Journal of Cold Regions Engineering

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.

Longitudinal dispersion is the spreading of suspended or dissolved substances caused by the combined action of differential advection and lateral mixing. Tracer tests in many rivers under open-water conditions have indicated that the temporal spread first increases linearly with downstream distance (linear range). It may ultimately grow in proportion to the square root of distance (Fickian range), very far below the point of release. Test data have been obtained in ice-covered rivers, starting in 1975. They show linear-range behavior even though the test reaches were as long as hundreds of kilometers. As in the case of open-water conditions, the rates of spread under an ice cover are related to the friction factor of the flow, being generally higher than the open-water values for equal friction factors. Based on early results in pipe flow, many water quality models assume Fickian dispersion, contrary to the field evidence. A more correct quantification of the dispersion process is outlined and implications to the method of computation are discussed.

The middle Mississippi River, which extends from the mouth of the Missouri River near St. Louis to the confluence with the Ohio River at Cairo, Ill., is a critical navigation route throughout the year. During cold periods, the ice accumulations and ice jams that form on this reach can delay or suspend winter navigation, incurring great costs to industry as well as cities and towns whose economies depend on river commerce. Much of this ice originates in the Missouri River. With the onset of warmer air temperatures, the rapid release of these ice accumulations can result in substantial damage to river structures such as dikes, revetments, and levees. This study analyzed historical data and used numerical hydraulic models to assess the possibility of structural solutions to these ice problems. The study identified reach locations where structural ice control might be possible. A simple computer model then simulated the upstream progression of ice covers on the middle Mississippi to assess the feasibility of various ice control alternatives. An ice retention structure located on the Missouri River near its mouth was found to be the most favorable of the structural ice control options considered.