Preparation of GLOF Hazard- Zonation and Safety and Evacuation Plan for Settlement 50 km Downstream of Imja Khola
The risk of GLOF has been increasing as a result of global warming and consequent melting of snow and ice, retreat of glaciers and expansion of existing glacial lakes, and emergence of new glacial lakes. Imja Glacial Lake was identified as high priority lakes needing immediate attention of GLOF risk reduction. The possible extensive damage is expected to occur along the entire length of the Imja Khola/Dudh Koshi valleys within 50 km. There are 5 VDCs namely Namche, Khumjung, Chaurikharka, Taksinda and Jubing which are located within 50 km distance downstream Imja Lake joining with Dudh Koshi River. This study delineatedflood depth/velocity taking reference from previous hydrological modeling results as well as cross sectional survey performed in 37 selected location of Imja Khola /Dudh Koshi section of the study area. The study area is 50 km downstream from Imja Lake in Solukhumbu District covering about 40 settlements from Chhukum to Chirdi Khola in Imja Khola and Dudh Koshi basin. Geological and geomorphical field observation and measurement followed by mapping was done too assess the geo-physical situation of the study area. Then geomorphic hazard mapping was carried out using terrain parameters (topography, geology, soil properties and landuse) expert rating method following MRE guidelines. Both flood and geomorphic hazard were integrated to produce a combined hazard map. The study also examined the socio-economic vulnerability and exposure of population, properties and infrastructures. In addition, the study identified the 12 evacuation centres connected by safe evacuation routes and supported by the availability existing infrastructure at or near the proposed location. Finally, the study prepared the safety –evacuation plan with earning warning system. The highlight of the study including results and safety- evacuation plan is summarized in the following section:
From the geomorphic hazard assessment following places area identified as high, moderate and low hazard zone.
High hazard area: End moraine wall of Amagablam Glacier, right valley sides near Chubejun Goth, at the several intermittent locations on left valley side slopes from near Kyobo Goth towards downstream to near Cholunche, right valley footslopes of Syormare and at steep slope towards downstream. Both valley side slopes at intermittent sites along the stretches from the Cholunche to Yaren, then from Omaka to Debuche, footslopes near Jandenma and Selawa,fan terrace wall of Manjo,Benkar, foot slope near Toktok and Gumela, Incised fan walls of Phakdin, Chusrma, valley foot slope of Ghat, valley foot slopes near Nurning and Ghat, Alluvial fan terrace wall of Thado Koshiigaon, and steep valley slopes of Nachipang, Muse, Nakchung, and Surke.
Medium hazard area: Most part of the study area lie in Medium hazard zone, which extend from valley foot slopes near Dusum , Chure, Syomare, Chaturje, Pangboche, Selawa to Larcha Dobhan, Similarly themedium hazard area extensive on foot slope, terrace, or fans locatedat Jorsalle, Manjo, Chamuwa, Toktok Gumela, Phakdin, Chermading,Chattuwa, Nurning, Thodo Kosigaon, Nachipang, Ghat Sangma, Nokechung,Surke, foot slope of Pakhapani. These medium hazard zones can be a potential highly hazardous in times of heavy rainfall and GLOF events because susceptibility of the slopes to failure and alluvial or colluvium or moraine deposits could be subject to intense erosion.
Low hazard zones: These zones are generally sites where slope failures are virtually absent such as glaciers, upper eiver or moraine terraces and stable slopes comprised of the hard and competent rock. Such areas include, upper valley slope of Syomare, and village site of Jorsalle, Benkar, Gumela, Thulo Gumela, Nakchung, and Surke.