Time filter

Source Type

Rue, Switzerland

Leite Ribeiro M.,Stucky SA | Schleiss A.J.,Ecole Polytechnique Federale de Lausanne
Swiss Competences in River Engineering and Restoration - Special Session on Swiss Competences in River Engineering and Restoration of the 7th International Conf. on Fluvial Hydraulics, RIVER FLOW 2014

River channel confluences form important morphological components of any river system. This article presents the results of an investigation on a natural river confluence in Switzerland. The aim of the field work performed at the confluence of the Sarine (main channel) and Gerine (tributary) Rivers near Fribourg (CH) is to analyze the interaction between morphological processes on the confluence and hydropower-affected hydrology of the main River. Important morphological changes have been observed over the last years, especially the deflection of the Sarine River and erosion of the left bank opposite of the tributary. Numerical calculations have shown that currently the minimal discharge of the Sarine River which transports the sediments annually deposited at the confluence is attained on average once each 2 years. Before the construction of the Rossens Dam, the minimum discharge was reached every year. This lack of yearly floods with sediment mobilization can explain the morphological changes occurred at the confluence since the construction of the dam. © 2014 Taylor & Francis Group, London. Source

Ribeiro M.L.,Ecole Polytechnique Federale de Lausanne | Ribeiro M.L.,Stucky SA | Pfister M.,Ecole Polytechnique Federale de Lausanne | Schleiss A.J.,Ecole Polytechnique Federale de Lausanne | Boillat J.-L.,Ecole Polytechnique Federale de Lausanne
Journal of Hydraulic Research

Piano Key Weirs (PKWs) are an alternative to linear overflow structures, increasing the unit discharge for similar heads and spillway widths. Thus, they allow to operate reservoirs with elevated supply levels, thereby providing additional storage volume. As they are relatively novel structures, few design criteria are available. Hence, physical model tests of prototypes are required. This study describes comprehensive model tests on a sectional set-up of several A-type PKWs, in which the relevant parameters were systematically varied. Considering data of former studies, a general design equation relating to the head-discharge ratio is derived and discussed. The latter is mainly a function of the approach flow head, the developed crest length, the inlet key height, and the transverse width. To extend its application range, case study model tests were analysed to provide a design approach if reservoir approach flow instead of channel flow is considered. © 2012 Copyright International Association for Hydro-Environment Engineering and Research. Source

Davalle E.,Lausannes Utilities Company | Filliez J.,Stucky SA
Houille Blanche

Lavey Hydroelectric Scheme is located in the French-speaking part of Switzerland. It was commissioned in 1950. Since then, and under an operating lease of 80 years, it produces about 400 GWh per year, covering 32% of the electricity needs of the City of Lausanne. At the start of the last decade, further to the political commitments (Energy 2050), Switzerland turned mainly to renewable energies. The City of Lausanne and its Public Utility, which produces and distributes electricity to more than 230'000 homes, have developed a project, called Lavey+, to increase the power and energy generation at Lavey power plant. Within the framework of the Lavey+ project, it was decided in 2008 to improve the present situation and to study the realization of a new water intake, a second headrace tunnel parallel to the existing one, to expand the present underground cavern, to put a fourth Kaplan turbine generator and to modernize the plant. To ensure a better operational flexibility, it is planned to connect the new gallery also to the third turbine, which is already in operation. Additional studies were also performed to improve the area of the reservoir in order to improve the conditions of bed load material transit. After more than 60 years of interruption, it was decided also to restore the passage of the fish fauna in the upstream and downstream migrations. Finally, a proposal to reassess the ecological flow, which would be annually modulated downstream from the dam, was made. © Société Hydrotechnique de France, 2015. Source

Schleiss A.J.,Ecole Polytechnique Federale de Lausanne | Manso P.A.,Ecole Polytechnique Federale de Lausanne | Manso P.A.,Stucky SA
Rock Mechanics and Rock Engineering

Using high-strength steels for pressure shafts and tunnel liners and taking into account significant rock mass participation allows the design of comparatively thin steel liners in hydropower projects. Nevertheless, during emptying of waterways, these steel linings may be endangered by buckling. Compared with traditional measures such as increased steel liner thickness and stiffeners, pressure relief valves are a very economical solution for protection of steel liners against critical external pressure and therefore buckling during emptying. A calculation procedure has been developed for the design of the required number and arrangement of pressure relief valves, and this has been used successfully in practice. Systematic model tests enabled the assumptions of the design method to be verified. © 2011 Springer-Verlag. Source

Leite Ribeiro M.,Ecole Polytechnique Federale de Lausanne | Leite Ribeiro M.,Stucky SA | Blanckaert K.,Ecole Polytechnique Federale de Lausanne | Blanckaert K.,CAS Research Center for Eco Environmental Sciences | Schleiss A.J.,Ecole Polytechnique Federale de Lausanne

The hydro-morpho-sedimentary processes in confluence hydrodynamic zones (CHZ) subject to a local widening of the tributary were investigated in a series of laboratory experiments that were representative of the 20 major confluences of the Upper Rhone River in Switzerland. Three discharge ratios (low, intermediate and high ratios of tributary to main channel discharge) were investigated for each of four tributary configurations (reference configuration with constant tributary width and three geometries of the local tributary widening). In all experiments, the local tributary widening caused substantial morphodynamic changes in the CHZ and moderate sediment redistribution in the post-confluence channel. At the entrance of the local widening, the tributary main flow corridor gradually widened. Towards the confluence mouth, it narrowed and deflected in downstream direction because of a zone of flow stagnation at the confluence upstream junction corner. Dry zones and flow stagnation zones occurred in the widening zone outside the tributary main flow corridor. The results indicate that a local tributary widening considerably enhances the variability of bed substrate, velocity and depth in the CHZ, and offers an appropriate habitat for a wider range of biota than the homogeneous channelized reference configuration. None of the investigated experiments resulted in adverse impacts on water surface elevation and thereby flood safety. On the basis of the laboratory experiments, the appropriate geometry of the local tributary widening is discussed, and quantitative guidelines for practical application are proposed. © 2014 John Wiley & Sons, Ltd. Source

Discover hidden collaborations