Disastrous Events on Kelash-Mansarowar Route, Dharchula Tehsil in Pithoragarh District, Uttarakhand in India

Localised heavy rains in the early hours of 14 August, 2017 in the catchment of the tributaries of Kali river, particularly Simkhola Gad and Malpa Gad, caused slope instability and damage in Mangti and Malpa areas respectively. As many as 9 persons were died while 18 persons went missing and 51 animals were lost in these incidences that caused heavy loss of other infrastructure and facilities. Changing pattern of rainfall, construction on loose soils/overburden materials, steep slopes, high altitudes, structural weaknesses and slope degradation processes have significantly increased slope instability in the area that has often resulted in devastated in the area. Besides, increasing economic opportunities in the vicinity of the roads encourages people to settle down in the proximity of the roads and streams. The present paper provides causes of devastation and issue related with this disaster with possible mitigation.

As communicated by District Emergency operation Centre (DEOC) Pithoragarh flash flood incidences took place at Mangti and Malpa areas on 14 August 2017 amid heavy rainfall at early morning (2:30 am) in the catchment of the tributaries of Kali River, particularly Simkhola Gad and Malpa Gad. Flash floods and toe erosion induced by incessant heavy rainfall in the devastated areas led to loss of human lives, infrastructure and property. This also triggered landslide and debris flow at many places in the vicinity of the devastated areas. No vehicular movement to Mangti and Malpa was thus possible after this tragedy. However, rainfall data could not be recorded due to the absence of meteorological observatories in devastated areas. The details of the losses are summarized in Table 1.
These devastated areas were investigated after the disaster and traverses were taken around the affected sites to examine the slope instability. Preliminary geological investigations of the study area has been carried out on the basis of Survey of India toposheet numbers 62 B/12 and 62 B/16 on 1:50,000 scale and final field checks. .

Pithoragarh: A disaster-prone district
Pithoragarh district is the easternmost frontier district of the Uttarakhand and falls in lesser and Higher Himalaya. Like any other hilly terrain of the state it is most vulnerable to natural disasters. Available extreme rainfall events are collected from various sources and are described in the sections below. During the monsoons of 1998 major rock fall occurred in Malpa that inflicted heavy losses in Malpa village in Pithoragarh district. More than 200 persons were killed in this incidence [4].
In the year 2005, near Dharchula and Munsiyari areas were badly affected due to cloudburst and heavy rainfall. A number of cultivation land and a bridge at Syangatha were washed off. Madkot area of Munsiyari has been destroyed due to lake formation by the Gori and Kali rivers

The study area
The area investigated lies in the Higher Himalaya in Dharchula Tehsil of Pithoragarh district of Uttarakhand, India and falls in the catchment of Kali River which makes the International boundary between India and Nepal ( Figure 1). Enroute to pilgrimage around KailashMansarovar in Tibet, Chota Kailash and Om Parvat in this region are main attractions. The devastated Mangti area (N 30°00'36.211" and E 80°43'7.925") is located at a distance of 30 kilometers from Dharchula town on the roadway. Malpa area (N 30°03'10.959" and E 80°46'12.755") can be approached by road till near Jibti village that is located at a distance of 36 km towards NNE direction from Dharchula. From Jibti one has to travel on foot for around 7 kilometers to reach Malpa village.

Geomorphology and geology of the area
Geomorphologically, the area is observed to be dissected by several ridges with deep valleys, rising to an elevation of nearly 2050 meters at Malpa area and minimum about 1650 at Mangi area. Geomorphic features of glacio-fluvial/fluvial and colluvial origin are generally observed in the area. The devastated Simkhola Gad is flowing from N-S, suddenly change in nala at Bridge from E-W and then thereafter it is following previous trend while Malpa gad is flowing from N-S with a gradient of 30° and both finally meet with Kali river. The devastated areas show complex landforms in which all aggradational and degradational features were present. In year 1998 huge amount of rock mass fell and destroyed Malpa village resulted huge landslide mass was accumulated over Malpa Gad. Similarly, a large amount of unconsolidated materials was also noticed along the left bank of Simkhola Gad in the area around Mangti. Cutting on the same materials was noticed in these areas by excessive discharge of the streams. The rock exposures on the right bank of Simkhola Gad area were observed to comprise of gneiss interbedded with thin bands of biotite schist belonging to the Rungling Formation of Central Crystallines. The foliation planes were observed to dip towards NE at angles 65º. The joints were observed to dip at steep angles towards NE and SSW (75º/50º and 60º/190º).
The rock exposures in Malpa area were observed to comprise of massive quartzite interbedded with thin bands of garnet-bearing sericite schist belonging to the Pandukeshwar Formation of Vaikrita Group of Central Crystallines. The foliation planes were observed to dip towards NE at angles 55º. Other two prominent structural weaknesses (joints) were observed to dip towards WNW at very steep angles (80º/310º) and towards SSE at steep angles (55º/170º).

Disastrous events of 14 August, 2017
Going to the Border Post Army persons were camped near Mangti area on the left bank of Simkhola Gad on 13 August, 2017. They were also parked their vehicles on the road and bridge at the same place. According to the local people, at early morning (2:30 am) high flash flood discharge of the Simkhola Gad contributed to the instability of the hill slopes of the Mangti area. The course of this gad was temporary blocked and water saturated debris overran the bridge, road and other structures. Around 50 meters road was washed off while barricading of bridge was also damaged in this incidence (Figure 2a). A number of places upstream to bridge around 2-3 meters thick pile of sediments were deposited on the right bank of Simkhola Gad (Figure 2b). The deposited sediments

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Causative factors and suggested measures
Localized heavy rainfall was observed in the areas around Mangti and Malpa in Pithoragarh district in the night of 13 August as also in early hours of 14 August 2017, resulted in flash floods and toe erosion in the Simkhola and Malpa gads respectively, which eventually turned into a disaster. These inflicted heavy losses of human lives, property and infrastructures in devastated areas. Heavy rainfall induced debris flows through streams was the main triggering factor for slope instability in the affected areas.
Additionally, steep slopes, high altitudes, structural weaknesses and infrastructure development initiatives in close proximity of streams, over loose soils/ overburden deposits are the other causative factors.
The devastated areas as Mangti and Malpa in Dharchula tehsil of Pithoragarh district covered under the present study are observed to face flash flood incidences. After the careful examination of geological and geo-environmental history of the area, the following suggestive measures are suggested: • It is suggested that appropriately designed bank protection walls should be constructed along the Simkhola Gad at Mangti area where road was washed off by stream. This practice will protect the road as well as bank of Simkhola Gad from stream erosion. Besides, damaged barricading of exist bridge should also be repaired.
• In the future, existing bridge of Mangti also needs to be relocated to upstream. This would protect the road along with left abutment of Bridge from the threat of flash flood.
• It is suggested that reconstruction of washed off pedestrian trek and bridge around the Malpa area. Alternative connectivity options, such as rope-ways would be better suited for the hills.
• In future recurrence of extreme rainfall events cannot be ruled out and therefore development like temporary camps, tourist camps and realignments of hazardous routes should be needed in safer location.
• Although it is difficult to forecast abnormally high precipitation and associated flash flood events, dense network of rain gauges is required for better understanding of this phenomenon.
• In view of the flash flood threat local population as well as other peoples are advised to stay away from loose soils/overburden materials and way of abandoned channels, particularly during monsoon.

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Discussion and Conclusion
Kali Valley in Pithoragarh district experienced maximum destruction caused by abnormally high precipitation and associated disasters. Geodynamic evolutionary history of the region indicates that Kali Valley is prone to abnormally high precipitation and associated flash floods. Additionally, steep slopes, high altitudes, structural weaknesses, heavy rainfall and increasing anthropogenic interventions in close proximity of streams, over loose soils/overburden materials have added to the devastating potential of the disaster. Concentration of economic opportunities and other facilities in close proximity of the roads encouraged people to settle down by the road side. Increased inflow of trade, tourist and pilgrim traffic in the area only encouraged this trend. All these changes are responsible for enhanced flash flood risk in the area.
Field investigations and the record of recent extreme rainfall events in the region also suggest that the areas in the proximity of streams should be kept free of encroachment and anthropogenic activity of all kinds. Apart from stringent regulation people should be made aware of the risks faced in the vicinity of the streams. During monsoon, relocation of population and infrastructure from high risk areas are suggested as possible solutions. Temporary camps and other facilities in close proximity of streams, over loose soils/overburden deposits is also dangerous, especially during spells of heavy rainfall and therefore such localities should be banned. In case, these activities could not be regulated all suggestive measures would remain a mere formality.