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North-flowing rivers of the pan-Arctic region have important effects on the Arctic Ocean, but their river-ocean interfaces, including some with vast deltas such as the Mackenzie, have complex hydrology and remain poorly understood. Analysis of 39 years (1973-2011) of water-levels and river discharge at the head of the Mackenzie Delta, 48 years (1964-2011) of water-levels in the mid-delta, and 28 years (1984-2011) of water-levels in the outer delta permitted evaluation of changes in the timing, duration, and magnitude of peak annual water-levels during river-ice breakup. The initiation date of freshet-discharge into the delta has not changed, but the duration from freshet initiation until peak water-levels in the central delta (i.e., duration of ice clearance) has shortened from 35 to 27 days since 1964. The height of annual water-level peaks in the outer delta at Reindeer Channel may have declined by ∼0.4 m from 1984 to 2010, but complicating factors may be influencing this result. Winter-discharge has increased by ∼21% from 1973 to 2011, but this amount is too small to cause a trend in total Mackenzie discharge. Breakup-discharge (i.e., occurring during ice clearance through the central delta) has not significantly changed. The lag time from freshet-discharge initiation into the delta until initial breakage of the river ice-sheet has declined by 6.6 days from 1974 to 2007 and is sufficient to account for the shortened period of river-ice clearance. Declining snow-pack depths during April suggest that river-ice may be melting earlier and more rapidly. [ABSTRACT FROM AUTHOR]

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]