Browsing Theses (Civil and Environmental Engineering) by Subject "Permafrost"
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Groundwater flow in a vertical plane at the interface of permafrostGroundwater dynamics in discontinuous permafrost aquifers are complex. The topography of permafrost redirects flow in difficult-to-predict directions that can be tens of degrees off from the regional flow direction. Large zones of permafrost vertically separate aquifers into supra and sub-permafrost portions. The flow dynamics in each portion of the aquifer may be dissimilar due to different controlling boundary conditions. In areas of discontinuities in permafrost, known as open taliks, groundwater in the two portions of the aquifer may mix. These areas of mixing are the focus of this study, in particular, the groundwater dynamics in taliks located in the floodplain of lower reaches of rivers. The study hypothesizes that groundwater flow in floodplain taliks of lower reaches of rivers will bifurcate between the supra and sub-permafrost portions of a discontinuous permafrost aquifer. To test this hypothesis gradient, magnitudes and flow directions were determined at several depths ranging from the water table to 150 ft. (45.7 m) below ground surface, using a linear interpolation scheme in various locations in a floodplain talik. Errors in water level measurements due to instrument errors as well as vertically moving wells were propagated into the gradient calculations by Monte Carlo analysis. Results from this research show that a vertical divide in groundwater flow forms a short distance below the top of permafrost. Groundwater flow above the divide routes into the unconfined supra-permafrost portion of the aquifer. Water below the divide flows into the confined portion of the aquifer below permafrost. The position of the vertical groundwater divide may adjust in relation to the water table position. Additionally, a methodology is presented for stochastically propagating measurement errors into gradient analyses by Monte Carlo analysis. Understanding the flow dynamics in discontinuous permafrost aquifers is key to the understanding of contaminant transport, aquifer recharge, and resource development in subarctic environments.
Permafrost geosystem assessment at the Beaver Creek Road experimental site (Alaska Highway, Yukon, Canada)An experimental site testing a range of engineering techniques for mitigating permafrost degradation along the Alaska Highway has been established in 2008 at Beaver Creek (Yukon, Canada). Based on the hypothesis that permafrost has a distinctive sensitivity to climate and terrain conditions at a local scale, a geosystem approach, which considers a set of components (e.g. permafrost, embankment, vegetation, hydrology and hydrogeology) and accounts for dynamics within a system, was applied to obtain a better understanding of local permafrost conditions and changes within the system. Therefore, this assessment, for ultimately measuring performance of the mitigation techniques, integrated the permafrost conditions, in terms of cryostratigraphic units and soil properties, with local climate, natural terrain and embankment conditions. The author, who participated in the site establishment, its baseline investigations and monitoring programs, presents here the baseline geosystem studies at the Beaver Creek Road Experimental Site with an emphasis on permafrost.
Processes controlling thermokarst lake expansion rates on the Arctic coastal plain of Northern AlaskaThermokarst lakes are a dominant factor of landscape scale processes and permafrost dynamics in the otherwise continuous permafrost region of the Arctic Coastal Plain (ACP) of northern Alaska. Lakes cover greater than 20% of the landscape on the ACP and drained lake basins cover an additional 50 to 60% of the landscape. The formation, expansion, drainage, and reformation of thermokarst lakes has been described by some researchers as part of a natural cycle, the thaw lake cycle, that has reworked the ACP landscape during the course of the Holocene. Yet the factors and processes controlling contemporary thermokarst lake expansion remain poorly described. This thesis focuses on the factors controlling variation in extant thermokarst lake expansion rates in three ACP regions that vary with respect to landscape history, ground-ice content, and lake characteristics (i.e. size and depth). Through the use of historical aerial imagery, satellite imagery, and field-based data collection, this study identifies the controlling factors at multiple spatial and temporal scales to better understand the processes relating to thermokarst lake expansion. Comparison of 35 lakes across the ACP shows regional differences in expansion rate related to permafrost ice content ranging from an average expansion rate of 0.62 m/yr on the Younger Outer Coastal Plain where ice content is highest to 0.16 m/yr on the Inner Coastal Plain where ice content is lowest. Within each region, lakes vary in their expansion rates due to factors such as lake size, lake depth, and winter ice regime. On an individual level, lakes vary due to shoreline characteristics such as local bathymetry and bluff height. Predicting how thermokarst lakes will behave locally and on a landscape scale is increasingly important for managing habitat and water resources and informing models of land-climate interactions in the Arctic.