River morphodynamics research for flood mitigation

这项研究将更好地了解河流地貌动态过程，以减轻洪水风险。洪水是加拿大代价最高的自然灾害。最近，全国各地的城市都发生了大江大洪水。2013年艾伯塔省洪水淹没了卡尔加里市中心，造成5人死亡，10万人疏散，损失60亿美元。洪水风险通常被定义在1：100年泛滥平原内，该泛滥平原是指在河流流动期间预计将被淹没的陆地表面，在任何给定的一年发生的可能性为1%。1：100洪水范围通常使用固定河床几何形状的一维或二维水动力模型来估计。然而，众所周知，洪水期间的泥沙输送会改变河流的水深，从而加剧洪水水位。例如，桥梁等水流障碍物上游的泥沙淤积会降低当地的水流输送能力，导致河流漫过堤岸。同样，洪水期间的泥沙输送可能导致河流的活跃迁移，造成基础设施的灾难性损失。尽管人们意识到了这一点，但在实践中很少考虑洪水过程中河床几何形态变化对洪水水位的影响。此外，简化的一维水力模型，甚至是二维模型，如果没有适当的设计和校准，就不能预测城市中心等风险最大的复杂地貌中快速变化的非均匀流洪水水位。制定应对这些挑战的解决方案迫在眉睫，因为气候变化似乎正在加快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，我将利用野外、实验室和数值模拟河流特征的方法来了解地形动力学过程、空间分布的水流和洪水范围之间的相互作用。这项研究将包括空间密集的三维非恒定流和复杂城市洪泛区泥沙输运的现场测量。这些现场数据将得到详细的实验室物理模型参数研究的补充，以检查不同的海岸线基础设施布置对河道地貌动力学和时空分布的漫滩洪水水位的影响。这些研究活动产生的数据将被用于开发改进的3D非稳定地形动力学河流模型，以预测复杂城市景观中的漫滩洪水水位。这些模型最终将用于开发和评估最优战略和设计标准，以减轻加拿大河流的洪水风险。因此，这项研究将有助于更好地保护加拿大社区免受洪水侵袭。

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.