River morphodynamics research for flood mitigation

这项研究将应用更好地了解河流形态动力过程，以减轻洪水风险。洪水是加拿大最昂贵的自然灾害。近期，全国多个城市发生特大河流洪水。2013年阿尔伯塔洪水淹没了卡尔加里市中心，造成5人死亡，10万人疏散，60亿美元的损失。洪水风险通常定义在1：100年一遇的洪泛区内，洪泛区是在任何给定年份发生概率为1%的河流流动期间预计被淹没的陆地表面。1：100洪水范围通常使用具有固定河床几何形状的一维或二维水动力学模型进行估计。然而，众所周知，洪水期间的沉积物迁移会改变河流的水深，从而加剧洪水水位。例如，在水流障碍物（如桥梁）上游沉积的泥沙会降低当地的水流输送能力，导致河流漫过河岸。同样，洪水期间的沉积物迁移可能导致河流迁移，造成基础设施的灾难性损失。尽管有这样的认识，在洪水期间的地形动力学河床几何形状的变化对洪水位的影响很少被考虑在实践中。此外，简化的一维水力模型，或甚至二维模型，如果没有适当的设计和校准，是不能够预测快速变化的非均匀流洪水位在复杂的景观，如城市中心，有最大的风险。为这些挑战制定解决方案迫在眉睫，因为气候变化似乎正在加速洪水事件的频率和规模，增加现有防洪工程失败的可能性。 对于拟议的研究，我将利用现场，实验室和数值模拟河流表征方法来了解形态动力学过程，空间分布的流量和洪水范围之间的相互作用。该研究将包括空间密集的三维非恒定流场和复杂的城市洪水区的泥沙输运的实地调查。这些现场数据将通过详细的实验室物理模型参数研究进行补充，以检查海岸线基础设施的各种安排对通道形态动力学和时空分布的漫滩洪水位的影响。从这些研究活动产生的数据将被用来开发改进的三维非稳定的形态动力学河流模型，预测在复杂的城市景观漫滩洪水位。这些模型最终将用于制定和评估最佳战略和设计标准，以减轻加拿大河流的洪水风险。因此，这项研究将导致更好地保护加拿大社区免受洪水的影响。

This research will apply better understanding of river morphodynamic processes to mitigate flood risk. Floods are the costliest natural hazard in Canada. Major river floods have occurred recently in cities across the country. The 2013 Alberta flood that inundated downtown Calgary resulted in five deaths, evacuation of 100,000 people, and $6B in damage. Flood risk is typically defined within the 1:100 year floodplain, which is the land surface predicted to be inundated during a river flow with a 1% likelihood of occurring in any given year. The 1:100 flood extent is usually estimated using a 1D or 2D hydrodynamic model with a fixed bed geometry. However, it is known that sediment transport during a flood can change the river bathymetry and thereby exacerbate flood levels. For example, sediment deposition upstream of flow obstructions such as bridges can reduce local flow conveyance capacity, causing the river to flow over its banks. Similarly, sediment transport during a flood can lead to active river migration causing catastrophic loss of infrastructure. Despite this awareneness, the influence on flood levels of morphodynamic river bed geometry change during the flood is rarely considered in practice. Furthermore, simplified one-dimensional hydraulic models, or even two-dimensional models if not properly designed and calibrated, are not capable of predicting rapidly varying non-uniform flow flood levels in complex landscapes such as urban centres where there is greatest risk. Developing solutions for these challenges is pressing, as climate change appears to be accelerating the frequency and magnitude of flood events, increasing the probability that existing flood protection works will fail. For the proposed research I will utilize field, laboratory, and numerical modelling river characterization methods to understand the interactions between morphodynamic processes, spatially distributed flow, and flood extents. The research will include spatially intensive field surveying of three dimensional unsteady flow fields and sediment transport in complex urban flood zones. These field data will complemented by detailed laboratory physical model parametric studies to examine the influence of various arrangements of shoreline infrastructure on channel morphodynamics and spatiotemporally distributed overbank flood levels. The data generated from these research activities will be utilized to develop improved 3D unsteady morphodynamic river models to predict overbank flood levels in complex urban landscapes. These models will ultimately be used to develop and evaluate optimal strategies and design standards to mitigate flood risk in Canada's rivers. This research will thus lead to better protection of Canadian communities from flooding.