Journal of Hydraulic Engineering

This study is devoted to advancing hydroenvironmental modeling of large-scale shallow water systems to the times of three-dimensional (3D) simulations, where the solution of advective transport of scalar is the focus. The solution to the transport model is demonstrated using a semi-implicit hydrostatic 3D flow model, which uses an Eulerian–Lagrangian method (ELM) and a prediction-correction method. A new 3D scalar advection scheme, the 3D flux-form ELM (FFELM), is proposed based on layer-integrated advection subequations. The new scheme allows large time steps for which the Courant number is greater than 1 and is parallelizable. A grid sensitivity study is performed using a solid-body rotation experiment, in which the FFELM is indicated to achieve the performance of second-order accuracy advection schemes and run stably under a time step for which the Courant number is much larger than 1. Moreover, a nested FFELM (FFELM-N) is proposed, in which the trajectory-tracking information of the ELM in the 3D flow model is reused to reduce the startup cost of the transport model. The new model is also tested using the real Jing-Dongting (JDT) river–lake system, for which the computational domain ($\mathrm{3,900}{\mathrm{km}}^2$ in the horizontal) is divided by a computational grid of $\mathrm{327,820}\times 10$ cells. A parallel run of the transport model (using 16 cores) is approximately 10 times faster than a sequential run. The runtime of the transport model using the FFELM-N is reduced to one-third that using the FFELM in both sequential and parallel tests. Using 16 cores, it takes 6.02 days to complete the calculation of a one-year unsteady process of flow and scalar transport in the JDT system, for which the runtime of the transport model using the FFELM-N is only 1.28 days.

The effectiveness of submerged vanes for stabilizing streamside bluffs varied over a 10-year monitoring period in a tributary to Lake Superior, United States. Submerged vanes are a river training device used to divert river flows away from eroding banks along meander bends and ultimately hold constant or reverse the direction of lateral migration. At the study site, the relatively steep slope, large substrate size, and flashy flow regime pushed the upper end of the design limitations of submerged vanes. Changes in channel location and morphology due to the vanes were monitored using repeat channel cross-section surveys along a 110-m reach. The vanes experienced 15 floods over the monitoring period. The two most damaging floods happened in the summer and fall of 2005 with annual exceedance probabilities of 7% and 6% respectively. A new data analysis method for rivers, using centroids of cross sections, was useful to track channel migration rapidly and objectively and, along with calculations of changes in bankfull channel size, provide metrics to describe channel change.

A new, concise theoretical model for simulation of unsteady, nonhydrostatic two-layer flow is presented. The formulation is systematically developed from the equations of motion of an ideal fluid using a perturbation technique with shallowness as the small parameter. The advantage of this model over many models in the field is that the shape of streamlines, or velocity and pressure distributions, are dictated by the model rather than being predetermined. This model also relaxes further assumptions involved in the previous formulations and can be used to simulate different two-layer flow cases. In some situations, simulation is impossible without considering the nonhydrostatic pressure, one of which is a two-layer approach-controlled flow. A laboratory transient two-layer flow experiment is conducted to examine transition to the approach-controlled flow, and the new equations are successfully applied to model this transient flow using a total variation diminishing (TVD) MacCormack scheme. Furthermore, new equations for single layer unsteady nonhydrostatic flow are presented and two-steady flow cases of flow over an obstacle and an undular hydraulic jump are excellently simulated.

Partial blockages commonly exist in water pipelines due to various physical, chemical, and biological processes, including sediment, corrosion, and biofilm. The formed blockages can result in low flowing capacity, additional energy loss, and water quality deterioration during the water conveyance process, such as urban water supply and drainage systems. This paper presents an investigation on the interaction of transient pressure waves with pipe-wall roughness and blockages in water pipelines. The analytical expression of wave propagation in a pipeline with rough blockages is firstly derived by multiscale wave perturbation analysis for transient pipe flows. The analytical results and analysis demonstrate that the wave scattering (amplitude damping and phase shifting) is dependent on the relationship between the incident wavelength and the correlation length of roughness-blockage disorders in the pipeline. The relative importance of pipe-wall roughness friction and pipe blockage constriction to wave scattering in terms of wave envelope attenuation and wave phase change is then investigated based on the analytically derived results. Two dimensionless parameters, which are functions of the properties of incident waves, pipe-wall roughness, blockage severity and range, and internal fluid conditions, are formulated to characterize such relevance and importance. For validation, the analytical results are compared with experimental data collected in this study based on a laboratory experimental test system. Finally, the key results and findings of this study are discussed for their applicability and implication to transient pipe flow modeling and pipeline condition assessment in practical applications.

A common approach used to mitigate riverbank erosion and maintain watercourse alignments has been through the application of riprap or larger, more stable particles to channel boundaries along reaches of interest. However, very often, these large particles become dislodged from their intended locations (failed erosion measures), becoming part of the bed material composition. In natural systems, large immobile sediments or boulders can also be found, which are often sourced from glacial erratics or colluvial inputs with different spacing and arrangements among them. In lower gradient gravel-bed channels, the impacts that large clasts may impart on river morphologies are uncertain and are studied in this paper. This paper utilizes laboratory experiments to evaluate the effects that varying spacing of large immobile particles in a gravel-bed channel have on sediment transport and bed morphology. The laboratory experiments consist of a series of test cases with a varying spacing of large immobile particles and one base case with no large immobile particles present. In each case, the flume bed was composed of a poorly sorted gravel mixture with a bimodal distribution of sand and gravel meant to be representative of a natural gravel-bed channel. The results of the test cases demonstrated that at a low spacing of large immobile particles, the transported material and the bed material both became coarser. At a medium spacing of large immobile particles, the bed material size and erosion reached a maximum, and the coarser bed material was transported at approximately the same rate as the finer material. Finally, at a high spacing of large immobile particles, the size of the transported material and bed material sizes were similar to that of the base case, and the sediment transport also had the strongest clockwise hysteresis trend, which ultimately led to a net erosion of the gravel-bed channel.

Advances in dam construction techniques have significantly increased the number of stepped spillways implemented worldwide. Although stepped chutes provide enhanced energy dissipation along the chute, as compared to smooth chutes, an adequate energy dissipater is usually needed at their toe to govern the remaining energy. Stilling basins downstream of stepped spillways are currently designed using the approaches developed for smooth chutes. As a stepped surface alters the structure of the approaching flow, such practice is questionable. This paper reports a study on the effect of stepped chute approach flows on the performance of a classical stilling basin. Physical modeling was conducted using a large-scale facility of a smooth and stepped spillway with a 30° sloping chute. Experiments were performed under different discharges, two step heights, and variable approach flow aeration. The characteristics of the hydraulic jump were described, focusing mainly on flow depth, bottom pressure, and length. The results indicated a significant effect of stepped chute approach flows on bottom pressure and length of the hydraulic jump. Near the jump toe, pronounced fluctuating and extreme pressures were observed after stepped chutes and attributed to the higher turbulence level of the incoming flow. The normalized hydraulic jump lengths were found to be about 17% longer downstream of stepped chutes as compared to smooth chutes.

The buildup of sediment deposits in reservoirs is a long-standing problem with serious consequences on the reservoirs’ functionality and the ecology of their river systems. In the last two decades, hydraulic dredging has been used as a more viable engineering solution to restore reservoirs’ sustainability. This study proposes a novel ejector-pump dredging system (EPDS) that solely utilizes hydraulic dredging for removal and transport of the sediments deposited at the reservoir’s bed. Unlike conventional dredging methods, air is injected into the header pipeline to create a turbulent three-phase flow regime that enhances the solids suspension and continuous flow in the system. Introducing air effectively reduces the critical value of the deposition velocity of the dredged solids and transports them in a slug flow regime. This technique minimizes the tendency of the sediment to settle, and therefore eliminates system plugging. A laboratory prototype of the proposed system has proven the efficacy of removal and transport of mixed-size sediments up to 150 mm. Field trials have further shown the feasibility of the proposed system. Removal of large sediments with productivity approaching $70{\mathrm{m}}^3/\mathrm{h}$ was made possible using the suction-type EPDS. The hopper-type EPDS enabled carrying the dredged material for up to 1,000 m without resorting to a booster pump. The developed system was successfully used as part of an integrated dredging management program carried out for the Oouchibaru, Saigo, and Yamasubaru dams in the Mimi River basin, Japan. The very low turbidity levels recorded during the sediment dredging and transport operations of EPDS are indicative of the eco-friendly performance of the system.

An analytical model for evaluation of boundary shear stress in compound open-channel bends is developed. Perpendicular volumetric elements are generated in all cross sections of a bend. Each element represents an equation with two parameters, including the secondary current parameter and momentum transfer coefficient, accounting for acceleration and internal forces. For each cross section with $N$ elements, $N$ equations with $N$ unknowns of streamwise depth-averaged velocity are derived. The boundary shear stress distribution is then calculated using the Darcy-Weisbach relationship. The momentum transfer coefficient is related to the geometric characteristics of the channel cross section and the bend. The present results were compared with the experimental data available in the literature. The experimental models have trapezoidal and rectangular main channels with both curved and straight paths. The results seem to be acceptable except at the interface of the main channel and floodplains, because of the planform vortices. Overall, the total results are satisfactory, and the present analytical model can be used to predict the boundary shear stress in simple and compound channels.

The present study investigated the occurrence and characteristic frequency of nappe oscillations on weirs by reanalyzing data from 52 experimental configurations. The considered configurations include various shapes of the weir crest and a range of weir geometric and hydraulic characteristics with two different scales. Nappes were either confined with lateral and back walls forming a nonvented air pocket between the nappe and the weir or unconfined with atmospheric pressure everywhere around the nappe. Oscillations occurred at nappes with uniformly distributed approaching flow of low velocity and unit discharge between 0.01 and ${0.06\mathrm{m}}^2/\mathrm{s}$, regardless of the model scale. Weir crests that favored nappe oscillations had an upstream profile without geometric discontinuities. A dimensionless frequency of nappe oscillations was expressed as a power function of the ratio of the fall height to the water depth at the point of detachment at the crest, separately for quarter-round and truncated half-round weir crests. The exponents of the two obtained power functions were very close to each other, which allows the usage of their average so that different weir crests exhibit solely offsetting curves.

Uncontrolled filling is often seen in storm sewers under wet weather conditions. This study develops a rigid-column model for rapid filling in a partially filled horizontal pipe with entrapped air. Numerical solutions compare very well with experimental measurements from earlier studies. Parametric analysis is conducted by nondimensionalizing the governing equations, and two typical scenarios are numerically investigated in detail: one with a fixed air pocket length and the other with a fixed air pocket volume under different tailwater depths. For the cases with a fixed air pocket length, the peak pressure becomes greater as the tailwater depth increases when the length ratio of the water column and the air pocket is large, whereas the trend is reversed when the length ratio is small. And the critical length ratio is system-dependent. In cases with a fixed air volume, the peak pressure is monotonically reduced with the increase in the tailwater depth. The proposed model can also be adapted for rapid filling with ventilation and surges in closed-conduit flows.

This paper reports the results of simulating the steady and cavitating flows through a low-head small-size Kaplan turbine. The computed hydraulic performance depicts a moderate efficiency of this Kaplan turbine owing to the high specific speed and the large gap between blades and shroud. The effects of blade setting angle, vane opening, discharge, and rotational speed on the hydraulic performance are discussed. The formation of cavities in the runner blades occurs at certain operating conditions and the cavities typically appear over the fore of blade suction side and the blade tip. In addition, the criteria of cavitation inception are revealed. These results provide useful information how to improve the design of this category of Kaplan turbines.