Journal of Hydraulic Engineering

A measuring system based on laser triangulation for ranging a turbulent water surface in a laboratory environment is presented in this paper. The system is composed of a light detection and ranging (LIDAR) device, serving as a light source, and a high-speed camera. Single-point illumination was chosen to facilitate the introduction of the epipolar line in the image-processing step and thus improve the distinction between primary and other reflections, which increase the uncertainty of the measurement and introduce noise. The system was used to measure the water surface in an open channel confluence, which is composed of main and tributary channels, which join at a 90° angle. The surface was measured for 2.01 s, resulting in 54,682 points measured in 543 profiles. The influence of image process parameters (height and width of filtering kernel and width of area surrounding the epipolar line) on smooth and rough water surface was studied. The results show that the parameters’ influence is at least an order of magnitude smaller than the amplitude of water surface fluctuation.

The advection equation is one of the most commonly used models in environmental fluid dynamics. Despite this, there exist very few analytical solutions to this equation for the case where the velocity field is spatially varying. In this work a class of solutions to the conservation form of the advection equation is defined in one and two dimensions using a particular change of variables. Example solutions are developed for constant, varying, and discontinuous initial density profiles, as well as for continuous and discontinuous velocity fields. The accuracy of four common finite-volume numerical methods is evaluated for eight test cases and compared to the exact solutions. The first- and second-order upwind methods and the upwind method with the van Leer and Superbee slope limiters are used. It is found that the upwind method with either of the slope limiters is well suited to numerically solving the advection equation with spatially varying velocity fields for most test cases, while, as is the case for nondivergent velocity fields, the first- and second-order upwind methods have some serious drawbacks.

The smoothed particle hydrodynamics (SPH) method was used to simulate the flow over smooth and stepped spillways in the nonaerated, skimming flow regime. Two-dimensional numerical simulations were carried out using the DualSPHysics software and compared with experimental data on a 2H:1V sloping spillway for smooth and stepped inverts. Continuous inflow fluid layers with constant height and uniform velocity were used to establish the flow rate on the broad crested weir. The ability of the SPH to reproduce the main flow characteristics was analyzed by comparing the numerical flow depths and velocity profiles with their experimental counterparts. Firstly, a convergence analysis was carried out for various initial particle spacing. The flow characteristics along the stepped spillway were more sensitive to the particle spacing compared to the smooth chute one. In general, the numerical flow depths compared well with the corresponding experimental data and with empirical formulas available in the literature. The velocity profiles, and the free-stream velocity in particular, were also well reproduced by the SPH method; however, larger differences were obtained near the solid boundary.

Low-level outlets are key safety elements of reservoir dams, especially for structures with high heads. Their main purpose is the regulation and—if required—rapid drawdown of the reservoir water level in case of maintenance works or structural damage to the dam. A common outlet configuration for high-head structures uses a high-pressure vertical slide gate discharging into a free-flow tunnel. The high-speed water jet in the outlet tunnel leads to considerable air entrainment and transport, resulting in negative air pressures, which can aggravate problems with gate vibration, cavitation, and slug flow. Sufficient air supply via an air vent mitigates such problems. However, current methods for estimating the required air demand do not incorporate all factors affecting design of air vents for low-level outlets. Therefore, tests were conducted in a 20.6-m-long hydraulic scale model at heads up to 30 m, to improve the general understanding of aeration processes, to determine the governing parameters affecting air demand, and to formulate a new air demand design equation. The results show that air demand is mainly a function of the Froude number at the vena contracta. Furthermore, the new design equation enables quantifying the effects of the air vent loss coefficient, air vent size, tunnel slope, and tunnel length on air demand.

Established water distribution systems (WDSs) typically consist of pipelines buried underground that are aging and deteriorating, and as such, it is difficult to assess their condition for maintenance and replacement. This paper proposes a novel hydraulic transient-based inverse wave reflectometry method (IWRM) for condition assessment of water pipelines in WDSs. Instead of using the method of characteristics (MOC) for the transient modeling, a computationally high-efficiency wave reflectometry method (WRM) has been developed to simulate the transient response of a pipe system. Further efficiency improvement has been made by simplifying the friction term in the WRM. An IWRM has then been developed by combining the WRM with a differential evolution algorithm to calibrate the locations and magnitudes of the pipeline impedance changes (wall thickness changes and wave speed changes) caused by deterioration. The IWRM is able to concentrate on the major wave reflections caused by pipe impedance changes and minimize the effects from background noise and other interferences, such as background pressure fluctuations (i.e., those caused by pump operations, tank level fluctuations, and household water usage) and wave reflections by pipe fittings. The proposed method has a high efficiency due to its fast WRM simulation and its small number of optimization variables. Extensive numerical verifications have been conducted on reservoir-pipeline-valve systems with a uniform deteriorated pipe section, a nonuniform deteriorated section, and multiple deteriorated sections. The deteriorated sections in these case studies were all well detected even though the pressure signals were contaminated with strong noise. Experimental verification has also been conducted on a laboratory copper pipeline with one thinner-walled pipe section successfully identified.

There is essentially no experimental data on Archimedes screw pump performance available in the literature that is sufficiently detailed for model validation. Experiments were conducted on a laboratory scale (0.3-m diameter) Archimedes screw pump to characterize the pumping efficiency of the screw pump at various inlet basin water levels and screw rotation speeds. The results provide new insights into the effect of inlet and outlet basin level on screw pump efficiency. The flow rate of water pumped is proportional to the rotation speed of the screw, and increases with increasing inlet basin depth until the basin level exceeds that needed to fully fill the screw without overflowing. Comparisons are made to available empirical and analytically derived guidelines regarding optimal lower basin water levels, upper basin water levels and rotation rates for an Archimedes screw pump. Some differences are noted between recommended optimal conditions for full-size screws from the literature, and the optimum conditions found for the tested laboratory-size screw. These differences are consistent with expected effects of scaling between different size screws.

The Bric Zerbino and Sella Zerbino barrages dammed two branches of the Orba Valley in Italy to create the Ortiglieto reservoir and supply the Molare hydropower plant. The secondary dam, the Sella Zerbino, was erected over a fault, whose geotechnical characteristics were deemed extremely poor. On August 13, 1935, a very intense and localized storm produced a flood that overtopped both dams. On that tragic occasion the Sella Zerbino Dam collapsed at 1:27 p.m. resulting in catastrophic destruction and 111 victims. Nevertheless, the Sella Zerbino tragedy was soon forgotten. The designers of the dam and the directors of the electric company [Officine Elettriche Genovesi (OEG)] managing the power plant were acquitted in the subsequent trial. This paper aims at revisiting and studying the historical case with current hydraulic and hydrologic knowledge to show that the flaws in the design process infringed even upon the Italian regulations on dam design and construction in place at that time. The rainfall event has been reconstructed to evaluate its return period. The flood wave entering the Ortiglieto reservoir has been evaluated. The dam-break wave propagation has been simulated with a two-dimensional (2D) model based on shallow water equations written in conservative form. A finite volume first-order numerical solver on an unstructured grid has been used to integrate the equations.

Velocity is one of the most important parameters of debris flows, and it is usually calculated using Manning formula in hydraulics, mostly ignoring the granular effects due to flow materials. This study proposes a method in term of grain composition of debris flow, incorporating the physical effects of grain on roughness. It is found that the Manning resistance coefficient can be well related to the grain size distribution (GSD) and thus the method is expected to have a wide application. A new formula incorporating the influence of granular effects is built based on observation data of debris flows in Jiangjia Gully (JJG), China, and then it is tested by data from debris flows in other regions.