The time-dependent bridge pier scour during flood waves is analysed. Scour experiments were conducted in a novel installation able to produce complex hydrographs with high precision. Experimental data were used to test scour formulas including a new mathematical model. Results confirm the reliability and superior performance of the proposed dimensionless, effective flow work based model under steady and unsteady hydraulic conditions. Analyses highlight the impact of different hydrographs on scour, demonstrating the strong control by the hydrograph shape of the temporal evolution of scour depth and scour rate, although final scour after a flood only depends on the total effective flow work exerted by the hydrograph on the sediment bed. Hysteresis between flow discharge and scour rate is reported and explained. Flow acceleration is shown to play a minor role in scouring. The proposed model is a promising alternative for computation of local scour under highly unsteady hydraulic conditions

Experimental results on the nature-like fishway induced flow field and its relation to fish behaviour are presented. A rocky-ramp with 5% slope was built along a 8.9 m × 0.9 m × 0.6 m laboratory flume, and acoustic Doppler velocity measurements were taken in a grid with 186 points for low, middle, and high discharges. The flow is characterized applying spatial and point analysis techniques. Point analysis consistently shows that the boulder to boulder distance is small enough to disrupt turbulent coherent structures. At boulder wakes no predominance of sweep and ejection events occur, evidencing a good resting place for fish migration. The nature-like rocky-ramp offers a diversity of flow conditions controlled by the boulders geometry that might allow a variety of fishes to develop their preferred paths characterized by flow properties with different magnitudes depending on the particular species. Obtained results compare well with similar ones reported for other standard fishways.Résumé : Cet article présente les résultats d'expériences concernant le champ de courant induit dans une passe migratoire d'aspect naturel et sa relation avec le comportement des poissons. Une rampe rocheuse ayant une pente de 5 % a été construite le long d'un canal jaugeur de laboratoire mesurant 8,9 × 0,9 × 0,6 m; des mesures de vitesse ont été prises au débitmètre acoustique selon une grille de 186 points à des débits faibles moyens et élevés. L'écoulement est caractérisé en appliquant des techniques d'analyse spatiale et par points. L'analyse par points montre de manière uniforme que la distance de rocher à rocher est suffisamment petite pour perturber les structures cohérentes de turbulence. Il n'y a aucune prédominance de balayage et d'éjection dans les sillages des rochers, prouvant qu'il s'agit d'un bon endroit de repos pour les poissons en migration. La rampe rocheuse d'aspect naturel offre une diversité de conditions d'écoulement contrôlées par la géométrie des rochers, ce qui pourrait permettre à plusieurs espèces de poissons de développer leur chemin préféré selon les propriétés d'écoulement de différentes amplitudes propres aux espèces particulières. Les résultats obtenus se comparent bien à d'autres résultats similaires rapportés pour d'autres passes migratoires standards. [Traduit par la Rédaction] Mots-clés : débitmètre acoustique, habitat du poisson, passe migratoire, écoulement, passes migratoires d'aspect naturel, turbulence.

Most artificial fish passes have been developed in Northern temperate rivers and are designed to serve large, migratory sport fish species (mostly salmonids). Experience in construction and maintenance of fish passes show that salmon-criteria are not adequate for flat-land rivers and non-sport fishes. Consequently, over the last decade, design criteria have changed to take requirements of target species into account. Extrapolation of these concepts to rivers in the Southern Hemisphere with different hydrological conditions and fish community composition is not straight forward. This review focuses on requirements for an adequate hydraulic design of passes for non-sport fish species bodied (\15 cm) threatened by small hydropower dams (with a typical head of 3-5 m). First, fragmentation of fish populations due to river obstructions that impede longitudinal movements is introduced from the perspective of environmental sustainability, taking the Chilean indigenous freshwater fish species as a study case. Subsequently, relevant properties of fish passages are reviewed, and experimental issues for maintenance in captivity and determination of swimming abilities in the laboratory are presented. Following dimensional considerations controlling scales for an adequate hydraulic design of fish passes, involving fluid, flow, fish, and pass properties are discussed. Finally, we postulate that successful passage design should consider habitat connectivity as the key concept for preservation of this highly threatened native fish fauna.

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