The fate of water from melting ground ice in degrading permafrost environment

在影响加拿大北部可持续发展的与永久冻土退化有关的地质灾害中，普遍存在融化下沉的脆弱性。多年冻土的融沉固结与含水率、冻融结构、土质、融化速率和孔压消散密切相关。然而，人们对融化的地面冰中的水在多年冻土退化中的命运知之甚少。孔隙水耗散是如何控制融化固结的？融化的水流入地下的地方呢？融水是在向深处的含水层补充能量，还是在地表迁移，最终进入湖泊、河流和海洋？ 作为一种研究假说和正反馈，融沉依赖于孔压的消散，加速了多年冻土的退化速度。地表暖边界向下向深层退化的多年冻土体移动，加速了多年冻土的融化。 为了验证这一研究假设，目标是： 1)在现场观察、描述和监测永久冻土退化过程， 2)通过室内试验测量富冰多年冻土的融化固结特性， 3)模拟多年冻土融化过程中融水的传热、融化固结和流动， 4)将这些模拟过程与观测结果进行比较，以及 5)对未来多年冻土的退化进行预测。 研究地点位于加拿大魁北克北部靠近Umiujaq的不连续的永久冻土带，那里的富含冰的永久冻土丘已经在退化。几个地点已经有了一系列长期监测的地温和融化沉降数据。 本研究计划中使用的方法在很大程度上依赖于使用不同监测技术(自动热敏电阻电缆、水位记录仪、激光雷达测量以及可见光和红外摄影测量)、岩土和地球物理工具(多年冻土采样、电阻率和地震折射层析成像)以及对富含冰的多年冻土样品进行的实验室测试(融化固结和水力传导性)进行的仔细实地观察得出的地面真实情况。将对热-水-机械过程进行数值模拟，以模拟不同气候变化情景下的永久冻土退化。 这项研究计划的预期结果是更好地了解多年冻土退化过程中发生的物理过程，并改进热传递的数值模拟，包括相变、融化固结、融水迁移和流动，以预测气候变化导致的永久冻土退化。根据本研究项目所发展的知识，可以制定适应策略，以确保加拿大北部的可持续发展。

Among the geohazards associated with permafrost degradation which impact the sustainable development of Northern Canada, the vulnerability to thaw subsidence is widespread. The thaw consolidation of permafrost is closely related to water content, cryostructure, soil texture, rates of thawing and dissipation of pore water pressure. However, little is known on the fate of water from melting ground ice in degrading permafrost. How does the pore water dissipation control the thaw consolidation? Where the meltwater is flowing into the ground? Is the meltwater recharging the aquifers at depths or is it migrating at the ground surface and ultimately finding its way in lakes, rivers, and oceans? As a research hypothesis and a positive feedback, the thaw subsidence which depends on the dissipation of pore water pressure accelerates the rate of permafrost degradation. The warm boundary at the ground surface is moving downwards toward the degrading permafrost body at depths which increases the permafrost thawing. For testing this research hypothesis, the objectives are to: 1) observe, describe, and monitor in the field the processes of permafrost degradation, 2) measure the thaw consolidation properties of ice-rich permafrost from laboratory tests, 3) simulate the heat transfer, thaw consolidation and flow of meltwater which are taking place in degrading permafrost, 4) compare these simulated processes with the observations, and 5) anticipate the permafrost degradation in the future. The study site is located in the discontinuous permafrost zone close to Umiujaq in northern Quebec, Canada, where ice-rich permafrost mounds are already degrading. Long-term monitoring series of ground temperature and thaw subsidence data are already available for several locations. The methodology used in this research program relies heavily on ground truth from careful field observations using different monitoring techniques (automated thermistor cables, water level loggers, LiDAR surveys and visible and infrared photogrammetry), geotechnical and geophysical tools (permafrost sampling, electrical resistivity and seismic refraction tomography), and lab tests on ice-rich permafrost samples (thaw consolidation and hydraulic conductivity). Numerical modelling of thermal-hydro-mechanical processes will be performed to simulate permafrost degradation following different scenarios of climate changes. The expected outcomes from this research program are a better understanding of the physical processes which are taking place in degrading permafrost and the improvement of numerical modelling of heat transfer with phase change, thaw consolidation, meltwater migration and flow to anticipate permafrost degradation due to climate changes. From the knowledge developed in this research program, adaptation strategies could be established to insure the sustainable development of Northern Canada.