Relocating levees further back from river channels to increase river–floodplain connection can reduce flood stages and provide a host of co-benefits. Modeling case studies show the significant potential of large levee setbacks for reducing flood stages; however, the difficulty of comparing between these case studies limits our understanding of how the hydraulic effects of setbacks vary in different settings. We filled this research gap by systematically modeling the hydraulic effects of setbacks across a range of river and flood conditions. We used unsteady, 1D Hydrologic Engineering Center-River Analysis System models to quantify changes in flood stage, channel velocity, and sediment transport capacity for various setback sizes with different river slopes, widths, floodplain roughness, and flood sizes (peak flows) and durations. Setbacks reduce flood stages within the setback, as well as up- and downstream. Channel velocity and sediment transport capacity both increased upstream and decreased within the setback. Channel slope, flood size, and flood duration had the largest influence on hydraulic changes. There are diminishing returns in hydraulic effects with increasing setback size. These results can help guide the design and prioritization of levee setback projects and help set reasonable expectations for the scale of changes to flood hydraulics relative to the size of the reconnected floodplain.

中文翻译：

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模拟堤坝退缩对洪水水力学的影响

将堤坝重新安置在远离河道的地方，以增加河流与洪泛区的连接，可以减少洪水阶段并提供许多协同效益。模型案例研究表明，大堤退缩对于减少洪水水位具有巨大潜力；然而，这些案例研究之间的比较困难限制了我们对不同环境下挫折的水力效应如何变化的理解。我们通过系统地模拟一系列河流和洪水条件下的挫折的水力效应，填补了这一研究空白。我们使用非稳态一维水文工程中心河流分析系统模型来量化不同河流坡度、宽度、漫滩粗糙度以及洪水规模（峰值流量）和持续时间的各种退缩尺寸的洪水阶段、河道速度和泥沙输送能力的变化。退缩减少了退缩内以及上游和下游的洪水水位。河道速度和泥沙输送能力在上游均增加，在退缩内减少。河道坡度、洪水规模和洪水持续时间对水力变化影响最大。随着挫折大小的增加，水力效应的回报递减。这些结果可以帮助指导堤坝退缩项目的设计和优先排序，并有助于对相对于重新连接的洪泛区大小的洪水水力变化规模设定合理的预期。