Articles | Volume 15, issue 10
Nat. Hazards Earth Syst. Sci., 15, 2425–2437, 2015
Nat. Hazards Earth Syst. Sci., 15, 2425–2437, 2015

Research article 26 Oct 2015

Research article | 26 Oct 2015

Repeated glacial lake outburst flood threatening the oldest Buddhist monastery in north-western Nepal

J. Kropáček1,2, N. Neckel1,a, B. Tyrna1,3, N. Holzer2, A. Hovden4, N. Gourmelen5,6, C. Schneider7, M. Buchroithner2, and V. Hochschild1 J. Kropáček et al.
  • 1Department of Geography, University of Tübingen, Ruemelinstr. 19–23, 72070 Tübingen, Germany
  • 2Institute for Cartography, Dresden University of Technology, Helmholtzstr. 10, 01069 Dresden, Germany
  • 3Geomer GmbH, Im Breitspiel 11b, 69126 Heidelberg, Germany
  • 4Department of Culture Studies and Oriental Languages, University of Oslo, Niels Henrik Abels vei 36, 0371 Oslo, Norway
  • 5Institut de Physique du Globe de Strasbourg, Université de Strasbourg, 5 Rue René Descartes, 67084 Strasbourg CEDEX, France
  • 6School of Geosciences, University of Edinburgh, Geography Building Drummond Street, Edinburgh, EH8 9XP, UK
  • 7Department of Geography, RWTH Aachen University, Templergraben 55, 52056 Aachen, Germany
  • anow at: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

Abstract. Since 2004, Halji village, home of the oldest Buddhist Monastery in north-western Nepal, has suffered from recurrent glacial lake outburst floods (GLOFs). A sudden englacial drainage of a supraglacial lake, located at a distance of 6.5 km from the village, was identified as the source of the flood. The topography of the lake basin was mapped by combining differential Global Positioning System (DGPS) measurements with a structure-from-motion (SFM) approach using terrestrial photographs. From this model the maximum filling capacity of the lake has been estimated as 1.06 ×10^6 m3 with a maximum discharge of 77.8 m3 s−1, calculated using the empiric Clague–Mathews formula. A simulation of the flooded area employing a raster-based hydraulic model considering six scenarios of discharge volume and surface roughness did not result in a flooding of the village. However, both the village and the monastery are threatened by undercutting of the river bank formed by unconsolidated sediments, as it already happened in 2011. Further, the comparison of the GLOF occurrences with temperature and precipitation from the High Asia Reanalysis (HAR) data set for the period 2001–2011 suggests that the GLOF is climate-driven rather than generated by an extreme precipitation event. The calculation of geodetic mass balance and the analysis of satellite images showed a rapid thinning and retreat of Halji Glacier which will eventually lead to a decline of the lake basin. As the basin will persist for at least several years, effective mitigation measures should be considered. A further reinforcement of the gabion walls was suggested as an artificial lake drainage is not feasible given the difficult accessibility of the glacier.

Short summary
The supraglacial lake basin was mapped by DGPS and the SFM approach from terrestrial photographs. The maximum filling capacity of the lake was estimated, with a maximum discharge of 77.8 m3/s, calculated using an empirical relation. The flooded area in the valley was delineated by employing a raster-based hydraulic model. A coincidence of the GLOF events with high values of cumulative above-zero temperature and precipitation calculated from the HAR data set was revealed.
Final-revised paper