This paper addresses subaqueous and subaerial patterns of geomorphic change across Montrose Beach, an urban embayment along Chicago’s engineered SW Lake Michigan coastline. Our goal was to better characterize the urban littoral zone, its sediment-transport processes, and associated shoreline morphodynamics (from the early 1950s to present). Succinct beach geomorphic responses to decadal base-level changes (i.e., regression during lake-level fall and transgression during lake-level rise) occurred once a morphologic threshold in the subaqueous portion of the system had been crossed. Despite continuous sand trapping, nearshore elevations were initially not conducive to promoting expansion of the subaerial beach environment, regardless of water-level condition. Rapid beach expansion after 1990 (by a factor of four in <25 years) was facilitated by prior decades of nearshore accretion. Shoreline morphodynamic trajectories and degree of coupling to nearshore sedimentary processes are important considerations for developing long-term beach-management strategies. Rapid cross-shore movements of the shoreline in response to oscillatory base levels are expected to persist at Montrose and other urban beaches of similar design (and nearshore conditions). This has important implications for managing urban lakefront ecosystems, including coastal dunes and shore-bird habitats. Few datasets have thus far quantified time-variant and threshold-driven patterns of beach geomorphic development along engineered coastlines. Such insights should help coastal managers better understand littoral sediment interconnectivity across the urban lakefront and anticipate future geomorphic trajectories of beach environments with anticipated decadal-scale oscillatory patterns in lake level.

本文探讨了蒙特罗斯海滩的水下和水下地貌变化模式，蒙特罗斯海滩是芝加哥工程西密歇根湖海岸线沿线的一个城市海湾。我们的目标是更好地描述城市沿海地区、其沉积物运输过程以及相关的海岸线形态动力学（从 1950 年代初至今）。一旦跨越系统水下部分的形态阈值，就会发生对十年基准水平变化的简洁海滩地貌响应（即湖平面下降期间的回归和湖平面上升期间的海侵）。尽管有持续的沙子捕获，但无论水位状况如何，近岸海拔最初都不利于促进水下海滩环境的扩张。1990 年后海滩的快速扩张（在 25 年内增长了 4 倍）得益于前几十年的近岸增生。海岸线形态动力学轨迹和与近岸沉积过程的耦合程度是制定长期海滩管理战略的重要考虑因素。预计在蒙特罗斯和其他类似设计（和近岸条件）的城市海滩，海岸线响应振荡基准水位的快速跨岸运动将持续存在。这对管理城市湖滨生态系统具有重要意义，包括沿海沙丘和滨鸟栖息地。迄今为止，很少有数据集能够量化沿工程海岸线的海滩地貌发展的时变和阈值驱动模式。这些见解应该有助于沿海管理者更好地了解整个城市湖滨的沿海沉积物相互联系，并预测未来海滩环境的地貌轨迹，以及湖平面上预期的十年尺度振荡模式。这对管理城市湖滨生态系统具有重要意义，包括沿海沙丘和滨鸟栖息地。迄今为止，很少有数据集能够量化沿工程海岸线的海滩地貌发展的时变和阈值驱动模式。这些见解应该有助于沿海管理者更好地了解整个城市湖滨的沿海沉积物相互联系，并预测未来海滩环境的地貌轨迹，以及湖平面上预期的十年尺度振荡模式。这对管理城市湖滨生态系统具有重要意义，包括沿海沙丘和滨鸟栖息地。迄今为止，很少有数据集能够量化沿工程海岸线的海滩地貌发展的时变和阈值驱动模式。这些见解应该有助于沿海管理者更好地了解整个城市湖滨的沿海沉积物相互联系，并预测未来海滩环境的地貌轨迹，以及湖平面上预期的十年尺度振荡模式。