Estimates of the Manning's coefficient for ice-covered rivers

The management of ice-covered rivers presents special issues with respect to planning, design and operation of a water resources project. To address these issues properly entails a good understanding of the hydraulics of ice-covered rivers, where the composite Manning's coefficient is a fundamental parameter. The aim of this paper is to obtain field estimates of the composite coefficient associated with the ice cover and riverbed. Using four different methods, this paper analyses a large volume of winter measurements of water velocities made from shallow ice-covered rivers in Canada. The results show that the composite Manning's coefficient ranges from 0.013 to 0.040 as winter averages, but can vary up to seven-fold through the winter. The slope of the energy grade line is difficult to measure in the field and thus is rarely available; it appears to be about 30% of the water slope. The method for determining the coefficient based on the logarithmic velocity distribution fitted to measurements has shown advantages, as revealed by comparing the results of the four methods. The estimates of the composite Manning's coefficient reported in this paper are useful for modelling ice-covered river flow and determining winter discharges. This is particularly true when site-specific data are unavailable.