Scientific papers
Physical modelling of pressurized flushing of non-cohesive sediment using lightweight material
Karmacharya, Sanat & Henry, Pierre-Yves & Bishwakarma, Meg & Aberle, Jochen & Rüther, Nils. (2019). Physical modelling of pressurized flushing of non-cohesive sediment using lightweight material. Journal of Physics: Conference Series. 1266. 012012. 10.1088/1742-6596/1266/1/012012.
In this study, pressurized flushing of non-cohesive reservoir sediment through a bottom orifice was simulated in laboratory experiments using lightweight material as model sediment. The experiments were carried out by varying flushing discharge, reservoir water level, thickness of sediment deposit layer and opening height of bottom orifice. The volumes of flushing cones formed with lightweight material were compared with volumes calculated using empirical relations proposed by past studies. The good trend observed in variation of dimensionless flushing cone volume against different dimensionless parameters justified the possibility of using the lightweight material as model sediment.
Three-Dimensional Numerical Study of Free-Flow Sediment Flushing to Increase the Flushing Efficiency: A Case-Study Reservoir in Japan.
Esmaeili, Taymaz & Sumi, Tetsuya & Kantoush, Sameh & Kubota, Yoji & Haun, Stefan & Rüther, Nils. (2017). Three-Dimensional Numerical Study of Free-Flow Sediment Flushing to Increase the Flushing Efficiency: A Case-Study Reservoir in Japan. Water. 9. 900. 10.3390/w9110900.
The catchment of the Dashidaira reservoir located on the Kurobe River has high sediment yield. Because of the sufficient available amount of water in the catchment during flood events, the free-flow sediment flushing operation with full water-level drawdown is employed every year to preserve the effective storage capacity of the Dashidaira reservoir. This paper focuses first on the numerical simulation of a previously conducted free-flow flushing operation in the Dashidaira reservoir using the available in situ obtained data. Afterwards, to improve the flushing efficiency, the effects of water and discharge manipulation and the construction of an auxiliary channel on the total volume of the flushed sediment were studied. A fully 3D numerical model using the finite volume approach in combination with a wetting/drying algorithm was utilized to reproduce the flow velocity field and simulate the movable bed variations. The outcomes revealed that increasing the average free-flow discharge during the free-flow stage by approximately 56%, in the form of multiple discharge pulses, can enhance the flushing efficiency by up to 13%, and the construction of an auxiliary channel in the wide midstream of the reservoir can locally increase the sediment erosion from this area.
Upgrading of a Norwegian pressurized sand trap combined with an open air surge tank
Richter, Wolfgang; Vereide, Kaspar; Zenz, Gerald. Upgrading of a Norwegian pressurized sand trap combined with an open air surge tank. Geomechanics and Tunnelling 2017 ;Volume 10.(5) s. 620-624
In 1988 the Tonstad power plant (Norway) was upgraded from 640 to 960 MW. The headrace system to the reservoirs was not upgraded except for an additional pressure shaft, surge tank and an additional sand trap. Even with about 50 % higher discharge in the main tunnel, the sand traps worked adequately after the commissioning. However, in recent years, higher flexibility of demand is challenging the power plant and has resulted in events with flushing of sediments to the turbines. Higher flexibility demands also challenge the current surge tank design. During one event, free surface flow is believed to have occurred in the sand trap since severe damage to two of the turbines was observed. This contribution presents the background of the power system situation at the Tonstad power plant and the current flexibility demands of the power market and its challenges for the hydraulic system, as well as the proposals to solve the sand trap issues and the oscillation demands for the surge tank. The paper discusses the possibility of utilizing a model predictive controller with real‐time flow simulations to solve the challenges without structural reconstruction, and possible options should structural reconstruction be necessary. The contribution compares analysed options for improving the efficiency of sand traps. Finally, an outlook is offered to future demands for flexibility in hydropower plants with increasing supply of renewable power sources.