One-dimensional hydraulic modelling of glacier lake outburst flood (GLOF) in Hunza sub-basin of Karakoram

Karakoram glacier lakes develop at high altitudes. Size of the glacier lake, the outburst mechanism, and the characteristics of floodplains are few driving forces that define glacier lake outburst flood (GLOF) hydraulics. This study analysed and compared ice-dammed GLOF hydraulics of two events in Hunza basin, including velocity, flood-flow and flow-area, using one-dimensional (1-D) steady state model. Moreover, a correlation is established between normalized indices for vegetation, water and moisture and GLOF events. Observations reveal that seepage, a sudden debris and dammed-water inrush through the subglacial path into impounded but retreating glacier termini is a key triggering factor for drainage of the lake twice, catastrophically. The transfer of GLOF momentum between the gorge and the adjacent floodplains significantly affected the shear-stress distribution in floodplain and gorge’s sub-sections. Moreover, the surface slope ∇zs of GLOFs played a vital role in the destruction of infrastructure than the riverine bed slope. These two GLOFs carry plenty of sediment and boulders and changed the fluid flow physics and made the “basic hydraulic assumptions in HEC-RAS” unsuitable for hydraulic modelling of GLOFs evolving in mountainous regions.