Floating Ice Booms: Prototype Test Results and a Case Study
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1 COST EFFECTIVE ALTERNATIVE FOR SINKING AND RE- FLOATING ICE BOOMS: PROTOTYPE TEST RESULTS AND A CASE STUDY Razek Abdelnour, Andrew Liddiard, Stéphane Dumont1 In North America, ice booms are deployed for a period of about five months during the winter season and are removed and, in some cases, transported to a storage area for the summer months. The boaters and the residents living along the river shores do not usually tolerate the presence of ice booms in the rivers and lakes beyond the ice season. Therefore, they expect, the boom to be removed out of sight as soon as the ice disappears. The removal of the boom is presently the option of choice for most large ice booms. This option also helps to protect it from wave damage that can be very significant in some situations. In less populated areas, the boom can be disconnected from one of the two ends then stretched out along one of the two sides of the river. The removal of an ice boom can be costly since all the components of each boom section need to be disconnected, removed from the water, transported and stored until it is again deployed before the following winter. This paper describes an alternative for the removal and re-deployment of an ice boom by submerging and later re-floating the pontoons. The method consists of injecting a predetermined amount of water into each pontoon and buoy without allowing the air to escape. The boom is re-floated simply by opening the valve and letting the water escape from each pontoon. The advantages of this method become even more attractive if the process can be carried out during winter, so the boom can be submerged before the ice break-up, when most of the damage to the boom takes place. This method can also be more advantageous in situations where the ice appears late in winter, and in some winters does not form at all. This method allows the deployment of the boom only a short period before the ice starts to form on the water surface, thus reducing the period during which the boom is exposed to wave storms and to debris, when significant wear was observed. The results of the prototype tests, where one entire section of boom was submerged and re- floated 19 weeks later under varying environmental and river and lake bottom conditions, provided data for evaluating the feasibility, the cost and the implementation of the proposed method. A case study where the costs and benefits from the proposed submergence and re-floating of three ice booms, Yamachiche, Lanoraie and Lavaltrie located on the St. Lawrence River was carried out. 1 311 leggett drive; [email protected] 2 LOCAL SCOUR AROUND CIRCULAR PIERS UNDER ICE COVERS N. L. Ackermann1, H. T. Shen2, and P. Olsson3 This paper presents the result of a laboratory investigation on the effect of ice cover on local scour around circular bridge piers. Experiments were performed in a 12-meter flume with re- circulating sediment discharge. Both smooth and rough artificial covers were used. The bed material consisted of uniform ripple-forming sand. The tests were run for both clear water as well as live bed conditions. The results showed that the existence of could increase the local scour depth scour by 25 to 35% from the free surface condition (Fig. 1). The largest difference occurs at a live bed condition when the flow velocity, U, is in the rage of 1.5 to 2 times of the critical velocity for bed movement, Uc. A rough cover gives slightly larger scour depth than a smooth cover. It was also observed that the movement of bed forms led to variations of scour depth with time. The movement of the bed forms and the variations of scour depth were recorded. The variations of the period of bed waves with respect to the relative flow velocity U/Uc for free surface and ice-covered conditions are compared. 2,5 2 1,5 D / s Y 1 Free surface Smooth cover 0,5 Rough cover 0 012345 U/Uc Figure 1 Relative scour depth plotted against relative velocity, a comparison between free surface flow and covered flow. 1 Professor of Civil and Environ. Engineering, Clarkson University, Potsdam, NY, 13699-5710, USA 2 Professor of Civil and Environ. Engineering, Clarkson University, Potsdam, NY, 13699-5710, USA 3 Licentiate, Division of Water Resources Engineering, Lulea University, S-97187, Lulea, Sweden 3 WAVE-ICE INTERACTION DURING ICE GROWTH: THE FORMATION OF PANCAKE ICE S. F. Ackley, H. H. Shen, M. Dai, and Y. Yuan1 Field investigations of Antarctic sea ice have shown, by its fine-grained frazil ice structure and surface topography features, that ice growth in the presence of waves accounts for a major fraction of the initial ice cover in the Antarctic regions. Pancake ice has been observed to grow in the presence of waves, on the few cruises that have been in the vicinity of the ice edge when the ice growth is occurring. Modeling of ice cover growth and correct parameterization of ice cover thickness, therefore mandates better understanding and quantification of the wave and ice interaction during ice growth in the presence of waves. However, the timing of cruises, to make appropriate wave and ice measurements to coincide with rapid ice cover growth and expansion (over hours to a day or two), is difficult and perhaps prohibitively risky when the success probability is small. To understand better the phenomenology of wave-ice interaction and provide some basis for quantifying the joint effects of waves and ice growth, we have undertaken laboratory studies of the growth of ice in wave fields and how the presence of ice subsequently dampens the wave field. The laboratory experiments, conducted under controlled thermal and wave conditions have allowed us to control the wave parameters and observe the ice growth from initial crystal formation to the final presence of a solid sheet of ice. Two laboratory campaigns were conducted, both at the Cold Regions Laboratory in Hanover, NH, USA. The first experiments were in an outdoor basin (20m x8m x2m) using salt water in ambient winter conditions. The second experiments were conducted in a 35 m x 1.3m x 0.6m hydraulic flume in a cold room at the same facility. The flume used urea doped water which, when frozen gives a sea ice simulant of slightly different mechanical properties (more brittle) when frozen into a thin sheet. A paddle driven by an electric motor was used to generate a wave field in both facilities. We found that pancake ice formed in the two facilities were similar in most important respects. Ice growth into pancakes formed by the initial packing of frazil crystals into larger discs by aggregation of crystals and subsequently into larger pancakes by the fusing together of the initial pancakes. The onset of disc and pancake formation as well as the subsequent size of the pancakes were highly dependent on the wave frequency and amplitude, along with an apparently critical cooling rate necessary to allow surface freezing and hardening of the pancakes so that they could survive collisions with other floes in the wave field. Initial comparisons with a numerical model developed using interparticle interactions with a discrete element simulation were qualitatively similar. Parameters relating the growth of the pancake ice to initial wave frequency and amplitude and subsequent ice effects on wave decay were both determined. 1 Department of Civil and Environmental Engineering. Clarkson University, Potsdam, NY 13699-5710, USA 4 ICE EFFECTS IN ARTIFICIAL HABITATS Knut Alfredsen1, Hans-Petter Fjeldstad2 and Einar Tesaker3 Various forms of artificial habitat measures have been constructed to mitigate flow changes in several regulated rivers in Norway. Such constructions are most often made to alleviate very low discharge and to enhance the ecological effects of minimum flow regimes. The artificial habitat may consist of successions of artificial pools, channels and riffles, often in combination with modifications to the river substrate. In later projects we have seen computer based habitat modelling tools applied in the planning of the artificial habitat to design the reach based on habitat preferences for the fish species found in the river system. One factor that is often overlooked in this process is the winter performance of the artificial habitat, both regarding cold temperature habitat and the direct influence of ice formation in the artificial habitat areas. This is due to a lack of inclusion of knowledge on the interaction between fish and ice is in the available habitat modelling tools, even if the importance of this is well documented in literature. Artificial habitat has been built on the Øyvollen reach of the Dalåa river in Norway as a part of the environmental mitigation after the refurbishment of the power plants in the Stjørdal river system. The foundation for this construction was a combination of a fish preference model and hydraulic modelling of the artificial reach. This paper outlines ongoing work to describe the differences between winter and summer conditions in the areas with artificial habitat at Øyvollen by a combination of field measurements and computer simulations using a two-dimensional hydraulic model. The study is both concerned with analyzing cold water temperature habitat preferences versus summer temperature habitat, and with the description of how ice formations in the reach may directly modify the man-made habitat constructs. Preliminary results show significant changes in available habitat at Øyvollen from summer to winter conditions, and that a formation of ice in the reach may have both positive and negative effects on the available habitat. The ultimate goal of the project is to generalize the findings so that the new tools could be incorporated in the tools used in the planning and design of such constructions and thereby ensure that both summer and winter conditions are considered when artificial habitat is designed in the future.