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In this article, we quantify the effects of a standing ice cover on the hydrodynamics of a mesotidal estuary. The Portneuf Estuary, Quebec, 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 attenuation peak ebb tide flow (200 [m.sup.3]/s) and flood tide flow (500 [m.sup.3]/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. DOI: 10.1061/(ASCE)0887-381X(2006)20:3(95) CE Database subject headings: Estuaries; Ice cover; Finite element method; Dimensional analysis.

This paper presents a new vertical 1D finite-element model to simulate the growth and decay of an ice cover (columnar ice, snow ice, slush, and snow cover consolidation) over a winter season in a partially mixed mesotidal estuary. In this study, we present, discuss, and validate boundary conditions as well as test and optimize the numerical model. Predictions from the model were assessed against field observations of ice thicknesses and internal temperatures taken over 3 years. This paper explains why ice in the estuary is almost completely composed of freshwater. We demonstrate how a columnar ice sheet grows over the first half of the winter season and is then melted from underneath during the second half of winter, especially where currents are strong. We also demonstrate that significant snow ice may form over the second half of winter if the ice cover survives long enough by resisting mechanical breakup of spring tides in March. DOI: 10.1061/(ASCE)0887-381X(2006)20:3(70) CE Database subject headings: Estuaries; Models; Salt water intrusion; Ice; Velocity; Hydrodynamics.

We undertook a three-year program to measure the magnitude of static ice forces in four reservoirs located in central and northern Quebec. These static forces may be generated by a temperature change or may arise from such other mechanisms as water level variations, wind, and current drag force. Field observations have revealed two important facts: (1) ice covers have circumferential cracks caused either by water level variations or thermal contraction, and (2) the static ice forces are, in some instances, sufficient to trigger an instability of the broken ice covers by buckling. Noting that an ice cover cannot transmit a force to a structure larger than its own resistance, we derive an upper bound for static forces by determining the in-plane compression force at which a fragmented ice cover collapses. Empirical formulas are presented for three typical structure shapes: retaining walls, sluice gates, and piers. These formulas correlate well with the field data collected from the four dam sites, and suggest that the maximum ice thrust may simply be defined as a function of ice thickness and contact geometry.