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

在退化的永久冻土环境中融化的地面冰所产生的水的命运

• 批准号: RGPIN-2017-06544
• 负责人: Fortier, Richard
• 金额: $ 1.75万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=680028
• 关键词: fate; water; melting; ground; ice

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.

在影响加拿大北方可持续发展的冻土退化地质灾害中，融沉的脆弱性是普遍存在的。多年冻土的融固结与含水量、冻土结构、土质、融化速率和孔隙水压力消散密切相关。然而，人们对融化的地面冰在退化的永久冻土中的水的命运知之甚少。孔隙水消散如何控制融积？在融水流入地下的地方？融化的水是在深层补充含水层，还是在地表迁移，最终进入湖泊、河流和海洋？* 作为一种研究假设和正反馈，融沉依赖于孔隙水压力的消散，加速了多年冻土的退化速度。地表的暖边界正向下移动，向深处的退化冻土体移动，这增加了冻土的融化。* 为了检验这一研究假设，目标是：*1）在现场观察、描述和监测冻土退化过程，*2）通过实验室试验测量富冰冻土的解冻固结特性，*3）模拟冻土退化过程中发生的传热、解冻固结和融水流动，***4）将这些模拟过程与观测结果进行比较，***5）预测未来的冻土退化。* 研究地点位于加拿大北方魁北克Umiujaq附近的不连续永久冻土带，那里富含冰的永久冻土土丘已经在退化。已经有几个地点的地面温度和融化沉降数据的长期监测系列。* 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，LiDAR调查以及可见光和红外摄影测量），岩土工程和地球物理工具（永久冻土取样，电阻率和地震折射层析成像）进行仔细实地观察的地面实况，以及对富冰永久冻土样品（解冻固结和水力传导性）的实验室测试。将进行热-水-力学过程的数值模拟，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成果是更好地了解永久冻土退化过程中发生的物理过程，并改进相变传热、解冻固结、融水迁移和流动的数值模拟，以预测气候变化导致的永久冻土退化。从本研究项目中发展的知识，可以建立适应战略，以确保加拿大北方的可持续发展。