Bed Roughness

The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10-100 km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

Estimating channel roughness is crucial for whatever engineering plans that have been in mind for any reach under consideration. Not only is resistance coefficient not a measurable quantity, but also various factors affecting on its value make its estimation a challenge. Despite of numerous methods available for roughness estimation, the complexity of some of available iterative schemes particularly with no mechanism for modifying initial guess in each iteration restrain numerical modelers to apply merely outdated resistance equations in practice. In order to improve the estimation of hydraulic resistance, a new straightforward flow-dependent scheme, which is capable of estimating Manning's coefficient due to grain and form roughness, is introduced. A large data is utilized to calibrate and testify the new scheme. The results of comparing the new scheme with that of different models available in the literature show that it achieves the best estimation results and yields to more than 0.87 and 0.67 for R 2 , 0.15 and 0.17 for mean absolute relative error for estimating grain and form Manning's coefficients, respectively. This comparison demonstrates that the results achieved by the new scheme are acceptably accurate in favor of roughness estimation.

This study uses machine learning (ML) to predict the end-depth structure's discharge and critical depth (yc). Linear regression, M5P, random forest, random tree, reduced error pruning tree, and Gaussian process (GP) are the ML methods used in this investigation. The findings indicate that the radial kernel function-based GP model is most suitable compared to other applied models with the lowest root-mean-square error = 0.0021, 0.007, normalized root-mean-square error = 0.0361, 0.0516 representing mean absolute error = 0.0015, 0.004 and the highest coefficient of correlation = 0.9912, 0.9916, Legates and McCabe's index = 0.8839, 0.9026 Willmott's index = 0.9956, 0.9956, and Nash Sutcliffe model efficiency = 0.9823, 09830 for yc for the end-depth structure (yc) and discharge (Q) with the testing stage, respectively. Results of the sensitivity study indicate that the friction coefficient is the most significant input variable compared to other parameters for predicting (yc) and flow running via the thickness model's last stage (Q) using this dataset

In this paper twelve different empirical resistance coefficients expressed in terms of Manning's roughness are used apiece in seventeen known compositing methods. The data obtained from ten different cross-sections of the Sefidrood River, Iran, are used for the evaluation of the empirical formulas. The present case-study is selected from a reach with gravel bed topology. Then no remarkable bed form exists. Comparison of the calculated discharges and resistance coefficients with measurements shows that the Keulegan formula used simultaneously with the Brownlie formula in different compositing methods results in highly over estimated discharges, while the Meyer-Peter & Muller, Marion, Chien-Mai formulas in conjunction with the total force approach match best with the measurements. Also comparison of the calculated discharges from empirical formulas in individual sections reveals that Chien-Mai and Subramanya formulas have the least discrepancies from measurements.

With the populations of anadromous salmonids in steep decline throughout California, many river restoration projects attempt to bring fish back to tributaries by enabling fish passage and creating spawning habitat. Carneros Creek, a tributary of the Napa River, is an incised and sinuous stream which poses a challenge for restoration planning land use management, as the watershed supports steelhead runs and valuable agricultural land. We documented the physical channel morphology of a 150 meter long reach in the Upper Carneros Creek using ground based Light Detection and Ranging (LiDAR) scans and assessed grain size using pebble counts in order to gain insight into restoration and management opportunities. These data provide a baseline geomorphic assessment for future restoration projects and allowed us to compare velocities predicted by 1-dimensional (1D) and 2-dimensional (2D) models. For the 1D model, we simulated flows by pulling out cross-sectional points from the LiDAR scans. Using a Manning's n value of 0.033 for clean, sinuous channels with some pools and riffles, we found 1D velocities at four cross-sections corresponded to 3.3 m/s, 2.3 m/s, 2.5 m/s, and 2.8 m/s with a mean velocity of 2.73 m/s. For the 2D model, we used FaSTMECH in U.S. Geological Survey's (USGS) Multi-Dimensional Surface Water Modeling System (MD_SWMS) based on LiDAR data. Our 2D velocity results decreased to an average of 0.85 m/s and ranged from 0 to 4.53 m/s based on local slope changes from the detailed channel morphology measurements. By adding grain size variable roughness to the 2D model, we saw a range of velocities from 0 to 1.98 m/s with an average of 0.65 m/s. We found that because 1D modeling of cross-sectional data using Manning's equation does not simulate flow curvature in bends, our 2D model can provide betterdefined velocities than a 1D model. Because Carneros Creek is listed as a viable migration passage for steelhead, restoration managers concerned about the level of incision and the 'flashy' nature of the stream should consider how the variability in channel morphology and geomorphology models influence velocity predictions that are important drivers of habitat quality for migrating fish and juveniles.

Uncertainty affects estimates of the power potential of tidal currents, resulting in large ranges in values reported for a given site, such as the Pentland Firth, UK. We examine the role of bottom friction, one of the most important sources of uncertainty. We do so by using perturbation methods to find the leading-order effect of bottom friction uncertainty in theoretical models by Garrett & Cummins (2005 Proc. R. Soc. A 461 , 2563–2572. ( doi:10.1098/rspa.2005.1494 ); 2013 J. Fluid Mech. 714 , 634–643. ( doi:10.1017/jfm.2012.515 )) and Vennell (2010 J. Fluid Mech. 671 , 587–604. ( doi:10.1017/S0022112010006191 )), which consider quasi-steady flow in a channel completely spanned by tidal turbines, a similar channel but retaining the inertial term, and a circular turbine farm in laterally unconfined flow. We find that bottom friction uncertainty acts to increase estimates of expected power in a fully spanned channel, but generally has the reverse effect in laterally unconfined farms....

Estimates of the heights of large (0.1-0.4 m heights and 1-10 m horizontal lengths) migrating bedforms on a sandy beach made with fixed, single-point altimeters are similar to heights estimated from profiles across the bedforms made with altimeters mounted on an amphibious vehicle that traversed the surf zone. Unlike many profiling systems, the robust, fixed altimeters can measure bedforms in bubbly, sediment-laden surfzone waters nearly continuously, including during storms, thus allowing investigation of the relationships between bedform heights and near-bottom velocities to be extended to a wide range of wave conditions. The fixed-altimeter observations of migrating bedforms suggest a sandy surfzone seafloor is not always smooth during energetic conditions with strong mean currents and large wave-orbital velocities.

A numerical analysis of the ridges on the bed of wide, open channels and their effects on the distribution of secondary currents and wall shear is undertaken using CFD (Computational Fluid Dynamics). The presence of the lines of boil, consisting of low speed streaks, periodically in the transverse direction, is reported in the literature due to the presence of the ridges. In the present work, simulations are run on channel sections with varying the number of ridges on the bed and the size of these ridges. The effect of these variations on the flow structures and shear stress distribution in wide open channels is reported. The results offer an interesting insight into the 3D (Three-Dimensional flow structures involved and the link between flow structures and bed morpho-dynamics in prismatic channels.

Subglacial roughness can be determined at variety of length scales from radio-echo sounding (RES) data; either via statistical analysis of along-track topography, or inferred from basal radar scattering. Past studies have demonstrated that subglacial terrain exhibits self-affine (fractal) scaling behaviour, where vertical roughness has a power-law relationship with the horizontal length scale. A self-affine statistical framework, which enables a consistent integration of topographic roughness and radar scattering, has yet to be applied to RES. Here we do this for recent RES data from northern Greenland, and demonstrate that subglacial topography exhibits pronounced spatial variation in the Hurst (roughness power-law) exponent. A radar scattering model then enables us to explain how the Hurst exponent exerts strong topographic control upon radar scattering, which we map using the waveform abruptness (pulse peakiness) parameter. Notably, lower abruptness (associated with diffuse scatt...

Uncertainty affects estimates of the power potential of tidal currents, resulting in large ranges in values reported for sites such as the Pentland Firth, UK. Kreitmair et al. (2019, R. Soc. open sci. 6 , 180941. ( doi:10.1098/rsos.191127 )) have examined the effect of uncertainty in bottom friction on tidal power estimates by considering idealized theoretical models. The present paper considers the role of bottom friction uncertainty in a realistic numerical model of the Pentland Firth spanned by different fence configurations. We find that uncertainty in removable power estimates resulting from bed roughness uncertainty depends on the case considered, with relative uncertainty between 2% (for a fully spanned channel with small values of mean roughness and input uncertainty) and 44% (for an asymmetrically confined channel with high values of bed roughness and input uncertainty). Relative uncertainty in power estimates is generally smaller than (input) relative uncertainty in bottom...

This paper examines the discharge and velocity distributions in natural open channel flows using the entropy theory. Flow measurements were carried out at four different cross‐sections in central Turkey. The mean and maximum velocities at these stations exhibited a linear distribution and the entropy parameter was calculated to be M=1.31. Using this value, discharges for all flow conditions were calculated as a function of the measured maximum velocities (umax). It was observed that the umax/H and zmax/H ratios remained relatively constant when 0.2≤y/T≤0.8, especially for the wider channels. Using these constant values for each station, umax and zmax could be determined solely as a function of the water depth H. Although the calculated velocities were higher than those measured at some verticals, the entropy‐based approach presents an attractive alternative to the traditional flow‐measurement techniques for the determination of flow properties because of its simplicity and quick app...

A hydraulic jump takes place when a shallow high-speed free-surface flow impinges into a deeper slower flow region. Besides a sudden increase in depth, the most significant flow features include large turbulence seen both at the free-surface and inside the jump roller, as well as substantial air entrainment into the roller. The flow hydrodynamics is extremely complicated because of the interactions between a large number of turbulent two-phase flow properties with a broad range of relevant length and time scales. This report presents a detailed experimental study of the hydraulic jump. The total pressure field was measured in a series of vertical cross sections conducted in the roller, using a miniature probe. The air-water flow properties were measured simultaneously at the same location with a dual-tip phase-detection probe. The instantaneous free surface positions were scanned non-intrusively with a series of acoustic displacement meters, including immediately above the total pressure and air-water flow measurement location. The investigations were characterised by partially developed inflow conditions with Froude numbers ranging from 3.8 to 8.5 corresponding to Reynolds numbers between 3.5×104 and 8.0×104. The time-averaged free surface and air-water flow properties showed good agreement with previous findings. The free-surface fluctuation amplitude and frequency were larger in the first half roller close to the toe, than in the second half of roller. The longitudinal jump toe oscillations were associated with an instantaneous deformation of the roller free-surface. The vertical distributions of time-averaged air-water flow properties showed two main air-water flow regions: namely the turbulent shear layer for y < y* and a recirculation region above. The total pressure measurement was validated in the shear layer through a comparison with theoretical calculations based upon the measured two-phase flow data. The results showed that the pressure distribution was quasi-hydrostatic in the roller taking into account the flow aeration. In the shear layer, the vertical profiles of mean pressure and pressure fluctuations exhibited some marked maxima. The magnitudes of mean and fluctuation maxima increased with increasing Froude numbers and decreased with increasing distance from the jump toe for a given Froude number. Some cross-correlation analyses were performed between any two instantaneous signals of the horizontal jump toe oscillations, vertical free surface fluctuations, instantaneous total pressure and instantaneous void fraction. Some marked maximum correlation coefficients indicated the co-variation relationships. The simultaneous sampling of instantaneous free-surface, total pressure and void fraction fluctuations indicated two different sub-regions in the shear layer: the main shear layer and the lower shear layer next to the invert. The characteristic differences of each sub-region were discussed in terms of the two-phase flow and turbulence properties.

Hydraulic jumps are induced in hydraulic facilities for the purposes of energy dissipation or flow aeration. Presently there is no means for a simple estimate of void fraction distribution and air entrainment flux, without detailed physical modelling. This paper presents a semi-theoretical model to simulate the void fraction and velocity distributions in hydraulic jumps characterized by partially-developed inflow conditions. Relationships were established between the inflow Froude number, jump roller length and key parameters that determine the full expression of void fraction and velocity profiles. The proposed model enables accurate prediction of void fraction, longitudinal velocity, and air flux using the inflow Froude number. The results indicated considerable air flux contribution of free-surface aeration, in addition to the singular air entrainment at the jump toe, for moderate to large Froude numbers. A Froude number between 8 and 9 tended to achieve highest aeration rate with maximum total air flux in the roller.

A hydraulic jump is a rapidly-varied open channel flow characterised by the sudden transition from a supercritical flow motion to a subcritical regime. The transition is associated with a rapid increase of water depth, a highly turbulent flow with macro-scale vortices, significant kinetic energy dissipation, a two-phase flow region and some strong turbulence interactions with the free surface leading to splashes and droplet projection. The phenomenon is not a truly random turbulent process because of the existence of low-frequency, pseudo-periodic coherent structures and fluctuating motion in the jump roller. This study presents new measurements of turbulent air-water flow properties in hydraulic jumps, including turbulence intensity, longitudinal and transverse integral length and time scales, for a range of Froude numbers (3.8 < Fr1 < 8.5) at large Reynolds numbers (3×10 4 < Re < 2×10 5). The results showed a combination of both fast and slow turbulent components. The respective contributions of the fast and slow motions were quantified using a novel triple decomposition technique. The results highlighted the 'true' turbulent characteristics linked to the fast, microscopic velocity turbulence of hydraulic jumps, while showing that slow-fluctuation turbulence intensity was a significant contribution to the total. The high-frequency advection length scale and integral turbulent length scale exhibited some maxima in the lower shear flow next to the invert. The turbulent length scales decreased along the roller as the fast turbulence was dissipated. Comparison between the longitudinal advection and integral length scales indicated that the advection and diffusion were not independent processes in the flow region immediately downstream of the jump toe. The impact of slow fluctuations was large in the free-surface region and relatively smaller in the lower shear flow.

A hydraulic jump is the sudden transition from a high-velocity impinging flow into a turbulent roller in an open channel. Substantial amounts of air are entrapped at the impingement point, and significant free-surface fluctuations take place above the roller. In the present study, some physical modelling was conducted in a relatively large sized facility. The flow conditions included a wide ranges of inflow Froude numbers and Reynolds numbers (3.8 , Fr 1 , 10.0, 2.1 £ 10 4 , Re , 1.6 £ 10 5). The fluctuating features of free-surface and roller position were investigated non-intrusively with a series of acoustic displacement meters. The characteristic frequencies of the fluctuating motions were documented, and some major roller surface deformation patterns were revealed. The air-water flow properties were investigated with an intrusive phasedetection probe. The void fraction and bubble count rate data were documented in the jump roller, together with the interfacial velocity distributions. The rate of air entrainment was estimated based upon the void fraction and interfacial velocity distribution data. Some simultaneous measurements of instantaneous void fraction and free-surface fluctuations as well as longitudinal jump front oscillations were conducted. The relationship between the rate of air entrainment and turbulent fluctuations is discussed. Both the turbulent fluctuation and aeration properties are basic design parameters in urban water systems in which a hydraulic jump may take place. The present work provides relevant information for water systems including covered channels and partially-filled pipes.

A free-surface flow can change from a supercritical to subcritical flow with a strong dissipative phenomenon called a hydraulic jump. Herein the progress and development in turbulent hydraulic jumps are reviewed with a focus on hydraulic jumps operating at large Reynolds numbers typically encountered in natural streams and hydraulic structures. The key features of the turbulent hydraulic jumps are the highly turbulent flow motion associated with some intense air bubble entraimnent at the jump toe. The state-of-the-art on the topic is discussed based upon recent theoretical analyses and physical data.

In the field of river restoration sciences there is a growing need for analytical modeling tools and quantitative processes to help identify and prioritize project sites. Twodimensional (2D) hydraulic models have become more common in recent years and with the availability of robust data sets and computing technology, it is now possible to evaluate large river systems at the reach scale. The Trinity River Restoration Program (TRRP) – Bureau of Reclamation in Northern California is now analyzing a 40 mile segment of the Trinity River to determine priority and implementation sequencing for its Phase II channel rehabilitation projects. A comprehensive approach and quantitative tool has recently been developed to analyze this complex river system. The 2D-Hydrodynamic-Based Logic Modeling (2DHBLM) tool utilizes various hydraulic output parameters combined with biological, ecological, and physical metrics at user-defined spatial scales and flow discharges to evaluate geomorphic characteri...

Velocity profiles were investigated for a natural stream by entropy theory. Flow was measured by Acoustic Doppler Velocimeter (ADV) at different times and periods during seven site visits on the Sarımsaklı stream, which flows through central Anatolia in Turkey. Entropy parameter M was calculated with two different approaches. One of them is linear distribution between mean and maximum velocities at these stations and the entropy parameter was calculated as M=2.9. Second one is the best entropy parameter which can be calculated by using u max and z max for measured verticals and found as M=2.83. Both approaches show good harmony with the measured data along the verticals. Errors between measured (u m) and calculated (u c) velocities for the whole depths were calculated. The relative mean errors for the seven measurements and each vertical is determined as 5.65% for the SDE (Sarımsaklı Dam Entrance) station. Ardıçlıoğlu et al. [8] investigated the applicability of logarithmic and entropy-based velocity distribution equations for rough-surface open-channel flow and suggested a new brought to you by CORE View metadata, citation and similar papers at core.ac.uk

A numerical analysis of the ridges on the bed of wide, open channels and their effects on the distribution of secondary currents and wall shear is undertaken using CFD (Computational Fluid Dynamics). The presence of the lines of boil, consisting of low speed streaks, periodically in the transverse direction, is reported in the literature due to the presence of the ridges. In the present work, simulations are run on channel sections with varying the number of ridges on the bed and the size of these ridges. The effect of these variations on the flow structures and shear stress distribution in wide open channels is reported. The results offer an interesting insight into the 3D (Three-Dimensional flow structures involved and the link between flow structures and bed morpho-dynamics in prismatic channels.

The hydraulic jump is a sudden transition from a supercritical flow to a subcritical motion, characterised by strong turbulence, air entrainment and energy dissipation. A hydraulic jump results in strong interactions between turbulence, free-surface and air-water mixing. Past research on hydraulic jump with bed roughness focused on the identification of basic parameters including conjugate depth ratio, roller length and mean velocity. However, to date, only very few studies have addressed the air-water flow parameters. This paper aims to investigate the basic parameters of air-water flow in hydraulic jump on pebbled rough bed. The experiments were performed in a channel with partially-developed inflow conditions. The gravel materials, mixed natural river pebbles, were installed on the bed for the whole length of the flume. A phase-detection double-tip conductivity probe was used to measure the basic air-flow properties. The experiments were conducted for discharges ranging from 0.06 to 0.1 m 3 /s, corresponding to inflow Froude numbers Fr1 between 1.7 and 2.84 and Reynolds number Re1 from 170,000 to 220,000. Comparisons between rough and smooth bed data, as well as with the literature highlighted some distinctive effects of the non-uniform bed roughness. The results on rough pebble bed showed a shorter roller length and higher magnitudes of air-flow properties including void fraction and bubble count rate than those on smooth bed, especially in the region close to the jump toe.

Hydraulic jumps occur when upstream supercritical flow suddenly transitions into downstream subcritical flows. Extremely turbulent flow of the hydraulic jump associated with the development of large-scale turbulence, surface waves and spray, air entrainment and energy dissipation. Hydraulic jumps are commonly taking place in natural waterways and hydraulic structures. Enhancement of energy dissipation, fluid mixing or flow re-aeration are the usage

Estimating channel roughness is crucial for whatever engineering plans that have been in mind for any reach under consideration. Not only is resistance coefficient not a measurable quantity, but also various factors affecting on its value make its estimation a challenge. Despite of numerous methods available for roughness estimation, the complexity of some of available iterative schemes particularly with no mechanism for modifying initial guess in each iteration restrain numerical modelers to apply merely outdated resistance equations in practice. In order to improve the estimation of hydraulic resistance, a new straightforward flow-dependent scheme, which is capable of estimating Manning's coefficient due to grain and form roughness, is introduced. A large data is utilized to calibrate and testify the new scheme. The results of comparing the new scheme with that of different models available in the literature show that it achieves the best estimation results and yields to more than 0.87 and 0.67 for R 2 , 0.15 and 0.17 for mean absolute relative error for estimating grain and form Manning's coefficients, respectively. This comparison demonstrates that the results achieved by the new scheme are acceptably accurate in favor of roughness estimation.

Estimating channel roughness is crucial for whatever engineering plans that have been in mind for any reach under consideration. Not only is resistance coefficient not a measurable quantity, but also various factors affecting on its value make its estimation a challenge. Despite of numerous methods available for roughness estimation, the complexity of some of available iterative schemes particularly with no mechanism for modifying initial guess in each iteration restrain numerical modelers to apply merely outdated resistance equations in practice. In order to improve the estimation of hydraulic resistance, a new straightforward flow-dependent scheme, which is capable of estimating Manning's coefficient due to grain and form roughness, is introduced. A large data is utilized to calibrate and testify the new scheme. The results of comparing the new scheme with that of different models available in the literature show that it achieves the best estimation results and yields to more than 0.87 and 0.67 for R 2 , 0.15 and 0.17 for mean absolute relative error for estimating grain and form Manning's coefficients, respectively. This comparison demonstrates that the results achieved by the new scheme are acceptably accurate in favor of roughness estimation.

A tidal bore is an unsteady flow motion generated by the rapid water level rise at the river mouth during the early flood tide under appropriate macro-tidal and bathymetric conditions. The present study investigated physically the turbulent properties of breaking tidal bores. The results were based upon some experimental measurements of free-surface fluctuations and turbulent velocities conducted on smooth and rough beds. Using an ensemble-averaging technique, the free-surface fluctuations of breaking tidal bores were characterised. Immediately prior to the roller, the free-surface curved gradually upwards, and the passage of the bore roller was associated with some large water elevation fluctuations. The turbulent velocity measurements were performed at several vertical elevations during the breaking bore. Both the instantaneous and ensemble-averaged velocity data highlighted some strong flow deceleration at all elevations. Close to the bed, the longitudinal velocity component became negative immediately after the roller indicating the existence of a transient recirculation. The vertical velocity data presented some positive, upward motion beneath the roller with increasing maximum vertical velocity at increasing elevation above the bed. The transverse velocity data show some large fluctuations with a non-zero ensemble-average after the roller passage, suggesting some secondary turbulent motion advected behind the bore.

A positive surge results from a sudden change in flow that increases the depth, and a geophysical application is the tidal bore. Mew experimental investigations were conducted in a rectangular channel and detailed unsteady velocity measurements were performed with high temporal and spatial resolution. The experiments encompassed undular and breaking bores in a horizontal slope and both smooth and rough invert conditions were tested. An undular bore was observed for surge Froude numbers less than 1.5. For Fr < 1.3, the undulations free-surface was smooth. For 1.3 < Fr < 1.45 to 1.5, some breaking was seen at the first wave crest. For Fr > 1.5, a breaking bore was observed. Detailed instantaneous velocity measurements showed a marked effect of the surge front passage. A comparison between undular and weak surge data suggested some basic differences. A systematic comparison was conducted to study the effects of bed roughness. The boundary friction contributed to some wave attenuation and dispersion. The instantaneous velocity data indicated a marked effect of the rough screens on the entire turbulent velocity field.

Bélanger equation: momentum equation applied across a hydraulic jump in a horizontal channel; the equation was named after Jean-Baptiste BELANGER (1828). Éteules: French for whelps. Fawer jump: undular hydraulic jump. Hydraulic jump: stationary transition from a rapid, high-velocity flow to a slower fluvial flow motion. Left bank: looking downstream, towards the river mouth, the left bank is on the left. Mascaret: French for tidal bore (Front page and Fig. i-1). Pororoca: tidal bore of the Amazon river in Brazil. Positive surge: a positive surge results from a sudden increase in flow depth. It is an abrupt wave front. The unsteady flow conditions may be solved as a quasi-steady flow situation and a positive surge is called a hydraulic jump in translation. Rapidly varied flow: is characterised by large changes over a short distance (e.g. sharp-crested weir, sluice gate, hydraulic jump). Right bank: looking downstream, towards the river mouth, the right bank is on the right. Roller: in hydraulic engineering, a series of large-scale turbulent eddies : e.g., the roller of a hydraulic jump. Shock waves: in a high-velocity, supercritical flows, a flow disturbance (e.g. change of direction, contraction) induces the development of shock waves propagating at the free-surface across the channel. Shock waves are called also lateral shock waves, oblique hydraulic jumps, Mach waves, cross-waves, diagonal jumps. Stilling basin: hydraulic structure for dissipating the energy of the flow downstream of a spillway, outlet work, chute or canal structure. In many cases, a hydraulic jump is used as the energy dissipator within the stilling basin. Surge : a surge in an open channel is a sudden change of flow depth (i.e. abrupt increase or decrease in deth). An abrupt increase in flow depth is called a positive surge while a sudden decrease in depth is termed a negative surge. Supercritical flow: flow characterised by a Froude number greater than unity. Tidal bore: positive surge of tidal origin developing in an estuary as the tide turns to rising. Undular hydraulic jump : stationary hydraulic jump characterised by steady stationary free-surface undulations downstream of the jump and by the absence of a formed roller. An undular jump flows is called Fawer jump in homage to C. FAWER's work. Undular surge: positive surge characterised by a train of secondary waves (or undulations) following the surge front. Undular surges are sometimes called Boussinesq-Favre waves in homage to the contributions of Joseph BOUSSINESQ and H. FAVRE. Weak jump: A weak hydraulic jump is characterised by a marked roller, no free-surface undulation and low energy loss. It is usually observed after the disappearance of undular hydraulic jump with increasing upstream Froude numbers. Whelps: waves behind the leading edge of the tidal bore front. For an observer standing on the bank, the whelps are the wave trains (incl. secondary waves) seen after the surge front passage.

A tidal bore is a wave propagating upstream as the tidal flow turns to rising. It forms during spring tide conditions when the flood tide is confined to a narrow funneled channel. To date, theoretical and numerical studies rely upon physical experiments to validate the developments, but the experimental data are limited mostly to visual observations and sometimes free-surface measurements. Herein turbulent velocity measurements were obtained in a large-size laboratory facility with a fine spatial and temporal resolution. The instantaneous velocity measurements showed rapid flow deceleration at all vertical elevations, and large fluctuations of all velocity components were recorded beneath the bore and secondary waves. A comparison between undular ͑nonbreaking͒ and breaking bores suggested some basic differences. In an undular bore, large velocity fluctuations were recorded beneath the first wave crest and the secondary waves showing a long-lasting effect after the bore passage. In a breaking bore, some large turbulent stresses were observed next to the shear zone in a region of high velocity gradients, while some transient flow recirculation was recorded next to the bed. The effects of bed roughness were tested further. The boundary friction contributed to some wave attenuation and dispersion, and the free-surface data showed some agreement with the wave dispersion theory for intermediate gravity waves. The instantaneous velocity data showed however a significant effect of the boundary roughness on the velocity field next to the boundary ͑z / d o Ͻ 0.2͒ for both undular and breaking bores. Overall the findings were consistent with field observations of tidal bores and highlighted the significant impact of undular ͑nonbreaking͒ bores on natural systems.

The spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented. Drawing on a LiDAR-derived, meter-scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage-dependent channel roughness, this study developed a meter-scale two-dimensional hydrodynamic model of ~ 28.3 km of a gravel/cobble-bed river corridor for flows ranging from 0.2-20 times bankfull discharge, with and without spatially distributed vegetation roughness. Results were analyzed to gain insight into stage-dependent and scale-dependent effects of vegetation on velocities, depths, and flow patterns. At the floodplain filling flow of 597.49 m 3 /s, adding spatially distributed vegetation roughness parameters caused 8.0 and 7.4% increases in wetted area and mean depth, respectively, while mean velocity decreased 17.5%. Vegetation has a strong channelization effect on the flow, increasing the difference between mid-channel and bank velocities. It also diverted flow away from densely vegetated areas. On the floodplain, vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs. For the river as a whole, as discharge increases, overall roughness increases as well, contrary to popular conception.

The open-source finite-element system Telemac has been applied to simulate various complex hydrodynamic and morphodynamic situations including waterways, curved channels, recirculating flows and wave-induced littoral transport. In the applications presented here, the sediment transport model is mainly restricted to the transport of non-cohesive sediments, which relies on classical semi-empirical concepts including sand grading effects, parameterization of secondary currents and wave effects. In comparison with other comprehensive modeling systems (Delft-3D, Mike-21, etc.), the main originality lies in the efficiency and flexibility of the finite elements. Thanks to the optimization of numerical schemes, parallelism, as well as tremendous progress in the performance of computers, bed evolution can be calculated on basin scale (10-100 km) and for the medium term (years to decades), without the use of hydrodynamic filtering methods. As a novelty in release 6.0, we present a method of feedback for the bed roughness, which reduces uncertainty in the prediction of both transport rates and flow velocities.

A numerical analysis of the ridges on the bed of wide, open channels and their effects on the distribution of secondary currents and wall shear is undertaken using CFD (Computational Fluid Dynamics). The presence of the lines of boil, consisting of low speed streaks, periodically in the transverse direction, is reported in the literature due to the presence of the ridges. In the present work, simulations are run on channel sections with varying the number of ridges on the bed and the size of these ridges. The effect of these variations on the flow structures and shear stress distribution in wide open channels is reported. The results offer an interesting insight into the 3D (Three-Dimensional flow structures involved and the link between flow structures and bed morpho-dynamics in prismatic channels.

Characterizing streambed morphology is crucial to better understand fluvial systems, since the streambed is an important control on stream dynamics, particle motion and bed stability. Measurement apparatus like terrestrial laser scanners or airborne Lidar systems are difficult to successfully apply in such environments, because they need free sight, elevated positions and good aerial or road access, which is generally not the case in mountain streams. Moreover, such streams are typically complex in shape and have a wide grain size distribution which complicates measuring with a single method. We present recently available Range Imaging cameras as a novel tool to obtain three-dimensional coordinates of rough surfaces. Mounted on a lightweight crane above the streambed, the cameras generate distance images without significant shadowing effects of large boulders. This experimental study evaluates the precision and the range of applicability of this method. We carried out laboratory and...

A modified log-wake law is proposed to describe turbulent velocity profiles in smooth rectangular open-channels. The new law consists of three components: a log term, a wake term, and a free surface term. The log term reflects the channel bed effect and predominates in terms of velocity magnitude; the wake term expresses the sidewall effect and can be neglected near the channel bed; and the free surface term satisfies the free surface boundary conditions. The modified log-wake law contains six parameters: (1) the von Karman constant κ ≈ 0.42; (2) the wake strength Π = κ; (3) the bed shear velocity u * b ; (4) the sidewall shear velocity u * w ; (5) the maximum velocity u max or the integration constant A; and (6) the velocity gradient at the upper boundary. The analysis clearly shows that the wake function results from sidewall effects. The modified log-wake law can replicate the velocity dip phenomenon in narrow channels at width-depth ratios less than 5. When the width-depth ratio exceeds 5, the maximum velocity occurs at the free surface. Finally, the modified logwake law compares very well with Coleman's, Lyn's and Muste and Patel's experimental data.

Flow over sand bed occurs frequently in nature. Riverbeds are usually composed of non-uniform sediment mixtures and the respective particle size distribution of sediment in transport is generally finer than the distribution of bed material because of selective transport. The experimental study has been carried out to observe the turbulent characteristics of flow in an alluvial channel composing of uniform sediment and nonuniform sediment mixture. Instantaneous velocity measurements were taken at the centre line of flume by the Acoustic Doppler Velocimeter (ADV).The present study addresses on the flow zone in the vicinity of the bed surface. The variations of stream wise velocity with vertical distance in flows with non-uniform sediment in the near bed region are smaller than uniform sediment. This increase in stream wise velocities was sufficient for increased rate of sediment transport with uniform sand bed channel. The profiles of Reynolds shear stress is slightly scattered in general and decreased with non-uniform sediment which signifies the lower momentum transfer towards the boundary. The distribution of Reynolds shear stress undergoes a damping due to a decreasing level of turbulence fluctuation within the wall shear layer.. In presence of non-uniform sand bed channel, increased in stream wise and decreased in vertical turbulence intensities are observed than turbulence intensities in uniform sand bed channel.

The relation between the equivalent roughness and different grain size percentiles of the sediment in gravel-bed rivers was determined under the hypothesis that the vertical distribution of the flow velocity follows a logarithmic law. A set of 954 data points was selected from rivers with gravel size sediment or larger, with a non-sinuous alignment and free of vegetation or obstacles. According to the results, the k s roughness is equivalent to approximately 2.4D 90 , 2.8D 84 , and 6.1D 50. No correlation was detected between the sediment sorting and the sediment mobility index on one hand, and, on the other, the coefficient of proportionality of each grain size percentile.

Velocity profiles were investigated for a natural stream by entropy theory. Flow was measured by Acoustic Doppler Velocimeter (ADV) at different times and periods during seven site visits on the Sarımsaklı stream, which flows through central Anatolia in Turkey. Entropy parameter M was calculated with two different approaches. One of them is linear distribution between mean and maximum velocities at these stations and the entropy parameter was calculated as M=2.9. Second one is the best entropy parameter which can be calculated by using u max and z max for measured verticals and found as M=2.83. Both approaches show good harmony with the measured data along the verticals. Errors between measured (u m) and calculated (u c) velocities for the whole depths were calculated. The relative mean errors for the seven measurements and each vertical is determined as 5.65% for the SDE (Sarımsaklı Dam Entrance) station.

On cherche ici à valider l’utilisation de profils de vitesses en canal ouvert à fond rugueux, formules logarithmiques ou fondées sur un principe d’entropie maximale. Pour atteindre cet objectif, 24 expériences de laboratoire, avec plus de 1200 points de mesures, ont été réalisées. Le nombre de Reynolds varie de 3.4 10 4 a 1.7 10 5 , et le rapport entre largeur (B) et profondeur (H) de 4.2 a 12.0. Les équations ne représentent pas bien la distribution de vitesse près du lit rugueux, ni près de la surface libre lorsque la vitesse maximale ne se trouve pas atteinte en surface ( dip effect ). Parmi les équations logarithmiques, la formulation de Coles se montre la meilleure en toutes régions d’écoulement. L’équation de l’entropie de Chiu présente de bons résultats, quoique s’écartant des résultats expérimentaux près du lit. Si le paramètre M est calculé par l’expression proposée ici, l’équation de Chiu devient meilleure en toutes circonstances. Les données expérimentales ont permis de f...

The paper presents a fuzzy logic speed control system based on fuzzy logic approach for an indirect vector controlled induction motor drive for high performance. The analysis, design and simulation of the fuzzy logic controller for indirect vector control induction motor are carried out based on fuzzy set theory. The proposed fuzzy controller is compared with PI controller with no load and various load condition. The result demonstrates the robustness and effectiveness of the proposed fuzzy controller for high performance of induction motor drive system.

We present an experimental analysis of hydraulic roughness variations due to changes in alluvial cover in a mixed bedrock-alluvial meandering channel with larger bedrock roughness than alluvial roughness. Three sets of experiments were conducted in a highly sinuous flume: one with bare bedrock, and two with enough sediment to cover 21% and 78% of the bedrock respectively. We compare our results with data from experiments previously conducted in the same flume with flat-and smooth-bed, and data from experiments with fully alluvial conditions. Our results show that: (i) hydraulic resistance in a mixed bedrock-alluvial channel changes with the degree of alluviation; (ii) hydraulic resistance is greater for bare-bedrock conditions, and decreases as sediment supply increases; (iii) if bedforms appear, hydraulic resistance may be larger than of bare bedrock conditions due to form drag; (iv) fluctuations in alluvial cover due to freely-migrating bars lead to instantaneous changes in hydraulic resistance.

Estimating channel roughness is crucial for whatever engineering plans that have been in mind for any reach under consideration. Not only is resistance coefficient not a measurable quantity, but also various factors affecting on its value make its estimation a challenge. Despite of numerous methods available for roughness estimation, the complexity of some of available iterative schemes particularly with no mechanism for modifying initial guess in each iteration restrain numerical modelers to apply merely outdated resistance equations in practice. In order to improve the estimation of hydraulic resistance, a new straightforward flow-dependent scheme, which is capable of estimating Manning's coefficient due to grain and form roughness, is introduced. A large data is utilized to calibrate and testify the new scheme. The results of comparing the new scheme with that of different models available in the literature show that it achieves the best estimation results and yields to more than 0.87 and 0.67 for R 2 , 0.15 and 0.17 for mean absolute relative error for estimating grain and form Manning's coefficients, respectively. This comparison demonstrates that the results achieved by the new scheme are acceptably accurate in favor of roughness estimation.

In free-surface turbulent flows, large amount of air may be entrapped and advected in the water current. The resulting air-water flows are frequently observed in natural water systems, where they are also relevant to water quality, ecological sustainability and integrated assessment within such systems. Herein, a review of physical and numerical modelling of air-water flows is developed, providing some fundamentals towards a consistent modelling of such flows to graduate and Ph.D. level students as well as young researchers in environmental sciences and engineering, with prerequisite knowledge in basic fluid mechanics. After some theoretical and metrology considerations, the main criteria for the design of physical models and the current literature on the numerical studies are discussed. Two case-studies, the hydraulic jump and the dropshaft, are used to show the application of such criteria and methods. Overall, the paper presents current knowledges/challenges on physical and numerical modelling of self-aerated free-surface flows.

The hydraulic jump is a sudden transition from a supercritical flow to a subcritical motion, characterised by strong turbulence, air entrainment and energy dissipation. A hydraulic jump results in strong interactions between turbulence, free-surface and air-water mixing. Past research on hydraulic jump with bed roughness focused on the identification of basic parameters including conjugate depth ratio, roller length and mean velocity. However, to date, only very few studies have addressed the air-water flow parameters. This paper aims to investigate the basic parameters of air-water flow in hydraulic jump on pebbled rough bed. The experiments were performed in a channel with partially-developed inflow conditions. The gravel materials, mixed natural river pebbles, were installed on the bed for the whole length of the flume. A phase-detection double-tip conductivity probe was used to measure the basic air-flow properties. The experiments were conducted for discharges ranging from 0.06 to 0.1 m 3 /s, corresponding to inflow Froude numbers Fr1 between 1.7 and 2.84 and Reynolds number Re1 from 170,000 to 220,000. Comparisons between rough and smooth bed data, as well as with the literature highlighted some distinctive effects of the non-uniform bed roughness. The results on rough pebble bed showed a shorter roller length and higher magnitudes of air-flow properties including void fraction and bubble count rate than those on smooth bed, especially in the region close to the jump toe.

The spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented. Drawing on a LiDAR-derived, meter-scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage-dependent channel roughness, this study developed a meter-scale two-dimensional hydrodynamic model of ~ 28.3 km of a gravel/cobble-bed river corridor for flows ranging from 0.2-20 times bankfull discharge, with and without spatially distributed vegetation roughness. Results were analyzed to gain insight into stage-dependent and scale-dependent effects of vegetation on velocities, depths, and flow patterns. At the floodplain filling flow of 597.49 m 3 /s, adding spatially distributed vegetation roughness parameters caused 8.0 and 7.4% increases in wetted area and mean depth, respectively, while mean velocity decreased 17.5%. Vegetation has a strong channelization effect on the flow, increasing the difference between mid-channel and bank velocities. It also diverted flow away from densely vegetated areas. On the floodplain, vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs. For the river as a whole, as discharge increases, overall roughness increases as well, contrary to popular conception.

This paper describes the conditions for initiation and maintenance of secondary currents in open channel flows. By analyzing the Reynolds equation in the wall-normal and wall-tangent directions, this study reveals that, like other types of vortices, the secondary currents are originated in the near-boundary region, and the magnitude (or strength) of secondary flow is proportional to the lateral gradient of near-wall velocity. The near-wall secondary flow always moves from the region with lower velocity (or lower boundary shear stress) to the location with higher velocity (or higher boundary shear stress). Subsequently, the near-boundary secondary flow creeps into the main flow and drives circulation within a region enclosed by lines of zero total shear stress, leading to anisotropy of turbulence in the main flow region. This paper also discusses typical secondary currents in open channel flows and presents the relationship between sediment transport and secondary currents. The formation of sand ridges widely observed on the Earth surface is explained in the light of the proposed relationship.

The hydraulic jump is a sudden transition from a supercritical flow to a subcritical motion, characterised by strong turbulence, air entrainment and energy dissipation. A hydraulic jump results in strong interactions between turbulence, free-surface and air-water mixing. Past research on hydraulic jump with bed roughness focused on the identification of basic parameters including conjugate depth ratio, roller length and mean velocity. However, to date, only very few studies have addressed the air-water flow parameters. This paper aims to investigate the basic parameters of air-water flow in hydraulic jump on pebbled rough bed. The experiments were performed in a channel with partially-developed inflow conditions. The gravel materials, mixed natural river pebbles, were installed on the bed for the whole length of the flume. A phase-detection double-tip conductivity probe was used to measure the basic air-flow properties. The experiments were conducted for discharges ranging from 0.06 to 0.1 m 3 /s, corresponding to inflow Froude numbers Fr1 between 1.7 and 2.84 and Reynolds number Re1 from 170,000 to 220,000. Comparisons between rough and smooth bed data, as well as with the literature highlighted some distinctive effects of the non-uniform bed roughness. The results on rough pebble bed showed a shorter roller length and higher magnitudes of air-flow properties including void fraction and bubble count rate than those on smooth bed, especially in the region close to the jump toe.

Seven series of laboratory experiments were carried out in a re-circulating glass sided tilting flume to investigate the instantaneous nearbed streamwise flow velocities in different duration of constant flowrates. Each series were observed at different time elapsed to represent the flow condition at different time of bed exposures. The instantaneous nearbed streamwise flow velocities were recorded using an Acoustic Doppler Velocimeter (ADV), which was positioned in such a way the probe could easily traverse the grid points to collect measurements. The experiments suggest that the instantaneous nearbed streamwise flow velocities within the grid varied throughout the constant flowrates with lower range of variations occurred in the shorter tests and wider variations in the longer tests.This means the constant flowrates produced different level of turbulences in a relatively small area even at adjacent points. With a relatively stable standard deviations regardless of the time elapsed...

Average shear stress is an important parameter for prediction of sediment transport, bank protection and other river engineering problems in natural streams. For this purpose velocity measurements were taken on Kızılırmak River sub branch, named Sarimsakli stream and Barsama station in center of Turkey. Acoustic Doppler Velocimeter (ADV) was used for this purpose at six different periods and flow conditions. Nikuradse’s equivalent sand roughnesses (ks) for each vertical along the wetted perimeter were determined using measured velocity distributions. Shear velocity (u*) and shear stress (meas) were determined then average values were calculated for each flow condition. The commonly used one-dimensional mean boundary shear stress equation at cross-section was re-arranged according to entropy parameter M and it reflects the real flow condition in natural stream.

ABSTRACT: The velocity and turbulence distributions of decelerating open-channel flow in a gradual expansion were measured using LDV equipment. The results show that the logarithmic law can describe the mean velocity in the bottom region well while the Coles&#x27; law can be applied to the outer region. The shear velocity can be determined both by the logarithmic fit of the mean velocity and by the fit of the Reynolds stress distributions. The turbulence intensities reach their maximum values at z/h= 0.1 to z/h= 0.15.

Riparian vegetation, an indicator of healthy river system, increases the hydraulic roughness and reduces the conveyance capacity of a channel. Vegetation provides dominant drag force influencing the velocity distribution, turbulence intensity and water depth. Thus, the study of hydraulic roughness due to vegetation is essential to determine the characteristics of flow. Traditionally, a constant Manning’s roughness value is assigned based on land cover maps and that does not adequately account for vegetation. The roughness due to vegetation are determined on the basis of its parameters like height, density, LAI and flexibility. Remote sensing data (LiDAR, aerial photos or satellite images) are preferred in determining detailed vegetation parameters to time consuming field data. The objective of this research was to evaluate the performance of remote sensing-based methods to estimate hydraulic roughness of vegetation. A Canopy Height Model (CHM) was used in this study to estimate the ...

In open channel flows, such as in streams and rivers, the hydraulic jump is a sudden transition from a high-velocity, supercritical flow into a slow-moving, subcritical flow. It is characterized by a sharp rise of the free-surface elevation associated with strong energy dissipation, large-scale turbulence, air entrainment, and spray. Its properties have been extensively studied over the last century. However, only a few studies have focused on the characteristics of a hydraulic jump flow over pebbled rough beds. This paper reports the results of an experimental study of a hydraulic jump flow over a pebbled rough bed, which is typical of natural bed condition, as well as on smooth bed as a reference. Basic flow properties in both the shear region and recirculation zones were investigated. Inflow Froude number Fr1 was in the range from 1.54 to 4.95 and from 1.31 to 2.87 for the smooth bed and the pebbled rough bed, respectively. Visual observations demonstrated some differences betwee...