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.

In this study, 3D coherent flow structures during incipient particle entrainment under unidirectional flow conditions were experimentally investigated. Time-resolved tomographic particle tracking velocimetry (TOMO-PTV) and the shake the box (STB) algorithm were applied to measure 3D-velocities in a hydraulic laboratory flume. Quadrant and octant analyses were performed, their probabilities of occurrence were determined, and the Q-criterion was used to visualize the dominant 3D-flow structures during particle dislodgement. The results showed that octants related to sweeps and ejections were dominant with a probability of 70%. Fifty ms prior to particle entrainment, only one single contributing octant was observed. At particle entrainment, a sweep, three retrograde vortices, and a prograde vortex paired with a retrograde vortex were identified in the flow field. Considering the whole measurement volume, a group of three hairpin-like structures passed the particle during entrainment. In conclusion, the TOMO-PTV method is well suited and enables novel insights on the interaction between coherent structures and incipient sediment motion.

Piano key weirs (PKWs) are nonlinear hydraulic structures that exhibit unsteady hydraulic phenomena. A study incorporating both physical and numerical modeling was undertaken to identify instabilities that are generated by flow. Several excitations were identified and a portion of their nature is characterized in this paper. These include a system of vortices in the inlet key induced by the breakdown of a free shear layer, oscillations of the overflow nappe, and surging of the air cavity underneath the nappe. Of these, the inlet key vortices were found to be of the most significance as they were observed to occur at nearly all modeled flows ($0.02<\mathit{H}/\mathit{P}<0.55$) and exposed the sidewall separating the inlet and outlet keys to periodic pressure fluctuations. These fluctuating pressure forces, although small ($\pm 10\%$ of the total pressure oscillating at $\sim 5\mathrm{Hz}$), are persistent and may cause structural vibrations. Reinforced concrete PKWs are sufficiently stiff to limit the amplitude of any deflections caused by these vibrations; however, thin, steel-plate PKWs may remain susceptible.

The entrainment of debris in tsunami-induced floods and storm surges can result in their accumulation on structures, a phenomenon known as debris damming. Such dams can decrease the stability of the affected structures by increasing the area of the flow obstruction, resulting in increased resistance forces. The formation of debris dams can also result in upstream water level rise. This study investigated the influence of idealized debris dam geometry on induced loads and changes in the free surface surrounding a circular column in steady-state flow conditions. Additionally, it investigated the resistance force coefficient of the debris dams. Results show that the presence of debris dams results in a significant increase of loading on structures. The increase in the resistance force was up to 7.7 times greater than the resistance force acting on the column with no debris present. The resistance force coefficients and the change in water depth were functions of the relative dam height and the Froude number, while the porosity had an insignificant impact on the effective resistance force coefficients.

The characteristics of turbulent flows around two weir-like obstacles made of rocks submerged in an open channel, known as a cross vane and W-weir, were analyzed. These structures consisted of multiple structural arms that are angled upstream and constructed in such a way that they span the entire width of a channel. These weir-like (or multiple-arm) structures have been widely used for stream restoration purposes. Nevertheless, little is known about the flow structures and turbulent flow mechanisms associated with these structures. In this study, by carrying out numerical simulations, the turbulent flow fields around a cross vane and W-weir with complex and realistic rock geometries were investigated. For the numerical simulations of the turbulent flow fields, the large-eddy simulation (LES) model that solves the three-dimensional (3D) Navier-Stokes equations together with the curvilinear immersed boundary (CURVIB) method was employed. For the validation, the computed results were first compared to experimental data obtained in a laboratory flume using acoustic Doppler velocimetry (ADV). The time-averaged velocity fields obtained from the LES model were subsequently analyzed to investigate the 3D flow structures, secondary flow patterns, and turbulent flow mechanisms around the cross vane and W-weir. In addition, the LES results were compared with those of five other single-arm structure cases to obtain comprehensive understanding of the flow mechanisms of various instream structures. The LES results showed that high streamwise velocity cores and secondary flow cells form downstream of the multiple-arm structures, and the numbers of them depend on the the number of the arms. Compared to single-arm structures, the multiple-arm structures generally showed larger drag coefficients and energy dissipation ratios, and larger energy and momentum correction factors in the vicinity of the structures.

Applied research projects can enhance student education in hydraulic engineering. This contention considers three lines of argument associated with societal context: historical necessity, educational merit, and issues associated with funding of universities. Necessity and merit are especially important in keeping engineering education meaningfully engaged with engineering practice. Funding issues reflect universities’ increased reliance on nonstate sources of funding. The lines of argument were supported using examples drawn mainly from a university hydraulics laboratory and a course on hydraulic structures. The examples involved basic hydraulics principles and broader considerations often arising in actual engineering projects. There are risks associated with applied research at a university, including diminished basic-research activity and perceived unfair competition. The paper concluded that hydraulic engineering students greatly benefit from exposure to applied research. However, hydraulic engineering education should align with a university’s core mission and stimulate fundamental research.

Fine sediment infiltration into gravel riverbeds adversely affects the riverine ecology and influences hyporheic exchange processes. So far, different sampling methods have been utilized to measure the amount of infiltrated sediment masses in the field and laboratory. Most of these methods disturb the sediment bed, and only a few provide a vertical gradation of infiltrated sediment masses. Therefore, this study presents the proof-of-concept for a nonintrusive and nondestructive technique for measuring the masses of infiltrated fine sediments in high-resolution vertical profiles using the gamma-ray attenuation (GRA) method in laboratory flume experiments. First, the principal functionality of the GRA method was successfully tested on preliminary experiments, which consisted of a box filled with spheres, known masses of infiltrated sediments, and water. Afterward, the GRA method was applied in a laboratory flume with a simplified gravel bed to test the repeatability of the measuring concept under varying boundary conditions. The accuracy of the measured infiltration masses for the preliminary box tests show a deviation of less than 5% compared to gravimetrically determined masses, which proves the applicability of the GRA method. Furthermore, the repeatability tests of the flume experiments yielded deviations from 1.4% to 7.7%, which is still in an acceptable range, considering the complexity of the infiltration process. Based on the obtained results, the nonintrusive and nondestructive GRA method provides a profound basis for further in-depth investigations of fine sediment infiltration and accumulation in gravel riverbeds.

A novel flow facility developed to enable a broad spectrum of fluid mechanics experiments involving complex geometries and employing high-fidelity optical diagnostics is described in this paper. The development of the facility, which comprises two fully operational refractive-index-matched (RIM) flow tunnels, was guided by the ambition to overcome experimental roadblocks that often inhibit the experimental study of high Reynolds-number geophysical and environmental flows with modern techniques, like particle image velocimetry. The methodology described in this paper leverages and integrates new technology, including rapid prototyping methods to fabricate geometrically complex flow models and advanced optical methods for probing the physics of fluid flows. The aim of this paper is to provide a full technical description of the facility, to introduce the experimental protocol, and to quantify measurement uncertainties associated with imperfect index match. This protocol has been applied in a number of recent and ongoing research projects wherein measurements that would be impossible in a standard wind or water tunnel due to limited optical access have been successfully enabled, demonstrating a new spectrum of capabilities. Examples of results obtained for three different geophysical applications are presented in this paper to highlight the technical challenges that have been tackled and to discuss suitability for potential new applications.

The saltating mode of sediment transport is the dominant mechanism of bedload transport in a fluvial stream, especially in mountainous rivers. In most simulation studies, the actual shapes of sediment particles are simplified considering the spherical shape of particles, which can affect the accuracy of the estimation of bedload transport rate. In this study, a model of sediment particle saltation by streamflow is presented, simulating the wall-shear turbulent flow over a sediment bed by large-eddy simulation and calculating the forces acting on the saltating particles by Newton’s second law of motion. The model was calibrated by using the experimental data from previous studies on particle saltation. To study the impact of particle shapes, the computational results of saltation lengths, heights, and velocities of different-shaped particles were analyzed. Then, three key parameters were used to estimate bedload transport rates: bedload concentration, saltation height, and particle velocity. By summarizing the above results, this work presents a formula of bedload transport rate that improves upon a previous well-celebrated formula from the literature. The proposed formula introduces shape factors of natural sediment particles.

Leonardo da Vinci is a fascinating and inspiring person, and is called a universal genius for his large variety of scientific and artistic interests and contributions, including military engineering, sculpture, painting, astronomy, botany, anatomy, solid mechanics, and so forth. One of his main interests was hydraulics. He made fundamental contributions to our field, and some of his inventions and intuitions continue to challenge hydraulic engineers and researchers. Probably everyone has come across one of his beautiful drawings. However, most ignore the fact that those drawings represent the effort of a human being to understand the governing laws of physical phenomena. In fact, each drawing can be considered a comprehensive representation of hydraulic phenomena, because they furnish insight into physics and stimulate future developments. Inspired by drawings of Leonardo, this paper illustrated an inductive–deductive methodology to teach hydraulics and the modern design of hydraulic structures at all levels of academic education. In so doing, once again we showed that Prof. Leonardo da Vinci still has a great deal to teach to future generations of engineers and researchers.

The Dutch River Waal, a branch of the Rhine, has been trained for centuries to mitigate the effects of ice-jams and improve navigation. The works, started in 1850, involved river straightening and narrowing by a series of transverse groynes. Besides fulfilling their goal, the groynes also created the need to raise flood protection works and caused undesirable channel incision. This study assesses the effectiveness of training the river with a longitudinal wall instead of with groynes. The investigation analyzes the long-term response of the historical river with a two-dimensional depth-averaged (2DH) morphodynamic model. The results show that the wall would create two parallel channels, one becoming deeper and the other one shallower. The former would be as suitable for navigation as an equally-wide channel obtained with groynes. The latter would contribute in conveying water during high flow events and improve the river ecology. Training the river with a wall would also lessen channel incision. The best performance is obtained if the wall is built on the channel centerline, starting just upstream of a point bar top.

Piano key weirs (PKWs) have been introduced in recent years as a hydraulically efficient and cost-effective type of spillway, and there are more than 30 PKWs under construction or already constructed globally. However, owing to the numerous geometric parameters and complex hydraulic characteristics of PKWs, the discharge capacity of a PKW is still difficult to estimate. To improve the overall understanding of the flow behavior in the vicinity of PKWs and to investigate the intrinsic link between the structural parameters and discharge capacity of PKWs, this study employs a combination of numerical simulations and physical model tests to investigate the hydraulic characteristics of PKW models (including flow regimes, water surface lines, streamlines, and flow velocities) under different water head conditions. Furthermore, based on the detailed flow field information provided by the numerical simulations, the internal mechanism for the discharge capacity of the PKW is revealed by analyzing the flow field under the weir crest and the distribution of turbulent kinetic energy near the PKW.

This work reports on a computational fluid dynamics (CFD) model for flow and local scour around a pipeline in steady currents that uses a mixed moving-mesh and fixed-grid method. It performs mesh motions for bed conforming without considering the pipeline and then simulates the pipeline with a fixed-grid approach after the mesh motion process has been completed. The proposed model combines the best properties of the boundary-fitted-grid and fixed-grid methods. In contrast to previous boundary-fitted-grid models, the present model uses masked elements to resolve the effects of a stationary object on the flow and sediment scour processes. This approach makes it possible to track directly the moving fluid–sediment interface using a very simple mesh setup, which is more practical for engineering computations than the existing models. The modeled results are compared to published laboratory measurements as well as to previous numerical predictions obtained by other models. The results show that the proposed model satisfactorily reproduces the features of the local scour observed in the experiments and thus can be a promising tool for modeling flow and sediment scour problems.

The bias error in moving-boat acoustic Doppler current profiler (ADCP) streamflow measurements can be separated into two classes: calibration and application. Accordingly, the total bias limit of measured discharges can be separated into two components: calibration and application error–caused bias limits (in terms of standard uncertainties). This technical note presents a simplified analytical Type B model for estimating the calibration error–caused bias limit using manufacturer specifications for ADCP and its internal sensors. The merit of the presented model is that it helps to gain insights into the effects of major calibration error sources and parameters on the calibration error–caused bias limit.