Morphodynamics of diversion channels in Northern Manitoba, Canada

Abstract

The 2-Mile and 8-Mile diversion channels in Northern Manitoba help to maintain the efficiency of Manitoba Hydro’s hydroelectric generating stations located downstream on the lower Nelson River and also assist with flooding control on Lake Winnipeg. Erosion within the channels has been consistently monitored for several decades to better understand these processes to ensure the future performance of the channels. Morphodynamic studies in these channels are complicated due to the high variability of the bed and bank material, the effect of severe cold weather on the erodibility of the channel banks, and the effect of the surrounding lakes on the hydrodynamic conditions of these channels. The present study includes field measurements, experimental testing, and hydrodynamic and thermal numerical modelling to quantify morphological changes within the channels. Moreover, 30 years of monitoring data were analyzed to validate the results of the study. Simple graphs were presented to estimate average applied shear stress over the channel banks and beds based on results of the calibrated and validated hydrodynamic models. Moreover, the effects of wave action on the total applied shear stress were investigated within the 2-Mile Channel under different flow conditions. Comparison between historical cross-sectional survey and results of the numerical models and experiments showed that subaerial processes, mostly freeze–thaw, could be a major eroding factor.