Hydrodynamics of Mesotidal Estuary in Winter

In this article, we quantify the effects of a standing ice cover on the hydrodynamics of a mesotidal estuary. The Portneuf Estuary, Québec, is 5.9?km in length and has a 3-m-deep thalweg. According to our numerical model simulations (using an adapted version of Environment Canada’s ONE-D model) and field measurements, the midwinter 50-cm-thick ice cover produced an attenuation of the neap tidal range (1.9?m) and spring tidal range (4.0?m) of 17 and 37%, respectively, near the upstream end of the estuary. The arrival of low water was also delayed by about 90?min at this location. At the mouth, the cover attenuated peak ebb tide flow (200?m3/s) and flood tide flow (500?m3/s) by approximately 18 and 13%, respectively. Here the peak flood flow was normally delayed by 41?min, while the ebb tide was usually advanced by 8?min. In general, the ice cover attenuated peak velocities by 12 to 20%, although at certain times and locations the ice cover could induce higher velocities than would be present under open water conditions. The ice cover also retarded and diminished the salt wedge intrusion and is expected to dramatically reduce the sediment transport processes, although its presence could cause some sporadic local increases in erosion.