Journal of Hydraulic Engineering

This paper, written to celebrate the 60th anniversary of the Journal of Hydraulic Engineering, examines scour evolution around sloped-crest structures, known as barbs. The results extend the literature database of hydraulic structures and provide the first experimental investigation of gravel bed scour around a sloped-crest barb structure for flow and sediment conditions that are representative of gravel bed rivers in mountainous to submountainous topography. The postulate examined in this study is that the degree of barb submergence or overtopping ratio triggers different interactions between the primary vortex and overtopping flow regime, which in turn affects scour progression (i.e., fast and slow phases of scour) as well as the location of the maximum equilibrium scour depth around the barb tip. The results of this study provide a fundamental insight of the interaction of a plunging jet and the primary vortex through complementary laboratory and numerical investigation. As the overtopping flow becomes of similar influence to the primary vortex, traditional scour prediction formulas tend to break down due to the interaction of the plunging jet and primary vortex which induces an intermittent flow behavior, and, hence, scour equilibrium takes nearly twice longer to be attained. The results of this study also highlight the beneficial utility of barbs for river training applications. In this manner, the sloped-crest feature of the barb has beneficial effects on flow as it transfers kinetic energy from the main core and tip of the structure to turbulent energy generation and dissipation on the lee side of the structure. The net result provides a hydraulic structural design for the barb that reduces the need for excessive stability measures to withstand high flows because maximum fluid shear at the tip and, hence, maximum scour are reduced relative to unsubmerged structures.

Although chute aerators have been investigated experimentally by many researchers, only a few studies have been conducted on the comprehensive air–water flow properties of the lower jet downstream chute aerators. In this study, after eliminating the upper aeration of the jet, a complete characterization was recorded and presented for the distributions of air concentration, air–water velocity, and bubble frequency. Based on these extensive tests, a comprehensive equation to compute the air concentration distributions of each zone was presented. The velocity distribution had a shape similar to that of shear air–water flows; however, the quantitative parameters differ in each zone. In the cavity zone, the position of the maximum air bubble frequency was largely within a region of relatively high air concentration and gradually approached an equal air concentration of 0.50. The location of the maximum air bubble frequency was approximately the same as that of the section maximum air concentration at a section in the impact zone, but lower than that in the equilibrium zone. Self-similar relationships between the air concentration and bubble frequency were proposed for each zone.

A maximum entropy (MaxEnt) method is developed to predict flow rates or pressure gradients in hydraulic pipe networks without sufficient information to give a closed-form (deterministic) solution. This methodology substantially extends existing deterministic flow network analysis methods. It builds on the MaxEnt framework previously developed by the authors. This study uses a continuous relative entropy defined on a reduced parameter set, here based on the external flow rates. This formulation ensures consistency between different representations of the same network. The relative entropy is maximized subject to observable constraints on the mean values of a subset of flow rates or potential differences, the frictional properties of each pipe, and physical constraints arising from Kirchhoff’s first and second laws. The new method is demonstrated by application to a simple one-loop network and a 1,123-node, 1,140-pipe water distribution network in the suburb of Torrens, Australian Capital Territory, Australia.

In this paper, the results of an investigation carried out to test the applicability of a flow-resistance law on gravel-bed rivers in southern Italy (fiumare) are reported. First, dimensional analysis and self-similarity theory are applied for deducing the flow-resistance law (i.e., relationship among friction factor, mean velocity, shear stress, and physical properties) for gravel-bed rivers with a high boulder concentration. The proposed approach is calibrated and tested using two independent data sets (104 reaches of some Calabrian fiumare). Then, the incomplete self-similarity hypothesis is also applied to theoretically deduce the flow-velocity profile, which was integrated for obtaining the flow-resistance law. The estimate performance of both approaches is verified by field measurements of flow velocity, water depth, river width, and bed slope carried out in previously used data sets. The analysis shows that the theoretical approach based on the power velocity distribution yields a flow-resistance law characterized, in the comparison between measured and calculated friction-factor values, by the lowest root-mean square error and the highest Nash-Sutcliffe index.

Low-head gated spillways provide controlled flow releases for defense against floods and a reliable supply of water for beneficial uses. In addition, a system of spillways in a large water resources system may be used for flow monitoring to assess compliance with water quality regulations and evaluate performance measures of ecological restoration projects. The flow discharge through spillways is typically calculated by rating equations applicable to free (uncontrolled) or gate-controlled flows under submerged and unsubmerged conditions. Depending on the spillway geometry, headwater and tailwater levels, and gate opening, four types of flow, each requiring a unique rating equation, can occur. However, the flow type for the given conditions must be classified first to ensure that the appropriate rating equation is used to compute discharge. Spillway flow classification requires identifying the transition thresholds between the various flow types. Results from a study conducted at the Georgia Institute of Technology to identify these transitions experimentally in a hydraulic model study of a South Florida Water Management District spillway are presented here. Results are summarized in a unified set of graphical transition curves for the four flow types in terms of the depth at the spillway crest. The depth at the spillway crest is also used to develop a head-discharge relationship for uncontrolled, submerged flow, the flow type that is the most difficult to predict.

A pseudo-three-dimensional particle tracking model of drifter paths has been developed to study the movement of scalars through a complex network of tidal channels and junctions. To better simulate dispersion caused by bifurcation and merging at junctions, a localized model is proposed in which particles move along potential flow streamlines through junctions. The model is applied to the Sacramento–San Joaquin Delta in the California Central Valley, and the approach reproduces the observed ultimate fate of the endangered native fish Delta smelt more accurately than a model that fully randomizes particle positions at junctions. The new model also reproduces the very large dispersion that has been previously inferred from Delta-wide heat balances; this large dispersion appears to be associated with flow splits at junctions. Overall, the streamline-following model is likely to be more accurate for long-term planning and management simulations of such complex estuaries than more commonly used cross-sectionally averaged Lagrangian transport equation solvers, which randomize concentration distributions of scalars at junctions, and thereby do not reproduce the increased dispersion mechanisms.

It has been well established in several experimental and modeling studies that leak areas are often not fixed, but vary as linear functions of pressure. Replacing this linear equation into the orifice equation results in a two-part modified orifice leakage equation with head exponents of 0.5 and 1.5. The purpose of this study was to incorporate the modified orifice equation into the hydraulic network formulation and evaluate its impact on model performance. The conventional and modified software were applied to 600 instances of stochastic leakage distributions in three different pipe networks. It was found that the conventional power leakage equation results in significant leakage volume and flow-rate errors under certain conditions. In addition, a problem of nonconvergence of the conventional global gradient algorithm for leakage exponents greater than 2 was observed and is discussed.

A submerged patch of finite-width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes. This experimental study used velocity and deposition measurements and flow visualization to determine how the height ($h$) and width ($D$) of a submerged patch of model vegetation with high stem density influenced the wake vortex structures and their impact on the deposition of suspended sediment. The enhancement of fine-particle deposition can provide an important positive feedback to patch persistence and growth. The distance over which deposition was enhanced ($L_{\mathrm{Dep}}$) was strongly correlated with the distance over which velocity remained depressed within the wake ($L_w$), which in turn depended on the wake vortex structures. The aspect ratio $D/h$ determined the orientation of the vortices formed in the wake. For $h<D$, a vortex in the vertical plane occurred within a few patch heights downstream from the patch. If present, the horizontal von Karman vortex was initiated at the same position. The Karman vortex was absent for $h/D<0.7$. For these cases ($h<D$), $L_{\mathrm{Dep}}$ scaled on the patch height. Specifically, $L_{\mathrm{Dep}}=(2.3\pm 0.5)$ $h$. For $h>D$, the vortex in the horizontal plane formed first (closer to the patch) and controlled the velocity recovery within the wake. For these cases ($h>D$), $L_{\mathrm{Dep}}=(2.1\pm 0.4)$ $D$. In field studies, these relations can be used to predict the length of the region favoring deposition ($L_{\mathrm{Dep}}$) from measured patch diameter ($D$) and height ($h$).

The overtopping failure of noncohesive earthen levees was investigated by considering sediment transport by flowing water and including slumping failure due to slope instability. The breach-shape evolution and breach hydrograph were measured during laboratory experiments. The experiments were performed with different inlet discharges and downstream boundary conditions. Detailed levee breach experimental results are presented, which may be used by other researchers to verify their computer models. A two-dimensional, finite-difference numerical model was developed, which solves the shallow-water equations along with the sediment-mass-conservation equation, in which a new source term is included to account for slumping failure. First, the hydrodynamic part of the model was validated against a steady flow through a levee breach. The predicted and the measured results are in good agreement in terms of the water depth and flow velocity within the main channel and the breach area. Then, the numerical model, which includes the modified sediment-mass-conservation equation, was validated by comparing the results with the test data of overtopping failure of a noncohesive earthen levee. The model successfully predicted the breach characteristics (i.e., breach-shape evolution and breach hydrograph). Moreover, a sensitivity analysis was conducted to study the effects of different model parameters on breach shape. It was observed that the breach dimensions (i.e., top width and maximum depth) are directly proportional to the Manning roughness coefficient and to the coefficient of the Meyer-Peter Müller formula. As the sediment repose angle increases, the breach top width decreases and the maximum depth of the breach increases.

Water-lubricated pipe flow technology is an economic alternative for the long-distance transportation of viscous oils, such as heavy oil and bitumen. In the industrial-scale application of this technology, a thin oil film is always observed to coat the pipe wall. The natural process of wall coating during the lubrication is often referred to as wall fouling. A wall-fouling layer produces ultrahigh values of hydrodynamic roughness ($\sim 1\mathrm{mm}$), which have not been studied sufficiently to date. In this work, the hydrodynamic effects of a viscous wall-coating layer were experimentally investigated. A customized flow cell was used for the purpose. The equivalent sand grain (hydrodynamic) roughness was determined using a methodology involving computational fluid dynamics (CFD) simulations. The hydrodynamic roughness was also determined from the measured topology (physical roughness) of the surface. Additional verification of the method was obtained by applying it to analyze the hydrodynamic roughness produced by sandpapers and biofouling layers. The primary outcome of the present study is the validation and application of a CFD-based methodology to quantify the hydrodynamic roughness produced by any surface, including viscous oil coatings and biofouled surfaces. Additionally, it has been shown that the hydrodynamic roughness of a viscous oil coating, for the range of conditions tested here, is much more dependent on the coating thickness than on the Reynolds number. This has significant implications for the modeling of lubricated pipeline flows involving heavy oil and water.

The Swiss confederation aims to phase out nuclear power production with its Energy Strategy 2050 program by increasing the renewable energy contribution to its overall energy generation. Hydroelectricity, which is the most important form of renewable energy in Switzerland, supplying almost 60% of the electricity in 2015, should increase its production capacity to achieve this goal. The case study presented in this paper focuses on the replacement of the third turbine in the Gondo high-head power plant with a turbine with a higher discharge capacity. The results of one-dimensional (1D) numerical simulations shown that throttling the surge tank is an efficient measure to adapt the existing hydraulic system for the increased discharge. Physical-scale modeling was performed to validate the design of the grid throttle placed at the bottom of the lower chamber of the existing surge tank. The grid throttle geometry and its head losses are compared with two existing similar throttles in Switzerland. Finally, prototype tests of the temporal evolution of water levels in the surge tank using the throttle coefficients obtained experimentally showed good agreement. Hybrid modeling using a combination of 1D numerical models, three-dimensional (3D) physical models, and prototype tests are highly recommended for checking the transient performance of the waterway after a refurbishment of turbines with increased design discharge. Furthermore, placing a throttle at the bottom of an existing surge tank is often an effective and economical solution in the case of small increases in installed capacity.

This study reports on the key findings from the application of a marsh-porosity model to a complex floodplain environment in northern Australia. The paper addresses the fundamental challenges associated with leakage in the marsh-porosity model, which have previously been described in the literature but have received little recent attention and for which limited guidance is available. A sensitivity analysis was carried out by adjusting the marshing parameters on the floodplain and assessing the effect on the simulated depth in Buffalo Creek. The statistical measures showed a significant improvement in the model performance at the most upstream site, using a combination of low porosity and element elimination on the floodplain. These measurements highlight the importance of focusing on the wetting and drying parameters as well as the bed roughness, in calibrating the marsh-porosity models in macrotidal floodplain environments. This paper also presents the parameter values and a summary of how they can be used to assist future practitioners.

One of the basic articles of discretization-based numerical modeling of three-dimensional shallow water equations is the spatial convergence of the mesh utilized. The process of creating a spatially converged mesh involves refining the mesh until the solution for the quantity of interest does not change within some user-defined tolerance. This process is cumbersome in three-dimensions, and in the absence of a spatially converged mesh, the numerical results may be erroneous. This technical note introduces a norm of the three-dimensional continuity equation residual-based refinement indicator to flag regions of the mesh requiring refinement. The method is implemented through $h$-adaption in a finite-element method–based code and results of this implementation are presented.

Research undertaken in the last two decades has demonstrated that hydraulic transient pressure waves, the phenomena behind water hammer, can be used as a tool for noninvasive and nondestructive condition assessment of long water transmission pipelines (in particular, detecting changes in the pipe wall properties). However, the spatial resolution of current transient-based technology is relatively low because the useful bandwidth of conventional valve-generated incident pressure waves is less than 100 Hz. This research develops a new transient pressure wave generator using controlled electrical sparks to provide high-frequency waves and improve the incident signal bandwidth. An electrical spark surrounded by water causes the development of a localized vapor cavity, the collapse of which induces an extremely sharp pressure pulse into the surrounding body of fluid. Experimental studies on a copper pipeline are conducted to investigate the usefulness of the pulse signals generated by the new spark generator for detecting thinner-walled pipe sections. Techniques are developed to analyze the wideband spark-induced pressure responses. The results show that the generated sharp pressure pulses have a useful frequency bandwidth up to 2 kHz. The success and accurate diagnosis of a thinner-walled section confirms that the dramatic improvement in bandwidth significantly enhances the spatial resolution of hydraulic transient-based pipe condition assessment.

Sediment transport studies that use radio frequency identification (RFID) tracers are now common in hydraulic studies because of the information the technique provides on the spatial and temporal variability of sediment movement. The technique has been underused relatively in laboratory studies, however, because of issues related to tag orientation and spatial resolution. The objectives of the current study were to (1) describe the design and construction of a flume and a RFID tracking system with the ability to locate tracer stones during experiments; and (2) present the results from preliminary performance tests. The design and tests were completed for vertically oriented RFID transponders, which was realistic for tracers in transport on the basis of a parallel effort to develop gyroscopic tracer stones. The constructed flume was unique because it was designed with a space under the floor of the channel that accommodated an RFID detection carriage. The carriage used three multiplexers and 12 antennae in combination with a laser rangefinder to detect and estimate the position of tracer stones. Wireless communication with a desktop computer was used. A programmable logic control system controlled the movement of the carriage. Preliminary tests conducted with vertically oriented RFID tags showed that a 23-mm RFID tag could be detected up to 21 cm above the flume floor with a streamwise position accuracy of $\pm 1\mathrm{cm}$. Steel cross members and multiple RFID tags locally decreased the detection range and precision of the position estimate. Zones of nondetection became larger as tags were closer together, and antennae only reliably detected the closest tag. When the antenna spacing was $\sim 20\mathrm{cm}$, the system was capable of operating in a maximum tracer density of $25\text{particles}/{\mathrm{m}}^2$. Spatially, nonuniform distributions of tracers required lower densities for reliable detection and positioning. Continued development using different antenna array designs and anticollision RFID tracers should increase the resolution and allow higher tracer densities.

Experimental results are presented for the rate of flushing of a dense fluid from an idealized two-dimensional square urban canyon as a function of the Richardson number of the flow, ranging from 0.06 to 4.1, and upstream surface topography. Experiments were run for a smooth upstream channel bed and two different rough upstream surfaces with surface roughness lengths of 1.3 and 2.4 mm for a building height of 100 mm. Increasing the upstream surface roughness increased the ambient flow turbulence intensity of the flow as it reached the upstream building and model urban canyon. For all Richardson numbers, the initial rate of flushing was independent of the upstream ambient turbulence and appeared to be dominated by the large-scale vortex that formed within the canyon due to the overflowing ambient fluid. However, for higher Richardson numbers (more stable canyon stratification), in the later stage of the flushing process, the rate of removal of dense fluid varied significantly with upstream conditions. Higher upstream ambient turbulence drove more rapid removal of dense fluid. This was not the case for lower Richardson flows in which the large canyon vortex continued to drive the flushing process and upstream conditions did not influence the flushing rate. These results indicate that a detailed understanding of the removal of dense gas pollutants from urban areas requires experimental data sets that include a range of upstream topographies and that, although important, field data from effectively flat smooth terrain will not fully elucidate the physics of urban dense gas dispersion.