ARTICLE Flow in nature-like fishway and its relation to fish behaviour F. Bretón, A.B.M. Baki, O. Link, D.Z. Zhu, and N. Rajaratnam Abstract: 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. Key words: ADV, fish habitat, fish passage, flow, nature-like fishways, turbulence. 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 a ` 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 a ` 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 a ` 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 a ` 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. 1. Introduction Fishways are hydraulic structures enabling fish to negotiate river obstructions such as dams, weirs, and under-road culverts. According to their design, one can distinguish standard and nature-like fishways. Standard fishways are built with so-called traditional materials such as concrete, steel or wood, and thus exhibit flat surfaces. They are useful only for a limited number of species. Standard fishways include pool type, vertical slots, Denil passes, eel ladders, fish locks, fish lifts and culverts (DVWK 2002). Nature-like fishways (see e.g., Cowx and Robin 1998; Wang and Katopodis 1999) are built with diverse materials like large wood debris, boulders, and riparian vegetation, imitating the natural stream geomorphological conditions (Parasiewicz et al. 1998). Thus, they create more diverse flow conditions within a cross section than standard fishways, being amenable to many species of fish and even also benthic organisms. DVWK (2002) and USBR (2007) provide design guidelines for this type of fishway. The ef- fectiveness of nature-like fishways is well documented. Eberstaller et al. (1998) reported a successful European grayling (Thymallus thy- mallus) migration, just prior to their spawning season, through two bypass channels in Austria (see also the experience of Schmutz et al. 1998 with pike perch, Stizostedion lucioperca). Aarestrup et al. (2003) monitored sea trout (Salmo trutta) movement through a 130 m long 1.6% slope nature-like bypass in Denmark. They reported that 50% of the fish could negotiate the fishway. Calles and Greenberg (2005) demonstrated the efficiency of a fishway consisting of a ramp of boulders (rocky-ramp) with a slope up to 2.5%. They observed migra- tions of various species reaching a combined efficiency of 74% (see also Calles and Greenberg 2007). Santos et al. (2005) were able to measure more than 7500 individual passages of striped mullet and other species (all with different life stages) in another nature-like bypass in Portugal. These examples confirm that this ‘nature-mimicking’ concept is both environmental friendly and good performing. According to several researchers (Cada and Odeh 2001; Nikora et al. 2003; Cotel et al. 2006) the properties of turbulence in a fishway might correlate with fish behaviour. Fish swimming per- formance within a fishway may depend on the intensity of turbu- lence (turbulent kinetic energy, Reynolds shear stress, and vorticity), its periodicity (time scale and dominant frequencies), its orientation (direction of vorticity and resultant forces), and on its length scale (eddy and vortex sizes) as discussed by Lacey et al. (2012). Recognizing that turbulence characteristics should be im- portant for fish passage, some studies on standard fishways hy- draulics have well described the turbulent flow field, including the analysis of distribution and quantification of turbulence prop- erties. For example, turbulence kinetic energy (TKE) is the most common variable to represent turbulence intensity. Guiny et al. (2005) reported maximum TKE values around 0.4 to 1.2 m 2 /s 2 , in pool-type fishways (depending on orifice sizes), whereas Silva et al. (2010) only found 0.02 m 2 /s 2 in the same kind of fishway. Liu et al. (2006) found 0.2 m 2 /s 2 in a vertical slot fishway and Received 18 July 2012. Accepted 19 March 2013. F. Bretón and O. Link. Departamento de Ingeniería Civil, Universidad de Concepción, Casilla 160-C Correo 3 Concepción, Chile. A.B.M. Baki, D.Z. Zhu, and N. Rajaratnam. Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB T6G 2W2, Canada. Corresponding author: Felipe Bretón (e-mail: fbreton@udec.cl). 567 Can. J. Civ. Eng. 40: 567–573 (2013) dx.doi.org/10.1139/cjce-2012-0311 Published at www.nrcresearchpress.com/cjce on 25 March 2013. Can. J. Civ. Eng. Downloaded from www.nrcresearchpress.com by University of Alberta on 06/12/13 For personal use only.