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Abstract:
Glacial Lake Outburst Floods (GLOFs) are a major hazard in high mountain areas, and can significantly impact transportation infrastructure, human settlements, water supplies, agricultural land, and important cultural and religious locations. Dynamic flow models are widely used for hazard assessment, preparedness planning and to support Early Warning Systems for other destructive sediment flows including flash floods and debris flows, and here we present results of their application and calibration for GLOFs. We use the LaharFlow model (www.laharflow.bristol.ac.uk), a dynamic sediment flow model for hazard assessment, which solves conservation equations for mass and momentum under the shallow layer approximation, to compute the flow dynamic properties. LaharFlow includes parameterizations for erosion and deposition, and the variation in flow solids concentration, friction and landscape change that result, and is freely-available as a webtool. We applied the model to recent case studies that represent a range of GLOF sizes: at Ghulkin (Pakistan, 2022), Shisper (Pakistan, 2020) and Lemthang Tsho (Bhutan, 2015), and also to potential future impacts on Paro (Bhutan). Source conditions were constrained using estimates of lake volumes and idealised hydrographs corresponding to an instantaneous moraine wall failure and slow drainage. The modelling shows good agreement for observed flow depths, speeds, erosion patterns and arrival times using parameters calibrated for other large debris flow settings. For the Paro example, we show how dynamic models can be used to identify locations for, and calibrate, early warning systems, and to assess potential impacts of GLOFs on communities living in high mountain environments.
