Abstract At approximately 18.0 ka, pluvial Lake Bonneville reached its maximum level. At its northeastern extent it was impounded by alluvium of the Marsh Creek Fan, which breached at some point north of Red Rock Pass (Idaho), leading to one of the largest floods on Earth. About 5320 km 3 of water was discharged into the Snake River drainage and ultimately into the Columbia River. We use a 0D model and a 2D non-linear depth-averaged hydrodynamic model to aid understanding of outflow dynamics, specifically evaluating controls on the amount of water exiting the Lake Bonneville basin exerted by the Red Rock Pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the Bonneville basin. These models are based on field evidence of prominent lake levels, hypsometry and terrain elevations corrected for post-flood isostatic deformation of the lake basin, as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood. Internal flow dynamics in the northern Lake Bonneville basin during the flood were affected by the narrow passages separating the Cache Valley from the main body of Lake Bonneville. This constriction imposed a water-level drop of up to 2.7 m at the time of peak-flow conditions and likely reduced the peak discharge at the lake outlet by about 6%. The modeled peak outlet flow is 0.85·10 6 m 3 s −1 . Energy balance calculations give an estimate for the erodibility coefficient for the alluvial Marsh Creek divide of ∼0.005 m y −1 Pa −1.5 , at least two orders of magnitude greater than for the underlying bedrock at the outlet. Computing quasi steady-state water flows, water elevations, water currents and shear stresses as a function of the water-level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the Bonneville Flood: About 18 days would have been required for the outflow to grow from 10% to 100% of its peak value. At the time of peak flow, about 10% of the lake volume would have already exited; eroding about 1 km 3 of alluvium from the outlet, and the lake level would have dropped by about 10.6 m.

中文翻译：

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晚更新世邦纳维尔湖洪水的计算流体动力学模拟

摘要 在大约 18.0 ka 时，洪积湖 Bonneville 达到了最高水位。在其东北部，它被 Marsh Creek Fan 的冲积层蓄水，冲积层在 Red Rock Pass（爱达荷州）以北的某个点破裂，导致地球上最大的洪水之一。大约 5320 公里 3 的水被排放到蛇河排水系统中，最终流入哥伦比亚河。我们使用 0D 模型和 2D 非线性深度平均水动力模型来帮助理解流出动力学，特别是评估 Red Rock Pass 出口岩性和几何形状对离开邦纳维尔湖盆地的水量的控制以及那些由 Bonneville 盆地内部湖泊的几何形状所强加。这些模型基于突出湖泊水位的现场证据，水位测量法和地形高程校正了洪水后湖盆的均衡变形，以及洪水初始和最终阶段出口处的地形重建。洪水期间博纳维尔湖盆地北部的内部流动动态受到将卡什山谷与博纳维尔湖主体分开的狭窄通道的影响。这种收缩使峰值流量条件下的水位下降高达 2.7 m，并可能使湖口的峰值流量减少约 6%。模拟的峰值出口流量为 0.85·10 6 m 3 s -1 。能量平衡计算给出了冲积沼泽溪分水岭的可蚀性系数估计值为 ∼0.005 m y -1 Pa -1.5 ，至少比出口处下伏基岩的可蚀性系数大两个数量级。计算准稳态水流量、水位高度、水流和剪应力作为湖水位下降和出口侵蚀的连续阶段的函数，给出切口速率的估计值和流出量的估计值博纳维尔洪水期间的水文过程线：流出量从其峰值的 10% 增长到 100% 需要大约 18 天。在流量高峰时，约10%的湖水量已经流出；从出口侵蚀约 1 km 3 的冲积层，湖水位将下降约 10.6 m。水流和剪应力作为湖中水位下降的函数以及出口侵蚀的连续阶段，给出了波纳维尔洪水期间切口率的估计值和流出水文过程线的估计值：大约 18 天将有流出量从其峰值的 10% 增长到 100%。在流量高峰时，约10%的湖水量已经流出；从出口侵蚀约 1 km 3 的冲积层，湖水位将下降约 10.6 m。水流和剪应力作为湖中水位下降的函数以及出口侵蚀的连续阶段，给出了波纳维尔洪水期间切口率的估计值和流出水文过程线的估计值：大约 18 天将有流出量从其峰值的 10% 增长到 100%。在流量高峰时，约10%的湖水量已经流出；从出口侵蚀约 1 km 3 的冲积层，湖水位将下降约 10.6 m。