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Although the effect of pressure relief and permeability increasing achieved by the technology of traditional hydraulic flushing (enlarging hole by high-pressure water jet) is great significance, it has some shortcomings, such as low efficiency, large consumption of water resources, and being difficult to guarantee the sizes of holes. The limitations of water jet are known as the main factors that would restrict the effective pressure relief in soft and low-permeability coal seam. For the purpose of solving the problems existing in the traditional technology, a new technology of mechanical cutting assisted by waterjet has been developed. Then, a numerical simulation method was employed to illustrate the flow field and the force characteristics of equipment equipped with new technology. Finally, the new technology and its supporting system were tested in the Xinjing Coal Mine, Shanxi Province, China. The test results obtained are as follows: the efficiency of mechanical cutting is much higher than that of hydraulic flushing; the maximum equivalent to enlarge hole radius is increased by 83.3% (t = 30 min), and the efficiency of the new technology is 3 times more than that of the traditional hydraulic flushing; the time used for gas drainage is increased by 19.3%, and the drainage efficiency is increased by 28%; the cost spent on gas control in one working face decreases by more than 14.7%. It is concluded that the new technology can efficiently enlarge borehole so as to enhance gas drainage in coal seam and decrease the cost of coal mining. [ABSTRACT FROM AUTHOR]

The concept of sustainable development is gaining popularity and hydroelectric projects designed and operated on this concept require sediment management as prime design criteria. Drawdown flushing is being practised in such projects for sediment management. Investigations using hydraulic models are required for the projects to address the site-specific design concerns. In the present study, simulations conducted using hydraulic model for sediment removal by drawdown flushing of the reservoir of Punatsangchhu hydroelectric project, Bhutan, is presented. The experiments on 1:100 geometrically similar scale model indicated that flushing is effective in maintaining the power intake area clear of sediment deposition. Deposition from the upstream reaches could not be flushed hydraulically. Furthermore, based on wide range of experimental data from hydraulic model studies, empirical equations have been developed for predicting the quantity of sediment that can be flushed from the reservoirs. The present equations have been developed including more parameters than those used in equations already available in literature. Two equations have been developed for different riverbed slope ranges with steep slope (0.005–0.04) and moderate slope (0.001–0.005). The equations developed were validated against different sets of data and it indicated that the predictions could be made within reasonable accuracy. These equations can be effectively used for hydraulic design of sediment removal from run-of-the-river hydropower reservoirs. [ABSTRACT FROM AUTHOR]

Sediment removal from reservoirs is the major challenge faced by developers of hydropower projects in the Himalayan region. Sediment removal can be achieved by drawdown flushing or sluicing. In drawdown flushing, the water level in the reservoir is lowered sufficiently to establish riverine flow conditions. A flushing channel will be developed and retrogressive erosion will take place. However in the case of sluicing, the water level is kept sufficiently high to maintain pressure flow conditions. During sluicing, the incoming sediment is passed through the sluices and since water level is not lowered, previously deposited sediment will not be removed. Only a scour cone will be developed in the vicinity of the low level sluice outlet. In the case of run-of-the-river hydropower projects, it is important to estimate the parameters of the scour cone such as length, width and depth. The projects are generally operated at MDDL during monsoon season, when sediment concentration is high. Power intakes are generally located very near to the dam and in the scour cone area. Hydraulic model studies carried out to investigate the development of scour cone under pressure flushing of a reservoir is presented in this paper. The experiments were carried out in a laboratory flume. A single spillway bay was reproduced in the model. Experiments were conducted by varying the sluicing discharge and water depth. The various parameters of the scour cone were measured. Dimensional analysis was carried out to establish the relationship of scour cone parameters and hydraulic parameters. The available relationships in the literature also were verified. [ABSTRACT FROM AUTHOR]

Run-of-the-river hydropower projects are developed based on the concept of sustaining reservoir life by sediment management. Sediment management is achieved by sluicing or drawdown flushing through low-level spillways. Simulations with numerical and physical models are essential for optimizing the design and operation of such projects. In this paper, numerical and physical model simulations carried out for sediment management of a run-of-the-river hydropower project are presented. For Devsari Hydroelectric Project, Uttarakhand, India, a physical model was constructed to a geometrically similar scale of 1: 60. Experiments were carried out for sediment management for various scenarios. One-dimensional model Hydrologic Engineering Center's –River Analysis System was used to simulate the longitudinal sedimentation and velocity profiles in the physical model. The numerical model was further applied to the prototype for predicting the long-term sediment deposition along the reservoir stretch. Results of the simulation indicated deltaic sediment deposition in the upstream reaches of the main Pinder and Kailganga rivers. The delta advanced towards downstream for lower reservoir operation levels. The flow velocities in the entire reservoir stretch were observed to be very low, thus confirming the design concept of reservoir functioning as a desilting basin. Experiments were carried out on the physical model for simulating sediment removal by drawdown flushing. It was observed that reservoir capacity can be restored by annual flushing during peak flows. Flushing with discharge of 300 m3/s for 12 h duration can remove about 0.0086 Mm3 of sediment and hence may be adopted for reservoir operation. [ABSTRACT FROM AUTHOR]