During pressure flushing of deposited sediments over large dam intakes, a funnel-shaped crater is formed due to considerable shear flow around the opening. Experiments with variable flow depth and discharge were conducted to determine the geometry of the flushing cone for fine, medium and coarse non-cohesive sediments. These sediments increase with increasing discharge and decrease with increasing reservoir depth and sediment particle size. Using the test results, two equations are proposed to estimate scour cone length and volume. While the water depth over the sediments is the most significant parameter in the collapse of sediments above the intake and initial development of the cone, the sensitivity analysis indicated that the intake flow velocity is the most significant parameter in determining the final equilibrium size of the scour cone. The results were compared with a previous study made with a small-scale model to confirm the proposal.

The Manning’s n-value, a fundamental resistance coefficient to balance driving forces of a river stream, is known to depend on the flow condition (depth and velocity) as well as vegetation condition (type and density). In this study, flume experiments were conducted to investigate the variation of n-value with flow and vegetation conditions for submerged vegetation in river beds, banks, and flood plains. Artificial plastic plants, for a length of 8 cm, were laid on the floor of a 4-m-long section of a variable slope flume. The Manning’s n-values were estimated for different slopes, discharges, flow depths, and vegetation densities. The results reveal that the Manning roughness coefficient (n) increases as vegetation density increases, whereas it decreases when the flow depth and velocity increase. The proposed physical model in this study was customized as a subroutine in a numerical model (FASTER) for a large river reach. The estimated water levels and discharges by the model were much closer to the fiel...

Optimal design of tunnels and surge tanks is a major concern in the implementation and operation of large hydropower plants, particularly those in which tunnels are long and water hammer is likely. In this paper, flow simulation and an optimization process have been linked in an iterative manner to develop a general model for the optimal design of hydropower tunnels and surge tanks for the emergency condition of operation (maximum surge pressure). The governing equations for the analysis of transient flow in conduits are solved using a finite difference scheme. Furthermore, a genetic algorithm (GA) optimization technique is utilized to select the optimal diameter for the headrace tunnel, penstocks, and surge tanks. The benefit-cost ratio is considered as the objective function in the optimization analysis. The proposed method was used to design diameters for Marun hydropower tunnels (an in-operation large hydropower dam located in southwest Iran). The results were compared with results from a nonl...

The use of polymeric pipes such as polyethylene (PE) and polyvinyl chloride (PVC) has recently increased in water distribution networks. This necessitates the understanding of the viscoelastic behaviour of these pipes in practice and in particular for transient flow analysis. The purpose of this study is to calibrate a developed numerical model based on the experimental results of transient flow in PE pipe networks. The linear viscoelastic model parameters were calibrated using the inverse transient analysis. Comparison of numerical results with experimental data indicated that the developed viscoelastic model was able to predict both pressure wave damping and dispersion in these pipe systems. Results confirmed a negligible viscoelastic effect of single pipe and pipe network on the linear viscoelastic model. Hence, the calibrated results of a single PE pipe were used to simulate the transient flow in the pipe network. The experimental and simulation results of pipe network transient flow in this study are new and advance previous studies.

The fall velocity of fine particles was measured in a column of height 2.50 m and diameter of 0.30 m to model the settling properties of cohesive sediments in lakes and large reservoirs. In contrast to the traditional particle-size-based methods, an approach relying on time and depth variation of sediment concentration was employed to estimate the mean value of fall velocity at any depth and time. Particles at greater depths, particularly for the samples with a higher rate of sediment concentration, accelerated faster and remained at higher velocities for a longer duration owing to a higher rate of flocculation. As a particular property of cohesive sediments, particles for all concentrated samples and in all depths reached their maximum fall velocity at around the same time—15 min after the start of the tests. The low concentration samples reached higher maximum velocities because of the lower rates of hindering, but for a much lower duration in comparison to the higher concentrated samples. An empirical ...