The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

In the 12 years since Dudgeon et al. (2006) reviewed major pressures on freshwater ecosystems, the biodiversity crisis in
the world’s lakes, reservoirs, rivers, streams and wetlands has deepened. While lakes, reservoirs and rivers cover only
2.3% of the Earth’s surface, these ecosystems host at least 9.5% of the Earth’s described animal species. Furthermore,
using the World Wide Fund for Nature’s Living Planet Index, freshwater population declines (83% between 1970 and
2014) continue to outpace contemporaneous declines in marine or terrestrial systems. The Anthropocene has brought
multiple new and varied threats that disproportionately impact freshwater systems. We document 12 emerging threats
to freshwater biodiversity that are either entirely new since 2006 or have since intensified: (i) changing climates; (ii)
e-commerce and invasions; (iii) infectious diseases; (iv) harmful algal blooms; (v) expanding hydropower; (vi) emerging
contaminants; (vii) engineered nanomaterials; (viii) microplastic pollution; (ix) light and noise; (x) freshwater salinisation;
(xi) declining calcium; and (xii) cumulative stressors. Effects are evidenced for amphibians, fishes, invertebrates, microbes,
plants, turtles and waterbirds, with potential for ecosystem-level changes through bottom-up and top-down processes.
In our highly uncertain future, the net effects of these threats raise serious concerns for freshwater ecosystems. However,
we also highlight opportunities for conservation gains as a result of novel management tools (e.g. environmental flows,
environmental DNA) and specific conservation-oriented actions (e.g. dam removal, habitat protection policies,managed
relocation of species) that have been met with varying levels of success.Moving forward, we advocate hybrid approaches
that manage fresh waters as crucial ecosystems for human life support as well as essential hotspots of biodiversity and
ecological function. Efforts to reverse global trends in freshwater degradation now depend on bridging an immense gap
between the aspirations of conservation biologists and the accelerating rate of species endangerment.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/brv.12480

Emerging threats and persistent conservation challenges for freshwater biodiversity

The Structure of Turbulent Shear Flow By Dr. A. A. Townsend. Pp. xii + 315. 8¾ in. × 5½ in. (Cambridge: At the University Press.) 40s.

/pdf/the-structure-of-turbulent-shear-flow-2yf3szhaqb.pdf

The Structure of Turbulent Shear Flow

The main impacts of riparian vegetation on hydrological processes are briefly reviewed in order to highlight needs and perspectives for research and management goals. This review is based upon three distinct influences of riparian vegetation on hydrological processes: (i) the control of runoff, i.e. the physical impact of living and dead plants on hydraulics, (ii) the impact of plant physiology on water uptake, storage and return to the atmosphere, and (iii) the impact of riparian vegetation functioning on water quality. Riparian vegetation influences runoff through complex hydraulic interactions during baseflows as well as overbank flows. The contribution of fine vegetational structures to landscape hydrological roughness needs to be considered in relation to the spatial complexity (patchiness, vertical stratification, rhizosphere) and temporal variability (phenology, succession) of plant communities. With the exception of some woody species, the uptake, storage and return of water to the atmosphere is poorly known for riparian communities, and therefore the assessment of the regional hydrological importance of the riparian corridor remains difficult to estimate. Although better understood than the above two influences of riparian vegetation on hydrological processes, there are still a number of unresolved issues concerning the role of riparian vegetation in controlling water quality. In particular, little is known about the coupling of microbial and vegetational functions in nutrient cycling and the dynamics of carbon release from coarse and fine plant debris. The influence of vegetation complexity and plant diversity on both qualitative and quantitative aspects of water cycling remains an important area for future research. Fundamental and management issues are identified in relation to the use of riparian vegetation as a model and as a tool.

Impacts of riparian vegetation on hydrological processes

Infrared thermography transforms the thermal energy, emitted by objects in the infrared band of the electromagnetic spectrum, into a visible image. This feature represents a great potentiality to be exploited in many fields, but this technique is still not adequately enclosed in industrial instrumentation because of a lack of adequate knowledge; at first sight, it seems too expensive and difficult to use. The aim of the present paper is to shortly overview existing work and to describe the most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to. Results may be regarded from two points of view, either as validating infrared thermography as a full measurement instrument, or as presenting infrared thermography as a novel technique able to deal with several requirements, which are difficult to perform with other techniques. This study is also an attempt to give indications for a synergic use of the different thermographic methods and sharing experiences in the different fields.

http://iopscience.iop.org/article/10.1088/0957-0233/15/9/R01/pdf

Recent advances in the use of infrared thermography

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.

/pdf/the-future-of-fish-passage-science-engineering-and-practice-4v49f72c79.pdf

The future of fish passage science, engineering, and practice

The discusser wishes to congratulate the authors for their authoritative paper. He believes that the work is a necessary addition to the topic of stepped spillway flow. The paper presents a true systematic study of skimming flow. Despite the outstanding insights of the study, the discusser wishes to point two weaknesses: an inadequate analysis of the air entrainment process and some limitations of the velocity probe measurements.

https://espace.library.uq.edu.au/view/UQ:9291/DIS_Cham.pdf

Characteristics of Skimming Flow over Stepped Spillways

This paper presents the results of an experimental study on the structure of turbulent flow near groin‐like structures. Based on experimental observations, the deflected flow has been analyzed using the model of the three‐dimensional turbulent boundary layer. The flow bounded by the separating stream line, the groin, and the adjacent bank has been analyzed by treating it as a shear layer in which the velocity profiles have been found to be similar. The amplified bed shear stress near the groin has also been analyzed using the similarity idea. Even though the majority of the present experiments were done with the thin‐plate groin, some observations were also made on a groin with a semicylindrical hose.

Flow Near Groin‐Like Structures

This paper presents the results of an experimental study on erosion caused by (submerged) plane wall jets of air and water on beds of sand and polystyrene in Part I and by (submerged) impinging plane jets of water and air on beds of sand. The characteristic features of the scoured bed in the asymptotic state has been analysed using dimensional analysis.

Erosion by plane turbulent jets

(1973). PLANE TURBULENT IMPINGING JETS. Journal of Hydraulic Research: Vol. 11, No. 1, pp. 29-59.

Nallamuthu Rajaratnam

Papers

The future of fish passage science, engineering, and practice

Characteristics of Skimming Flow over Stepped Spillways

Flow Near Groin‐Like Structures

Erosion by plane turbulent jets

Plane turbulent impinging jets