Dynamic simulation of catastrophic late Pleistocene glacial-lake drainage, Altai Mountains, central Asia

Numerical simulations of the catastrophic draining of Pleistocene glacial-lake Kuray–Chuja quantify the discharge history of the draining event in detail. The plan-view basin flows are modelled as water emptied due to the instantaneous failure of the impounding ice-dam when the lake was at maximum capacity. The Chuja Basin water exited as a jet-flow into the Kuray Basin via a narrow conjoining valley. The peak discharge from the Chuja Basin is determined to be 1.20 × 10⁷ m³ s⁻¹, and the peak discharge (3.19 × 10⁷ m³ s⁻¹ &gt; <i>Q</i> ≤ 2.0 × 10⁷ m³ s⁻¹) that flowed from the Kuray Basin at the failed impoundment is also calculated for two limiting conditions. The variations in lake volume and depth indicate complete drainage within 50 h. In both basins, fields of relict gravel bedforms reflect sediment transport due to entrained lake-bed sediments. Thus, in addition to the general overview of drainage, the detailed temporal and spatial evolutions of drainage parameters are reported, including for the locations of the bedform fields. Local flow above the bedforms is considered in relation to thresholds for sediment motion, bedform development, and orientations. Within the simple bathymetry of the Chuja Basin, the flow field was fairly uniform with flow conducive to bedform evolution only occurring close to the exit from the basin, which accords with field evidence. In contrast, within the Kuray Basin, the flow responded sensitively to the complex bathymetry, which included rapid changes in flow direction due to interaction of the Kuray water with the jet-flow from Chuja, and as submerged ridges shoaled. Thus the Kuray flow field was complex but with time-dependent flow conditions in accordance with bedform development. It is concluded that the location of the bedforms can be explained in terms of the flow modelling and suggestions are made as to how future drainage models might be improved.

本研究针对更新世冰川湖库赖-楚佳（Kuray–Chuja）的灾难性溃决开展数值模拟，细致量化了该溃决事件的泄流时序演化过程。模拟中设定，当该冰川湖蓄至最大库容时，拦挡的冰坝瞬时溃决，湖水随即尽数泄出，以此构建湖盆的平面流场。楚佳湖盆的水体以射流形式，经由狭窄的连接河谷注入库赖湖盆。经测算，楚佳湖盆的峰值泄流量为1.20×10⁷ 立方米每秒；此外针对两种极限工况，还计算了冰坝溃决时库赖湖盆的峰值泄流量范围为3.19×10⁷ 立方米每秒 > Q ≤2.0×10⁷ 立方米每秒。湖体容积与水深的变化特征显示，整个溃决泄流过程可在50小时内完成。两个湖盆中均分布有古砾石床形地貌群（relict gravel bedforms），其发育特征反映了裹挟湖床沉积物的泥沙输移过程。因此，本研究除概述整体溃泄过程外，还报告了泄流参数的详细时空演化特征，包括床形地貌群的分布位置。同时，研究还结合泥沙起动临界条件、床形地貌发育规律及其取向特征，分析了床形地貌上方的局部流场特征。楚佳湖盆的水深地形较为简单，其流场整体相对均匀，仅在靠近湖盆出口处才出现有利于床形地貌发育的流态，这一结果与野外实测证据相符。与之形成鲜明对比的是，库赖湖盆的流场对复杂水深地形响应极为敏感：库赖湖水体与楚佳湖注入的射流相互作用，加之水下浅脊处水深变浅，导致流向快速变化。因此库赖湖盆的流场结构复杂，且流场条件随时间动态变化，与床形地貌的发育过程高度契合。研究最终表明，床形地貌群的分布位置可通过流场模拟结果得到合理解释；同时，本文还就未来溃泄流模型的改进方向提出了针对性建议。