Journal of Hydraulic Engineering

Many skeletonization methods are available to simplify the configuration of urban water distribution systems (WDS) to enable hydraulic modeling and analysis. However, these approaches are generally based on steady-state hydraulic analysis, and hence the skeletonized systems cannot represent the underlying transient properties of the original systems, resulting in potential risk when handling transient events (e.g., pipe bursts). To this end, this paper proposes a transient-based method to ensure the skeletonized systems can capture the overall transient properties of the original WDS. Two criteria are proposed as principles to skeletonize pipes in series, and three assessment metrics are adopted to evaluate the transient performance of the skeletonized systems. Two WDS are used to demonstrate the effectiveness of the proposed method. Results show that the skeletonized systems produced by the proposed approach match well with the original WDS in transient dynamics. Although not all transient details can be captured, the proposed approach significantly outperforms the traditional steady-state–based method. The proposed approach offers an important tool to enable effective skeletonization of WDS for transient modeling and analysis.

Characteristics of turbulent length scales and anisotropy in different regions of a submerged turbulent plane offset jet are analyzed. The manifestation of the preattachment, impingement, and wall jet regions, including the outer and inner layers of the jet, recirculatory bubble, and circulatory flow zones are demonstrated by the velocity vector diagram. The results of the turbulent length scales (the Taylor microscale and the Kolmogorov length scale) show that the jet layer is characterized by a reduction in the length scales as compared with the recirculatory bubble and circulatory flow zones. To analyze the turbulence anisotropy, at first, the terminologies used for the axisymmetric limits of the Lumley triangle based on the Reynolds stress tensor are revisited and explained through an improved conceptual illustration. In the Reynolds stress anisotropy analysis, the anisotropic invariant maps formed by the data plots suggest that in the preattachment region, starting from the wall, the anisotropy tends to reduce toward the three-dimensional isotropy along the left-curved boundary of the Lumley triangle up to the half-depth of the recirculatory bubble zone. Then, the data plots take a turn toward the left vertex of the triangle with a further increase in vertical distance up to the inner separation line of the offset jet, exhibiting an affinity toward the two-dimensional isotropy. Within the jet layer, the data plots form a looping trend. By contrast, in the circulatory flow zone, the data plots belong close to the left-curved boundary of the Lumley triangle, moving slightly toward the left vertex of the triangle.

Nappe oscillation is a phenomenon that can have an undesirable impact to the local environment (e.g., nearby residences, and parks) as the phenomenon has been observed to produce a significant level of noise caused by acoustic pressure waves. As a result, a detailed investigation was undertaken to identify practical and effective mitigation solutions to address these effects for free-overfall structures. Nappe oscillations were studied using a prototype-scale linear weir (weir length of 3.5 m and fall height of 3 m), a high-speed camera, and audio equipment. The effectiveness of various crest modifications to reduce nappe oscillation and any corresponding impacts to hydraulic efficiency were evaluated. The test matrix included the optimization (position and spacing of elements) of three mitigation solutions: 12 configurations with projecting elements, 5 configurations with deflectors, and 1 configuration with a step. These three countermeasures proved to be effective after the optimization of their characteristics. In particular, deflectors or a step produced the maximum noise reduction while decreasing the discharge coefficient by less than 3% over the range of experimental conditions.

This note presents laboratory measurements of the drag coefficient for a finite patch of vegetation that was simulated with a limited number of rigid cylindrical rods. The experiment was designed based on an analogy between the drag imposed by a vegetation patch in an open-channel flow and that experienced by the patch settling in a water tank. The results show that the average drag coefficient calculated from the measured settling velocity can be expressed as a function of the patch porosity. The experimental data are also consistent with previous predictions by large eddy simulations.

Vertical-slot fishways (VSFs) are hydraulic structures which allow fish to swim around obstacles in rivers. These structures are subject to variations in discharge of either hydrological or operational origin, which result in nonuniform water depth profiles. These profiles are manifested as differences in the water drops across the slots ($\mathrm{\Delta }H$) and mean depths ($h_0$) across the pools. Although nonuniform conditions are present in most VSFs, they are rarely considered in the design and evaluation of fishways. This study provides an introductory analysis of how nonuniform water depth profiles affect the hydrodynamics within the pools of VSFs. This study shows that flow patterns are controlled by changes in $\mathrm{\Delta }H$ and $h_0$ in addition to slope and other geometrical alterations, as previously suggested. Nonuniformity alters the flow structure in pools and the spatial distributions of hydrodynamic variables. Consequently, critical thresholds of hydrodynamic variables for fish may be reached in VSFs designed with recommended slopes when operating under nonuniform conditions.