Dominique Courret

Macroroughness ramps (e.g. with a rough bed and protruding blocks evenly distributed in staggered rows) are nature-like fishways offering a wide range of flow conditions and are expected to be very efficient tools to reduce the impact of weirs on the free movements of most life-stages of riverine fish species. However, their in situ efficiency has not been evaluated yet. Here, we used Radio Frequency Identification (RFID) telemetry to monitor during two years the displacement of eleven fish species, on such a macroroughness ramp located on a tributary of the Loire River in France. We (1) evaluated the migration rates of tagged fish species, poorly documented so far; (2) quantified macroroughness ramp attraction and efficiency; and (3) assessed the influence of fish species, fish length and environmental conditions (river discharge and temperature) on these efficiency estimates. All the species detected downstream of the weir successfully crossed the ramp, although at varying rates. Depending on the analytical approach (considering the whole study duration or taking into account different fish attempts), the ramp attraction efficiency ranged between 65.5% and 52.9%, the ramp passage efficiency between 81.8% and 77.0% and the overall efficiency between 53.6% and 41.6%. Fish between 70 and 451 mm in total length were detected crossing the ramp, usually within a short time. In comparison with the efficiency results available for other types of fishways, the macroroughness ramp studied here ranks among the most efficient devices for fish movement restoration.

Low bar spacing trash racks have been widely investigated in order to guide fish toward bypasses. In addition to this biological function, the formulae to predict head losses, for hydropower plants, are still being discussed. This paper investigates and models the global head losses generated by inclined trash racks with six different bar shapes and two different supports, in an open channel for six angles and two low bar spacings. The girders that supported the trash racks were U-shaped and different profile shapes. In addition to the previously studied rectangular and “hydrodynamic” bars, four new bar shapes, combining different leading and trailing edges, were investigated. Water depths were measured upstream and downstream of the rack for each configuration, and head loss coefficients were characterized and modeled. Three of these new bar shapes generated lower head losses than the hydrodynamic bar shape. The most efficient bar profile reduced the shape coefficient by 40% compared to the hydrodynamic profile and by 67% compared to the conventional rectangular profile. Concerning the supports, the use of a profiled girder to replace a conventional U-shaped girder also significantly reduced the head losses. The addition of the girder effect in a global formula increased its accuracy in predicting head losses of inclined trash racks upstream of hydropower plants.

La Houille Blanche - Revue internationale de l eau, est une publication de la Société Hydrotechnique de France

International audienceThe Authors thank the Discussers for their observations on our two papers. Four main points, related to head-loss predictions for angled trashracks, have been underlined by the Discussers and are discussed here.[...

Experimental results for fish-friendly trashracks placed in an open water channel are presented. Model trashracks with different bar shapes, spacing and angles were tested. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. Previous head-loss equations found in the literature were applied to these configurations and were compared with measurements. A new head-loss equation is proposed that takes into account the effect of the different tested parameters. Velocity measurements provided new results and answers concerning downstream-migration aspects such as admissible approach velocities and guidance efficiency as a function of the trashrack angle.

Experimental results are presented for trashracks placed in an open water channel with different bar shapes, spaces between bars and screen inclination angles. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. A new head-loss equation is proposed that takes into account the effect of the different tested parameters and demonstrates the need to separate the effect of the trashrack bars, which is directly related to the inclination of the trashrack, from the effect of the transversal elements such as spacer rows whose effect on the flow is not altered by rack inclination. Velocity measurements also adduce rules for efficient water intakes complying with fish-friendly criteria.