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

加拿大的大多数北部社区位于沿海地区，为航道、传统狩猎场和重要的文化生态系统服务提供了重要的通道。随着气候变化，由于快速变暖以及相关的冰川退缩和季节性海冰减少，北极变得特别动态。这导致沿海社区的洪水和侵蚀风险增加，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，北极地区的海岸线平均每年后退0.5米左右。这种撤退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，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热应力和机械应力共同作用于海岸，这一过程被称为热机械侵蚀（TME）。当水进入海岸的新区域时，例如在大的浪涌事件期间，就会发生侵蚀。温暖的咸水引起热梯度和咸水梯度，这可以启动永久冻土解冻。解冻的永久冻土土壤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运输。在沿海断崖上，这一过程形成了一个热机械生态位，最终导致块体破裂，使更多的材料暴露在侵蚀应力下。由于大多数用于检查海岸过程的模型都是针对南部海岸线开发的，导致北部侵蚀的独特过程没有得到很好的捕捉，这在知识和工程工具方面都造成了严重的差距。拟议项目的主要目标是开发一个模型，以调查和预测沿永久冻土海岸线的TME。建议的项目旨在采用自底向上的方法进行模型开发，从TME的基本过程开始，并在以后的迭代中构建复杂性。基于先前对TME的经验观察，将开发一个数值模型，将机械过程与密度相关的水流、溶质（盐）输送、以及与盐度相关的冻融热传递联系起来。该模型将通过一组物理模拟实验来验证，以研究暴露在波浪作用下的冻土样品的侵蚀。土壤样品将被放置在一个环境控制单元中，以限制样品的海边表面的热过程。理想化的实验设置将使模型能够根据特定的热机械过程进行评估。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局限性。该项目将培养至少4名HQP（1名研究实习生，2名硕士和1名博士），由INRS和Dalhousie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，该模型可以帮助社区评估沿海退缩的风险，以及加拿大永久冻土海岸线沿线基础设施的设计。

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.