Abstract Effects of lake level fluctuations on coastal bluff erosion in the Great Lakes are pervasive and of significant concern to policy-makers and property owners. Previous studies of bluff erosion have primarily estimated two-dimensional bluff recession rates over years to decades. However, bluff erosion is an irregular process in time and space so averaging coarse resolution observations over long time periods may neglect important processes driving erosion. To address this we use photogrammetric surveys of a Lake Michigan bluff to create four high resolution (10 cm) digital elevation models (DEMs) that span one year with images collected from small unoccupied aerial systems (sUAS). The elevation models were differenced to compare variations in sediment loss to modelled time-series of wave data, atmospheric temperature and lake level. The sub-annual erosion rates calculated from sUAS surveys were compared to long-term recession rates obtained by digitizing historic aerial imagery. The rate of erosion of the bluffs is a time dependent function of two factors: (1) the supply of sediment to lower regions on the bluffs from mass wasting and (2) increased wave erosion resulting from above-average lake levels and intensified onshore wave energy. These factors combine in the early spring when wave energy is elevated and atmospheric temperatures increase, causing reduction in bluff sediment strength by thawing, as well as an increase in porewater pressure from snow melt. Most importantly, above-average lake levels sustained in the longer term (multiple years) are required for the combination of (1) and (2) to result in substantial bluff erosion.

中文翻译：

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响应五大湖水位季节性波动的三维断崖演化

摘要 湖泊水位波动对五大湖沿岸悬崖侵蚀的影响是普遍存在的，并且是决策者和财产所有者的重要关注点。先前对断崖侵蚀的研究主要估计了数年至数十年的二维断崖衰退率。然而，断壁侵蚀是一个不规则的时间和空间过程，因此对长时间的粗分辨率观测进行平均可能会忽略驱动侵蚀的重要过程。为了解决这个问题，我们使用密歇根湖虚张声势的摄影测量调查来创建四个高分辨率（10 厘米）数字高程模型 (DEM)，这些模型跨越一年，其中包含从小型无人航空系统 (sUAS) 收集的图像。高程模型被区分以将沉积物损失的变化与模拟的波浪数据、大气温度和湖泊水位的时间序列进行比较。将 sUAS 调查计算出的次年侵蚀率与通过数字化历史航拍图像获得的长期衰退率进行比较。断崖的侵蚀速率是两个因素的时间依赖函数：(1) 由于质量浪费而向断崖较低地区供应沉积物；(2) 高于平均水平的湖泊水位和增强的陆上波浪导致波浪侵蚀增加活力。这些因素在早春结合起来，当波浪能升高且大气温度升高时，通过解冻导致钝性沉积物强度降低，以及雪融化引起的孔隙水压力增加。最重要的是，(1) 和 (2) 的组合需要长期（多年）维持高于平均水平的湖泊水位，才能导致大量的断崖侵蚀。