Developing a model to assess the erosion of permafrost coastlines in Northern Canada

加拿大的大多数北方社区都位于沿海地区，那里是通往航道、传统狩猎场和重要文化生态系统服务的关键通道。随着气候变化，北极由于迅速变暖和相关的冰川退缩和季节性海冰减少而特别活跃。这导致沿海社区遭受洪水和侵蚀的风险增加，因为更多的开放水域导致更高的海浪和风暴潮。这些压力导致许多地区的海岸线迅速后退，北极地区平均每年后退约0.5米。这种退缩对社区产生了重大影响，因为它威胁到基础设施，文化遗址和淡水资源，并产生连锁反应，例如将污染物和储存的碳释放回环境中。与温带和热带海岸线不同，永久冻土海岸线的侵蚀是由于通过称为热机械侵蚀（TME）的过程作用于海岸的热和机械应力。当水进入海岸的新区域时，例如在大的浪涌事件期间，可能会发生侵蚀。温暖的盐水会引起温度和盐浓度梯度，这可能会引发永久冻土融化。融化的永久冻土大大降低了土壤强度，因此很容易通过波浪和水流的机械作用被侵蚀和搬运。在沿海的悬崖上，这一过程形成了一个热机械生态位，最终导致块体破坏，使更多的材料暴露在侵蚀应力下。由于大多数用于研究沿海过程的模型是为南部海岸线开发的，没有很好地捕捉到北部驱动侵蚀的独特过程，从而在知识和工程工具方面造成了严重的差距。拟议项目的主要目标是开发一个模型，以调查和预测TME沿着永久冻土海岸线。拟议的项目旨在采取自下而上的方法来开发模型，从TME的基本流程开始，并在以后的迭代中建立复杂性。根据以前的经验观察TME，将开发一个数值模型，机械过程与耦合密度相关的水流，溶质（盐）运输，和热传递与盐度相关的冻融。该模型将使用一组物理模拟实验进行验证，以调查暴露于波浪作用的冻土样品的侵蚀。土壤样品将被放置在环境密封装置中，以限制样品海滨表面的热过程。理想化的实验装置将使该模型进行评估，对特定的热机械过程。还将进行实地活动，以帮助确定数值模型和物理模型实验的关键限制。该项目将培训至少四名HQP（一名研究实习生，两名硕士和一名博士），由INRS和达尔豪西大学共同监督。该项目将为开发一个模型提供一个重要的起点，该模型可帮助社区评估沿海后退的风险以及加拿大永久冻土带沿着基础设施的设计。

Most Northern communities in Canada are located in coastal areas, which provide critical access to shipping lanes, traditional hunting grounds and important cultural ecosystem services. With climate change, the Arctic has been particularly dynamic due to rapid warming and associated glacier retreat and seasonal sea ice reduction. This has led to an increasing risk of flooding and erosion in coastal communities, as more open water results in higher waves and storm surges. These stresses have contributed to the rapid retreat of the coastlines in many areas, with the average retreat in the Arctic around 0.5 m per year. This retreat has a significant impact on communities as it threatens infrastructure, cultural sites, and freshwater resources, with cascading impacts such as releasing pollutants and stored carbon back into the environment.Unlike for temperate and tropical coastlines, the erosion of permafrost coastlines is due to both thermal and mechanical stresses acting on the coast through a process known as ThermoMechanical Erosion (TME). Erosion can occur when water accesses new areas of the coast ' for example, during a large surge event. The warmer, saline water induces thermal and saline gradients, which can initiate permafrost thaw. Thawed permafrost soils have greatly reduced soil strength and can therefore be easily eroded and transported through the mechanical action of waves and currents. At coastal bluffs, this process forms a thermomechanical niche, eventually leading to block failure that exposes more material to erosive stresses. As most models used for examining coastal processes were developed for southern shorelines, the unique processes driving erosion in the North are not well captured, creating critical gaps in both knowledge and engineering tools. The primary objective of the proposed project is the development of a model to investigate and predict TME along permafrost coastlines. The proposed project aims to take a bottom-up approach to model development, starting with the fundamental processes of TME and building in complexity at later iterations. Based upon previous empirical observations of TME, a numerical model will be developed that links mechanical processes with coupled density-dependent water flow, solute (salt) transport, and heat transfer with salinity-dependent freeze-thaw. The model will be validated using a set of physical modelling experiments to investigate the erosion of frozen soil samples exposed to wave action. The soil sample will be placed in an environmental containment unit to limit thermal processes to the seaside face of the sample. The idealized experimental setup will enable the model to be evaluated against specific thermomechanical processes. A field campaign will also be performed to help identify key limitations of the numerical model and physical model experiments. The project will train at least four HQP (one research intern, two Masters and one PhD) jointly supervised between INRS and Dalhousie University. This project will provide an important starting point for the development of a model that can aid communities in assessing the risk of coastal retreat as well as the design of infrastructure along Canadian permafrost coastline.