Effects of ice on the hydraulics of Mackenzie River at the outlet of Great Slave Lake, N.W.T.: a case study

Abstract

The effects of ice on the conveyance characteristics of the Mackenzie River at the outlet of Great Slave Lake are modeled on the basis of cross section surveys, discharge measurements, and water surface profiles taken during open water and ice covered conditions. The calibrated bed roughness values, expressed in terms of Mannings n, range from 0.020 to 0.030. Based on measured ice thicknesses ranging from 0.6 to 1.2 m in the study reach upstream of Providence Narrows, the calibrated roughness of the 1992 late winter ice cover is 0.015. Discharge estimates, based on this late winter ice cover calibration, measured water surface profiles, and documentation of major ice movements during April and May of 1992, show relatively good agreement with the discharge measurements taken at the same time. The analysis indicates that flow in the channel just downstream of Great Slave Lake is uniform under both open water and ice covered conditions. However, stage–discharge relationships at the Water Survey of Canada gauging station are affected by variable backwater conditions, particularly when an ice accumulation develops in Providence Rapids. Key words: ice, breakup, backwater curves, hydraulic resistance, river.