Search Results (4)

For water temperature stratified reservoirs, stratified water intake structures are used to extract surface warm water to reduce the adverse effects of low-temperature discharge on river habitats and agricultural irrigation. A physical simulation method has been explored and used to conduct the comparative experimental study on the efficiency of the three types of intake structures: a traditional stoplog gate intake, a stoplog gate with a horizontal curtain and a vertical curtain upstream of the intake. In order to extend the laboratory results to the prototype, a similarity relationship for water temperature stratification was derived based on the principle of equal density stratification Froude number between the model and the prototype, as well as the functional relationship between water density and temperature. The similarity relationship makes it possible to simulate the same prototype density flow under different laboratory water temperature conditions, and this was confirmed through experiments conducted in several months with different water temperatures. Under constant water flow conditions, a stable target water temperature distribution can be formed in the experimental model through continuous stratified heating and real-time power regulation, to simulate the density flow generated by various intake operation in water temperature stratified reservoir. The relationships between the intake water temperature and the reference water temperature at intake depth in reservoir were analyzed to distinguish the difference of water intake efficiency. The experimental results showed that, the traditional stoplog gate has a relatively lower efficiency in extracting warm water affected by the lower edge expansion of the drag layer into the cold water zone below the intake elevation; by setting horizontal curtain to prevent the cold water from climbing below, it is helpful to improve the water intake efficiency; by setting vertical curtain in the upstream area of the intake, the velocity of warm water in the upper part of the drag layer increases, and the intake efficiency has been significantly improved. The above research provides a scientific approach for mechanism research and mathematical model validation of thermal density flow. Full article

The discharge of low-temperature water from the middle and lower layers of thermally stratified dam reservoirs leads to thermal pollution and adversely affects fish production and reproduction in downstream rivers. Selective water withdrawal using stoplog gates is an effective approach to address this issue. However, comprehensively and effectively evaluating the effects of stratified withdrawal and optimizing the scheduling of stoplog gates to provide better ecological services to downstream habitats pose significant challenges for reservoir managers. In this study, an equivalent elevation method (EEM) was developed based on in situ observation data of water temperature. The EEM calculates the equivalent withdrawal elevation (EWE) in the far dam area corresponding to the discharge-water temperature (DWT), facilitating the evaluation of stoplog-gate effects. EEM was applied to a thermally stratified dam reservoir in southwestern China (Guangzhao reservoir, GZ). The results showed a significant positive correlation (r > 0.7, p < 0.05) between DWT and the vertical-water-temperature structure in the far dam area. The average EWEs for the 5-layer, 4-layer, and 3-layer stoplog gates in GZ were 697.2 m, 690.8 m, and 689.9 m, respectively. Utilizing the EEM findings, a scheduling operation scheme was proposed to improve DWT while reducing the number of stoplog-gate operations, thereby increasing their efficiency and saving the cost of invested labor and time. This method provides a reference for reservoir managers in optimizing stoplog-gate-scheduling strategies to mitigate potential risks to aquatic ecosystems caused by abnormal water temperature. Full article

A stop-log gate, installed in water intake of hydropower project, has become an effective facility in achieving selective withdrawal and temperature control for the sake of benefiting downstream ecosystems. Hence, it is of great importance to comprehensively explore the water intake hydraulics with the gate, not limited to some specific case studies. This study deals, through laboratory experiments and numerical simulations, with flow features of such a gate-functioned intake. The physical model test is used to validate the numerical simulation. Subsequently, a series of numerical cases considering different hydraulic and geometric conditions are performed to help look into the behaviors. Particular attention is paid to the flow regimes, head loss and flow velocity distributions. The results showcase the effect of the gate on the intake flow regime, and in terms of head loss and flow velocity distribution, the influences of the upstream water head, intake chamber width and withdrawal depth are revealed in detail. An empirical expression, with regard to the coefficient of head loss, is derived and validated by data from the available literature. Moreover, it is found that the maximum velocity at trash rack section is dependent exclusively on the relative withdrawal depth and always occurs at a certain height range above the gate. These results may provide a meaningful reference for the research of water intake with similar situations. Full article

The impoundment and power generation of dams cause the temperature of released water much lower than the original rivers in the thermal stratified reservoirs. In addition, the released low-temperature water would damage the downstream habitats of fish and other biological groups seriously. Available facilities, such as stop log gate intakes and multi-level intakes, are built to alleviate the problem. For overcoming the limitations of traditional facilities on construction conditions and the improved effect of water temperature, a new facility of the temperature control curtain (TCC), with the advantages of convenient regulation and no hydropower loss, has been proposed recently. However, to the author’s knowledge, the theory of TCC is not abundant, with incomplete experimental tests and few numerical simulations. In this paper, a rectangular tank is designed specifically to conduct experimental tests to verify the effects of TCC and explore its potential impacts on released water temperature (RWT) under four major influencing factors. The study results show that TCC has significant effects on improving RWT, with a maximum increase of 8.3 °C. In addition, a three-dimensional hydrodynamic model with the same size of experimental model is established for further research. The results show that RWT is mainly related to the temperature distribution of a reservoir and the water-retaining proportion of the curtain. Finally, a basic principle for TCC construction is proposed and all these laid an important theory foundation for its application in engineering practice. Full article