Journal of Hydraulic Engineering

Vegetation as multiple stems in various configurations or an isolated stem profoundly alters turbulent flows. Past research has shown that these alterations influence sediment transport and stream morphology, but entail complex interactions and feedbacks between flow, vegetation, and sediment processes that involve many parameters. These interactions are examined here for a variety of macrophyte patterns and scales in riverine environments. Flow Reynolds number, canopy density, and submergence ratio are just a few of the key parameters that influence the spatial variability of the flow, momentum transfer, vortex shedding and dissipation, and instantaneous stresses that are known to affect sediment and morphological processes in rivers. Knowledge gaps, though, still remain. A taxonomy that classifies vegetated flows as dense, sparse, or isolated on the basis of threshold parameters like the ratio of stem diameter to stem spacing would be useful for comparing studies among researchers and predicting likely morphological pathways. More research is needed to quantify thresholds and empirical relationships for flow–vegetation–sediment interactions so that aquatic macrophyte plantings can be used more effectively in water resource management. Field measurements of plant, canopy, and plant patch characteristics for these macrophytes would also be desirable.

Side weirs count among the important hydraulic structures for flow derivation in flood schemes or sewer networks. In this paper, the prismatic side weir in the rectangular channel is considered for entirely subcritical flow. Based on the momentum and energy equations, relationships are developed for the lateral outflow intensity, the local lateral outflow angle, the energy and momentum correction coefficients, and the relationship between the local streamwise component of the lateral outflow velocity and the average channel flow velocity. The governing equations are then numerically solved and the results compared with hydraulic laboratory observations, indicating that the momentum approach may be considered superior to the energy approach. The role of the momentum and energy correction coefficients is thereby particularly analyzed, stating that their correct inclusion both as absolute values and their local variation along a side weir have to be accounted for if the local discharge relative to the approach flow discharge tends to zero.

This paper presents results of an experimental study on three-dimensional scour at submarine pipelines with uniform sediment under a unidirectional current in clear-water conditions. The data show that propagation of the scour hole in the transverse direction of flow may be divided into a rapid and a slack phase of development. The former is characterized by a higher and constant velocity, whereas the latter a lower and reducing propagation velocity. Four nondimensional parameters are identified and their effects examined experimentally. Pipeline embedment and water depth to pipeline diameter ratios, which represent the stability force, inhibit the scouring process, resulting in a reduced propagation velocity and a dominant slack phase of development. Conversely, Froude number and Shields parameters represent the environment force; they enhance the scouring process, causing a high propagation velocity and a dominant rapid phase of development. The experimental results reveal that the scour process is not sensitive to Shields parameter under clear-water conditions but is closely related to the other three parameters. The effect of all the parameters can be viewed in a balance between the environment and stability forces.

Roller compacted concrete (RCC) stepped spillways are growing in popularity for providing overtopping protection for aging watershed dams with inadequate auxiliary spillway capacity and for the construction of new dams. Site conditions, such as limited right-of-way, topography, and geological formations, often dictate that these spillways converge. Convergence increases the flow depth near the training walls and alters the stilling basin design requirements as compared with traditional straight spillways. A simplified control volume momentum analysis is presented for predicting the minimum vertical training wall height necessary to prevent wall overtopping in converging stepped spillways. An expression is developed to predict vertical training wall height as a function of centerline flow depth, centerline velocity, chute slope, and convergence angle. A three-dimensional $3(\mathrm{H}):1(\mathrm{V})$ sloping stepped spillway model with an ogee crest and convergence ranging from 0–70° was constructed to verify this relationship. The evaluation showed approximately 2% error for all combined convergences. Because the relationship is based on momentum principles, it provides design engineers with a method for determining minimum training wall height requirements under nonair entrained flow conditions for a range of design conditions (e.g., chute slopes, convergences, and step heights).

When a sediment beach covered by stones or an armor layer is exposed to breaking waves, the turbulence generated by the breaking waves can cause mobilization and removal of the sediment underneath the stones. In two earlier studies by the Technical University of Denmark (DTU)-group, the suction removal of sediments from between armor blocks has dealt with the case of steady current and nonbreaking waves. The present study is an extension of these studies and the results will be presented in a similar way. The critical conditions for removal of sediment are determined. It is found that the onset of removal of sediment is governed by three parameters: (1) the sediment mobility (based on the sediment size, wave height, and wave period), (2) the ratio between the sediment size and the stone size, $d/D$, and (3) surf similarity parameter, $\xi =\tan (\beta )/(H_0/L_0{)}^{0.5}$. The variation of the critical mobility number for removal of sediment as function of $d/D$ and $\xi$ is determined for the range $0.001<d/D\le 1.0$ and $0.15<\xi <6.00$. The experiments were made on $1:2$, $1:14$, and $1:30$ slopes. Spilling, plunging, and surging breakers were used in the experiments. Both one and two layers of armor stones and rectangular blocks were studied.

The hydraulic performance of pumps in a cooling water intake is directly affected by the nonuniformity of the approach flow at each pump bay, which in turn is influenced by the strength of the cross-flow at the pumps’ common forebay. The effect of the cross-flow velocity at the forebay on the swirl angle in the pump suction pipes is investigated in a hydraulic model of the seawater intake at the Aliveri Power Plant in Greece. The particular intake features two pumps, and a total of 10 cases were examined based on differing values of water depth, number of pumps in operation, and pump flow rate. Velocity measurements at the forebay-dividing cross section were obtained by an acoustic Doppler velocimeter (ADV), while swirl angle in the suction pipe was measured by a vortimeter. A highly nonuniform velocity profile develops at the forebay, when one of the two cleaning channels is closed, and the swirl angle depends solely on the intake forebay geometry when the mean cross-flow velocity drops below a critical value.

This paper shows an approach that is useful for evaluating the resistance to flows in narrow open channels. A series of experiments were first carried out in a smooth, rectangular, open channel for which the aspect ratio varied from 0.12 to 1.53. Experimental data collected were then used to validate a resistance formula that was proposed previously by modifying Prandtl’s friction law.