Mean flow properties and turbulent characteristics of uniform open-channel were experimentally studied in a reasonably steep channel with an erodible gravel bed. A recently developed Acoustic Doppler Velocity Profiler (ADVP) was used to obtain instantaneously the information on profiles. From these measurements, mean velocities, turbulence-intensities as well Reynolds-stress profiles obtained. The experimental results show that: i) velocity profile can be expressed by log-law Br ≃ 8.42 inner...

A method is proposed to reduce the noise contribution mean turbulence parameters obtained by 3D acoustic Doppler velocity profiler measurements. It based on a spectrum reconstruction from cross-spectra evaluations of two independent and simultaneous measurements same vertical component over whole water depth. The spectra variances are calculated removed for three fluctuating components measured in turbulent, open-channel flow. corrected show −5/3 slope inertial subrange delimited frequency...

The influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components instantaneous velocity vector particle concentration with an acoustic flux profiler. measurements were carried out in clear water particle-laden open-channel flows. In both cases, they clearly show predominance ejection sweep phases that are part a burst cycle. analysis further demonstrates importance sediment resuspension transport. Ejections...

Abstract Although three-receiver acoustic Doppler velocimeters (ADV) can accurately measure the three-dimensional mean flowfield, their turbulence measurements suffer from parasitical noise contributions. By adding a fourth receiver and optimizing transducer configuration, results be considerably improved. Redundant information is obtained for all velocity components, which theoretically allows to achieve noise-free measurements. Experiments show that contribution not completely eliminated...

ABSTRACT Shear velocity u * is an important parameter in geophysical flows, particular with respect to sediment transport dynamics. In this study, we investigate the feasibility of applying five standard methods [the logarithmic mean profile, Reynolds stress turbulent kinetic energy (TKE) wall similarity and spectral methods] that were initially developed estimate shear smooth bed flow over a loose coarse gravel ( D 50 = 1·5 cm) under sub‐threshold conditions. The analysis based on...

The measurement of suspended sediment, particularly in field settings, is important the documentation sediment transport and deposition. Many techniques have been used with varying degrees success. techniques, including their operating principles, advantages, disadvantages are discussed. discussed include acoustic, bottle, pump, focused beam reflectance, laser diffraction, nuclear, optical backscatter, transmission, spectral reflectance. Emphasis placed on instrumentation as this area...

A monostatic acoustic Doppler velocity profiler (ADVP) for use in hydraulic research is presented including signal treatment algorithms. The 1-MHz ADVP used the present study has an accuracy better than 2 mms˙s−1 with a range of up to 100 cm velocities 290 cms˙s−1 and resolution 256 points profile. Results measurements uniform flow two laboratory open channels smooth gravel beds compare favorably established distribution laws mean velocity, variance, Reynold's stress, indicating that...

During the winters of 1998 and 1999, observations were made cascading cold water from nearshore, shallow “shelf” zones down sloping sides Lake Geneva. Cascading starts on average 10 hours after onset surface cooling. The draining descends like a gravity current, downslope speed head these slugs water, U , has mean value 5.2 cm s −1 with persisting, average, for 8 hours. When Monin‐Obukov length scale at surface, L is negative, implying convection occurs, /| |> 1,where shelf depth,...

We analyzed season-long water level records at 12 stations around the Lake of Geneva (local name Léman) for evidence internal seiches modified by Coriolis force and compared results with predictions from a two-layer numerical model real bottom topography typical wind situations. Results are also those obtained current temperature measurements in lake. Agreement was satisfactory all cases. Model both indicated that only three seiche modes excited: 1st mode 3rd mode, which Kelvin-seiche...

Measurements of water velocity and turbulence in a flume using Doppler sonar operating at 1 MHz are presented. Analysis the results shows that instrument qualifies as very useful tool for nonintrusive accurate measurement vertical profiles horizontal u w well parameters including ¯u′w′ Reynold's stress component. The circulating is filtered, so backscattering signal relates primarily to temperature microstructure occurring λ/2, with λ=0.15 cm being wavelength. Quantitative measurements...

In lentic water bodies, such as lakes, the temperature near surface typically increases during day, and decreases night a consequence of diurnal radiative forcing (solar infrared radiation). These variations penetrate vertically into water, transported mainly by heat conduction enhanced eddy diffusion, which may vary due to atmospheric conditions, wave breaking, internal dynamics body. two processes can be described in terms an effective thermal diffusivity, experimentally estimated....

Hyperpycnal (negatively buoyant) river inflows into lakes or reservoirs plunge upon entry, generating gravity-driven underflows near the bed. When density excess of these is primarily due to high sediment concentrations, they are referred as turbidity currents. If encounter a layer equal density, will detach from bed and intrude water column, forming an interflow. In currents, such underflow-interflow transitions often happen through process called ‘lofting’, whereby flow...

Turbidity currents represent a distinctive type of subaqueous density currents, characterized by excess that is due to the sediment load. are important in lakes, reservoirs and oceans have implications on hazard management, reservoir sedimentation water quality. The existence turbidity has been inferred 19th century from canyons lake bottoms 20th successive cable breaks telecommunication cables ocean floor. From 1990s on, Acoustic Doppler Current Profiler’s (ADCP) allowed measuring...

We conducted a combined field and numerical study of the effects episodic internal Kelvin-type waves on bottom boundary turbulence exchange passive tracer between main basin side large lake (Lake Geneva). High-resolution measurements vertical current structure near entrance 25-km-long 70-m-deep revealed that hypolimnetic speeds frequently exceed 0.2 m s™1, leading to turbulent layer several meters thick with logarithmic profiles region strong shear across thermocline. The time series...

Abstract We examine nearshore and pelagic current variability in Lake Geneva, a large deep lake western Europe, using observations from several measurement locations three‐dimensional numerical model for the period 2014–2016. Linear internal seiche modes excited by wind forcing clearly appear as peaks energy spectra measurements offshore locations. In contrast, data, where currents interact with bed, reveal negligible contribution of seiches to total kinetic energy. A similar contrast is...

Abstract Submesoscale filaments are a well‐documented feature of oceanic flow fields. Based on the analysis high‐resolution 3D numerical simulations, field observations, and remote sensing imagery, this study, carried out in Lake Geneva, Western Europe's largest lake, provides for first time evidence that submesoscale also exist lake. Field observations confirm submesoscale, cold‐water formed at edges center counterclockwise rotating large‐scale gyre during summertime above thermocline, as...

Abstract. Records of wind, air temperature and pressure from nine stations, situated along the shoreline Lake Geneva, Switzerland, were analyzed for summer period May to September. At all stations consistent appearance significant spectral peaks changes in wind direction at diurnal frequency indicates importance lake-land breezes. It is shown that surrounding topography has a strong modifying effect (temporal spatial) on breeze. Superimposed this cyclic pattern, short episodes winds with...

An ultrasonic constant-beam-width transducer system which is capable of generating an extended focal zone by electronically focusing the beam over desired water-depth range described. Beam directivity measurements show that higher and reduction in side-lobe level lead to increase signal-to-noise ratio up 15 dB compared with a plane disc transducer. It also allows one attain significant undesirable spectral broadening effects case transducers lower final resolution interfere correct...

Three-dimensional (3-D) quasi-instantaneous acoustic Doppler velocity profiles at the center of uniform, turbulent open-channel flow over smooth and rough beds have been analyzed for dynamics coherent structures. The qualitative aspects simultaneously measured Eulerian shear stress signatures identify structures in water column. A cumulant discard method is applied to describe statistical properties covariance terms u'w' along mean v'w' across relative their time means. Conditional...

ABSTRACT Large‐scale flow structures (LSFS) in the streamwise direction are important features of gravel‐bed river flows, because they may contribute to sediment transport and gas exchange. In present study, these detected using Huang's empirical mode decomposition reconstructed with phase‐averaging techniques based on a Hilbert transform velocity signal. The analysis is fluctuating component 15 quasi‐instantaneous profiles measured three‐dimensional (3D) acoustic Doppler profiler (ADVP) an...