Journal of Hydraulic Engineering

There is no accepted standard equation for predicting flow resistance in gravel rivers. This is mainly because of the lack of an effective approach for describing the roughness of the gravel surface. This paper aims at describing the roughness of gravel surfaces based on characteristics of the elevation field rather than conventionally used grain size distribution. A new parameter—the coarseness parameter—in addition to the steepness parameter and standard deviation of the elevation field is proposed for characterizing the roughness of gravel surfaces. Two groups of rough surfaces (A and B) were generated using unconditional Gaussian simulation to study the influence of the coarseness and steepness parameters on effective roughness. The effective roughness of groups A and B was calculated by a two-equation turbulence model, and a quantitative relationship between the effective roughness and proposed parameters was derived. The resulting relationship derived from groups A and B was validated using data from flume experiments (group C). The results confirm the dependence of the effective roughness on the proposed parameters.

The authors previously described a new method [based on the new discrete vapor cavity model (new DVCM)] for numerical prediction of pressure changes during the water hammer with liquid column separation together with results of preliminary experimental verification of this method. This paper is a continuation of the research and includes results of additional laboratory tests and visualization of the cavitation zones generated during transient flow with liquid column separation. The results of these studies provide a better understanding of the phenomenon. It is shown that the phenomenon can have a distributed nature, which means that gas-vapor zones may be observed not only locally, in the vicinity of the shutoff valve, but may be spread along the pipeline length, and the intensity of this phenomenon decreases with distance from the valve. Laboratory test results were also used for further verification of the new DVCM. This verification shows that agreement between calculated and experimental results strongly depends on the friction model incorporated into the calculation. This agreement also depends on the intensity of liquid column separation: for cases of severe separation, the differences between numerical and measured pressure changes are small and accepted from the practical point of view.

Bridge piers having a nonuniform cross section over their height are termed as compound bridge piers. Mostly circular piers resting on large diameter wells or caissons (termed here as a circular compound bridge pier) are adopted for use in the Indian subcontinent for the road and railway bridges. In the present study, a new mathematical model is proposed for computation of temporal variation of scour depth at circular compound bridge piers. Two series of laboratory experiments were conducted to collect data for model application. In the first series of experiments, the data on temporal variation of scour depth were collected, albeit up to the transient (developing) stage of scour, around the circular uniform piers and circular compound piers for the clear-water scour condition. The second series of experiments was carried out to measure the size and hence the area of the principal vortex of the horseshoe vortex system and to determine the bed shear stress at the upstream face of the scour hole around the circular uniform piers and the circular compound piers. The mathematical model proposed in this paper has the capability to compute the temporal variation of scour depth around circular compound piers for all possible cases of footing position with respect to bed level, i.e., footing above the bed level, footing at the bed level, and footing below the bed level.

The major obstacles to simulating flood flow in the Yellow River are its high sediment concentration, complex compound cross section, and rapid change in channel planform. This paper presents an improved one-dimensional numerical model that takes into account the effect of sediment concentration and bed change on mass and momentum conservation of flood flow in the Yellow River. The model is calibrated and then validated by simulating three individual flood events. Results show that an increase in sediment concentration leads to a reduction in flood wave celerity and peak discharge. The generalized likelihood uncertainty estimation (GLUE) method is used to evaluate the uncertainty of modeling results. A sensitivity index, analogous to the Nash–Sutcliffe efficiency factor, is adopted to quantify the sensitivity of calibration parameters. The modeling results are sensitive to the choice of Manning’s roughness coefficient and the empirical recovery coefficient for suspended sediment transport at reaches of transitional channel planform.

To measure velocity components using the laser Doppler anemometry (LDA)in a cylindrical surface, as in a hydrocyclone, traditionally, one encloses the top circular tube of the hydrocyclone with a flat surface box to minimize the refraction effects of laser beams caused by the curved solid walls. In this brief study, an alternative procedure is suggested to reorient the laser beams to measure the mean and fluctuation velocity components. Adopting the beam orientation suggested—at a single point in the flow field—the axial and circumferential mean velocity components, along with the corresponding turbulent normal and shear stress components, can be determined. Test results confirm that the proposed method is valid to get data related to the mean velocities and the Reynolds stresses at a single point in the flow field of a hydrocyclone. The suggested procedure with slight modifications can be applied to measure velocities in the flow field formed by other circular surfaces, such as cones.

Vegetation growing on the surface of a streambank has been shown to alter the shear stresses applied to the boundary, but basic questions remain regarding the influence of vegetation and streambank configurations on near-bank hydraulics. In the present study, Froude-scaled flume experiments were used to investigate how changes in vegetation density (ratio of frontal area to channel area, including both stems and leaves) and bank surface angle influence near-bank turbulence intensities (${\mathrm{RMS}}_{u,v,w}$) and Reynolds stresses (${\tau }_{uv}$ and ${\tau }_{uw}$) estimated using velocities obtained with an acoustic Doppler velocimeter positioned beneath the canopy. Results illustrate how, with increasing vegetation density, turbulence intensities and Reynolds stresses decreased along the sloped bank surface but increased at the base of the slope and within the main channel. The steeper bank angle resulted in greater vertical stresses on the bank surface than the shallower angle, but lateral momentum exchange was larger than vertical exchange along the base of the slope, regardless of bank angle. Leaves were an important influence on near-bank turbulence intensities and Reynolds stresses, whereas the influence of bank slope was small relative to the influence of vegetation density.

The average bed shear stress and bed friction factor of samples with any roughness was derived from the head loss between upstream and downstream of a test section in an erosion tunnel. The method was validated in both hydraulically smooth (plexiglass; Reynolds number less than 25,000) and rough regimes (calibrated particles with known roughness). As a first step toward using this method on natural sediment, this method was tested with experimental mesocosms assembled from field collected materials (sieved sediments; diatoms). Bed shear stress measurement precision was high enough in the experiments to detect a positive significant relationship between bed friction factor and core roughness. The observed bed friction factor increase could be related to diatom growth but not to diatoms biomass.

The central basin of Lake Erie has chronic hypoxia that is exacerbated by strong seasonal temperature stratification near the lake bed. A computational study was conducted to determine the feasibility of mechanically mixing the water column by using a bubble plume system to reduce stratification, thus facilitating vertical transport of oxygen. The most efficient design delivered an air flow rate of $0.4–0.5{\mathrm{m}}^3{\mathrm{s}}^{-1}$ through 40–50 non-interacting plumes, which only mix the watercolumn during the late summer hypoxic events. The optimal efficiency was computed using a new metric, which neglects changes in stratification resulting from meteorologically induced mixing, relative to those from artificial mixing.

The sediment erosion rate flume (SERF) is used to evaluate various methods to estimate shear stresses in a flume-style erosion rate testing device. Results show that direct shear stress measurements most closely correspond to shear stress estimates obtained from the Colebrook equation using a roughness height of approximately 77% of the sediment particle diameter. Using pressure drops to estimate shear stress appears to underestimate rough sample (grain sizes $>0.25\mathrm{mm}$) stresses. Likewise, smooth-wall assumptions and analytical methods also appear to produce lower than expected results for similar heights. Colebrook equation results should be interpreted as “instrument specific” because of the different devices’ hydraulic diameters.

This paper presents the results of an experimental investigation on the roller length of both classical and B-jumps on smooth beds. Using the measurements conducted in this investigation and those available in the literature, a new relationship is proposed for estimating the roller length of classical and B-jumps on smooth beds. Finally, it is demonstrated that the proposed equation is also applicable to estimate the roller length of hydraulic jumps on rough horizontal beds.