Sediment Evacuation from Reservoirs through Intakes by Jet-Induced Flow

Reservoir sedimentation is considered as a sustainability problem. A concept getting down to the root of the cause was developed and tested in laboratory experiments. The idea is to maintain sediment in suspension, i.e., avoiding its settling near the dam by generating a jet induced artificial flow field and related turbulence (rotational flow), enabling the release of suspended sediment through the power intake. Therefore, a perpendicular jet configuration consisting of four jets arranged in a horizontal plane was investigated in a rectangular basin equipped with an outlet structure. The influence of its geometric parameters and the jet discharge on the sediment release was analyzed in detail. The flow pattern and its effect on the sediment release efficiency were evaluated, by measurements of turbidity and flow velocity. Depending on experiment duration and discharge, an ideal parameter set was identified resulting in a release efficiency between 1.5 and 2 compared to the reference case without jets. (C) 2014 American Society of Civil Engineers

Release of suspension particles from a prismatic tank by multiple jet arrangements

The performance of circular and linear jet arrangements on the release of suspended sediment out of a prismatic tank has been investigated. Experiments conducted are (1) without any forced jet stirring (reference case), (2) four jets arranged in a horizontal circle and (3) aligned jets; they were all in a tank containing water with a known homogeneous initial suspended sediment concentration. The concentration of the suspended sediment inside the tank and released through the outlet is monitored over time, and the evacuated sediment ratio (ESR) is defined, computed, and used as a metric for comparison between the various configurations. The idealized suspended sediment release is also calculated and compared to measured quantity. In order to explain the significant differences in evacuated sediment ratio, the induced circulation is analyzed by measuring the flow field on two vertical planes using the ultrasonic Doppler method. The geometrical parameters of the jet arrangement, the outlet elevation as well as the discharge of the jets are varied. Thus, the optimal parameter combination regarding sediment release can be identified. Finally, recommendations regarding jet arrangement and jet discharge practice in conditions of high sediment release are given. (C) 2016 Elsevier Ltd. All rights reserved

Numerical Simulations of an Innovative Water Stirring Device for Fine Sediment Release: The Case Study of the Future Trift Reservoir

Reservoir sedimentation and consequently lack of storage volume and perturbation of the operation of intakes and bottom outlet is a key challenge affecting both hydropower production as well as dam safety and flood management. In the framework of a peer-reviewed research project (Jenzer-Althaus, 2011) an innovative countermeasure, called SEDMIX, was proposed allowing to keep in suspension or re-suspend the fine particles near the power water intakes, thanks to an optimized arrangement of four water jets producing an upward whirling flow like produced by a mixer. With such a system, the suspended particles can be conveyed downstream at acceptable rates through the power waterways during the normal operation of the hydropower plant. Although experimental studies have shown the very promising efficiency of such a device in simple cases and by numerical simulations in a laboratory reservoir, SEDMIX performance has not been investigated yet in a real-life reservoir under prototype conditions. The aim of this study is therefore, to analyze the performance of a real-sized SEDMIX operating in the future Trift reservoir via numerical analyses. This study allows to validate or to improve SEDMIX optimal configuration experimentally determined. The numerical simulations are performed for different positions and heights for the SEDMIX device. The performance of SEDMIX in each position has been evaluated and tested for different jet discharges. The analysis of the numerical simulation results shows that the presence of SEDMIX does create a vortex flow pattern and sediment movement upward. The sediment volume fraction in the higher layers of the reservoir increases and consequently the evacuated volume of fin sediments increases for simulation using the SEDMIX device comparing those without the device