponding author address: Vinay Chaudhary, SASE-RDC, Himparisar, Sector 37 A, Chandigarh 160036, India; tel: 0172-699804-06; fax: 0172- 699802; email: vinay_sase@rediffinail.com 569 or rains. Due to prevalence of warmer temperatures, the snow cover very soon changes into isothermal snow pack at O°e. The avalanche activity is quite high, with most of the avalanches triggering during snowfall as direct action avalanches due to excessive overburden or within 24 hours after a major snowfall on a clear sunny day. The peak winter avalanches are generally moist slab avalanches and late winter avalanches are melt avalanches (thaw avalanches) containing snow, mud and stones. The terrain and meteorological factors characterizing LHZ are shown in Table 1. The salient deductions regarding the avalanche occurrence in LHZ are as follows: (Sharma and Ganju : 1999). Major avalanches occur: • During snowstorms when overburden exceeds 200 Kg/m 2 after terrain irregularities get filled up with 150 cm of standing snow; • within 24 h of storm on a clear sunny/windy day; • radiation may cause loose snow surface avalanches; • in spring, after snow-pack becomes isothermal, full-depth or even surface avalanches trigger; • few delayed action avalanches on northern slopes trigger.