Journal of Hydraulic Engineering

New long-duration clear-water scour data were collected at single cylindrical piers with the objective of investigating the effect of sediment coarseness, $D_p/D_{50}$ ($D_p$ = pier diameter; $D_{50}$ = median grain size) on the equilibrium scour depth and improving the scour depth time evolution modeling by making use of the exponential function suggested in the literature. Experiments were carried out for the flow intensity close to the threshold condition of initiation of sediment motion, imposing wide changes of sediment coarseness and flow shallowness, $d/D_p$ ($d$ = approach flow depth). The effect of sediment coarseness on the equilibrium scour depth was identified; existing predictors were modified to incorporate this effect for $U/U_c\approx 1.0$; $D_p/D_{50}>\approx 60$ and $d/D_p\ge 0.5$; the complete characterization of a known scour depth time evolution model was achieved for $U/U_c\approx 1.0$, $60<D_p/D_{50}<500$ and $0.5\le d/D_p\le 5.0$.

The propagation of dry granular flows, such as rock and snow avalanches, can be described by depth-averaged models. Different from classical shallow-water equations, these models take into account the anisotropy of normal stresses inside the flowing pile through using an earth pressure coefficient in the pressure term. A new regularization function for calculating the pressure coefficient in the Savage-Hutter-type models at the early stages of dam-break flows and collapses is proposed. In such circumstances the flow lines are significantly curved with respect to the basal surface and a special treatment of the earth-pressure coefficient is required for obtaining a satisfactory agreement with experimental data. The comparison between numerical simulations and laboratory experimental data shows an apparent improvement in describing the early stages of dam-break waves over rough beds. The comparison with experiments over smooth bed surface exhibits minor evidence of improvement. Nonetheless, in this case the proposed formula yields results similar to what obtained by the original Savage-Hutter formula.

The collection of floating woody debris at flow control structures, such as spillways and weirs, can potentially result in reduced discharge efficiency (higher upstream head for a given weir discharge). Compared to less hydraulically-efficient control structures, piano key weirs have higher discharge efficiency (lower upstream heads for a given discharge), which may increase the likelihood of woody debris collection. A systematic laboratory study was conducted to evaluate the interaction between various piano key weir geometries and woody debris types and sizes. The results of individual (noncumulative) debris tests indicated that floating debris blockage probability is highly influenced by trunk diameter and upstream head. The effects of debris accumulation on the upstream head varied with the value of the debris-free reference upstream head condition. At lower upstream reference head values, the cumulative debris tests indicated a relative increase of the debris-associated upstream head of approximately 70%; higher upstream reference head values produced upstream head increases limited to approximately 20%.

In this study, the authors solve the shallow water equations (SWE) with smoothed particle hydrodynamics (SPH) for one-dimensional (1D) nonrectangular and nonprismatic channel flows with open boundaries. To date, 1D SPH-SWE has been only developed to simulate rectangular prismatic channel flows with closed and open boundaries. However, for practical hydraulic problems, channel cross sections are not always rectangular and prismatic. A general approach is proposed in this study to extend the engineering application range of 1D SPH-SWE to nonrectangular and nonprismatic channels with open boundaries by introducing the wetted cross-sectional area and the water discharge in SWE and combining the method of specified time interval with the inflow/outflow algorithm. Three benchmark study cases, aiming at testing various steady flow regimes in nonrectangular and nonprismatic channels, are adopted to validate the newly proposed approach. Through the investigation of the convergence analysis and numerical accuracy test of the study cases, the results show that the present SPH-SWE approach is capable to model 1D nonrectangular and nonprismatic channel flows with open boundaries.

Accurate and practical models are in demand for optimization of ozone contactor designs. This paper reports results from Reynolds-averaged Navier-Stokes simulation (RANS) of the flow and passive nonreactive tracer transport inside a multichambered, laboratory-scale ozone contactor using a structured, collocated, finite volume discretization. Simulations are posed following previously published laboratory experiments. Results are presented in terms of velocity distributions, tracer concentration distributions, and tracer residence times. The flow is characterized by short-circuiting and dead zone regions that reduce the hydraulic (disinfection) efficiency or baffling performance of the contactor. RANS-predicted cumulative residence time distribution (RTD) of the tracer (released at the inflow as a pulse) is shown to be in excellent agreement with published experimental data despite the under resolution of the RANS methodology compared with better-resolved methodologies, such as large-eddy simulation (LES). The authors also compare the baffling performance and friction energy loss (molecular and turbulent) of three ozone contactor configurations by RANS simulation. A trade-off between baffling performance and energy loss is identified for the first time, as previous works have focused on baffling performance only. However, it is seen that the overall energy saving afforded by increasing the hydraulic efficiency (thus requiring less energy for ozone generation) offsets the energy increase required for driving the flow through a more hydraulically efficient contactor (characterized by more baffles). Overall, it is seen that energy considerations associated with contactor hydraulic efficiency (i.e., energy loss due to friction, and thus energy to drive the flow, and energy required for ozone generation) are important for determining the operational costs of a water treatment plant.

Water quality treatment via constructed storm-water wetlands (CSWs) is intimately linked to system hydraulics. Previous works have attempted to define the relationship between performance and wetland design variables (e.g., length, width, area). However, these works suffer from two major flaws: small sample size and/or nonrandom samples. The authors provide a framework herein to overcome these flaws. The goals of this research were to develop a methodology for creating randomly generated wetland designs and to use these designs to develop a set of equations for predicting peak flow reduction. Two thousand randomly generated wetland designs were generated using a five-tiered approach. Channel length and roughness were highly correlated with peak flow reduction and explained 83% of the total variability within the data set. Because of the large number of randomly generated designs, the regression equations presented herein prevent bias toward nonrandom designs. These equations represent the most general predictive performance equations developed to date and can be used to aid in CSW design.

This paper analyzes the groundwater flow system in an unconfined downward-sloping aquifer of semi-infinite extent in response to localized transient recharge. The aquifer is in contact with a water body of constant water level at one end and receives localized transient recharge from a recharge basin of finite width. The mathematical model is based on the Boussinesq equation with Dupuit-Forchheimer assumption, in which the spatial coordinate of the recharge basin is treated as an additional parameter. Analytical solutions of the linearized Boussinesq equation are obtained using the Laplace transform technique by dividing the aquifer in a three-zone system containing both Dirichlet and Neumann boundary conditions at the hypothetical interfaces. Upward- and zero-sloping cases are deduced from the main results by appropriately adjusting the slope parameter. To assess the validity and efficiency of the linearization method, the nonlinear Boussinesq equation is also solved using a fully explicit predictor-corrector numerical scheme. A numerical example is used for illustrating the effects of various parameters such as aquifer’s bed slope, spatial coordinate of the recharge basin, and recharge rate on the dynamic profiles of phreatic surface.

A characteristic particle method is proposed to simulate a water hammer in piping systems. Two types of regular particles are designed to trace the solution evolution along their corresponding characteristic lines. Besides these regular particles, shock particles with dual states are introduced to follow the shock formed from the amalgamation of characteristic lines. These dual states are derived to satisfy the Rankine-Hugoniot relation across a shock. Particles are implanted in regions without sufficient number to ensure solution accuracy. In this manner, the solution can be accurately resolved both in smooth regions and in those across a shock. The feasibility of the proposed characteristic particle method is validated by numerically solving some test problems and by comparison with the Godunov-type finite volume methods, method of characteristics, or available exact solutions. The computational results demonstrate that the present formulation will be a useful tool to simulate flow transient processes in a piping system.

Case studies of energy loss over bed forms in gravel-bed rivers are needed to determine local loss coefficients for modeling and design. In this study, an intense field campaign in two rivers is used to determine energy loss and calculate local energy loss coefficients ($K_e$) for riffle-pool units. Velocity head, water surface elevations, and energy coefficients ($\alpha$) are determined at up to eight cross sections at each site over a range of discharges including, at one site, the bank-full discharge. The water surface and energy grade line are relatively flat as flow enters the pool and relatively steep as flow leaves the pool. In both watercourses and at all discharges, $\alpha$ is higher in pools (i.e., velocity is more heterogeneous) and lower in riffles (velocity is more homogeneous). In a short but deep pool forced by a large fallen tree (Moras Creek), $K_e=1.7–2.0$. This high value is explained by a pool obstruction that results in a series of gradual and sudden flow transitions. In a long and relatively shallow pool (Ditton River), $K_e\sim 0$. This low value is explained by the uncertainty in resistance partitioning and the variability of models for skin friction. Future research should determine the range of local energy loss coefficients in natural and constructed bed forms in rivers.

The straits connecting two large water bodies show very strong and highly stratified currents related to meteorological, morphological, and hydrodynamic conditions. The Bosphorus is one such strait, connecting the Black Sea and the Sea of Marmara. In general, there is a two-layer current system in the strait. The southward barotropic flow is driven by the sea-level difference between these two seas, with the Black Sea having the higher level. The northward baroclinic flow, however, is driven by the difference in density (which is predominantly governed by salinity) between the Black Sea and the Sea of Marmara. In this study, the effect of the duration of a given barotropic forcing on the Bosphorus current structure was modeled by using a three-dimensional hydrodynamic modeling approach. The approach is based on a number of unstructured flexible meshes and uses a finite volume solution technique. These meshes are based on linear triangular elements. Using $k\text{-}\epsilon$ turbulence and a hydrostatic pressure assumption, the same magnitude of forcing was modeled for five different durations. The model results and measurements show that in the first four cases, which were of shorter duration, one-layered flow dominated the whole channel, while in the fifth case, a two-layer flow persisted.