Numerical modelling of Glacial Lake Outburst Floods using physically based dam-breach models

Abstract

Abstract. The rapid development and instability of moraine-dammed proglacial lakes is increasing the potential for the occurrence of catastrophic Glacial Lake Outburst Floods (GLOFs) in high-mountain regions. Advanced, physically-based numerical dam-breach models represent an improvement over existing methods for the derivation of breach outflow hydrographs. However, significant uncertainty surrounds the initial parameterisation of such models, and remains largely unexplored. We use a unique combination of numerical dam-breach and two-dimensional hydrodynamic modelling, employed with a Generalised Likelihood Uncertainty Estimation (GLUE) framework to quantify the degree of equifinality in dam-breach model output for the reconstruction of the failure of Dig Tsho, Nepal. Monte Carlo analysis was used to sample the model parameter space, and morphological descriptors of the moraine breach were used to evaluate model performance. Equifinal breach morphologies were produced by parameter ensembles associated with differing breach initiation mechanisms, including overtopping waves and mechanical failure of the dam face. The material roughness coefficient was discovered to exert a dominant influence over model performance. Percentile breach hydrographs derived from cumulative distribution function hydrograph data under- or overestimated total hydrograph volume and were deemed to be inappropriate for input to hydrodynamic modelling. Our results support the use of a Total Variation Diminishing solver for outburst flood modelling, which was found to be largely free of numerical instability and flow oscillation. Routing of scenario-specific optimal breach hydrographs revealed prominent differences in the timing and extent of inundation. A GLUE-based method for constructing likelihood-weighted maps of GLOF inundation extent, flow depth, and hazard is presented, and represents an effective tool for communicating uncertainty and equifinality in GLOF hazard assessment. However, future research should focus on the utility of the approach for predictive, as opposed to reconstructive GLOF modelling.

3‐D uncertainty‐based topographic change detection with structure‐from‐motion photogrammetry: precision maps for ground control and directly georeferenced surveys

“…Increasingly, digital photographs are being used to generate such topographic data (particularly from consumer cameras and unmanned aerial vehicles (UAVs)), supported by processing software based on structure from motion (SfM). Such techniques are being used to, for example, model fluvial processes and drive hydraulic models (Woodget et al , ; Dietrich, ; Javernick et al , ), reconstruct the propagation of glacial outburst floods (Westoby et al , ), understand wave run‐up and coastal cliff erosion (James and Robson, ; Casella et al , ), quantify eroded soil and gully volumes (Castillo et al , ; Gomez‐Gutierrez et al , ; Eltner et al , ), examine landslide and glacier movement (Lucieer et al , ; Ryan et al , ), characterise ice surface roughness to parameterise surface melt models (Smith et al , ) and determine the evolution of active lava flows and domes (James and Varley, ; James and Robson, ). The flexibility of SfM‐processing enables a wide range of imagery and imaging geometries to be used and is central to the widespread adoption of HiRT techniques.…”

The State of Remote Sensing Capabilities of Cascading Hazards Over High Mountain Asia

“…DEMs are fundamental inputs when modeling downstream flood propagation, either in first-pass GIS-based assessments (e.g., Huggel et al, 2004;Mergili and Schneider, 2011;Watson et al, 2015;Rounce et al, 2017b) or in physically-based hydrodynamic models (e.g., Westoby et al, 2014aWestoby et al, , 2015Worni et al, 2014;Lala et al, 2018). Spatial and temporal resolution is a limitation in the HMA region where only 30 m resolution global products are widely available, such as the Shuttle Radar Topography Mission (SRTM) or ALOS World 3D (AW3D30) DEMs.…”

“…GMELT provides many of these modeling outputs and forecasted products to help quantify potential changes over HMA on scales that could inform hazard processes, such as how glacier changes may influence glacial lake distributions, areas, and potential glacial outburst floods or how changes in permafrost may affect landslide distributions. Other efforts such as flood routing models can provide a framework for exploring the connectivity among elements in the cascading hazard chains and webs such as the behavior for how a GLOF may impact downstream populations (Westoby et al, 2015;Schwanghart et al, 2016;Rounce et al, 2017a).…”

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

“…Due to the fact that nobody ever witnessed the drainage of the lake during a flood event, there is no data available to simulate a specific event, like the 2011 flooding. Although numerical approaches can be used to model an outburst hydrograph for glacier dammed 20 lakes (Vincent et al, 2010;Westoby et al, 2014), such models could not be applied in our case because most of the necessary parameters like drainage tunnel size, temperature or filling level of the lake are unknown. Therefore, we decided to deal with this parameter uncertainty by modelling different scenarios using a set of parameters (Table 1).…”