To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Many global challenges, though interconnected, have been addressed singly, at times reducing one problem while exacerbating others. Nexus approaches simultaneously examine interactions among multiple sectors. Recent quantitative studies have revealed that nexus approaches can uncover synergies and detect trade-offs among sectors. If well implemented, nexus approaches have the potential to reduce negative surprises and promote integrated planning, management and governance. However, application and implementation of nexus approaches are in their infancy. No studies have explicitly quantified the contributions of nexus approaches to progress toward meeting the Sustainable Development Goals. To further implement nexus approaches and realize their potential, we propose a systematic procedure and provide perspectives on future directions. These include expanding nexus frameworks that consider interactions among more sectors, across scales, between adjacent and distant places, and linkages with Sustainable Development Goals; incorporating overlooked drivers and regions; diversifying nexus toolboxes; and making these strategies central in policy-making and governance for integrated Sustainable Development Goal implementation. Sustainability challenges, such as feeding people with fewer resources, involve challenges at the nexus of multiple issues, such as food, water and energy. This Review explores such nexus approaches, surveying their use towards sustainable development challenges, discussing examples, and proposing a systematic procedure and future directions.

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Nexus approaches to global sustainable development

Attraction and passage efficiency were reviewed and compared from 19 monitoring studies that produced data for evaluations of poolâandâweir, Denil, verticalâslot and natureâlike fishways. Data from 26 species of anadromous and potamodromous fishes from six countries were separated by year and taxonomic family into a matrix with 101 records. Attraction performance was highly variable for the following fishway structures: poolâandâweir (attraction rangeâ=â29â100%, meanâ=â77%, medianâ=â81%), verticalâslot (attraction rangeâ=â0â100%, meanâ=â63%, medianâ=â80%), Denil (attraction rangeâ=â21â100%, meanâ=â61%, medianâ=â57%) and natureâlike (attraction rangeâ=â0â100%, meanâ=â48%, medianâ=â50%). Mean passage efficiency was inversely related to mean attraction efficiency by fishway structure type, with the highest passage for natureâlike fishways (rangeâ=â0â100%, meanâ=â70%, medianâ=â86%), followed by Denil (rangeâ=â0â97%, meanâ=â51%, medianâ=â38%), verticalâslot (rangeâ=â0â100%, meanâ=â45%, medianâ=â43%) and poolâandâweir (rangeâ=â0â100%, meanâ=â40%, medianâ=â34%). Principal components analysis and logistic regression modelling indicated that variation in fish attraction was driven by biological characteristics of the fish that were studied, whereas variation in fish passage was related to fishway type, slope and elevation change. This metaâanalysis revealed that the species of fish monitored and structural design of the fishways have strong implications for both attraction and passage performance, and in most cases, existing data are not sufficient to support design recommendations. Many more fishway evaluations are needed over a range of species, fishway types and configurations to characterize, to optimize and to design new fishways. Furthermore, these studies must be performed in a consistent manner to identify the relative contributions of fish attraction and passage to overall fishway performance at each site.

Performance of fish passage structures at upstream barriers to migration

Much effort has been devoted to developing, constructing and refining fish passage facilities to enable target species to pass barriers on fluvial systems, and yet, fishway science, engineering and practice remain imperfect. In this review, 17 experts from different fish passage research fields (i.e., biology, ecology, physiology, ecohydraulics, engineering) and from different continents (i.e., North and South America, Europe, Africa, Australia) identified knowledge gaps and provided a roadmap for research priorities and technical developments. Once dominated by an engineering-focused approach, fishway science today involves a wide range of disciplines from fish behaviour to socioeconomics to complex modelling of passage prioritization options in river networks. River barrier impacts on fish migration and dispersal are currently better understood than historically, but basic ecological knowledge underpinning the need for effective fish passage in many regions of the world, including in biodiversity hotspots (e.g., equatorial Africa, South-East Asia), remains largely unknown. Designing efficient fishways, with minimal passage delay and post-passage impacts, requires adaptive management and continued innovation. While the use of fishways in river restoration demands a transition towards fish passage at the community scale, advances in selective fishways are also needed to manage invasive fish colonization. Because of the erroneous view in some literature and communities of practice that fish passage is largely a proven technology, improved international collaboration, information sharing, method standardization and multidisciplinary training are needed. Further development of regional expertise is needed in South America, Asia and Africa where hydropower dams are currently being planned and constructed.

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The future of fish passage science, engineering, and practice

Fishways and other passage facilities frequently prevent or delay the passage of fishes, highlighting the need for effectiveness monitoring. We reviewed the scientific literature from 1960 to 2008 reporting on effectiveness monitoring of fish passage facilities to assess what taxa and life-stages have been studied, the questions that are asked during evaluation, and how these varied over time or by geographic region. We identified 96 peer-reviewed articles of which 68% focused on passage by adult fishes. Salmoniformes was the most studied order (58% of studies). The focus of fishway evaluations did not change over the years, but varied significantly by geographic region. Studies from the tropics had a broader taxonomic scope than studies from temperate locations. Exogenous mechanisms of passage failure, such as environmental, structural and behavioural factors, were studied in 90% of studies from North America but only 50% of studies from Europe, South America and Australia. Endogenous (i.e. physiological) mechanisms affecting passage success were not often assessed anywhere, though they were a powerful means of evaluating mechanisms of failure. Few studies monitored migration after fish had left a facility. To improve effectiveness monitoring of passage facilities, we suggest that both endogenous and exogenous mechanisms need to be studied in an integrated fashion to understand passage failure and to inform design or operational changes that could improve passage efficiency. In addition post-departure monitoring is required to more completely assess the fitness consequences of passage.

http://faculty.forestry.ubc.ca/hinch/Roscoe&Hinch_FF_2010.pdf

Effectiveness monitoring of fish passage facilities historical trends, geographic patterns and future directions

SUMMARY The effect of turbulent eddy diameter, vorticity and orientation on the 2 min critical swimming speed and stability of creek chub ( Semotilus atromaculatus ) is reported. Turbulent eddies were visualized and their properties were quantified using particle image velocimetry (PIV). Flow fields with an increasing range in eddy diameter were created by inserting cylinder arrays upstream from the swimming test section. Eddy vorticity increased with increasing velocity. Two orientations of eddies, eddies spinning about a vertical axis and eddies spinning about a horizontal (wall-to-wall) axis, were investigated. Stability challenges were not observed until the largest (95th percentile) eddy diameters reached 76% of the fish body total length. Under these conditions fish were observed to spin in an orientation consistent with the rotational axis of the large eddies and translate downstream. These losses in postural control were termed ‘spills’. Spills were 230% more frequent and lasted 24% longer in turbulent flow fields dominated by horizontal eddies than by vertical eddies of the same diameter. The onset of spills coincided with a 10% and 22% reduction in critical swimming speed in turbulent flows dominated by large vertical and horizontal eddies, respectively. These observations confirm predictions by Pavlov et al., Cada and Odeh, Lupandin, and Liao that the eddy diameter, vorticity and orientation play an important role in the swimming capacity of fishes.

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The effects of turbulent eddies on the stability and critical swimming speed of creek chub (Semotilus atromaculatus).

The physical habitat requirements of cover, depth, and current speed for brown trout Salmo trutta are associated with high shear zones in stream flows, which in turn result in high turbulence. Observations were made on current speeds and turbulence intensity (TI) in a sand-bed trout stream. Exemplary transects showed that current speeds ranged from 0 to 60 cm/s and that TI ranged from 0 to 0.7. Turbulence intensity was inversely related to current speed. Brown trout were usually found in the lower 5 cm of the stream, where shear forces result in high turbulence. Locations occupied by brown trout had lower TI than similar locations without brown trout but higher TI than is typical of an average stream.

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Do Brown Trout Choose Locations with Reduced Turbulence

Effective fishway design requires extensive integration of biological and hy- draulic data. Many relevant biological parameters remain poorly characterized, however, and the lack of adequate biological data has long been recognized as a central weakness in fish passage technology. This is of particular concern given the growing recognition of the impor- tance of passing a broad diversity of species. Part of the reason for this weakness is the diffi- culty of identifying relevant biological, hydraulic, and other physical parameters. We propose that by both exploring questions suggested by current knowledge, and also by increasing the frequency and refining the methods with which fishways are evaluated, two results can be achieved: our understanding of design effectiveness can be improved, and research questions can be prioritized through adaptive management. We describe a framework and rationale for fishway evaluations that identifies several promising avenues of research. Understanding correlates of passage performance is increasingly important as fish passage needs expand on a global scale.

Fishway Evaluations for Better Bioengineering: An Integrative Approach

Synopsis Over the past century, many ideas have been developed on the relationships between water flow and the structure and shape of the body and fins of fishes, largely during swimming in relatively steady flows. However, both swimming by fishes and the habitats they occupy are associated with vorticity, typically concentrated as eddies characteristic of turbulent flow. Deployment of methods to examine flow in detail suggests that vorticity impacts the lives of fishes. First, vorticity near the body and fins can increase thrust and smooth variations in thrust that are a consequence of using oscillating and undulating propulsors to swim. Second, substantial mechanical energy is dissipated in eddies in the wake and adaptations that minimize these losseswould be anticipated. We suggest that such mechanisms may be found in varying the length of the propulsive wave, stiffening propulsive surfaces, and shifting to using median and paired fins when swimming at low speeds. Eddies in the flow encountered by fishes may be beneficial, but when eddy radii are of the order of 0.25 of the fish’s total length, negative impacts occur due to greater difficulties in controlling stability. The archetypal streamlined ‘‘fish’’ shape reduces destabilizing forces for fishes swimming into eddies.

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Turbulence: does vorticity affect the structure and shape of body and fin propulsors?

Following Bradshaw’s analogy between rotating and stratified flows, the turbulence within a vortex is analyzed using a new model for stratified entrainment. At the vortex radius where the tangential velocity is a maximum, the model predicts that the flow is so strongly “stratified” that even the smallest turbulent eddies are incapable of transporting fluid there. The growth of the vortex is thus limited by molecular viscosity, even though the vortex Reynolds number is large. The model prediction is compared to experiments in the literature of wingtip vortices. The result is consistent with the remarkable observations of laminar-like growth of this turbulent flow.

Aline Cotel

Papers

The effects of turbulent eddies on the stability and critical swimming speed of creek chub (Semotilus atromaculatus).

Do Brown Trout Choose Locations with Reduced Turbulence

Fishway Evaluations for Better Bioengineering: An Integrative Approach

Turbulence: does vorticity affect the structure and shape of body and fin propulsors?

Turbulence inside a vortex