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Select this Article		Simplified Approach for the Optimal Sizing of Throttled Air Chambers Giuseppe De Martino and Nicola Fontana Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000633 Posted ahead of print 15 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Among water hammer damping devices, air chambers are often used in pumping plants to reduce pressure surges to acceptable values. The chamber is more effective if a throttling device is used, resulting in a reduction of the required volume. Using the rigid column theory (incompressible flow) and the De Sparre rule, Evangelisti provided design charts for a simple and fast sizing of air volume and orifice diameter. Nevertheless, in many cases the pressure pattern is far from being constant during the first quarter of the transient period and lower pressures can be attained; furthermore, the rigid column model is not able to reproduce elastic phenomena arising from throttling and so water hammer equations should be used instead. Although orifice induced pressure waves are evident only in the first part of the transient, differences between air chamber pressure and pipe pressure can be quite significant. Negative pressure surge should be limited, since column separation and cavitation could occur as consequence of low pressures. Since the maximum downsurge inferred from the Evangelisti's charts does not ensure safe design, a simplified approach was proposed in the paper to design throttled air chambers under the elastic hypothesis. The analysis showed small deviations between the minimum pressure and the design pressure, unlike the inelastic approach, which exhibits even very large differences with water hammer equations.

Select this Article		Role of Turbulence and Particle Exposure on Entrainment of Large Spherical Particles in Flows with Low Relative Submergence Ambuj Dwivedi, Bruce Melville, M. ASCE, Arved J. Raudkivi, Asaad Y. Shamseldin, and Chiew Yee Meng Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000632 Posted ahead of print 15 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Laboratory experiments of sediment entrainment were carried out in a flume for different flow configurations with particle image velocimetry (PIV) used to measure the flow velocity. The experiments were done in low submergence condition. Measurements revealed that the vertical distribution of streamwise flow velocity, at the instant of entrainment, is significantly different from the temporal mean flow profile. The role of turbulence for a given flow depth is found to decrease with increase in exposure of the particle. An expression for threshold velocity is proposed, which accurately represents the enhanced near bed turbulence during entrainment. A Shields type parameter, expressed in terms of critical near bed flow velocity rather than shear velocity, is used to define the sediment transport threshold.

Select this Article		Emptying of Large‐Scale Pipeline by Pressurized Air Janek Laanearu, Ivar Annus, Tiit Koppel, Anton Bergant, Sašo Vučković, Qingzhi Hou, Arris S. Tijsseling, Alexander Anderson, and Jos M. C. van 'tWestende Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000631 Posted ahead of print 15 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Emptying of an initially water‐filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air‐water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water‐air “tail”. Measured discharges, water‐level changes and pressure variations along the pipeline during emptying are compared using Control Volume model results. The CV model solutions for a non‐stratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure and water level, but by considering water‐column mass loss due to the water‐air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air‐cavity celerity is close to its critical value at the instant of minimum flow acceleration. The influences of driving pressure, inertia and friction predominate, with the observed water hammer caused by the initiating downstream valve opening not significantly influencing the water‐air front propagation.

Select this Article		Inception Point of Air Entrainment and Training Wall Characteristics of Baffles and Sills on Stepped Spillways H. K. Zare and J. C. Doering Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000630 Posted ahead of print 15 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract An experimental study of new proposed stepped‐spillway configurations, using sills or baffles on the steps treads with sharp or rounded brinks, is introduced to investigate the location of and the flow depth at inception point of air entrainment and the training wall height. The silled‐shifted rounded spillway is recommended to be used in terms of cavitation damages mitigation as it gives the smallest inception point length among all spillways for large roughness Froude numbers. The baffled‐edged spillway gives the largest inception point depth among the spillways for large roughness Froude numbers and consequently is not favourable. The baffled‐shifted sharp spillway is the most efficient regarding to the cost of construction as it gives the smallest training wall height among spillways for large roughness Froude numbers range. The location and depth of inception point of air entrainment as well as the training wall height were expressed as functions of a so‐called roughness Froude number in empirical equations to develop design guidance for the proposed spillway configurations.

Select this Article		LDA Measurement in Cylindrical Containers without Using Planar Secondary Units A. S. Ramamurthy, R. Tadayon, and M. Al Kayed Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000629 Posted ahead of print 15 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract To measure velocity components using the Laser Doppler Anemometry (LDA) in a cylindrical surface as in a hydrocyclone, traditionally one encloses the top circular tube of the hydrocyclone by a flat surface box to minimize the refraction effects of laser beams caused by the curved solid walls. In this brief study, an alternative procedure is suggested to reorient the laser beams to measure the mean and fluctuation velocity components. Adopting the beam orientation suggested, at a single point in the flow field, the axial and circumferential mean velocity components together with the corresponding turbulent normal and shear stress components can be determined. Test results confirm that the proposed method is valid to get data related to the mean velocities and also the Reynolds stresses at a single point in the flow field of a hydrocyclone. The suggested procedure with slight modifications can be applied to measure velocities in the flow field formed by other circular surfaces such as cones.

Select this Article		Effects of Vegetation Canopy Density and Bank Angle on Near‐Bank Patterns of Turbulence and Reynolds Stresses Nicole M. Czarnomski, Desireé D. Tullos, Robert E. Thomas, and Andrew Simon Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000628 Posted ahead of print 14 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Vegetation growing on the surface of a streambank has been shown to alter the shear stresses applied to the boundary, but basic questions remain regarding the influence of vegetation and streambank configurations on near‐bank hydraulics. In the present study, Froude‐scaled flume experiments were used to investigate how changes in vegetation density (ratio of frontal area to channel area, including both stems and leaves) and bank surface angle influence near‐bank turbulence intensities (RMS_u,v,w) and Reynolds stresses (τ_uv and τ_uw) estimated using velocities obtained with an acoustic Doppler velocimeter positioned beneath the canopy. Results illustrate how, with increasing vegetation density, turbulence intensities and Reynolds stresses decreased along the sloped bank surface but increased at the base of the slope and within the main channel. The steeper bank angle resulted in greater vertical stresses on the bank surface than the shallower angle, but lateral momentum exchange was larger than vertical exchange along the base of the slope, regardless of bank angle. Leaves were an important influence on near‐bank turbulence intensities and Reynolds stresses, while the influence of bank slope was small relative to the influence of vegetation density.

Select this Article		Accounting for Rough Bed Friction Factors of Mud Beds Due to Biological Activity in Erosion Experiments Katell Guizien, Francis Orvain, Jean‐Claude Duchêne, and Pierre Le Hir Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000627 Posted ahead of print 14 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract The average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel. The method was validated in both hydraulically smooth (plexiglass, Reynolds number less than 25,000) and rough regimes (calibrated particles with known roughness). As a first step toward using this method on natural sediment, we tested this method with experimental mesocosms assembled from field collected materials (sieved sediments, diatoms). Bed shear stress measurement precision was high enough in the experiments to detect a positive significant relationship between bed friction factor and core roughness. The observed bed friction factor increase could be related to diatom growth but not to diatoms biomass.

Select this Article		Feasibility of Bubble Plume Destratification of Central Lake Erie Leon Boegman and Sylvia Sleep Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000626 Posted ahead of print 14 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract The central basin of Lake Erie has chronic hypoxia that is exacerbated by strong seasonal temperature stratification near the lake‐bed. A computational study was conducted to determine the feasibility of mechanically mixing the water column, using a bubble plume system, to reduce stratification; thus facilitating vertical transport of oxygen. The most efficient design delivered an air flow rate of 0.4–0.5 m³ s⁻¹ through 40–50 non‐interacting plumes, which mix the watercolumn only during the late summer hypoxic events. The optimal efficiency was computed using a new metric, which neglects changes in stratification resulting from meteorologically induced mixing, relative to those from artificial mixing.

Select this Article		The Effect of Corrugated Bed on Hydraulic Jump Characteristic Using SPH Method Ming‐Jyh Chern and Sam Syamsuri Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000618 Posted ahead of print 28 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract A hydraulic jump is a common phenomenon which can be observed in open channels flow such as rivers and spillways. It can cause damage of the downstream bed and bank of the channel due to the process of continuous erosion and degradation. In order to reduce the hydraulic jump destruction, the energy in the hydraulic jump must be dissipated as much as possible. One method to increase dissipation of energy is using a corrugated bed. In order to know the effect of a corrugated bed on the hydraulic jump, a smoothed particle hydrodynamics (SPH) model is applied to investigate the characteristics of hydraulic jumps in various corrugated beds. A variety of corrugated beds which are smooth, triangular, trapezoidal, and sinusoidal are considered. The opening of a gate is changed to adjust the hydraulic jump. The conjugate depth ratio, the jump length, the bottom shear stress distribution, and the energy dissipation are reported. The results of the present study are in a good agreement with previous studies. Energy dissipation is compared among corrugated beds and a smooth bed. It is found that the sinusoidal bed can dissipate more energy than other beds. As a result, corrugated beds can be used to enhance energy dissipation of hydraulic jump in the open channel. In general, the proposed SPH model is capable of simulating the effect of corrugated beds on hydraulic jump characteristics.

Select this Article		Pressure Surges Following Sudden Air Pocket Entrapment in Stormwater Tunnels Jose G. Vasconcelos, A. M. ASCE and Gabriel M. Leite Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000616 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Deep stormwater storage tunnels may undergo pressurization during intense rain events; in the process, air pockets may become entrapped and pressurized, causing significant flow changes. Currently the role of nearby surge relief structures is uncertain as far as air‐water interactions are concerned. This work presents results from experimental and numerical investigations on air pocket entrapment and compression following reflection of inflow fronts on system boundaries. Steady flows were established in the pipe apparatus, having the upstream portion flowing in pressurized regime while the downstream flowed in free surface conditions. Sudden flow obstruction caused by valve maneuvering at the downstream end generated unsteady conditions that were monitored by transducers and MicroADV probe. Partial valve maneuver runs were performed and aiming to represent cases where surge relief is provided during air pocket compression/expansion cycles. While experiments performed without surge relief (complete valve obstruction) yielded an oscillatory pressure pattern upon air pocket entrapment, when relief was available a single pressure pulse pattern was observed instead and no sub‐atmospheric pressures were recorded. A simple two‐phase model that includes essential features of the problem was developed and its pressure predictions compared well with the experimental data.

Select this Article		Investigations on the Trajectory of Large Sandbags in Open Channel Flow M. Elkholy and M. Hanif Chaudhry, F. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000614 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Investigations to understand the mechanics of motion of large sandbags and to compute their trajectories are reported in this paper along with the details of the experimental set‐up and procedures. The motion of sandbags is recorded from the side of a flume by a high‐definition CCD (charge‐coupled device) camera and the digital particle tracking Velocimetry (DPTV) technique is used to track the motion of the bags. An equation is developed for the normalized maximum horizontal settling distance from the experimental data. It is found that the particle velocity normal to the flow depends mainly on the characteristic diameter of the particle and the Froude number of the flow while the particle velocity in the streamwise direction shows lower dependency on the Froude number. Analysis of the particle tumbling shows that the Magnus force may be neglected for modeling the trajectories of sandbags in uniform flows. A model for the particle motion is developed by solving the Lagrangian equation numerically. Two approaches for computing the trajectory of the sandbags are investigated. The results show that the approach in which the drag coefficient is varied based on the orientation of the particle gives better results than if the drag coefficient is kept constant and is based on the broadside orientation of the particle. The results also show that the change in the drag coefficient may be as low as 28% to as high as 76% based on the orientation of the particle with respect to the flow.

Select this Article		Variance of Discharge Estimates Sampled Using Acoustic Doppler Current Profilers from Moving Boats Carlos M. García, Leticia Tarrab, Kevin Oberg, Ricardo Szupiany, and Mariano I. Cantero Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000558 Posted ahead of print 14 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a model for quantifying the random errors (i.e., variance) of acoustic Doppler current profiler (ADCP) discharge measurements from moving boats for different sampling times. The model focuses on the random processes in the sampled flow field and has been developed using statistical methods currently available for uncertainty analysis of velocity time series. Analysis of field data collected using ADCP from moving boats from three natural rivers of varying sizes and flow conditions shows that, even though the estimate of the integral time scale of the actual turbulent flow field is larger than the sampling interval, the integral time scale of the sampled flow field is on the order of the sampling interval. Thus, an equation for computing the variance error in discharge measurements associated with different sampling times, assuming uncorrelated flow fields is appropriate. The approach is used to help define optimal sampling strategies by choosing the exposure time required for ADCPs to accurately measure flow discharge.

Select this Article		Velocity Distribution in Open Channel Flows: An Analytical Approach for the Outer Region Laurent Lassabatere, Jaan Hui Pu, Hossein Bonakdari, Claude Joannis, and Frédérique Larrarte Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000609 Posted ahead of print 12 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an integration procedure for the Reynolds‐Averaged Navier‐Stokes equations for the determination of the distribution of the streamwise velocity using the vertical component. This procedure is dedicated to the outer region and central part of channels. The proposed model is applicable to both rough and smooth flow regimes, provided the velocity at the inner / outer boundary has been properly defined. To generate a simplified expansion, a number of hypotheses are proposed, focusing in particular on the analytical modeling of the vertical component by adopting a negligible viscosity. The proposed hypotheses are validated by the experimental data existing in the literature. The proposed simplified expansion is studied through a sensitivity analysis and proved consistent in regards to model experimental data. The proposed model seems capable to model different kinds of flows, including dip phenomenon flow patterns.

Select this Article		Estimation and Measurement of Bed Material Shear Stresses in Erosion Rate Testing Devices Raphael W. Crowley, David Bloomquist, James R. Hayne, Courtney M. Holst, and F. D. Shah Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000608 Posted ahead of print 12 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The Sediment Erosion Rate Flume (SERF) is used to evaluate various methods to estimate shear stresses in a flume‐style erosion rate testing device. Results show that direct shear stress measurements most closely correspond to shear stress estimates obtained from the Colebrook Equation using a roughness height of approximately 77% of the sediment particle diameter. Using pressure drops to estimate shear stress appears to underestimate rough sample (grain sizes greater than 0.25 mm) stresses. Likewise, smooth‐wall assumptions and analytical methods also appear to produce lower than expected results for similar heights. Colebrook Equation results should be interpreted as “instrument‐specific” due to different devices' hydraulic diameters.

Select this Article		Erratum for “Physical and Numerical Modeling of the Entrainment by a High‐Concentration Mud Suspension” by A. W. Bruens, J. C. Winterwerp, and C. Kranenburg A. W. Bruens, J. C. Winterwerp, and C. Kranenburg Journal of Hydraulic Engineering doi:http://dx.doi.org/ Posted ahead of print 31 March 2012 Full Text: \| Download PDF
		Abstract Unavailable

Select this Article		Case Study: Numerical Simulation of Unsteady Hyper‐Concentrated Sediment‐Laden Flow in the Yellow River Li He, Jennifer G. Duan, Guangqian Wang, and Xudong Fu Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000599 Posted ahead of print 30 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The major obstacles for simulating flood flow in the Yellow River are its high sediment concentration, complex compound cross section, and rapid change of channel planform. This paper presents an improved one‐dimensional numerical model that takes into account the effect of sediment concentration and bed change on mass and momentum conservation of flood flow in the Yellow River. The model is calibrated and then validated by simulating three individual flood events. Results show that an increase of sediment concentration leads to a reduction of flood wave celerity and peak discharge. The Generalized Likelihood Uncertainty Estimation (GLUE) method is used to evaluate the uncertainty of modeling results. A sensitivity index, analogous to the Nash‐Sutcliffe efficiency factor, is adopted to quantify the sensitivity of calibration parameters. The modeling results are sensitive to the choice of Manning's roughness coefficient and the empirical recovery coefficient for suspended sediment transport at reaches of transitional channel planform.

Select this Article		Experimental Investigation of the Influence of Baffle Position on the Flow Field, Sediment Concentration and Efficiency of Rectangular Primary Sedimentation Tanks Mahdi Shahrokhi, S. M. ASCE, Fatemeh Rostami, S. M. ASCE, Md Azlin Md Said, Saeed Reza Sabbagh Yazdi, and Syafalni Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000598 Posted ahead of print 29 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Sedimentation due to gravitation is applied extensively in water and wastewater treatment to remove suspended solids. Suitable baffle configurations may help form favorable flow fields and increase the efficiency of a primary sedimentation tank. Experimental tests were performed to determine the best position for a baffle in a rectangular primary sedimentation tank. The experimental measurements consisted of three parts. First, the velocity fields were measured using an Acoustic Doppler Velocimeter. The concentration at different vertical and horizontal points was then evaluated. Finally, the removal efficiency of the sedimentation tank was measured. The results of the present study indicate that a uniform flow field in the settling zone is enhanced when the baffle position provides a small volume of circulation regions. In this case, the maximum concentration of the suspended sediments inside the settling zone and the highest removal efficiency are achieved.

Select this Article		Novel Sensitive Liquid Level Measuring Devices Michael Poreh Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000597 Posted ahead of print 29 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The present analysis shows that the vertical movement of spring‐suspended containers that communicate with a liquid in a reservoir is proportional to the change of the liquid level in that reservoir and demonstrates how they could be used as sensitive liquid level measuring devices, which are easy to build, calibrate and use.

Select this Article		Investigation of Hydraulic Transients in a Pipeline with Column Separation Adam Adamkowski and Mariusz Lewandowski Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000596 Posted ahead of print 29 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Authors of this paper in earlier publication presented a new method (based on the new discrete vapor cavity model — the New DVCM) of numerical prediction of pressure changes during the waterhammer with liquid column separation together with results of preliminary experimental verification of this method. This paper is a continuation of research on this topic. It presents the results of additional laboratory tests, extended with visualization of the cavitation zones generated during the transient flow with liquid column separation. The results of these studies provide a better understanding of this phenomenon. Among others they showed that the phenomenon can have a distributed nature, which means that the gas‐vapor zones may be observed not only locally, in the vicinity of the shut‐off valve, but they may be spread along the pipeline length, and the intensity of this phenomenon decreases with distance from the valve. The laboratory test results were also used for further verificat ion of the New DVCM. This verification shows that an agreement between calculation and experimental results strongly depends on the friction model that was incorporated into calculation. It was indicated that the agreement depends also upon the intensity of liquid column separation ‐ for the cases of severe separation the differences between numerical and measured pressure changes are small and accepted from practical point of view.

Select this Article		Conversions of Surface Grain‐Size Samples Collected and Recorded Using Different Procedures David J. Graham, Anne‐Julia Rollet, Stephen P. Rice, and Hervé Piégay Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000595 Posted ahead of print 24 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Information about the grain‐size distribution of the surface layer of sediment exposed on river beds is often critical in studies of fluvial hydraulics, geomorphology and ecology. A variety of sampling and analysis techniques are in common usage which produce grain‐size distributions that are not directly comparable. This paper seeks to explore the appropriate conversions between different types of surface grain‐size sampling methods. This is particularly timely in the light of increasingly widespread use of automatic and semi‐automatic image‐based measurement methods, the comparability of which with conventional measurement methods is relatively poorly constrained. For conversions between area‐by‐number (paint‐and‐pick) and grid‐by‐number (pebble count) samples, the empirically‐derived conversion factor (±2.2) was found to be greater than that predicted by the Kellerhals and Bray model (±2), but the errors associated with using the value predicted by the model were small (3.8% in mm). For conversions between areal samples recorded by count and weight, the empirically‐derived conversion factor was approximately ±2.9, but the use of the value predicted by the Kellerhals and Bray model (±3) resulted in only small errors (5.2% in mm). Similarly, for conversions between image‐based grain‐size distributions recorded in area‐by‐number and grid‐by number form, the emipirically‐derived conversion factor was ±1.9, but the using the model value of ±2 resulted in only small errors (4.1% in mm). Although these results are specific to the datasets analysed, the variety of sedimentary conditions included gives us confidence that the results are representative.

Select this Article		The Influence of River Discharge and Dredging on Tidal Wave Propagation; the Modaomen Estuary Case Huayang Cai, Hubert H. G. Savenije, Qingshu Yang, Suying Ou, and Yaping Lei Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000594 Posted ahead of print 22 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Dredging and flow reduction in the Modaomen estuary in China have had a measurable impact on tidal propagation and damping. In this paper we assess the impacts of these human interventions through the use of a new analytical hydraulic model procedure. The model calculates tidal propagation and damping as a function of bathymetry and river discharge through a simple iterative procedure with explicit analytical equations. The results obtained are accurate and allow both an analysis of the historic development and a sensitivity analysis to assess the effect of possible further dredging and flow reduction. Particularly in the upper reaches of the estuary, tidal damping and wave celerity are sensitive to dredging and flow reduction. Historic analysis shows that due to these activities, since 1993, the tidal amplitude in the Modaomen estuary increased by more than 0.1 m, while the travel time of the tidal wave decreased by 30 min in the middle part of the estuary and up to 80 min in the upper reaches. In the future, the tidal amplitude and the wave celerity would increase even further if flow reduction and dredging continue. Moreover, this development would increase the risk of salinization in the estuary and facilitate the inland propagation of storm surges.

Select this Article		Temporal Variation of Scour around Circular Compound Piers Umesh C. Kothyari and Ashish Kumar Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000593 Posted ahead of print 22 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Bridge piers having non‐uniform cross‐section over their height are termed as compound bridge piers. Mostly circular piers resting on large diameter well or caissons (termed here as circular compound bridge pier) are adopted for use in the Indian sub‐continent for the road and railway bridges. In the present study a new mathematical model is proposed here for computation of temporal variation of scour depth at circular compound bridge pier. Two series of laboratory experiments were conducted to collect data for model application. In the first series of experiments the data on temporal variation of scour depth were collected albeit up to the transient (developing) stage of scour, around the circular uniform piers and circular compound piers for clear‐water scour condition. The second series of experiments was carried out to measure the size and hence the area of the principal vortex of the horse‐shoe vortex system and to determine the bed shear stress at upstream face of the scour hole around the circular uniform pier and the circular compound piers. The mathematical model proposed herein has the capability to compute the temporal variation of scour depth around circular compound pier for all possible case of footing position with respect to bed level i.e. footing above the bed level, footing at the bed level and footing below the bed level.

Select this Article		Removal of Sediment from between Armor Blocks. Part 3: Breaking Waves Anders Wedel Nielsen, B. Mutlu Sumer, and Jørgen Fredsøe Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000592 Posted ahead of print 20 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract When a sediment beach covered by stones or an armor layer is exposed to breaking waves, the turbulence generated by the breaking waves can cause mobilization and removal of the sediment underneath the stones. In two earlier studies by the DTU‐group the suction removal of sediments from between armor blocks has dealt with the case of steady current and non‐breaking waves. The present study is an extension of these studies and the results will be presented in a similar way. The critical conditions for removal of sediment are determined. It is found that the onset of removal of sediment is governed by three parameters: (1) the sediment mobility (based on the sediment size, wave height and wave period), (2) the ratio between the sediment size and the stone size, d/D, and (3) surf similarity parameter, ξ=tan(β)/(H₀/L₀)^0.5. The variation of the critical mobility number for removal of sediment as function of d/D and ξ is determined for the range 0.001<d/D≤1.0 and 0.15<ξ<6.00. The experiments were made on 1:2, 1:14 and 1:30 slopes. Spilling, plunging and surging breakers were used in the experiments. Both one and two layers of armor stones and rectangular blocks were studied.

Select this Article		Skimming, Non‐Aerated Flow on Stepped Spillways over RCC Dams Inês Meireles, Floriana Renna, Jorge Matos, and Fabián Bombardelli, A. M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000591 Posted ahead of print 12 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The non‐aerated region may occupy a large portion of the skimming flow in steep, stepped spillways, particularly for relatively high unit flow rates. In spite of the numerous contributions on the hydraulic properties at both the inception point of air entrainment and the aerated region, much less is known regarding the flow in the non‐aerated region. In this manuscript, new empirical evidence, based on an extensive dataset obtained during several years in a large‐scale facility, sheds light on the features of the non‐aerated flow region. Diverse ways to locate and estimate the main hydraulic properties at the inception point are first discussed and compared. Then, expressions capable of characterizing the main flow variables along the non‐aerated region are presented, namely the boundary‐layer development, the velocity distribution, the equivalent clear‐water depth, the characteristic depth taking into account the free‐surface unsteadiness due to turbulence, and the energy dissipation. The energy dissipation is observed to be larger than that for smooth spillways, although much smaller than values typically reported for aerated flows at the toe of stepped spillways.

Select this Article		Road Salt Impact on Lake Stratification and Water Quality Eric V. Novotny and Heinz G. Stefan Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000590 Posted ahead of print 12 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Runoff from roadways on which road salt (NaCl) has been applied for driving safety in winter can form a saline water layer at the bottom of a lake, pond, reservoir, or river impoundment. Natural vertical mixing of lentic surface water bodies can be hindered by the presence of a benthic saline layer and thereby affect lake water quality and ecology. To study the formation and disappearance of the saline layer, temperature and specific conductance profiles were measured intermittently over two years (2007, 2008) and at high frequency duringone year (2009) in an urban lake of the northern temperate region (Tanners Lake, Oakdale, Minnesota). Erosion of the saline layer in the spring occurred only in year 2007. In years 2008 and 2009 the saline layer persisted throughout the summer only to be removed during fall turnover when thermal stratification was at a minimum. In all three years salinity dominated density stratification after ice‐out, but was quickly overtaken by temperature stratification as the epilimnion warmed. We modified our deterministic, unsteady dynamic 1‐D lake temperature and dissolved oxygen model MINLAKE by including vertical salinity gradients and used it to simulate summer stratification and mixing dynamics in Tanners Lake. The daily adjustment of the hypolimnetic eddy diffusion as a function of Lake Number was an important component in the developed model. This addition allowed mixing in the hypolimnion to be stronger in the fall and spring when the lake stratification was weaker than in the summer after thermal stratification formed. Model results of dissolved oxygen in the water column demonstrated that the saline benthic layer can prevent dissolved oxygen from reaching lake sediments. The adverse consequences of dissolved oxygen depletion on phosphorus recycling from the sediments, benthic microbial communities and fish habitat are well known. Overall, the results show how salinity from road salt applications can influence water quality and natural mixing in urban lakes.

Select this Article		Dilution and Penetration of Vertical Negatively Buoyant Thermal Jets Nadeem Ahmad and Raouf E. Baddour, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000588 Posted ahead of print 3 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Five series of experiments were performed to study the penetration and dilution properties of vertical negatively buoyant thermal jets (thermal fountains). The flow was turbulent and the densimetric Froude number Fr based on the radius of the discharge varied from 4.7 to 24. The experiments were conducted in the laboratory by discharging hot water vertically downward into a colder water environment that had a temperature greater than 15C°. Under these conditions the water equation of state was practically linear, and the downward negatively buoyant thermal jet was dynamically similar to an upwards negatively buoyant dense jet of equal densimetric Froude number. The temperature fields associated with the negatively buoyant jets were measured with arrays of fast responding thermocouples and used to study the jet penetration and dilution properties. Detailed analyses of the temperature data revealed large fluctuations of jet penetration in the vertical direction. The mean and maximum vertical jet penetrations obtained in this study using temperature data were consistent with the results of previous studies based on visual data. In contrast, less fluctuations of jet penetration occurred in the horizontal direction, and the maximum horizontal penetration of the return flow, at the level of the source (z=0), was δ_m = 1.40 r₀ Fr. This value is about one half of the mean vertical jet penetration. On the other hand, the minimum dilution of the returning fluid at the source height just outside of the nozzle was μ_min= 0.58 Fr.

Select this Article		Performance of Baffle Blocks in Submerged Hydraulic Jumps A. Habibzadeh, S. M. ASCE, M. R. Loewen, and N. Rajaratnam, F. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000587 Posted ahead of print 3 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract An experimental study was conducted investigating submerged hydraulic jumps with baffle blocks. An extensive series of tests were completed which covered a range of Froude numbers, submergence factors and block arrangements. Dimensional analysis was used to interpret the results and study the effect of each parameter. Two flow regimes, the deflected surface jet (DSJ) and reattaching wall jet (RWJ), were observed. The occurrence of a particular regime depends on the block shape and location as well as the Froude number and submergence factor. The DSJ regime was found to dissipate more energy due to the formation of the deflected jet and its impingement on the water surface. The DSJ regime is almost as efficient in dissipating energy as the free hydraulic jump. This flow regime also had a smaller reverse flow region compared to the RWJ regime. Empirical equations were derived for predicting the critical values of the submergence factor at which each flow regime forms. The efficiency of the submerged hydraulic jump with blocks in dissipating energy was compared to that of free without blocks as a function of submergence factor.

Select this Article		Separation Zone in Flow past a Spur Dyke on Rigid Bed Meandering Channel Kedar Sharma and Pranab K. Mohapatra Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000586 Posted ahead of print 3 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Flow past a spur dyke on rigid bed meandering channel with trapezoidal cross‐section has been studied experimentally. Accoustic Doppler Velocimeter (ADV) was used to measure the velocities. The results show that, length of the downstream separation zone changes according to the location of the spur dyke. It varies from 4.0 to 22.8 times the spur dyke length. In addition, the separation zone at higher elevations is wider compared to that near the bed for most of the locations of the spur dyke. Effect of contraction ratio and inflow Froude number on separation zone is also presented.

Select this Article		Accounting for Directional Devices in WDN Modeling Orazio Giustolisi, Luigi Berardi, and Daniele Laucelli Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000585 Posted ahead of print 27 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This work presents a modification to steady‐state Water Distribution Network (WDN) simulation models in order to account for directional devices such as check valves and flow control valves. These devices, allowing water flow control in a definite direction, are important in order to manage the hydraulic system functioning over time by considering the variation of some boundary conditions as for example required demands and tank levels. However, the simulation models are built on the assumption that water can flow in both directions of each pipe in the hydraulic system and the information on directionality of some devices is not automatically allowed. Thus, in WDN models those devices are currently modeled using a heuristic approach, intermixed with solving the problem of steady‐state WDN analysis. For this reason, a different approach using content and co‐content theory was recently proposed in order to define the conditions that guarantee the existence and uniqueness of the solution. The alternative proposed here presents an adjustment of the energy balance equations to account for flow control valves. Check valves are treated as a special case of flow control valves, while the directionality of pumps, which are equipped with a check valve to avoid reverse flow, is modeled by means of their implicit check valve. Once the status of such directional devices is identified, a topological analysis of the network is performed. The methodology is applied to the demand‐driven and pressure‐driven analysis of a WDN solved by means of the global gradient algorithm, although it could be easily extended to other algorithms.

Select this Article		Converging Stepped Spillways: A Simplified Momentum Analysis Approach Sherry L. Hunt, E.I.T., M. ASCE, Darrel M. Temple, P.E., M. ASCE, Steven R. Abt, P.E., F. ASCE, Kem C. Kadavy, P.E., and Greg Hanson, P.E., M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000584 Posted ahead of print 25 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Roller compacted concrete (RCC) stepped spillways are growing in popularity for providing overtopping protection for aging watershed dams with inadequate auxiliary spillway capacity and for the construction of new dams. Site conditions, such as limited right‐of‐way, topography, and geological formations, often dictate that these spillways converge. Convergence increases the flow depth near the training walls and alters the stilling basin design requirements as compared to traditional straight spillways. A simplified control volume momentum analysis is presented for predicting the minimum vertical training wall height necessary to prevent wall overtopping in converging stepped spillways. An expression is developed to predict vertical training wall height as a function of centerline flow depth, centerline velocity, chute slope, and convergence angle. A three‐dimensional 3(H):1(V) sloping stepped spillway model with an ogee crest and convergence ranging from 0 to 70° was constructed to verify this relationship. The evaluation showed approximately 2% error for all combined convergences. Because the relationship is based on momentum principles, it provides design engineers with a method for determining minimum training wall height requirements under non‐air entrained flow conditions for a range of design conditions (i.e. chute slopes, convergences, step heights, etc).

Select this Article		Three‐Dimensional Scour at Submarine Pipelines Yushi Wu and Yee‐Meng Chiew, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000583 Posted ahead of print 25 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents results of an experimental study on 3‐dimensional scour at submarine pipelines with uniform sediment under a unidirectional current in clear‐water conditions. The data show that propagation of the scour hole in the transverse direction of flow may be divided into a rapid and a slack phase of development. The former is characterized by a higher but constant, while the latter a lower and reducing propagation velocity. Four non‐dimensional parameters are identified and their effects examined experimentally. Pipeline embedment and water depth to pipeline diameter ratios, which represent the stability force, inhibit the scouring process, resulting in a reduced propagation velocity and a dominant slack phase of development. Conversely, Froude number and Shields parameters represent the environment force; they enhance the scouring process, causing a high propagation velocity and a dominant rapid phase of development. The experimental results reveal that the scour process is not sensitive to Shields parameter under clear‐water conditions, but is closely related to the other three parameters. The effect of all the parameters can be viewed in terms of a balance between the environment and stability forces.

Select this Article		Flow Resistance in Smooth Rectangular Open‐Channels with Low Aspect Ratios Ba Tuyen Nguyen and Nian‐Sheng Cheng Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000582 Posted ahead of print 25 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract This note shows an approach that is useful for evaluating the resistance to flows in narrow open channels. A series of experiments were first carried out in a smooth rectangular open channel of which the aspect ratio varied from 0.12 to 1.53. Experimental data collected were then used to validate a resistance formula that was proposed previously by modifying Prandtl's friction law.

Select this Article		Subcritical Side‐Weir Flow at High Lateral Discharge Oscar Castro‐Orgaz and Willi H. Hager, F.ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000581 Posted ahead of print 21 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Side‐weirs count among the important hydraulic structures for flow derivation in flood schemes or sewer networks. Herein, the prismatic side‐weir in the rectangular channel is considered for entirely subcritical flow. Based on the momentum and energy equations, relationships are developed for the lateral outflow intensity, the local lateral outflow angle, the energy and momentum correction coefficients, and the relation between the local streamwise component of the lateral outflow velocity and the average channel flow velocity. The governing equations are then numerically solved and the results compared with hydraulic laboratory observations, indicating that the momentum approach may be considered superior to the energy approach. The role of the momentum and energy correction coefficients is thereby particularly analysed, stating that its correct inclusion both as absolute values and its local variation along a side‐weir have to be accounted for if the local discharge relative to the approach flow discharge tends to zero.

Select this Article		Experimental Investigation of the Effects of Pipe Material on the Leak Head‐Discharge Relationship Marco Ferrante Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000578 Posted ahead of print 16 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The Torricelli's formula is often used to define the dependence of the leak outflow on the flow conditions inside the pipe and on the leak characteristics. Some tests carried out at the Water Engineering Laboratory of the University of Perugia, Italy, show that differences in the leak head‐discharge relationships may arise even when the same leak is machined in pipes with the same inner diameter but of different thickness and material. These data can still be explained by the Torricelli's formula if the possible variation of the leak area due to the head is considered. When the pipe material behaves in a linear and elastic fashion, the leak area variation with the head is linear, while other formulations are needed when elastoplastic or viscoelastic materials are used. As a consequence this effect can produce different leak head‐discharge relationships, depending on the constitutive law and behavior of the pipe material.

Select this Article		Effect of Friction on Spurious Oscillations in Open Channel Modeling with Variable Bathymetry or Roughness Mohammad Mostafa Ali and Peter Steffler, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000577 Posted ahead of print 16 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Numerical issues for the friction dominated Steady state Saint‐Venant equations with a shock capturing upwind finite element scheme are studied using non‐uniform flow test cases and Fourier analysis. The friction dominated case is a common phenomenon in open channel flow modeling when the depth becomes small compared to the discretization length. In the non‐uniform flow test cases abrupt slope changes and abrupt roughness changes are introduced and in the Fourier analysis a periodic bed perturbation is used. Non‐dimensional parameter groups identified are: the upwinding coefficient, the number of elements per wavelength, the average flow Froude number, and the numerical Friction number. The results show that errors in both depth and discharge variables are observed whenever there is any perturbation in the bed topography or bed roughness. These errors increase with increasing Froude number and increasing numerical Friction number. A combined friction parameter is introduced for practical application. The combined friction parameter can be used to specify minimum depths or to guide mesh refinement. The analysis framework developed can also be used for other numerical schemes.

Select this Article		Instability Theory of Sand Ripples Formed by Turbulent Shear Flows Sujit K. Bose and Subhasish Dey Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000524 Posted ahead of print 6 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract A theory of turbulent shear flow over a sand bed is developed addressing the instability principle of the fluid‐granular bed interface leading to the formation of ripples. The Reynolds averaged Navier‐Stokes (RANS) equations and the time‐averaged continuity equation are analyzed using a 1/7‐th power law of the time‐averaged streamwise velocity and treating the curvilinear streamlines by the Boussinesq approximation. The integration of the RANS equations leads to a governing dynamical equation of flow over a mobile bed. A near‐bed flow layer of 3.5 times the ripple height is considered being affected by the ripples. The dynamical equation of the mobile sand bed is based on the Exner's sediment continuity equation in conjunction with the Meyer‐Peter and Müller bed‐load transport formula as modified to account for the effect of local bed slope due to bedforms. The coupled dynamical equations are then analyzed to estimate the parameters for the instability that results in the formation of ripples on the bed. The nondimensional ripple length (ratio of ripple length to sand size) increases with an increase in Shields parameter. The theoretical results have an agreement with the experimental data.

Select this Article		Effect of Cross‐Flow Velocity at Forebay on Swirl in Pump Suction Pipe: Hydraulic Model of Seawater Intake at Aliveri Power Plant in Greece Athanassios A. Dimas and Andreas P. Vouros Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000576 Posted ahead of print 3 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The hydraulic performance of pumps in a cooling water intake is directly affected by the non‐uniformity of the approach flow at each pump bay which in turn is influenced by the strength of the cross‐flow at their common forebay. The effect of the cross‐flow velocity at the forebay on the swirl angle in the pump suction pipes is investigated on a hydraulic model of the seawater intake at the Aliveri Power Plant in Greece. The particular intake features two pumps, and a total of ten cases were examined based on differing values of water depth, number of pumps in operation and pump flow rate. Velocity measurements at the forebay dividing cross‐section were obtained by an acoustic Doppler velocimeter (ADV), while swirl angle in the suction pipe was measured by a vortimeter. A highly non‐uniform velocity profile develops at the forebay, when one of the two cleaning channels is closed, and the swirl angle depends solely on the intake forebay geometry when the mean cross‐flow velocity drops below a critical value.

Select this Article		Erratum for “Two‐Phase Simulation of Wave‐Induced Tunnel Scour beneath Marine Pipelines” by Abbas Yeganeh‐Bakhtiary, Mohammad Hossein Kazeminezhad, Amir Etemad‐Shahidi, and Jaco H. Baas Abbas Yeganeh‐Bakhtiary, Mohammad Hossein Kazeminezhad, Amir Etemad‐Shahidi, and Jaco H. Baas Journal of Hydraulic Engineering doi:http://dx.doi.org/ Posted ahead of print 2 February 2012 Full Text: \| Download PDF
		Abstract Unavailable

Select this Article		Tsunami Response in Semi‐Enclosed Tidal Basins Using an Aggregated Model Susana Bastón, Maitane Olabarrieta, Pedro Lomónaco, Fernando J. Méndez, and Raúl Medina Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000573 Posted ahead of print 31 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract An aggregated model to evaluate tsunami response in semi‐enclosed water bodies is presented in this work. The model is based on one‐dimensional shallow water equations and can include long‐wave external forcing such as a tsunami. It has been successfully validated against experimental data from a physical model, and its predictions for a case study have been compared with results from the COMCOT numerical model. The model can be used as a predictive tool because a calibration using a theoretical value for expansion and contraction losses has been performed, and differences with the typical calibration are less than 10% which is considered acceptable. This allows using the model in the absence of measured data, which is very difficult to obtain in case of a tsunami event. A case study for the Gulf of Cádiz (Spain) has been simulated with the COMCOT model. The aggregated model predicted the response for a harbor more accurately than for estuarine systems with tidal flats. Nevertheless, the aggregated model has been demonstrated as a useful general tool to predict the response of semi‐enclosed tidal basins to a tsunami event, and hybrid models coupling advanced models to simulate ocean tsunami propagation with the model presented here would be useful in developing coastal warning alert systems.

Select this Article		Use of Index Gradients and Default Tail‐Water Depth as Aids to Hydraulic Modeling of Flow‐through Rockfill Dams David Hansen and Ali Roshanfekr Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000572 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract In order to assess the potential for unraveling failure of flow‐through rockfill dams, a systematic study of three aspects of the hydraulic design of these structures was conducted. The first concerned finding that gradient which is most useful in independently computing the height of the point of first flow emergence. The method presented is based on the idea of the angle of the emergent flow field within the toe of the structure. As an outcome, the second presents a method for independently computing the variation in hydraulic head within that vertical which allows the toe of the structure (i.e. downstream of the vertical associated with first flow‐emergence) to be isolated. It is based in part on a separate parametric study of 24 numerically‐simulated flow‐through rockfill dams. In the third, the gradient that will allow for the independent estimation of the default tail‐water depth is presented and verified, with the help of laboratory results. It is hoped that these three computational tools will facilitate the design and assessment of flow‐through rockfill structures, as a particular class of pseudo‐hydraulic structure.

Select this Article		Wave Damping and Smoothing in the Unsteady Pipe Flow Marek Mitosek and Romuald Szymkiewicz Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000571 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract A modification of the governing equations for unsteady pipe flow is proposed, based on the results of many experiments carried out for steel and HDPE pipes of various lengths. Strong damping and smoothing of the pressure wave observed in the experiments suggest that these effects are caused not only by the liquid viscosity, represented in the governing equations by an algebraic term, but also by some others processes, which are not described by these equations. The phenomena observed in physical experiments, such as time‐varying pressure wave celerity and smoothing of the wave front cannot be reproduced by the standard unsteady pipe flow model even if various modifications of the formula for shear stress available in the literature are applied. For this reason an attempt of taking into consideration additional dissipative processes was undertaken. On the basis of an approximate model of the elastic behavior of the liquid and wall pipe material, an approach accounting for the variable pressure wave celerity is proposed. Moreover a diffusive term reproducing the irreversible processes at the pressure wave front is introduced into the dynamic equations. The numerical tests showed that the proposed approach leads to a better agreement between the computational and experimental results.

Select this Article		Improvements in Flow Rate Measurements by Flumes Wojciech Dabrowski and Urszula Polak Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000567 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Imperfections of the ISO 4359 standard related to the application of a boundary layer concept for predicting flow rates through rectangular and U‐shaped flumes are described in detail. The main equation for a flume flow chart results from a system of equations consisting of the energy equation and two continuity equations. The first equation requires a different modification of the stream width and depth when the boundary layer concept is applied to all three equations. Additionally, the modification of the stream dimensions should refer to the cross section in the throat where the critical depth occurs instead of calculating it at the very end cross section of the flume throat, as suggested by the ISO 4359 standard. To improve the accuracy of flow rate computations, the critical depth position in Venturi and Palmer ‐ Bowlus flumes was predicted numerically by solving an ordinary differential equation which describes the water surface profile of steady gradually varied flow in open channels of prismatic and non prismatic cross sections. Computing the stream modification for the position of the critical depth in a flume throat resulted in the reduction of the highest relative error of flow prediction for the Palmer‐Bowlus flume in a sewer of the inside diameter D= 0.762m from 3.3% to 0.8%, for D = 0.381m from 3.7% to 1.2%, for D=0.203m from 4.3% to 3.2%, and for D=0.102m from 5.2% to 3.5%. In addition, a simple algebraic equation for calculating the critical depth position in Venturi flumes was developed. Calculation of the stream modification in the cross section of a flume throat in which the critical depth occurs was proved to improve the accuracy of flow rate computations both for Venturi and for Palmer ‐ Bowlus flumes. However, for the latter type of flume, no such simple algebraic equation for the position of critical depth could be developed successfully. In this case, still some improvements of flow rate calculations could be achieved by modifying the stream dimensions in the way described by ISO 4359 but for the middle of the throat rather than at its end.

Select this Article		On the Applicability of the De Marchi Hypothesis for Side Weir Flow in the Case of Movable Beds Enio Paris, Luca Solari, and Giulio Bechi Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000566 Posted ahead of print 20 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Side weirs are widely used hydraulic structures typically designed and studied in the case of fixed bed conditions. In the case of subcritical flows, the hydraulics of side weirs can be modelled using the classical De Marchi hypothesis. In the present work, a generalization of this hypothesis is developed for the case of side weirs over movable beds. Experiments showing the effects and feedbacks between the spilling discharge and the bed morphodynamics are presented. The application of the experimental observations to the generalized De Marchi hypothesis clearly show that the functioning of side weirs on a movable bed can be modelled using this hypothesis. These findings could be instrumental for the design and verification of these structures.

Select this Article		Piano Key Weir Submergence in Channel Applications M. R. Dabling, S. M. ASCE and B. P. Tullis, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000563 Posted ahead of print 20 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Weir submergence can influence head‐discharge relationships for weirs used in channel applications when high tailwater conditions exist due to a downstream control. Weir submergence describes a condition where the water level downstream of the weir exceeds the weir crest elevation. When a weir becomes submerged, the driving head required to pass a specific discharge over the weir can increase significantly relative to a free‐flow condition. In this study, the effects of tailwater submergence on laboratory‐scale piano key weir head‐discharge relationships were evaluated experimentally and compared with previously published data for labyrinth and sharp‐crested linear weir submergence. The results of this comparison show that for relatively low levels of submergence, the piano key weir requires less upstream head relative to the labyrinth weir to pass a given discharge. This increase in efficiency was minimal (<6%), and was reversed at higher submergence levels.

Select this Article		Mixing of Multiple Buoyant Jets Joseph H. W. Lee, F. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000560 Posted ahead of print 20 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract I am grateful to the American Society of Civil Engineers for the opportunity to give this Hunter Rouse Lecture. It is indeed a great honor to be linked, even in a small way, with this historic name. I am very thankful for this appreciation of my work; this honor no doubt should also be shared with my postgraduate research students. I have never met Dr. Rouse in person; nevertheless I have seen him in action in the classic fluid mechanics films of the Iowa Institute of Hydraulic Research ‐ which I use in my undergraduate teaching. His book “Elementary mechanics of fluids” (Rouse 1946) has always been on my book‐shelf. And his classic papers on turbulent plumes have shed an important insight ‐ that engineering is concerned with the art of approximation, and relatively simple and scientifically sound models can be combined with laboratory experiments to solve complex hydraulic engineering problems.

Select this Article		Scaling of Velocity Profiles for Depth‐Limited Open Channel Flows over Simulated Rigid Vegetation Nian‐Sheng Cheng, Hoai Thanh Nguyen, Soon Keat Tan, and Songdong Shao Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000562 Posted ahead of print 20 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Using the plane mixing layer analogy, a length scale is proposed to normalize velocity profiles for the vegetated open channel flows. The new scaling is better than those based on the logarithmic, velocity‐defect and power laws in collapsing the velocity profiles, which include measurements conducted in this study and also those reported in the literature for a variety of flow and vegetation configurations. An eddy viscosity model is also developed to justify the scaling argument. This study is limited to rigid vegetation submerged in depth‐limited flows, of which the flow depth is not greater than twice the vegetation height.

Select this Article		Variance of Discharge Estimates Sampled Using Acoustic Doppler Current Profilers from Moving Platforms Carlos M. García, Leticia Tarrab, Kevin Oberg, Ricardo Szupiany, and Mariano I. Cantero Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000558 Posted ahead of print 16 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a model for quantifying the random errors (i.e., variance) of acoustic Doppler current profiler (ADCP) discharge measurements from moving platforms associated with different sampling times. The model focuses on the random processes in the sampled flow field and has been developed using statistical methods currently available for uncertainty analysis of velocity time series. Analysis of field data collected using ADCP from moving platforms from three natural rivers of varying sizes and flow conditions shows that, even though the estimate of the integral time scale of the actual turbulent flow field is larger than the sampling interval, the integral time scale of the sampled flow field is on the order of the sampling interval. Thus, an equation for computing the variance error in discharge measurements associated with different sampling times, assuming uncorrelated flow fields is appropriate. The approach is used to help define optimal sampling strategies by choosing the exposure time required for ADCPs to accurately measure flow discharge.

Select this Article		Arced Labyrinth Weirs B. M. Crookston, A. M. ASCE and B. P. Tullis, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000553 Posted ahead of print 5 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The discharge capacity and hydraulic efficiency of a labyrinth weir can be increased with an Arced cycle configuration. An Arced geometric layout for labyrinth weirs is presented, including nomenclature for arc‐specific geometric variables. Discharge coefficients as a function of H_T/P for half‐round trapezoidal Arced labyrinth weirs with 6° and 12° sidewall angles are also presented. The hydraulic performance of the tested Arced labyrinth weir geometries is compared to Projecting and in‐channel labyrinth configurations and to an arced weir (horseshoe weir) with a half‐round crest, including the effects of approaching flow conditions and local submergence. Differences between geometrically similar and geometrically comparable Arced labyrinth weirs are identified and discussed.

Select this Article		A Turbulent Based Model for Surface Erosion of Cohesive Soils Ali R. Sharif and Joseph F. Atkinson Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000551 Posted ahead of print 5 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract A model is proposed for surface erosion of cohesive soils based on physical interaction of turbulent bursts with the sediment bed. More specifically, the model deals with floc by floc erosion, appropriate for conditions of relatively low shear stress. The role of turbulent burst structures on entrainment of particles has been well established. A number of models have been developed for soil erosion based on interaction of turbulent burst structures with sediment beds in open channel flow. What has been lacking in this type of model and other models for surface erosion of cohesive soils in general is an understanding of the aggregate size distribution in cohesive sediment beds. In this study a relation is developed for aggregate size distribution as a function of bed bulk density and fractal dimension of aggregates in soils, and this relation is incorporated in a turbulent burst erosion model. The model is applied to experimental data and the resulting model parameters are found to compare closely to their physical values as reported in the literature.

Select this Article		Density Functions for Entrainment and Deposition Rates of Nonuniform Sediment Mohamed Elhakeem and Jasim Imran, M. ASCE Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000549 Posted ahead of print 10 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract A model was developed for the prediction of the density functions of entrainment and deposition rates of nonuniform sediment. The model incorporated both statistical and deterministic parameters in its formulation. The model parameters were related to the hydraulic conditions of the flow and the properties of the sediment mixtures using dimensional and multivariate regression analyses. Laboratory experiments were conducted to identify the shape of the density functions for various grain size fractions, and to advance the theoretical formulations of the model. The experiments were also used to validate and estimate the model parameters. The experiments have shown that the density functions of the total entrainment and deposition rates can be approximated quite satisfactorily with the normal distribution curve; however the density functions of the individual fractions within the sediment mixture depart from the normal distribution curve assuming various distributions. Therefore, the normal distribution equation was modified by introducing a bias‐function to adjust the normal distribution curve to fit the distributions of various grain size fractions within the sediment mixtures. The proposed model approximated satisfactorily the density functions of various grain size fractions of the sediment mixtures. The deviation between the measured and predicted values was less than 25% for most of the fractions, which confirms the validity of the proposed approach for the prediction of the entrainment and deposition rates of various fractions.

Select this Article		Orifice Spillway Aerator: Hydraulic Design V. V. Bhosekar, V. Jothiprakash, and P. B. Deolalikar Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000548 Posted ahead of print 9 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Orifice spillways are in vogue for the dams in the hilly regions where the spillway has to cater for dual function of flood disposal and flushing of sediment through the reservoir. Deep seated orifice spillways are subjected to cavitation damage as the cavitation index drops below the critical cavitation index of 0.2 due to negative pressures on the profile and high flow velocities. Aerators are provided for mitigating cavitation damage. Design guidelines for aerator of orifice spillways are scanty and not reported much in the literature so far, thus still remains grey area in the field of spillway aerator design. The present study investigates the performance of an offset aerator with and without ramp for deep seated orifice spillway on physical and numerical model. Performance of the aerator for varying discharges, heads and gate openings is studied for varying cavity sub‐pressures. Results in respect of jet length, cavity sub‐pressure and air entrainment coefficients are presented in the form of non‐dimensional plots. From this study, it is found that the non‐dimensional jet length is in the range of 2 to 35 and increases as the cavity sub‐pressure approaches atmospheric pressure. It is also found that the air entrainment increases with increase in Froude number, ramp height and cavity pressure. From the present study results, equations for jet length and air entrainment coefficient are developed and are presented for the orifice spillway aerator.

Select this Article		A Depth‐Averaged Two‐Dimensional Model of Unsteady Flow and Sediment Transport Due to Non‐Cohesive Embankment Break/Breaching Weiming Wu, Reza Marsooli, and Zhiguo He Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000546 Posted ahead of print 9 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract A depth‐averaged two‐dimensional model has been developed in this paper to simulate the unsteady flow and non‐cohesive sediment transport due to embankment break and overtopping breaching. The model adopts the generalized shallow water equations that consider the effects of sediment transport and bed change on the flow, thus leading to coupled calculations of these processes. It computes the non‐equilibrium total‐load sediment transport and considers the non‐cohesive embankment slope avalanching. The model solves the governing equations using an explicit finite volume method on a rectangular grid, with the HLL approximate Riemann solver to handle the mixed‐regime flows generated by embankment break/breaching and the MUSCL piecewise reconstruction method to reach second‐order accuracy in space. It uses a varying time step length that satisfies both the CFL condition and the limitation that the bed change is less than about ten percent of the local flow depth at each time step. Validations using laboratory and field experiments showed that the developed model predicts generally well the embankment‐break wave propagation over movable beds, the induced sediment transport and bed changes, and the temporal evolution of non‐cohesive embankment breach.

Select this Article		Physical and Numerical Modeling of the Entrainment by a High‐Concentration Mud Suspension A. W. Bruens, J. C. Winterwerp, and C. Kranenburg Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000545 Posted ahead of print 9 December 2011 Full Text: \| Download PDF See Also: Erratum
	+ -	Show Abstract This paper presents the results of a physical and numerical model study on the entrainment by a high‐concentration, cohesive sediment suspension. This turbulent, near‐bed suspension is referred to as a Concentrated Benthic Suspension (CBS). In the current configuration, the CBS entrains low‐concentrated overlying water. The results of the physical and numerical experiments are in line with the results of similar experiments, published in literature, where, in contrast, the upper, turbulent layer entrains water and sediment from the lower layer. The entrainment rate for these experiments is almost inversely proportional to the bulk Richardson number E ∝ Ri_∗⁻ⁿ, with n ≈ 1, indicating a profound effect of the side wall of the experimental facility. We anticipate that the conditions studied in this paper are characteristic for the behavior of many high‐concentration systems, such as the mouth of the Amazon River, and in the Loire Estuary and Ems River. A sequence of entrainment during high flow velocities, and settling/consolidation during low flow velocities, driven by tidally‐induced horizontal pressure gradients, keeps the sediment fluid, and mobile; this process can be referred to as tidal pumping. The experimental results could be reproduced to a fair degree by a 1DV POINT MODEL. This, however, does not necessarily imply that state‐of‐the‐art numerical engineering models are readily applicable for simulations of the hydro‐sedimentological conditions in complicated systems, such as the Amazon mouth and Loire estuary. In these systems, one expects a gradual transition from a fully turbulent upper part of the CBS layer, to laminar conditions deeper down within this layer, with increasing values of viscosity and yield strength; such transition is not accounted for in state‐of‐the‐art turbulence models. Yet, the current work provides a framework for a better understanding of these systems.

Select this Article		Hydraulic Analysis of Suspended Sediment Removal from Stormwater in a Standard Sump Adam Howard, Omid Mohseni, John Gulliver, and Heinz Stefan Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000544 Posted ahead of print 8 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Standard sumps (manholes) are common features of urban stormwater collection systems, and there are anecdotes suggesting that standard sumps can improve stormwater quality. However, no data on the effectiveness of sumps as treatment devices, especially for suspended sediment removal and the associated required maintenance schedule of the sumps could be found. Such data could justify giving pollution prevention credit for the use of standard sumps to transportation departments of cities, counties and state agencies. To assess the effectiveness of standard sumps as stormwater treatment devices, a laboratory study was conducted. Three goals were achieved in this study: (1) sediment capture and sediment washout were measured in four configurations of a straight flow‐through standard sump; (2) performance functions for the efficiency of suspended sediment removal in a standard sump were developed; and (3) performance functions for sediment washout from a standard sump were developed. To determine whether they remove suspended sediment from stormwater runoff, two standard sumps of different sizes were tested in a laboratory setting. Removal efficiency under low flow conditions as well as washout rates under high flow conditions were measured. The sumps did remove suspended sediment at low flows, but at high flows the washout rate was substantial. The data collected were used to develop two performance functions, one for suspended sediment removal (deposition) in a sump at low flow, and one for sediment washout from the sump at high flow. Four sump configurations were tested under a wide range of flow characteristics. The principal independent variables such as sump dimensions, sediment settling velocities and hydraulic parameters were grouped into dimensionless numbers that were related to performance of all designs tested. These performance functions can be used to select appropriate designs and analyze the performance of existing standard sumps. Overall, the data collected show that standard sumps can be used as pre‐treatment devices for stormwater if properly selected and maintained.

Select this Article		SPH Modeling of Shallow Flow with Open Boundaries for Practical Flood Simulation R. Vacondio, B. D. Rogers, P. K. Stansby, and P. Mignosa Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000543 Posted ahead of print 8 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract A SPH (Smoothed Particle Hydrodynamics) numerical model for the Shallow Water Equations (SWEs) is presented for simulating flood inundation due to rapidly‐varying flow such as dam breaks, tsunamis, levee breaches, etc. Important theoretical and numerical developments have recently been made and the model has been extended here by incorporating these and implementing open boundary conditions, resulting in a general, accurate computational tool suitable for practical application. The method is attractive for flood simulation over large domains where the extent of inundation is unknown because computation is only carried out in wet areas and is dynamically adaptive. The open boundary algorithm is quite general, based on a simplified version of the characteristics method, handling both supercritical and subcritical inflow and outflow. This is tested against reference solutions for flows over a hump involving shocks. The model is then applied, to two quite different flood inundations resulting from the Okushiri tsunami in Japan and from a hypothetical dyke breach at Thamesmead in the UK. The SPH‐SWE model compares well with established commercial and state‐of‐the‐art finite volume codes.

Select this Article		Two‐Phase Simulation of Wave‐Induced Tunnel Scour beneath Marine Pipelines Abbas Yeganeh‐Bakhtiary, Mohammad Hossein Kazeminezhad, Amir Etemad‐Shahidi, and H. Baas Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000540 Posted ahead of print 2 December 2011 Full Text: \| Download PDF See Also: Erratum
	+ -	Show Abstract An Eulerian two‐phase flow model was presented and employed to investigate wave‐induced tunnel scour beneath a marine pipelines. The model is based on the Euler‐Euler coupled governing equations for the fluid and sediment phases, i.e. time‐averaged continuity and momentum equations were solved for both phases with a modified k‐ϵ turbulence closure for the fluid phase. Fluid‐particle, particle‐particle and fluid‐structure interactions were implemented in the simulation. The model accounts for the interphase momentum exchange by considering the drag, lift and added mass forces. The flow model was validated against an oscillatory flow around an isolated cylinder and a cylinder close to a rigid wall. The two‐phase model was also validated against an oscillatory sheet‐flow motion above a plane bed. Then, the two‐phase model was used to simulate the wave‐induced tunnel scour beneath the pipeline laid on a plane erodible bed. Comparison between the numerical results and experimental measurements indicates that the model simulates the bed profile successfully during the tunnel scour stage. Investigations revealed that the tremendous sediment transport takes place during the tunnel scour stage under high turbulence intensity. A phase‐lag was observed between the flow velocity in the scour hole and the free stream velocity.

Select this Article		Effects of Vegetation on Turbulence, Sediment Transport and Stream Morphology V. S. Neary, S. G. Constantinescu, S. J. Bennett, and P. Diplas Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000168 Posted ahead of print 8 July 2011 Full Text: \| Download PDF
	+ -	Show Abstract Vegetation as multiple stems in various configurations or an isolated stem profoundly alters turbulent flows. Past research has shown that these alterations influence sediment transport and stream morphology, but entail complex interactions and feedbacks between flow, vegetation and sediment processes that involve many parameters. These interactions are examined here for a variety of macrophyte patterns and scales in riverine environments. Flow Reynolds number, canopy density, and submergence ratio are just a few of the key parameters that influence the spatial variability of the flow, momentum transfer, vortex shedding and dissipation, and instantaneous stresses that are known to affect sediment and morphological processes in rivers. Knowledge gaps, though, still remain. A taxonomy that classifies vegetated flows as dense, sparse or isolated based on threshold parameters like the ratio of stem diameter to stem spacing would be useful for comparing studies among researchers and predicting likely morphological pathways. More research is needed to quantify thresholds and empirical relationships for flow‐vegetation‐sediment interactions so that aquatic macrophyte plantings can be used more effectively in water resource management. Field measurements of plant, canopy and plant patch characteristics for these macrophytes would also be desirable.

Select this Article		Sensitivity of Field Data Estimates in One‐Dimensional Hydraulic Modelling of Channels R. W. Kuta, W. K. Annable, and B. A. Tolson Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000187 Posted ahead of print 14 November 2009 Full Text: \| Download PDF
	+ -	Show Abstract A hydraulic simulation study was carried out for Red Hill Creek, an urban stream channel in Ontario, Canada. Over one million simulations were conducted using the HEC‐RAS4b model to evaluate the sensitivity of model predictions to field data accuracy, density and estimation techniques and provide guidance towards balancing human resource allocation with model accuracy. Increased cross section discretization, and improved estimates of floodplain roughness dominate the accuracy of the results of computed water surface elevations. For a range of field hours available for data collection, a sampling strategy focused on maximizing the number of sparsely detailed cross sections is shown to outperform a sampling strategy using the same number of field hours to sample fewer cross sections with a higher resolution.

Select this Article		Hydraulic Relations for Clinging Flow of Sharp‐Crested Weir Xin Zhang, Linjuan Yuan, Ruwu Peng, and Zhang Chen Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000186 Posted ahead of print 14 November 2009 Full Text: \| Download PDF
	+ -	Show Abstract Available discharge coefficient formulae for sharp‐crested weirs are only applicable to the free flow regime. To extend the range of discharge measurement by a rectangular sharp‐crested weir, critical heads of the transition flow regime, the head‐discharge relation for clinging and free flow, and the discharge coefficient for clinging flow were investigated experimentally based on more than 300 experimental points with head ranging from 0.0048 to 0.0455 m. The results indicate that the transitions from clinging to free flow and vice versa do not occur at the same head. Upper and lower critical heads, H_u,crit and H_l,crit, can be identified at which these transitions occur. For the condition studied, the head relation between clinging and free flow is found to be linearly correlated at the same discharge. Expressions for the discharge coefficient for clinging flow are developed.

Select this Article		A Dimensionless Method to Characterize the Mixing Effects of Surcharged Manholes Virginia Stovin, Ian Guymer, and Shing‐Tak Lau Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000183 Posted ahead of print 14 November 2009 Full Text: \| Download PDF
	+ -	Show Abstract Solute transport processes affect the performance of a wide range of water engineering structures. In the context of urban drainage, the effects of dispersion may act to reduce peak concentrations associated with intermittent discharges, or cause pollutants to be retained for longer or shorter durations than mean travel times would predict. With respect to surcharged manholes, previous research employed laboratory experiments to identify best‐fit parameter values for the first‐order ADE (Advection‐Dispersion Equation) and ADZ (Aggregated Dead Zone) routing models. This paper presents data from a new set of smaller‐scale laboratory measurements, and demonstrates that the threshold depth separating two distinct hydraulic regimes can be identified independently of scale. However, the fitted ADE and ADZ routing model parameters are not generally amenable to conventional hydraulic scaling, because the models do not provide good fits to the observed data. An alternative approach is proposed, based on the Cumulative Residence Time Distribution (CRTD). This approach is shown to be scalable and practical. The solute transport characteristics of a specific configuration of surcharged manhole are shown to be characterized by just two dimensionless CRTDs, corresponding to pre‐ and post‐threshold surcharge depths.

Select this Article		Experimental Investigation of Clear‐Water Local Scour of Compound Piers B. Ataie‐Ashtiani, Z. Baratian‐Ghorghi, and A. A. Beheshti Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000184 Posted ahead of print 14 November 2009 Full Text: \| Download PDF
	+ -	Show Abstract Local scour around complex piers under steady clear‐water condition was studied experimentally for a variety of configuration, including different sizes and shapes of complex piers. A total of 70 experiments were carried out. Three sets of experiments were performed over the entire range of possible pile cap elevations for complex piers with different geometrical characteristics. The collected data are used to quantify the pile cap elevations that maximize or minimize the local scour depth. Some of the available methodologies to estimate the maximum local scour depth around such complex piers are evaluated. Finally, using data collected in this study and data collected by other researchers, correction factors are proposed for the HEC‐18 (Hydraulic Engineering Circular Number 18) and Coleman (2005) methodologies, in order to improve the predictions.

Select this Article		Uniform Flow of Modified Bingham Fluids in Narrow Cross Sections Alessandro Cantelli Journal of Hydraulic Engineering doi:http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0000058 Posted ahead of print 6 February 2009 Full Text: \| Download PDF
	+ -	Show Abstract A model of modified Bingham fluid is used to investigate uniform mudflows in narrow cross sections of the kind typical of hillslope incisions. The problem is tackled both numerically and experimentally. Experiments were performed using Carboxymethylcellulose, a shear thinning fluid whose rheological behaviour can be interpreted by a modified Bingham fluid model. For narrow rectangular, trapezoidal and triangular cross sections, the capability to flow has been expressed by a general relationship that defines a dimensionless coefficient (ƒ) as a function of two dimensionless parameters: the Bingham number and an aspect ratio of the channel. We also derive plots for the critical Bingham number for incipient flow of modified Bingham fluids as a function of the aspect ratio of the channel. The present calculations and the experimental results demonstrate that the narrow character of the channel as well as its shape strongly affect the flow conductance and the critical value of the Bingham number.