Journal of Hydraulic Engineering

As a gravel bed river armors, a bed surface often develops clusters as part of its structure. The influence of sand on armoring and the impact of clusters on the surrounding flow processes were investigated through flume experiments. Armored beds were created from four different sediments, which progressively increased from 1–38% sand in the bed sediment, extending from gravel framework to sand matrix beds. Turbulent kinetic energy (TKE) and $xz$-direction Reynolds stress calculated from velocity profiles showed the clusters increased turbulence and induced formation of recirculation cells. Similar recirculation cells formed downstream of every cluster, but the strength and orientation of these cells varied with bed condition. The increase in sediment sand content and change in bed condition from gravel framework to sand matrix correlated to an increase in the energy and momentum in the recirculation cell but a reduction in cluster influence across the flow profile. Results show that the sand content of the bed sediment during armoring was a primary factor affecting the influence of a cluster on the local flow field and the overall bed surface stability.

An analysis is presented of the 309 known laboratory data for local scour depth developed by two-dimensional (2D) horizontal jets, which leads to development of a new comprehensive prediction equation. The new equation comprises a number of mutually independent multiplying factors, which account for the effects on local scour depth of the characteristics of the applied jet flow and the bed sediment, as well as the extent of a downstream protective apron. When unitized in terms of the jet thickness, the equation shows that the maximum possible dimensionless local scour depth is equal to three times the jet Froude number expressed in terms of jet velocity and jet thickness. The equation is compared to most of the existing predictive equations by applying each equation to the existing data, the comparison indicating that the new method has superior performance. Indeed, many of the existing predictive equations are shown to perform poorly when judged against the known laboratory data. The known existing equations are listed in the paper.

Detailed mean flow characteristics generated by a staggered arrangement of boulders in a rock-ramp-type naturelike fish pass were investigated experimentally at three different channel slopes (5%, 3%, and 1.5%). The results showed that this type of fish pass can produce adequate water depth and favorable flow velocity suitable for fish passage. Three different characteristic velocity regions were identified, namely, downstream of boulders (wake region), intermediate region, and upstream of boulders. Some general correlations were developed for predicting the flow depth and velocity in a rock-ramp fish pass as a function of normalized discharge. Moreover, a flow-resistance analysis based on basic concepts for wake-interference flow regime in this fish pass has resulted in a general equation for the average velocity. This study improves the understanding of the complex flow characteristics in a rock-ramp fish pass.

The authors developed an innovative two-dimensional finite-volume model for overland flow, which is capable of simultaneously applying the kinematic wave approximation and the full Saint-Venant (dynamic) equations to different regions of the modeled domain. A locally based criterion is employed to determine the applicability limits for the kinematic approximation. The model assesses the flow and topography on a cell-by-cell basis at each time step over an unstructured, triangular grid and determines the appropriate solution method for each individual cell. Several case studies are shown that illustrate the adaptive kinematic-dynamic model’s flexibility and robustness. The effects of the user-defined limit for the kinematic wave approximation and the abrupt switch from one solver to another are explored for the adaptive kinematic-dynamic model.

In this study, the relationship between the conventional power equation and the fixed and variable area discharges (FAVAD) equation for modeling leakage as a function of pressure was investigated. It is shown that different leakage exponent (or $N1$) values are obtained for the same leak when measured at different pressures. An analytical exploration of the two equations shows that the leakage exponent tends to 0.5 when the system pressure tends to zero, and to 1.5 when the system pressure tends to infinity. A dimensionless leakage number $L_N$ is defined as the ratio between the variable and fixed portions of a leak, and it is shown that a single function can be used to describe the relationship between the leakage number and leakage exponent. This model was combined with previous research to accurately predict the leakage exponents of several published studies in cases where elastic deformation occurred.

The detection of localized deterioration that is distributed along pipelines, including wall thickness reduction caused by large scale corrosion, is essential for targeted pipeline maintenance and the prevention of pipe failure. This paper proposes a novel technique for the detection of distributed deterioration along a pipeline by estimating the distribution of pipeline properties using a measured pressure transient trace. The proposed technique is referred to as reconstructive method of characteristics (MOC) analysis, and it is an inverse process of the traditional forward MOC calculation. The reconstructive MOC analysis reconstructs the MOC grid and estimates the pipe parameters, such as impedance and wave speed, reach by reach from downstream to upstream. Numerical simulations are performed on a pipeline with three pipe sections of impedance changes. These deteriorated sections are accurately detected and located by using the new technique. Experimental verification is also performed by successfully detecting a section of pipe with a thinner wall thickness in a single pipeline.

The failure of a natural or an artificial dam often leads to catastrophic flooding downstream. Studies have been conducted to investigate the mechanisms of single dam failure and the propagation of dam-break flood wave. However, little attention has been paid to the cascade failure of two or more sequential dams. In this article, consequences of a dam-break flood wave down a channel exerting pressure load on a downstream dam with different backwater effects were studied experimentally. Three typical flood patterns were observed for different downstream reservoir water depths. High precision pressure sensors were employed to measure the pressure load at different heights on the dam. Changes of the maximum pressure load were measured as the bed slope and the upstream and downstream reservoir water depths varied. An empirical formula was obtained by linear regression to predict the maximum pressure load. Additionally, a sinusoidal attenuation function was introduced to describe the time evolution of pressure load exerted on the downstream dam, and its parameters were determined using the measurement data in different cases.

The flow structure of vertical and horizontal planes in a stilling basin with five parallel offset jets in a twin-layer configuration for four offset ratios ($S_1/h=1,2,3,4$) has been investigated. The velocity distribution was measured, processed, and subsequently used to characterize the flow structure. The flow pattern in the stilling basin exhibits a mixing flow pattern of jets and hydraulic jumps. As the downstream water depth increases in the stilling basin, five different flow patterns appear successively: free jets, hydraulic jumps, submerged jets and hydraulic jumps, mixed submerged jets and critical jumps, and mixed submerged jets and submerged jumps. The results indicate that the velocity distributions in the vertical and horizontal planes of the lower-layer orifices and in the potential core region of the upper-layer orifices are similar to the classical jet; in other regions, the velocity distribution is similar to the hydraulic jump. In addition, the energy dissipation ratio increases with the increasing Froude number, with a value of greater than 70% at $\mathsf{F}>8.0$. The energy dissipation ratio in the stilling basin with five parallel offset jets in a twin-layer configuration is, on average, 5% larger than that of the SBJ basin and 13% larger than that of the classical jump basin.

Sudden starting and stopping of turbines and pumps lead to highly unsteady flow in tailrace channels of hydropower plants (HPP). Submergence of Pelton turbines and air entrainment in pumps due to surge waves must be avoided by technical measures. The existing 240 MW Veytaux pumped-storage plant in Switzerland will be enlarged by a new powerhouse adding another 240 MW, using the same tailrace channel and intake. Therefore, surge waves, induced by the two combined HPPs’ operation, were investigated using a physical model. For its validation, the flow behavior of the present scheme was tested and compared to prototype measurements. The enhanced scheme was investigated to analyze critical scenarios, to optimize the plant operation rules, and to define its limits. The effect of the layout on wave reflection in pump mode is highlighted and compared to theoretical approaches.

Experimental results for flow in a 16.5% sloping channel over various kinds of submerged artificial large-scale roughness elements are presented. Eight different shapes of obstacles are tested, as follows: (1) standard baffle blocks, (2) cubes, (3) half-cubes, (4) angles, (5) cylinders, (6) vertical rods, (7) hemispheres parallel to the flow, and (8) hemispheres normal to the flow. Based on depth measurements, the effective Manning’s coefficient is determined and the respective equivalent sand roughness is evaluated. The results are given in nondimensional terms and compared with previous research. The effects of shape, size, and density of the obstacles on flow resistance are discussed.