Accelerating global warming has led to the retreat of glaciers and the concurrent expansion of glacial lakes in the Himalayas, increasing the risk of glacial lake outburst floods (GLOFs) with potential to destroy infrastructure and lives in the downstream river valley. In the Sikkim Himalayas, the potentially hazardous Gurudongmar lake complex (GLC) consists of four lakes containing approximately 148 × 106 m3 of water with an enlargement rate of 74 ± 3 %. Therefore, evaluating possible GLOF hazards from GLC under the current scenario is very important. We have presented in this paper an integrated and robust GLOF model that combines the physical moraine-dam breach using TELEMAC 2D and SISYPHE with 1-D inundation modelling using HEC-RAS for the multi-lake complex to estimate the peak flood (m3/s), flood depth (m), and flow velocity (m/sec) and finally assess the downstream inundation exposure. The present study also incorporates different breaching scenarios calculated based on remote sensing and field survey data of surrounding moraine-dam parameters of the GLC. In the largest-cases of GLOFs, with an 80 % overtopping dam breach, the flood peak would reach 5833.7, 7684.0, and 8882.0 m3/s for scenarios 1C, 4C, and 5C, respectively. These floods would release a total volume of 39.9, 48.5, and 59.4 × 106 m3 of water for the three scenarios, respectively. The downstream flood exposure assessment is based on different land use types and flood heights observed across nine scenarios (labelled 1A–5C) for each settlement using a 15 × 15 m fishnet method. The results for all 19 settlement sites along the main Tista River channel show a logical trend of increasing potential exposures. However, when the water volumes from GL-2 and GL-1 or GL-3 and GL-1 are combined, the risk of a potential flood rises. An increase in the potential flood depth directly results in higher exposure to infrastructure. The GLOF exposure levels for each scenario at 19 settlement sites differed. However, the Thangu Valley and Chungthang town have the highest inundation exposure due to their size and potential losses. This research article contributes to developing moraine-dam erosional breach modelling for multi-glacial lake outburst scenarios and downstream flood exposure assessment in the Hindu Kush-Karakoram-Himalayan region.

中文翻译：

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东喜马拉雅山脉多冰川湖溃决过程侵蚀坝决口建模及下游洪水暴露评估


全球变暖加速导致喜马拉雅山冰川消退和冰川湖同时扩张，增加了冰川湖决堤洪水 （GLOF） 的风险，有可能摧毁下游河谷的基础设施和生活。在锡金喜马拉雅山，具有潜在危险的 Gurudongmar 湖综合体 （GLC） 由四个湖泊组成，其中包含大约 148 × 106 m3 的水，扩大率为 74 ± 3 %。因此，在当前情况下评估 GLC 可能造成的 GLOF 危害非常重要。我们在本文中提出了一个集成且强大的 GLOF 模型，该模型将使用 TELEMAC 2D 和 SISYPHE 的物理冰碛坝决口与使用 HEC-RAS 的一维洪水建模相结合，用于多湖复合体，以估计峰值洪水 （m3/s）、洪水深度 （m） 和流速 （m/sec），最后评估下游洪水暴露。本研究还纳入了基于 GLC 周围冰碛坝参数的遥感和野外调查数据计算的不同决口情景。在最大的 GLOF 情况下，如果大坝决口 80%，情景 1C、4C 和 5C 的洪峰将分别达到 5833.7、7684.0 和 8882.0 m3/s。在这三种情况下，这些洪水将分别释放 39.9、48.5 和 59.4 的总体积× 106 m3 的水。下游洪水暴露评估基于使用 15 × 15 m 渔网方法对每个定居点在 9 种情景（标记为 1A-5C）中观察到的不同土地利用类型和洪水高度。蒂斯塔河主河道沿线所有 19 个定居点的结果表明，潜在暴露量呈增加的逻辑趋势。 但是，当 GL-2 和 GL-1 或 GL-3 和 GL-1 的水量组合在一起时，潜在洪水的风险就会增加。潜在洪水深度的增加直接导致对基础设施的风险增加。19 个定居点的每种情景的 GLOF 暴露水平不同。然而，由于面积和潜在损失，Thangu Valley 和 Chungthang 镇的洪水风险最高。本研究文章有助于为兴都库什-喀喇昆仑-喜马拉雅地区的多冰川湖溃决情景和下游洪水暴露评估开发冰碛-大坝侵蚀裂口建模。