Journal of Hydraulic Engineering

Freshwater mussels are bivalve mollusks that inhabit the substrates of rivers. Their conservation is important to maintain a healthy river ecological system. The present study uses state-of-the-art experimental and numerical techniques to investigate flow and turbulence structure and to estimate the bed friction velocity distributions around a cluster of three semiburrowed mussels placed at a bottom of a flat-bed channel. The ability to describe and quantify these processes and mechanisms is a prerequisite to understanding how mussels are dislocated from the bed and to better comprehend biological aspects related to the life and role (e.g., nutrient transport) of these aquatic organisms. The large-eddy simulation (LES) study provides a detailed discussion of the flow physics and the role of large-scale coherent structures for a case in which the incoming flow is perpendicular to the shells of the mussels. For this limiting test case, strong necklace vortices develop around the upstream base of the mussels and massive separation occurs past the mussels. This provides an extremely complex turbulent flow field that is very challenging to predict using numerical models. As part of the study, data from particle image velocimetry (PIV) are compared with LES. The model can be used as a tool to investigate flow and transport processes at mussel scale for a variety of relevant flow conditions.

The prediction of the transport of sediments in streams is of crucial importance for many geophysical and industrial applications. Most of the available formulas for sediment transport are empirical and apply to situations near initiation, where a few erratic particles are seen jumping and rolling over an immobile bed. However, they are commonly adopted for predicting massive transport of sediments, although more rigorous approaches exist. The latter make use of constitutive relations from kinetic theories of granular gases, but require the numerical integrations of complicated, nonlinear differential equations, hence discouraging their usage for practical purposes. A new, explicit formula for predicting intense sediment transport is proposed here, based on kinetic theories of granular gases and incorporating in a simple yet rigorous way the possibility of turbulent suspension of the particles. It is shown that this formula, unlike others, can quantitatively reproduce physical experiments on steady, uniform flows of natural and artificial particles and water over horizontal, movable beds taken from the literature. These findings suggest that granular physics is now mature enough to provide practical tools in fields that were so far mainly empirically oriented.

It is common knowledge that a relationship exists between the volumetric sediment concentration, the percentage of clay mineral content, and the activity of clay minerals (which is related to the clay type) and the yield stress of a debris flow mass. In this paper, the effect of four types of common clay minerals (montmorillonite, illite, chlorite, and kaolin) on the yield stress of mixtures were investigated in a quantitative way. Laboratory experiments were carried out with single and mixed clay mineral types, various volumetric concentrations, and percentages of clay mineral content. For the same clay content and same volumetric concentration, a decreasing effect was found, respectively, of $\text{montmorillonite}>\text{illite}>\text{kaolin}$ on the yield stress of the flow mixture, whereas the effect of chlorite was equal to that of kaolin. A concept of equivalent clay mineral percentage ($P_0$) is introduced in this paper, in which the value of 1 is taken as the characteristic coefficient of kaolin in the experiments. Compared to kaolin, the coefficients of montmorillonite, illite, and chlorite appeared to be 1.7, 1.3, and 1, respectively. An equation is proposed to calculate the yield stress of debris flows as a function of the volumetric concentration and equivalent clay mineral percentage. The formula is applicable for the calculation of yield stress of single clay and mixed clay type minerals in debris flows. The formula proved to be accurate after validation with data from other studies.

The model presented in this paper preserves lake at rest conditions in sloped prismatic conduits. These schemes are based on the two-governing equation model in which open-channel flows are simulated using the Saint-Venant equations and pressurized flows using the compressible water hammer equations. The model in this paper preserves lake at rest conditions (horizontal still water) regardless of the conduit slope, resolves moving jump discontinuities over dry beds in sloped conduits, and resolves small perturbations from steady states, even when adjacent to dry regions. The preserving steady-state capability of this model is of particular importance in continuous long simulations when the conduits are relatively steep ($|S_o|>\sim 0.5\%$. Two main contributions are presented in this paper, namely, (1) a new method for water stage reconstruction is presented that preserves lake at rest conditions regardless of the pipe slope, and (2) a horizontal system of coordinates, instead of the commonly used inclined coordinate system, is used for facilitating the implementation of the proposed well-balanced scheme to complex systems. In the horizontal coordinate system, the cross section of a circular pipe becomes an ellipse. The hydraulic characteristics of an ellipse are presented. Good results are achieved in the test cases.

Mixed flows in storm water systems (SWSs) generate a set of complex phenomena that are difficult to capture in modeling. Shock-fitting and shock-capturing techniques are the two main numerical approaches employed today, but these require a number of assumptions and simplifications that can compromise their accuracy. As a result, the current software and models are unable to adequately simulate the complex multiphase, multiregime, and flow instabilities that result from mixed flow. Significant contributions going back to the 1960s have used models to better understand mixed flows and sought to integrate the obtained data into the SWS design process. This paper reviews these attempts and compares and evaluates the models currently in use. It constitutes a valuable resource for new researchers in the field and professional readers looking for ways to make decision making in SWS more efficient.

Explicit analytical assessments of numerical errors in solutions of decaying standing waves in pipes are obtained using analyses based on the fixed-grid method of characteristics and are used as a quantitative basis for comparing alternative grid types, sizes, and shapes. It is shown that the influences of friction and interpolation combine in a nonlinear manner, but that the combination has the form of a product so that the two effects may be considered independently to a certain extent. The analysis is presented for finite pipes, thus creating both upper and lower limits for the range of possible standing wave frequencies. It is found that frequencies in the upper half of the range are strongly damped. The performances of diamond and rectangular grids are compared, but there is no clear winner because, for equivalent computer resources, each has both advantages and disadvantages. The overall purposes of the paper are to move toward methods of (1) relieving untrained software users from tasks related to grid selection and (2) assisting third parties in assessing the validity of numerical results undertaken by others.

Management efficiency of water distribution networks (WDNs) is of relevant interest for the water industry, and operational optimization plays an important role. The energy to pump water is a significant element of operational costs and depends on electricity tariffs varying over time. As a result, pumping optimization accounting for electricity costs and relevant boundary conditions of a WDN, e.g., demands, is of practical interest. When the electricity tariffs are lower, for example, during the night hours, optimization generally results in pumping more water during those hours, if the presence of tanks, which are internal to the hydraulic system, allows for water storage. Nevertheless, the pressure and therefore, water leakage of the network greatly vary from night to daylight hours. Pressure and leakage generally increase in the night because of a lower level of demands and a greater level of pressures. Previous studies rarely account for this. This work investigates pumping optimization background leaks, i.e., the nonrevenue water cost beside the energy cost. It is shown and discussed that the reduction of background leaks conflict with, and generally dominate, energy cost.

Culvert rehabilitation is a cost-effective alternative to culvert replacement for many applications where the culvert has reached the end of its useful life. When a profile-walled existing (host) culvert is relined with a smooth-walled pipe, the culvert flow velocities typically increase, the corresponding flow depths decrease, and the resulting flow conditions can create a potential barrier to fish passage. In an effort to provide some baseline data for fish passage through baffled culvert liners, fish passage behaviors of wild brown trout through prototype-scale 0.61-m-diameter, 18-m-long smooth-walled baffled and nonbaffled culverts were observed in the laboratory under a variety of culvert slopes and discharges. The baffles significantly increased the range of culvert slopes and discharges over which the fish could successfully pass. The baffled culvert hydraulic roughness coefficient (Manning’s $n$) increased 274% (approximately equivalent to corrugated metal pipe values) relative to the nonbaffled culvert.

A one-dimensional depth-averaged velocity deformation model is developed to study the characteristics of the unsteady flows in open channels. The vertical profile of the streamwise velocity is expressed in a power series, and the coefficients of the velocity are evaluated by using the unsteady equation of motion. A concise form of the friction velocity for unsteady nonuniform flow is then proposed by utilizing the coefficients of the power series. The applicability of the model is validated with experimental data, producing reasonably good agreement between the model results and the observed data. Finally, the deformation of velocity at the surface is assured by comparing velocity distribution of numerical model with the computational results from a previous model.

Jet deflection and energy dissipation of ski jumps guarantee the safety of hydraulic structures. Deflectors on spillways and bottom outlets are mostly complex constructions. The aim of this study is to find simple-shaped deflectors allowing for jet deflection into the tailwater, thereby characterizing the parameters of the trajectory under different approach flow conditions. The test program included eight right-angled tetrahedrons and two vertical plate deflectors. A systematic variation of the approach flow depth and Froude number, in combination with different deflector alignments, resulted in basic principles for deflector design. To study scale effects caused by viscosity and surface tension, three symmetric deflectors were tested as a model family at different approach flow depths. The results indicate the importance of the approach flow Froude number and the relative deflector height on the jet trajectory. The relevant jet parameters, including the deflection angle, the maximum jet elevation, and the jet impact onto the tailwater channel, are specified.

A three-dimensional (3D) numerical model based on unstructured grids has been used to study flow and bed evolution in a laboratory meandering channel bend. The model employs the Reynolds-averaged Navier-Stokes equations and the low-Reynolds-number $k-\omega$ turbulence model for flow simulation. The model incorporates the suspended-load transport module and the bed-load transport module to simulate sediment transport and employs the sediment continuity equation to calculate channel bed evolution. The numerical simulation is performed in a meandering channel with a movable bed, in which the suspended load is comparable to the bed load. The model captures the main features of the bathymetry at equilibrium conditions. The streamwise velocity profiles and the suspended sediment concentration profiles at equilibrium conditions are also predicted by this simulation, and the agreement with the measured data is generally reasonable. The influence of including the suspended load is revealed by the comparison between the results obtained with total-load model and bed-load model in the meandering channel.

This paper presents and discusses a simple method to deal with zero flows in Newton solvers for water distribution systems, in particular in a previously published global gradient algorithm. The method consists in replacing the Hazen-Williams head loss–flow relationship for flows below a certain threshold with a linear relationship, which coincides with Hazen-Williams’ at zero, but has a nonzero derivative at that point, thus avoiding computational troubles associated with zero flows. Manual and automatic random testing of example networks shows that the proposed method compares well with both the algorithm adopted in water distribution modeling software and the recently proposed regularization method in convergence rate while outperforming them in computational veracity and applicability range.