Railway Dams in Australia: Six Historical Structures

With the European settlement of Australia in the 19th century, the industrial development of the continent was closely related to the construction and extension of railway lines. Numerous railway dams were built to provide water for the steam locomotives and several are still used today. In this paper, the authors reviewed six railway dams. One, the 75-Miles dam, was a thick concrete arch dam, the first concrete arch dam in Australia and possibly in the world. The Tallong dam, completed in 1883, is an unique brick buttress-slab structure. The de Burgh dam, 1907-1908, was the first reinforced-concrete thin-arch dam in Australia. The other three structures were thin concrete arch dams but their reservoirs rapidly silted up, one being subjected to the most extreme recorded sedimentation rate in Australia. The background of the railway engineers is discussed. It is shown that, in the 19th century, the railway engineers had a broad-based education, and their expertise led to advanced dam designs (e.g. 75-Miles dam, de Burgh dam)

Flow patterns in nappe flow regime down low gradient stepped chutes

Although modern gravity dam spillways include often steep chutes operating in skimming flow regime, succession of free-falling nappes (i.e. nappe flow regime) are more common on low gradient chutes and cascades, and this flow situation received little attention to date. New experiments were conducted in nappe flows without hydraulic jump in two large-size facilities with flat slopes. The flow on the stepped cascade displayed complex, three-dimensional patterns. Detailed air-water flow measurements were performed in the jet, at nappe impact and in the downstream flow region. Key results demonstrated that the flow on each step was rapidly varied (RVF), highly three-dimensional and strongly aerated

The Hydraulics of Roman Aqueducts: What do we know? Why should we learn ?

The Roman engineers were at the forefront of science and their engineering heritage included some magnificent aqueducts, many of which are still standing. While some scholars suggested that Roman engineers did not know the basic principle of conservation of mass, the Roman aqueducts provide a clear demonstration of the high level of hydraulic engineering expertise. The successful design and operation of these outstanding systems were massive achievements by modern standards. The development of regulation basins, culverts and energy dissipators was far from obvious. It is the writer's opinion that the leading Roman hydraulic engineers involved with the major aqueducts in Gaul and North-Africa understood the concepts of continuity and momentum

Impact of Commercial Search Engines and International Databases on Engineering Teaching and Research

For the last three decades, the engineering higher education and professional environments have been completely transformed by the "electronic/digital information revolution" that has included the introduction of personal computer, the development of email and world wide web, and broadband Internet connections at home. Herein the writer compares the performances of several digital tools with traditional library resources. While new specialised search engines and open access digital repositories may fill a gap between conventional search engines and traditional references, these should be not be confused with real libraries and international scientific databases that encompass textbooks and peer-reviewed scholarly works. An absence of listing in some Internet search listings, databases and repositories is not an indication of standing. Researchers, engineers and academics should remember these key differences in assessing the quality of bibliographic "research" based solely upon Internet searches

Culvert hydrodynamics to enhance upstream fish passage: fish response to turbulence

Waterway culverts are very common structures along water systems, ranging from rural roads to national highways and urban drainage networks. Current design guidelines are inadequate for fish passage, especially small-bodied Australian native fish species. Physical modelling was conducted in the laboratory under controlled flow conditions with the aim to maximise slow flow and recirculation regions suitable to upstream passage of small fish. An asymmetrical boundary roughness configuration was tested, consisting of a rough invert and rough sidewall, and the results were compared to a smooth boundary configuration. The hydrodynamic measurements showed the marked effect of boundary roughness on the distributions of time-averaged velocity and velocity fluctuations. Experiments were also conducted on two small fish species (Silver perch, Duboulay's Rainbowfish). This roughness configuration appeared to provide secondary current regions next to the rough sidewall and at the corner between the rough sidewall and channel bed

Characteristics of clustered particles in skimming flows on a stepped spillway

Air–water flows at hydraulic structures are commonly observed and called white waters. The free-surface aeration is characterised by some intense exchanges of air and water leading to complex air–water structures including some clustering. The number and properties of clusters may provide some measure of the level of particle-turbulence and particle–particle interactions in the high-velocity air–water flows. Herein a re-analysis of air–water clusters was applied to a highly aerated free-surface flow data set (Chanson and Carosi, Exp Fluids 42:385–401, 2007). A two-dimensional cluster analysis was introduced combining a longitudinal clustering criterion based on near-wake effect and a side-by-side particle detection method. The results highlighted a significant number of clustered particles in the high-velocity free-surface flows. The number of bubble/droplet clusters per second and the percentage of clustered particles were significantly larger using the two-dimensional cluster analysis than those derived from earlier longitudinal detection techniques only. A number of large cluster structures were further detected. The results illustrated the complex interactions between entrained air and turbulent structures in skimming flow on a stepped spillway, and the cluster detection method may apply to other highly aerated free-surface flows

The known unknowns of hydraulic engineering

Hydraulic engineers and researchers deal with scientific challenges involving turbulent flow motion and its interactions with the surroundings. Turbulent flows are characterised by unpredictable behaviour, and little systematic research has yet been conducted in natural systems. This paper discusses the implications of recent developments in affordable instrumentation previously characterised by intrinsic weaknesses that adversely affect the quality of the signal outputs. A challenging application is the unsteady turbulence field in tidal bores. The interactions between open channel flows and movable boundaries and atmosphere illustrate another aspect of our limited knowledge. Rapid siltation of reservoirs and air entrainment in turbulent free-surface flows are discussed. In both applications, hydraulic engineers require some broad-based expertise. In turn the education of future hydraulic engineers is of vital importance

Reply to discussion by G. Carosi and H. Chanson on "Turbulence characteristics in skimming flows on stepped spillways"

A main technical issue seems to be associated with the structure of the two-phase air–water flow skimming over the pseudo-bottom formed by the step edges. This is a difficult topic. In the air–water skimming flow, the microscopic structure of the gas–liquid mixture is closely linked with the interactions between turbulent vortices and air–water entities (bubbles, droplets, packets) (e.g., Chanson and Toombes 2002; Carosi and Chanson 2008; Gonzalez and Chanson 2008). In the high-velocity free-surface flow, the strong interactions between the turbulent waters and the atmosphere lead to a complete deformation at the interface. Through the free-surface, air is continuously trapped, and the resulting air–water mixture extends through the entire flow (Rao and Kobus 1971; Wood 1991; Chanson 1997). The air–water flow is characterized a complicated two-phase turbulent motion with void fractions ranging from some small, often nonzero values close to the invert to 100% above a pseudo "free-surface" that is usually defined as the location where the void fraction equals 90% (Cain and Wood 1981; Wood 1991; Chanson 1997; Matos 2000). The notion of "effective homogenous flow" contradicts detailed measurements conducted with accurate instrumentations in large-size facilities with well-controlled flow conditions and it is obsolete. Recent findings (Carosi and Chanson 2008) demonstrated in fact a marked changed in flow properties for C ~ 0.95 to 0.97, that is consistent with earlier studies suggesting the use of Y95 or even Y98 as the characteristic air–water flow thickness (Jevdjevich and Levin 1953; Aivazyan 1986)