Assessment of annual high-water events for the Mackenzie River basin, Canada

River ice break-up is known to have important morphological, ecological and socio-economic effects on cold-regions river environments. One of the most persistent effects of the spring break-up period is the occurrence of high-water events. A return-period assessment of maximum annual nominal water depths occurring during the spring break-up and open-water season at 28 Water Survey of Canada hydrometric sites over the 1913-2002 time period in the Mackenzie River basin is presented. For the return periods assessed. 13 (14) stations are dominated by peak events occurring during the spring break-up (open-water) season. One location is determined to have a mixed signal. A regime classification is proposed to separate ice- and open-water dominated systems. As part of the regime classification procedure. specific characteristics of return-period patterns including alignment, and difference between the 2 and 10-year events are used to identify regime types. A dimensionless stage-discharge plot allows for a contrast of the relative magnitudes of flows required to generate maximum nominal water-depth events in the different re,nines. At sites where discharge during the spring break-up is approximately one-quarter or greater than the magnitude of the peak annual discharge, nominal water depths can be expected to exceed those occurring during the peak annual discharge event. Several physical factors (location. basin area, stream order, gradient, river orientation, and climate) are considered to explain the differing regimes and discussed relative to the major sub-re-ions of the MRB. Copyright (C) 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada.