Developing winter flow rating relationships using slope‐area hydraulics

Abstract

AbstractDespite recent advances in instrumentation and modelling methods, accurate determination of river discharge under an ice cover still requires direct measurement. Published flows at hydrometric gauging stations are based on interpolation between a few measurements that are carried out during each winter. The feasibility of using slope‐area hydraulics to develop discharge‐stage rating relationships is explored at two stations, Peace River at Peace Point and Mackenzie River at Arctic Red River. Records at both gauges contain key information for understanding local ice jamming processes, which are known to control the long‐term maintenance of the aquatic ecosystems in the respective deltas. For each site, the variations of reach‐average hydraulic parameters with stage are first determined from several nearby cross‐sections. This information is then used to calculate hydraulic resistance characteristics during the ice season based on archived discharge measurement data, which also include ice cover thickness. The Peace River flow measurements indicate a well‐defined seasonal variation in hydraulic resistance, with the exception of years with large slush deposits under the solid‐ice sheet. Slush effects are negligible at the Mackenzie River gauge site, but the stage‐flow relationship is complicated by a variable water surface slope, a result of downstream control by the Beaufort Sea. This feature is most pronounced during the pre‐breakup period when flows are rising sharply and renders flow estimation uncertain. A nearby water‐level gauge would help quantify the slope and increase confidence in winter flow estimates. Copyright © 2010 in the right of Canada.