Session C8: Development of Criteria for the Design and Dimensioning of Fish-Friendly Intakes for Small Hydropower Plant

Abstract: To conciliate the hydroelectric production and the restoration and protection plans of migratory species, in particular salmon (Salmo salar), sea trout (Salmo trutta) and eel (Anguilla anguilla), and more generally the longitudinal continuity for fish species, it is necessary to avoid or at least reduce damages to fish passing through turbines. The best way to reduce fish mortality would be to install fish-friendly turbines, but it is not a cost-effective solution on existing installations and in the present state of the art their use is very limited in terms of head and discharge ranges. Transforming conventional intakes into socalled “fish-friendly” ones is therefore considered as one of the most acceptable solutions. We present here the development of criteria for the design and dimensioning of fishfriendly intakes for small hydropower plants in France (up to ≈ 100 m3/s until now). These criteria were established from the feedback following the evaluation of existing downstream bypasses in France and abroad, and from hydraulic studies on downscale models. Fish-friendly intakes comprise a trashrack designed to guide fish towards its downstream end and to the entrances of bypasses, through which fish safely reach the tailwater. Criteria concern (1) the clear space between bars to avoid the passage of fish through the trashrack and via turbines, (2) the inclination or angulation of the rack to guide fish towards the bypasses located at its downstream end, (3) the normal velocity through the rack to avoid fish impingement, and (4) the number, positions, dimensions, and discharge of bypasses to collect the fish. New formulae have also been proposed to evaluate head-losses for inclined or angled trashracks with low bar-spacing

Behaviour and passage of European silver eels (Anguilla anguilla) at a small hydropower plant during their downstream migration

Between 2004 and 2007, 116 downstream migrant silver eels (Anguilla anguilla) were monitored at a hydropower plant on the Gave de Pau river in South-West France using radio and PIT telemetry. The objectives of the study were: (i) to determine the environmental conditions when eels arrived and passed the facility; (ii) to determine the rate of eel escapement (passage other than via the turbines); (iii) to describe the behaviour of eels faced with the intake structure and the permeability of the intake trashracks for the different sizes of eel; and (iv) to determine whether surface bypasses originally designed for salmon could be effective for eels. Five types of behaviour of silver eels in the forebay and at the plant intakes were identified. The study showed the key factor influencing both eel behaviour and the route taken through the plant was variation in river discharge. Escapement rate was related to eel length and the spill flow to river flow ratio, which could be described by a logistic regression model. The surface bypasses originally designed for salmon were found to aid downstream eel migration significantly. At velocities < 0.40 m·s−1, no eels, even the largest, for which the racks are a physical barrier, were found impinged on the trashracks

An experimental study of turbulent flow in vertical slot fishways

The vertical slot fishways are hydraulic structures that allow the upstream migration of fishes through engineering constructions or natural obstructions in rivers. This type of pool fish pass is generally very effective in ensuring passage of the target species, particularly diadromous species. However, visual observations have shown that certain small species may be trapped in the large recirculation zones and seem to have difficulty in rapidly passing through very large pools. An experimental study was undertaken to characterize the turbulent flow for various configurations of vertical slot fishways and to determine how their characteristics might be modified in order to facilitate the passage of small species. The characteristics of mean flow and turbulence were studied by PIV and visualizations for several different slopes, flow discharges and pool widths. The results showed that the flow pattern always takes one of two topology models depending on the ratio length/width of the pool. In order to study the extent to which the dimensions of recirculation zones can be reduced, the effect of the insertion of vertical cylinders within the pools was visualized

Impacts écologiques des éclusées hydroélectriques. Caractérisation des régimes d’éclusées et Retour d’expérience sur la Maronne

Les éclusées hydroélectriques peuvent impacter de manière conséquente les populations de poissons, et plus particulièrement compromettre le recrutement des espèces diadromes comme le saumon. Pour progresser dans la compréhension des impacts et la définition des mesures de mitigation, il s’avère nécessaire de coupler des suivis biologiques long-terme, une analyse hydrologique avec une caractérisation des régimes d’éclusées, ainsi qu’une approche hydromorphologique. Une méthodologie de caractérisation hydrologique des régimes d’éclusées est dans un premier temps présentée. Leur diversité et leur importante variabilité sont illustrées. On présente ensuite le retour d’expérience acquis sur la Maronne, cours d’eau affluent de la Dordogne en aval d’Argentat soumis aux éclusées de l’aménagement de Hautefage. Les suivis biologiques et les études hydrologiques et hydromorphologiques ont permis de mieux appréhender et quantifier certains impacts (exondations de frayères, échouages-piégeages d’alevins), d’étayer des mesures de mitigation et d’en évaluer l’efficacité. L’intérêt de travaux ponctuels sur la morphologie en complément des mesures sur la gestion des débits est également illustré. Des résultats positifs ont déjà été obtenus. Les réflexions se poursuivent sur la Maronne pour obtenir une situation vraiment satisfaisante. Cet exemple montre que l’état actuel des connaissances ne permet pas, sur un cours d’eau donné, de prédéfinir des mesures de mitigation des impacts des éclusées, tout en garantissant leur efficacité. Cela amène à prôner la mise en place de démarche d’étude similaire sur d’autres cours d’eau, pour identifier les réponses des communautés biologiques en fonction des caractéristiques des éclusées et des hydrosystèmes

Modification of vortex structures in fishways by cylinder adjunction

The improvement of devices that allow the upstream migration of fishes through engineering constructions or natural obstructions in rivers is now a real priority to maintain the biodiversity. Vertical slot fishways are commonly used and are very effective in ensuring unhindered passage of the species of large size fishes [1]. The flows within these hydraulic structures are turbulent [2] and present unsteady vortex dynamic in relation to the geometric parameters of the pools (slopes, flow discharges and pool widths). The modes of locomotion of the fish depend to the species and are the object of several recent studies [3]. The fishes use the fluid motion generated inside the pools to the propulsion and to move easily upstream in the fishway. Nerveless the species with small sizes have some difficulties to upstream migrate because the kinematic energy and the velocity are too large for them. An experimental study is undertaken to characterize the turbulent flow for various configurations of vertical slot fishways and to determine how their characteristics might be modified in order to facilitate the passage of small species. Particle Image Velocimetry is achieved to analyze the effects of vertical cylinders within the pools on the dimensions of recirculation zones and the turbulence intensity. Mean velocity and fluctuation measurements inside a pool with and without cylinder are compared. The unsteady behaviours and the vortex flapping are examined

Numerical simulations of fish-friendly angled trashracks at model and real scale

Several amphihaline species, such as silver eels, suffer high mortality rates during their downstream migration, due to their passage through turbines. The combination of adapted trashracks (inclined or angled screen, lower bar spacing, …) with bypasses can efficiently prevent these mortalities. A numerical study has been carried out with such angled trashracks. Numerical results with model scale racks were validated against previous experimental results on model trashracks, resulting from head loss and velocity distribution measurements (Raynal et al., 2013). Real scale racks were then computed in order to evaluate the influence of both the bar spacing and the channel width on velocity distributions in real dimensions. The mesh generation and the numerical simulations were performed by the open source CFD software suite OpenFOAM. The trashrack solid comprised basic elements, individually created using CAD software and directly inserted in OpenFOAM’s mesh generation utility. For small scale configurations, grid refinement was applied at the flume walls, at trashrack bars and downstream of the trashrack, whereas only bars were refined for real scale racks. The resulting number of cells ranged between 100,000 and 1,500,000. Steady state results were obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations for an incompressible and monophasic flow. The k-ε, k-ε-based RNG, k-ω, k-ω-based shear stress transport (SST) and Spalart-Allmaras models were examined to select the most appropriate one in terms of computation time and result accuracy. Results show that the k-ε-RNG is the model best agreeing with experimental results. Two-dimensional calculations seem to provide quite satisfactory results although both the head losses and the size of the recirculation zone downstream of the trashrack are slightly under-estimated. Real scale results confirm experimental ones and show that the bar spacing slightly effects upstream velocity profiles. Downstream of the rack, simulations with different flume width demonstrated that the size of the recirculation zone is proportional to the channel width

Study on fish-friendly inclined and angled trashracks

This paper presents the results on trashrack head losses obtained by Raynal et al. [2013 a,b], [2014] for several configurations. More especially, it compares the head loss formulae proposed in these studies with various equations from the literature to improve energy losses prediction in fish-friendly configurations. These new predictive laws of head losses are applied to the renovation of a hydropower plant and show that inclined trashracks or angled trashracks with streamwise bars are reliable solutions when the bar spacing is reduced