Search Results (3)

Since their development, as a result of an improvement of labyrinth weirs, Piano Key Weirs (PKWs) have been implemented as (a) a flood safety structure for gravity dams, allowing to also increase their storage volume, and (b) in river systems to increase the water level for hydropower or navigation purposes. The rectangular folded crest, consistent with apexes inclined by turns in the upstream and in the downstream direction, turns the PKW a device with a high discharge capacity, especially useful during wet extreme events. Nevertheless, several modifications have been implemented in the PKW geometry, capable to improve and, in some cases, worsen their efficiency. Herein, an experimental and numerical assessment, using the ANSYS Fluent Computational Fluid Dynamics (CFD) software, of the discharge coefficient is presented for two PKW configurations, evaluating the specific discharge over the upstream, downstream, and lateral crests, the velocity in the inlet and outlet keys, and the water surface profile, as well. The investigated configurations are a symmetric type A, designed following the recommended optimal values, and a type B model, with the same geometric features as type A. Results showed that for the specific geometries, the type B is more efficient for lower head; however, once the filling of the outlet key occurs, the type B efficiency is reduced, leading to type A becoming more efficient. Full article

To understand the long-term fate of fish assemblages in the context of global change and to design efficient restoration measures in river management, it is essential to consider the historical component of these ecosystems. The human-impacted Seine River Basin is a relevant case that has experienced the extinction of diadromous fishes over the last two centuries and has recently witnessed the recolonization of some species. One key issue is to understand the historical evolution of habitat accessibility for these migratory species. Thanks to the unique availability of historical, mainly hand-written sources of multiple types (river engineering projects, navigation maps, paper-based databases on oxygen, etc.), we documented and integrated, in a geographic information system-based database, the changes to physical and chemical barriers in the Seine River from the sea to Paris for three time periods (1900s, 1970s, and 2010s). The potential impact of these changes on the runs of three migratory species that have different migratory behaviors—Atlantic salmon, allis shad, and sea lamprey—was evaluated by ecological connectivity modeling, using a least-cost approach that integrates distance, costs, and risks related to barriers. We found that accessibility was contrasted between species, emphasizing the crucial role of the migration type, period, and level of tolerance to low dissolved oxygen values. The highest disruption of ecological connectivity was visible in the 1970s, when the effects of large hypoxic areas were compounded by those of impassable navigation weirs (i.e., without fish passes). As the approach was able to reveal the relative contribution of physical and chemical barriers on overall functional connectivity, it may constitute a model work in assessing the functioning of large river ecosystems. Full article

Despite ubiquitous warming, the lower Oder River typically freezes over almost every year. Ice jams may occur during freeze-up and ice cover breakup phases, particularly in the middle and lower reaches of the river, with weirs and piers. The slush ice and ice blocks may accumulate to form ice jams, leading to backwater effects and substantial water level rise. The small bottom slope of the lower Oder and the tidal backflow from the Baltic Sea enhance the formation of ice jams during cold weather conditions, jeopardizing the dikes. Therefore, development of an ice jam flood forecasting system for the Oder River is much needed. This commentary presents selected results from an international workshop that took place in Wrocław (Poland) on 26–27 November 2018 that brought together an international team of experts to explore the requirements and research opportunities in the field of ice jam flood forecasting and risk assessment for the Oder River section along the German–Polish border. The workshop launched a platform for collaboration amongst Canadian, German and Polish scientists, government officials and water managers to pave a way forward for joint research focused on achieving the long-term goal of forecasting, assessing and mitigating ice jam impacts along the lower Oder. German and Polish government agencies are in need of new tools to forecast ice jams and assess their subsequent consequences and risks to communities and ship navigation along a river. Addressing these issues will also help research and ice flood management in a Canadian context. A research program would aim to develop a modelling system by addressing fundamental issues that impede the prediction of ice jam events and their consequences in cold regions. Full article