Journal of Hydraulic Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

The paper deals with a unique spillway which incorporates an aerator in each flip bucket with the intention to aerate the flow and avoid subatmospheric air cavities enclosed by the jets. In terms of jet breakup and stability, the physical models and the prototype lead to contradicting conclusions. With sealed aerators, the models exhibit intact air cavities featuring negative air pressure, suggesting the aeration need. Computational fluid dynamics (CFD) is performed to determine the reason for the discrepancy. Both the prototype observations and CFD indicate that the jets break up as a result of air entrainment; the resulting cavity air-pressure drops are insignificantly small. The discrepancy is due to the small model scale, in which the threshold flow velocity for air entrainment is not met and the prerequisite for jet breakup does not exist. To correctly reproduce similar water–air flow phenomena, the model should be large enough to meet the air-entrainment criterion. When questioning a small-scale model with air-cavity formation, CFD simulations should be performed to check the model results and make corrections, if needed.

This study builds upon established methods for using acoustic Doppler current profilers (ADCPs) to measure velocities to include another measurement technique—longitudinal measurements—which are increasingly being used in open channel flow studies. Longitudinal measurements are collected in paths that parallel the streamwise direction as opposed to transect measurements, which are collected perpendicular to the flow direction. This study analyzed ADCP data that were collected concurrently using stationary, transect, and longitudinal collection methods in order to determine which method can be used to most effectively develop interpolated velocity maps. Data from the Pecatonica River in Freeport, Illinois, and the St. Joseph River in Berrien Springs, Michigan, were used as case studies for comparing measurement techniques. To compare interpolated velocities calculated using the longitudinal data collection technique with a traditional transect data collection scheme, the variables of data density and data collection effort were systematically altered to investigate both methods. Data collection effort time was utilized to provide equivalent velocity comparison between the ADCP data collection techniques. Plots that compared interpolated transect and longitudinal velocities to transect and stationary data illustrated that the longitudinal interpolated velocities match the known data and mimic the cross section velocity trend better than the interpolated transect depth averaged velocities. The longitudinal measurement technique was substantially better at describing the depth averaged velocity variation for the river reaches investigated.

Previous experimental research on the effects of debris on pier scour has focused primarily on circular and rectangular piers with debris present just under flow free surface. Debris-induced scour around sharp-nose piers, which are typical of masonry bridge piers, and the effect of debris elevation on pier scour have seldom been studied before. This paper aims to fill this knowledge gap. It presents results from flume experiments investigating scour around a sharp-nose pier under shallow flow conditions with angle of attack relative to the pier being zero. Uniform sand is used as bed material. Debris is modeled as stationary and extending only upstream of the pier. Three simplified debris geometries (cylinder, half-pyramid, and plate) are studied. Results show that scour depth decreases as debris gets closer to the bed with maximum scour depth occurring when debris is located just under the flow free surface. Interestingly, scour depths produced by debris in shallow flow are observed to be comparable to those produced by deep flow in the absence of debris. This finding highlights the importance of monitoring debris accumulation at bridges in nonflood conditions. Results also show that the volume of the scour hole around a pier increases quadratically with maximum scour depth. This information is useful for postflood scour remedial works. Lastly, the collected laboratory measurements are used to compare four popular equations for scour estimation on their ability to predict debris-induced scour. The Colorado State University (CSU) equation is found to offer the most accurate predictions.

The hydrodynamics of a two-vent turbulent forced plume propagating in a linear stratification has been studied by a series of laboratory experiments using the two-tank method and the particle image velocimetry (PIV) technique. The velocity fields and turbulence characteristics of a two-vent plume under different source buoyancy flux, ambient stratification, and nozzle distance are analyzed quantitatively. The increase of maximum penetration of a two-vent plume is mainly due to the attenuation of buoyancy gradient caused by less entrainment of ambient fluid in the region between the two vents. The energy spectra do not exhibit a sizable range of the Kolmogorov $-5/3$ slope, indicating that no substantial inertial subrange is present in this small-scale plume in a linear stratification generated in the laboratory. Both turbulent kinetic energy and dissipation increase with the decrease of distance between the two plumes, indicating that the interaction, entrainment, and mixing in a two-vent plume stem greatly enhance energy production and dissipation. The maximum turbulent viscosity in a two-vent plume, however, presents a three-stage variation. An increase of viscosity in the second stage appears in the mixing region of the neutral buoyancy layer between the two plumes when the normalized distance $L/Z_{\max }$ is in the range of 0.3–0.6; this increase is attributed to flow rebound after overshooting and a strong entrainment and mixing in this region due to lateral flow convection. A new semiempirical formula for the maximum penetration and new scaling relationships for the maximum turbulent viscosity of a two-vent plume are proposed and verified by the PIV experimental data.

A new, three-parameter friction model at the boundaries of free surface flow is proposed. The model is valid for all flow and roughness characteristics and it is proposed to replace the widely used Manning equation in the flood simulation models. In the gauged flow domains, the parameters of the model can be calibrated directly using the appropriate field data. For the ungauged flow domains, the parameters are estimated following a four-step procedure: (1) selection of roughness zones; (2) generation of synthetic data from water depth—flow velocity—roughness height combinations; (3) calculation of shear stresses using a physically based equation; and (4) estimation of the model parameters through regression toward the results of this equation. The proposed friction model is used in the case study of the Tous dam break in Spain in 1982, as it was simulated by the two-dimensional hydrodynamic model FLOW-R2D. The results of this application show that the proposed friction model performs slightly better than the commonly used Manning equation.

Low-head dams are capable of creating dangerous countercurrents just downstream from the structure. These dangerous countercurrents are known as submerged hydraulic jumps and are responsible for hundreds of fatalities at numerous low-head dams across the United States. The countercurrent creates high upstream-directed surface velocities across the width of the channel, making it nearly impossible for a trapped individual to escape. This submerged jump can occur for a range of upstream and downstream conditions. A multiple partial width deflector design for the downstream side of the dam was tested in the laboratory to determine effectiveness in completely or partially eliminating the submerged hydraulic jump. The results demonstrate that a dramatic reduction in upstream-directed surface velocities over a wide range of headwater and tailwater conditions is possible. The dam modification is relatively inexpensive, simple to install, and designed such that an individual will likely escape the submerged jump without severe injury or harm. The design is ready for prototype testing.

Side weirs are widely used to divert a part of the discharge in irrigation channels and sewer systems. To increase the discharge capacity of linear side weirs at constant length in a channel bank, the application of folded plan forms such as the labyrinth and piano key in a side configuration warrants further research. In this experimental study, nine piano key side weirs and nine rectangular labyrinth side weirs with the same crest print and three linear side weirs were investigated. Free surface flow characteristics (e.g., water surface profiles, flow pattern, and deflection angles) were studied in a subcritical regime. Using De Marchi’s model, discharge coefficients of the side weirs were estimated. Results show significantly higher discharge coefficients for the folded shape side weirs compared with the linear side weirs. Although the results indicate no significant difference in discharge coefficients between the piano key and the rectangular labyrinth side weirs, the former is the better alternative to overcome space or other construction site limitations.

Pipe wall condition assessment is critical for targeted maintenance and failure prevention in water distribution systems. This paper proposes a novel approach for condition assessment of water pipelines by adapting the layer-peeling method. This method was previously developed for, and applied to, tubular musical instruments. In the proposed approach, the impulse response function (IRF) of a pipeline is obtained using measured pressure traces resulting from transient events. The original layer-peeling method is further developed for application to water transmission pipelines by (1) modifying the end boundary from being an acoustic source tube to a closed valve; (2) incorporating the effects of unsteady friction and pipe wall viscoelasticity into the layer-peeling algorithm; and (3) incorporating frequency-dependent wave reflections and transmissions. Using the IRF and the modified layer-peeling method, the impedance of a pipeline can be estimated section by section from downstream (the dead end) to upstream of the pipeline. The distribution of wave speeds and wall thickness can then be determined. In this study, numerical verifications were conducted using the pipeline pressure responses simulated by the method of characteristics (MOC). The deteriorated pipe sections (sections with changes in impedance) were accurately detected using the new approach. Experimental verification of the result was conducted on a laboratory copper pipeline. A short section of pipe with a thinner wall thickness was successfully detected.

In an attempt to develop risk-assessment engineering tools, a method is presented that involves the application of a simplified model that represents periodic permanent roll waves in Herschel–Bulkley laminar fluid flows. Using data from in situ sparse measurements during the August 1998 event at Acquabona Creek in the Dolomites (Eastern Italian Alps) previously, the missing rheological properties of the fluid and dynamical characteristics of the flow were estimated in order to perform a case study of the Acquabona site to explore the validity of the proposed model. The use of roll-wave theory to predict the flow properties during such events was considered. The mathematical model for roll waves was able to estimate the characteristics of the waves under the given flow conditions. The proposed model was also used to study of the influence of rheological properties on the waves’ characteristics. The results show the importance of the rheological properties and roll-waves theory to predict the flow height. Finally, the model’s potential to be a tool for risk assessment was tested and its usefulness demonstrated.

High pressure surges induced by the sudden closure of check valves can cause severe damage to mechanical and hydraulic facilities. A three-dimensional unsteady numerical simulation of a dual disc check valve closure induced by upstream pump shutdown was performed and validated experimentally. An overset mesh was applied to achieve a full closure of the check valve discs and capture pressure surges accurately. The velocity field graphs improve the understanding of the flow field evolution during the transient event. The impact of system outlet pressure, initial flow rate, and pump shutdown speed on pressure surges was investigated to explore factors that affect the amplitude of pressure surges. This work improves the understanding of check valve closure behavior, which is beneficial to check valve design, selection, and operation. Additionally, this work proves that overset mesh technology could be applied to other similar flow domain breaking cases.

Current design methods and research have primarily investigated the hydraulic characteristics of labyrinth weirs when the approach flow is perpendicular to the weir axis, a condition consistent with most in-channel and in-reservoir applications where the approach velocity is negligible. In some cases, a perpendicular approach flow and weir axis alignment may not be possible. The head–discharge characteristics of a four-cycle, 15° labyrinth weir with a channelized approach flow were evaluated with three different approach flow angles (0°, 15°, and 45°) using laboratory-scale physical models. Although the data presented are specific to the geometry of the weir and channels tested, they provide a general indication of variations in discharge efficiency as a function of approach flow angle. The experimental data were also compared with the head–discharge characteristics of a prototype labyrinth weir model study that featured significant approach flow angles. For approach flow angles under 15°, no measurable loss in discharge efficiency occurred, relative to an approach flow angle of 0°. The discharge efficiency reduced by as much as 11% for the 45° approach flow angle case. Flow instability was observed downstream of the weir, producing unique flow patterns in the labyrinth cycles and on the spillway apron.

The impact pressure and force of debris flows on round and square piers were studied experimentally in a flume. Three distinctive flow regimes, namely, Types A, B, and C, were identified. Each debris flow regime has its unique behavior around the pier, which, in turn, influences the pressure and force on the structure. Two dimensionless numbers, namely, the grain Reynolds number and the modified Savage number, have to be used in combination for the classification of the three regimes. Both impact pressure and drag coefficients depend on debris flow regimes. For practical purposes, the pressure coefficient is 0.76 and 1.47 for Type A and Type B, respectively. The drag coefficient is 1.23 and 0.58 for Type A flow around square and round piers, respectively; in contrast, it is approximately 0.9 for Type B, regardless of the pier shape. The hydraulic model is unsuitable for nonfluid-like Type C flow, and the pressure and drag coefficients are not well defined. A new scaling law for impact pressure coefficient was also proposed.