# Numerical Simulation and Sensitivity Analysis of Sediment Issues in Pumped Storage Power Stations: Sediment Conveyance of Turbine and Sedimentation of Reservoirs

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## Abstract

**:**

## 1. Introduction

_{2}emissions peak before 2030 and achieve carbon neutrality before 2060”. Under this vision, the thermal power generation method originally used for peak load regulation has been limited, which results in an energy gap in the economic society. The urgent requirement for a new clean energy source that operates flexibly has been put forward by China’s economic society. Pumped storage power stations (PSPSs) with a rapid start and stop, flexible adjustment, and abundant reserves can alleviate the pressure of peak load regulation to a great extent, preventing major power accidents and ensuring the safe operation of the power grid [1,2,3]. At present, a number of PSPSs have been built and put into operation in China, such as Baoquan PSPS in Henan and Pushihe PSPS in Liaoning [4]. Since 2017, the scale of PSPSs under construction in China has ranked first in the world for many consecutive years [5].

## 2. Methods

#### 2.1. Model Establishment

- (1)
- Basic equation of 1D unsaturated sediment transport model

- (2)
- Sediment-carrying capacity formula

- (3)
- Virtual diversion/confluence mode near water inlet/outlet

- (4)
- TSC calculation

#### 2.2. Calculation Conditions

^{3}/s, the average annual suspended sediment transport is 105,000 t, and the average annual incoming sediment concentration is 1.092 kg/m

^{3}. The bed load transport is calculated as 30% of the suspended sediment.

^{3}. The dead water level is 3747.00 m. The normal water level of the lower reservoir is 3275.00 m, with the corresponding storage capacity of 1.482 billion m

^{3}. The dead water level is 3240.00 m.

- (1)
- Calculation domain

- (2)
- Sediment gradation

^{3}. The daily initial water level of the lower reservoir is determined using the dispatching mode of the MED hydropower station. According to the dispatching mode of the MED hydropower station, the water level of the lower reservoir is shown in Figure 6, varying between 3240.00 m and 3275.00 m within a year. The water level of the upper reservoir changes between 3751.25 and 3780.00 m only with the pumping/power generation process, the variation of water level of the upper reservoir along with the pumping/power generation process is shown in Figure 7.

#### 2.3. Model Calibration

^{3}/s, which is closest to the multi-year average in several measured data. The results of water surface line comparison are shown in Table 3. It can be seen from the table that the water surface line calculated via the model is in favorable agreement with the measured one, and the absolute error of water depth in most sections is less than 7 cm, which proves the reliability of the model principle and the method. The model could, therefore, be used for subsequent calculations. The final roughness factor taken is 0.045.

## 3. Results

- (1)
- Sedimentation in reservoirs

- (2)
- Sediment concentration via the turbine

^{3}during 100 years of operation, the average TSC at pumping time per decade is 0.078~0.087 kg/m

^{3}, and the median particle size D

_{50}is less than 0.006 mm.

## 4. Discussion

#### 4.1. Sensitivity Analysis of Suspended Sediment Gradation

- (1)
- Sedimentation in reservoirs

- (2)
- Sediment concentration through turbine

^{3}to 0.054~0.057 kg/m

^{3}, which has a 30.8~34.5% reduction. Compared with the natural condition, the median particle size D

_{50}of the sediment concentration through pumping units will increase somewhat, but it is still less than 0.008 mm.

#### 4.2. Sensitivity Analysis of the Water Level of the Lower Reservoir

- (1)
- Sedimentation in reservoirs

- (2)
- Sediment concentration through turbine

^{3}, which is 12.6~13.1% lower than that of the natural condition, and the median particle size D

_{50}of sediment through pumping units is still less than 0.006 mm.

#### 4.3. Sensitivity Analysis of Coefficients of Sediment-Carrying Capacity Formula

- (1)
- Sedimentation in reservoirs

- (2)
- Sediment concentration through turbine

^{3}to 0.083~0.085 kg/m

^{3}, which has a 1.2~1.4% reduction, and the median particle size D

_{50}of sediment through pumping units is still less than 0.006 mm.

## 5. Conclusions

- (1)
- After 100 years of operation, the sedimentation elevation near the inlet/outlet is 3214.92 m, and the siltation rate of the GK River is 92.2%. The average TSC at pumping time per decade is 0.078~0.087 kg/m
^{3}, and the median particle size D_{50}is less than 0.006 mm. - (2)
- The TSC is sensitive to the use of suspended sediment gradation, it will decrease by 30.8~34.5% when the incoming sediments of particle sizes less than 0.002 mm (which accounts for 3.95% of the totality) are replaced with incoming sediments of particle sizes between 0.002 mm and 0.004 mm. At the same time, the sedimentation thickness of the upper reservoir will decrease by 20.9%, and the siltation rate of the lower reservoir will increase by 2.4%.
- (3)
- The TSC is sensitive to the water level of the lower reservoir, and it will decrease by 12.6~13.1% as the water level of the lower reservoir rises by 17.55 m. This represents an increase of 8.4% in average water depth and 26.4% in storage capacity. At the same time, the sedimentation thickness of the upper reservoir will decrease by 32.2%, and the siltation rate of the lower reservoir will increase by 2.5%.
- (4)
- In the case of reasonable coefficient values, the TSC is insensitive to the coefficients of the sediment-carrying capacity formula. It will increase by 1.2~1.4%, as the coefficient of the sediment-carrying capacity formula m changes from 1.12 to 0.666 or the index of the sediment-carrying capacity formula K changes from 0.2 to 0.6. At the same time, the sedimentation thickness of the upper reservoir will decrease by 7.2%, and the siltation rate of the lower reservoir will increase by 1.7%.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 10.**Changes in sediment concentration via the turbine (TSC) at pumping/power generation time in 100 years.

**Figure 12.**The gradation curves of pumping turbine sediment and incoming sediment in the 10th decade.

**Figure 14.**Changes in the upper reservoir bottom elevation under natural condition and contrast condition 1.

**Figure 15.**Changes in TSC at pumping time in 100 years under natural condition and contrast condition 1.

**Figure 16.**Sediment gradation curves of pumping turbine under natural condition and contrast condition 1 in the 10th decade.

**Figure 18.**Changes in the upper reservoir bottom elevation under natural condition and contrast condition 2.

**Figure 19.**Changes in TSC at pumping time in 100 years under natural condition and contrast condition 2.

**Figure 20.**Changes in daily average TSC at pumping time for the first decade under contrast condition 2.

**Figure 22.**Changes in the upper reservoir bottom elevation under natural condition and contrast condition 3.

**Figure 23.**Changes in TSC at pumping time in 100 years under natural condition and contrast condition 3.

**Figure 24.**Changes in daily average TSC at pumping time for the first decade under contrast condition 3.

Year | Average Discharge (m ^{3}/s) | Suspended Sediment Transport (×10^{3} t) | Average Sediment Concentration (kg/m^{3}) |
---|---|---|---|

High flow year | 4.73 | 174.3 | 1.170 |

Relatively wet year | 3.84 | 133.3 | 1.102 |

Normal flow year | 2.95 | 99.5 | 1.070 |

Relatively dry year | 2.30 | 80.7 | 1.105 |

Low flow year | 1.92 | 38.5 | 0.631 |

Average | 3.05 | 105 | 1.092 |

Time | Pumping (−)/Power Generation (+) Flow (m^{3}/s) | Notes |
---|---|---|

22:00~06:00 | −316.875 | Pumping |

06:00~09:00 | 0 | Stilling |

09:00~15:00 | 422.5 | Power generation |

15:00~22:00 | 0 | Stilling |

Distance from Dam (km) | Thalweg Elevation (m) | Measured Water Level (m) | Calculated Water Level (m) |
---|---|---|---|

0.00 | 3118.69 | 3119.20 | 3119.20 |

0.74 | 3129.97 | 3131.38 | 3131.44 |

1.49 | 3144.89 | 3145.38 | 3145.32 |

2.47 | 3174.62 | 3175.08 | 3175.08 |

2.94 | 3187.20 | 3187.70 | 3187.64 |

3.25 | 3194.47 | 3194.98 | 3195.06 |

4.43 | 3226.91 | 3227.39 | 3227.40 |

5.85 | 3267.20 | 3267.75 | 3267.77 |

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**MDPI and ACS Style**

Liu, C.; Yu, M.; He, X.; Wang, K.; Shao, Y.
Numerical Simulation and Sensitivity Analysis of Sediment Issues in Pumped Storage Power Stations: Sediment Conveyance of Turbine and Sedimentation of Reservoirs. *Water* **2023**, *15*, 3531.
https://doi.org/10.3390/w15203531

**AMA Style**

Liu C, Yu M, He X, Wang K, Shao Y.
Numerical Simulation and Sensitivity Analysis of Sediment Issues in Pumped Storage Power Stations: Sediment Conveyance of Turbine and Sedimentation of Reservoirs. *Water*. 2023; 15(20):3531.
https://doi.org/10.3390/w15203531

**Chicago/Turabian Style**

Liu, Chuang, Minghui Yu, Xin He, Kaixuan Wang, and Yuying Shao.
2023. "Numerical Simulation and Sensitivity Analysis of Sediment Issues in Pumped Storage Power Stations: Sediment Conveyance of Turbine and Sedimentation of Reservoirs" *Water* 15, no. 20: 3531.
https://doi.org/10.3390/w15203531