Frederick A. Michel

Bathymetric mapping and sub-bottom profiling through lake ice with ground-penetrating radar

Bathymetric mapping of lakes with sonar is essentially limited to the ice-free summer months. Recent developments in ground-penetrating radar technology have greatly increased its portability and capabilities for imaging through fresh water. The suitability of a backpack portable ground-penetrating radar (GPR) system for bathymetric mapping of ice-covered Arctic lakes was investigated by performing grid surveys on three lakes with water depths up to 19 m. It was demonstrated that GPR can now be used to quickly produce high quality bathymetric maps and sub-bottom profiles showing sediment type and lacustrine sediment thickness. While water depths were measured with a precision of ±3%, lacustrine sediment thickness measurements (up to 5 m) had an estimated precision of ±15%.

Glacial hydrological system characterization using ground‐penetrating radar

Hydrological systems near the terminus of a high Arctic glacier and a proglacial icing on Bylot Island, Canada, were investigated using ground-penetrating radar (GPR). The ice thickness and the location and depth of tunnels within the glacier and icing were imaged. Modelling of the GPR response was utilized to predict the data quality and to assist in its interpretation. The unique properties of the ice enabled velocity determinations from the diffraction patterns generated by point-source reflectors as well as traditional velocity surveys. The propagation velocity of the radar pulses through the ice depended on the air and water content in the ice. The identification of drainage tunnels was attained through pulse polarity analysis and interpolation between the profiles in gridded surveys. It was found that reflectivity analysis may enable GPR to be used for acquiring three-dimensional information on the thermal structure of glaciers. The much more complicated structure of the icing was imaged with higher frequency antennae and it was found that general ice types could be mapped using radar stratigraphical analysis. Both buried slush mounds and subsurface channel fills were identified within the icing. A portion of the icing near the centre of the valley floor, that has persisted perennially for over 50 years, was found to be sitting on a slightly higher area of the valley bottom and thus was not subjected to the same hydrothermal erosional forces as the edges of the icing, setting up a feed-back loop encouraging the preservation of the central core of ice and promoting the destruction and rebuilding of the edges every year.

Characterizing a Faulted Aquifer by Field Testing and Numerical Simulation

Faulted aquifers constitute one of the most complex geological environments for analysis and interpretation of hydraulic test data because of the inherent ability of faults to act not only as highly transmissive zones but also as hydraulic barriers. Previous studies of the fractured carbonate aquifer at Carleton University, Ottawa, Canada, characterized the flow regime as predominantly linear, but with limited radial nature, and undertook to analyze constant discharge test data using both radial and linear flow models. When used as direct input to a numerical model, the hydraulic parameters, calculated directly from hydraulic test data, were inappropriate and resulted in a poorly calibrated model. While our interpretation of the faulted aquifer remains linear-radial in nature, parameter estimation by numerical simulation highlighted the presence of hydraulic barriers associated with the faults. These barriers are not readily apparent in the constant discharge test data and act to modify the hydraulic test curves at early to mid time, leading to incorrect estimates of the hydraulic parameters. This paper describes the conceptual model and the numerical approach, and demonstrates the importance of using transient simulations for model calibration.

Hydrogeochemistry and geothermal characteristics of the White Lake basin, South-central British Columbia, Canada

Abstract Hydrogeochemistry and geothermal characteristics of the Tertiary White Lake basin are described in order to provide constraints on the hydrogeology and thermal regime of the basin. The basin can be divided into three flow subsystems on the basis of chemical and isotopic variations. The groundwaters evolve chemically from young Ca–Mg–HCO3 type waters in the shallow surficial sediments to Na-dominated waters in the deeper intermediate system. Surface waters and shallow groundwaters collected from wells completed in overburden have undergone extensive evaporation as evidenced by their enriched δ18O and δ2H composition. Minor evaporation identified in the isotope composition of groundwater from domestic wells completed in bedrock, as well as from springs, suggests a local to intermediate origin for these waters, and perhaps mixing with shallow evaporative waters. In contrast, the uniform isotope signatures of deep basin waters measured both spatially and vertically suggest recharge at higher elevations, and a much deeper circulation system that is essentially isolated from the shallow subsurface. Chemical geothermometry indicates that spring waters and bedrock well waters have equilibrated at temperatures of less than 20 and 60°C, respectively. Groundwaters encountered by deep diamond drill holes, with equilibration temperatures of less than 80°C, are representative of intermediate flow systems, and may serve to modify the heat flow regime in the basin. Regional groundwater flow within the basin is complex due to numerous faults that exert a strong influence on fluid circulation patterns. Transport of heat in the subsurface, which has resulted in variations in the measured thermal gradients across the basin, occurs either at depths greater than those investigated in this study or has been significantly influenced by the circulation of cooler groundwater in the central part of the basin.