Periodic Glacial Lake Outburst Floods threatening the oldest Buddhist monastery in north-west Nepal

Abstract

Since 2004 Halji Village, home of the oldest Buddhist Monastery in north-west Nepal has suffered from recurrent Glacial Lake Outburst Floods (GLOFs). Studies of recent satellite images identified a supra-glacial lake, located at a distance of 6.5 km from the village, as a possible source of the flood. During a field survey in 2013, the finding was confirmed and several entrances to en-glacial conduits which are draining the lake were found. The topography of the lake basin was then mapped by combining Differential Global Positioning System (DGPS) measurements with a Structure From Motion (SFM) approach from terrestrial photographs. From this model the maximum filling capacity of the lake has been estimated as 1.06 × 106 m3 with a maximum discharge of 77.8 m3 s−1 calculated using an empirical relation. The flooded area in the valley has been estimated by employing a raster-based hydraulic model considering six scenarios of discharge volume and surface roughness. To understand the changes in glacier geometry in the last decade the thinning and retreat of Halji Glacier have been analysed by geodetic mass balance measurements and a time series of satellite images respectively. The GLOF occurrences have further been correlated with cumulative temperature and cumulative liquid precipitation calculated from the High Asia Reanalysis (HAR) dataset. Finally, effective mitigation measures and adaption strategies for Halji village have been discussed.