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Ice processes in general, and ice jams in particular, play a dominant role in the hydrologic regime of Canadian rivers, often causing extreme floods and affecting the life cycle of many aquatic, terrestrial, and avian species. Various numerical models have been developed to help simulate the formation and consequences of these very dynamic and often destructive jam events. To test and compare the performance of existing models, a series of three tests have been devised and coordinated by a task force appointed by the Committee on River Ice Processes and the Environment (CRIPE). The results indicate that the overall performance of the models is good when calibration data are available, but considerably more varied when the models are applied in uncalibrated or 'blind' mode. However, the diversity of results in the blind mode may be attributed more to the variations in perceptions of the physical processes by the users, as compared to the mechanics of the numerical computations. Key words: Calibration, case study, field data, ice jam, model testing, numerical model, river. Les processus de glaces en general, et les embacles en particulier, ont un role predominant dans le regime hydrologique des rivieres canadiennes, causant souvent des inondations extremes et touchant le cycle de vie de plusieurs especes aquatiques, terrestres et aviaires. Plusieurs modeles numeriques ont ete developpes pour aider a simuler la formation et les consequences de ces evenements d'embacle tres dynamiques et souvent destructeurs. Pour verifier et comparer le rendement des modeles existants, une serie de trois essais a ete concue et coordonnee par un groupe de travail assigne par le CRIPE (Committee on River IceProcesses and the Environment). Les resultats indiquent que le rendement general des modeles est bon lorsque les donnees d' etalonnage sont disponibles, mais varie considerablement lorsque les modeles sont appliques en mode << aveugle >> ou non etalonne. Toutefois, la diversite des resultats en mode << aveugle >> peut etre attribuee plus aux variations dans les perceptions des procedes physiques par les utilisateurs, que par la mecanique des calculs numeriques. Mots-cles : etalonnage, etude de cas, donnees de terrain, embacle, essai de modele, modele numerique, riviere. [Traduit par la Redaction], 1. Introduction Ice processes play a dominant role in the hydrologic regime of Canadian rivers and are intimately related to the life cycle of many aquatic, terrestrial, and avian species. [...]

River ice jams are a common occurrence on northern rivers, and their formation can present a severe flood risk to nearby communities. As more and more river regulation projects are developed to provide an alternative to fossil fuels for electrical power-generating capacity, our need to understand the mechanisms associated with ice jam formation under variable flow conditions becomes more vital. This is because, at present, hydropeaking operations are often severely curtailed during the ice-affected seasons due to concerns that sudden flow fluctuations might instigate ice jams and associated flooding. Here, an experimental investigation explores the effects of rapid increases in discharge on ice jam formation and evolution. It is found that the thickness of ice jams formed under highly dynamic flow conditions tend to be slightly thinner than those formed during steady carrier flows for comparable discharges. Also, despite the highly dynamic nature of these consolidation events, the resulting ice thicknesses appear reasonably well approximated by steady flow theory. DOI: 10.1061/(ASCE)0887-381X(2007)21:3(72) CE Database subject headings: Ice flow; Steady flow; Thickness; Hydrodynamics; Rivers: Hydraulics.

Ice jams pose a significant threat to human safety and property and represent one of the most dynamic of river ice processes. A key limitation in the advancement of knowledge of ice jam formation is the lack of quantitative data describing these dynamics, which is essential also for validation of advanced computational models. In this study, an experimental investigation of ice jam formation under steady carrier discharge was undertaken. Thus, unsteady effects were entirely due to the ice jam formation process itself. Quantitative data describing the variation in discharge, ice jam thickness, water level variation, and ice cover progression provides unprecedented data describing the dynamics of ice jam formation. While the processes of ice jam formation are indeed dynamic, the results of this investigation suggest that the analysis of ice jams formed under steady carrier flow conditions may be adequately handled by the usual steady flow ice jam stability relationships. The applicability of the popularly applied wide jam theory approach to modeling ice jams is further supported by this investigation. CE Database subject headings: Ice jams; Ice formation; Dynamics; Rivers.

The article focuses on the innovative ways used by Fort Worth and Dallas, Texas to sustain local economic initiatives focusing on job creation. Topics discussed include the creation of the EB-5 Immigrant Investor Program that would benefit foreign nationals, the underutilization of the program during the financial crisis, and the plan of the two cities to develop creative ways to promote foreign direct investment.