Assessment of Geo-hazards and Mitigation Measures at Palchan Station, Manali (Himachal Pradesh)

Palchan station is located near Manali in the Kullu district of Himachal Pradesh (India) at right bank of river Beas and Pagal Nallah along NH-3 at an altitude of 2400 meters (approx.), whereas village Palchan is located towards left bank. In the vicinity of this station, there are threats of avalanches in winters and flash floods during rainy season. The effect of avalanche and flood are studied for the safety measures of the Palchan station.

Three vulnerable points of the Pagal Nallah from where flood may likely to enter into the settlement area during peak flood discharge are considered for the further analysis. In addition to the field visit, optical remote sensing products of this area were also analysed to understand the topography of the terrain, characteristics of the avalanche sites and spreading of debris deposition. The satellite imageries are also used to study the extreme events.

Avalanche flow simulation software developed by DGRE is used to study the threat of avalanche hazard and it was found that the station is not located in the trajectory of avalanche flow path. To estimate the peak flood discharge of Pagal Nallah, different methodologies i.e. based on local flood level indication using Manning’s equation, rational method, Dicken’s formula and Inglis formula were used. The maximum discharge obtained from observed data is 1021 cumecs. The protection structure along the river embankment proposed at three locations each having dimensions 25 m long and 3 m high. These structures are proposed consisting of reinforced stone pitching having welded mesh made up of 10 mm diameter TMT bars at spacing of 35-50 cm C/C. Additionally, a synthetic rubber mat (25 mm thick) with accessories to be placed on top of water side vertical face of protection wall to impart abrasion resistance and provide high impact strength against flowing boulders of varying size from 50 cm to 150 cm.