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One of the key issues associated with the hypothesis of catastrophicsubglacial drainage of the Livingstone Lake event is whether flows of such large magnitudes are physically feasible. To explore this issue, a one-dimensional hydraulic network flow model was developed to investigate the range of peak discharges and associated flow parametersthat may have been carried by a tunnel channel network in south-eastAlberta, Canada. This tunnel channel network has been interpreted elsewhere to carry large discharges associated with subglacial meltwater flows because of the convex longitudinal profiles of individual channels. This computational modelling effort draws upon established andverified engineering principles and methods in its application to the hydraulics of this problem. Consequently, it represents a unique and independent approach to investigating the subglacial meltwater hypothesis. Based on the modelling results, it was determined that energylosses resulting from friction limit the maximum peak discharge thatcan be transported through the tunnel channel network to 107 m3 s-1, which is in reasonable agreement with previous estimates of flood discharges for proposed megafloods. Results show that flow through channels with convex longitudinal profiles occurs when hydraulic head exceeds 910 m (Lost River) and 950 m (Sage Creek), respectively. These are considerably below the maximum head capable of driving flow through the system of 1360 m, beyond whichice is decoupled from the bed across the pre-glacial drainage divide. Therefore, it is concluded that these model results support the hypothesis of catastrophic subglacial drainage during the Livingstone Lake event. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes frazil ice events detected using upward looking sonars, one high (546kHz) and one low (235kHz) frequency, during the 2009/2010 freeze-up field deployment on the North Saskatchewan River, Edmonton, AB, Canada. The field acoustic data have been processed to compute time series of the depth averaged volume backscatter strength, S vd (dB). A review of three scattering models: the sphere, prolate spheroid, and disk models, together with their formulation, assumptions and limitations are presented. Estimation methods for the concentrations and sizes from S vd (dB) using scattering models are discussed. The applicability of the three scattering models to measuring suspended frazil ice was investigated using laboratory data reported by Ghobrial et al. (2012a). It was found that the laboratory measured concentrations were in a good agreement with concentrations estimated with these scattering models. It was also found that the disk model is the most applicable because it provides more realistic particle sizes. In total, eight frazil events were detected with the sonars during the field deployment. Preliminary linkages between the meteorological (air and water temperatures) and surface ice conditions measured at the site, and the duration and magnitude of the detected frazil events are presented. Both the laboratory results and the disk scattering model were used to estimate frazil ice concentration and sizes from the field data. Concentrations ranging between 0.01 and 0.05% and disk radii between 0.13 and 0.21mm have been estimated. [Copyright &y& Elsevier]

Abstract: This paper describes an algorithm that has been developed to process field data from two upward looking sonars, one high (546kHz) and one low (235kHz) frequency, a 2MHz current profiler and a monitoring station, to measure surface ice characteristics on the North Saskatchewan River in the north east of Edmonton, AB, Canada, during the 2009/2010 freeze-up season. The algorithm used to calculate pans/rafts drafts and lengths, and the surface ice concentration is described. The validity and the accuracy of this technique were tested and computed surface ice conditions are presented. For the purpose of examining the effects of hydro-meteorological conditions on measured pan characteristics, the freeze-up period was divided into three distinct stages depending on the measured surface ice concentration. Pan/raft drafts were found to range from 0.1 to 1.0m and pan/raft lengths from 0.6 to 8.0m. The sonar proved to be very accurate in detecting the exact surface ice conditions locally above the sonar beam. However, interpretation of the results can sometimes be challenging, especially when physical processes such as bridging affect local ice conditions. Therefore, additional visual observations (e.g. time lapse photography) of surface ice conditions are recommended to aid in the interpretation of sonar measurements. [Copyright &y& Elsevier]