# Water Residence Time in a Typical Tributary Bay of the Three Gorges Reservoir

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

^{2}[19]. Its annual flow is 951.3 km

^{3}. The TGD, located at the end of the upper Yangtze River, is 185 m high. Construction began in 1998 and was completed in 2003. The TGR is currently one of the largest reservoirs in the world, with a capacity of 39.3 billion m

^{3}over a length of 663 km and an average width of 1.1 km [20,21].

## 2. Model Setup

#### 2.1. Study Area

^{2}, a length of 31.4 km, and an annual average discharge of 2.54 m

^{3}/s which is much lower than that of the Yangtze River’s ~11,000 m

^{3}/s. After the impoundment of the TGR, a 6-km-long bay was formed, which was influenced by TGR regulation, which can modify the water level from 145 m to 175 m. Hereafter, this area is called Zhuyi Bay (ZB) in this paper. The ZB’s average depth is 36.23 m and its maximum water depth is 80 m when the TGR is at the highest level in the winter (up to 175 m). The wind over ZB is weak with an annual mean wind speed of 1.5 m/s.

#### 2.2. Hydrodynamic Model

#### 2.3. Diagnosing RT by the Adjoint Method

## 3. Results

#### 3.1. Validation of the Hydrodynamic Model

#### 3.2. Annual Mean RT of ZB

^{2}/s. For the average water depth of 20 m, the timescale of vertical mixing is about 1.5 days, which is much smaller than that of the horizontal transport. Therefore, the annual mean RT exhibits little vertical variability.

#### 3.3. Seasonal Variation of RT

## 4. Discussion

#### 4.1. Relationship between RT and TGR Regulation

#### 4.2. Influences of Dynamic Processes on the RT

#### 4.3. The Potential Relationship between RT and Algal Blooms in the Tributary

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Abbreviations

Acronym | Full Name |

TGR | Three Gorges Reservoir |

TGD | Three Gorges Dam |

ZB | Zhuyi Bay |

RT | Residence time |

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**Figure 1.**Illustration of the domain of interest, with (

**a**) the Yangtze River basin. (

**b**) the location of the Zhuyi Bay (ZB).

**Figure 4.**Comparison of the observed and simulated velocity profiles at site OBS for the 12 months in 2014. Blue circles denote simulation, and red circles denote observation.

**Figure 5.**Comparison of observed and simulated water temperature profiles at site OBS for the 12 months in 2014. Blue circles denote simulation, and red lines denote observation.

**Figure 6.**Vertical mean (

**a**), surface (

**b**), and bottom (

**c**) RT (days) averaged over 2014. The contour interval is five days. (

**d**) difference between the surface and bottom RT. Positive value denotes larger RT in surface layers. The contour interval is two days.

**Figure 7.**Vertical profile of the annual mean RT (days) along the deep channel section. The contour interval is five days.

**Figure 8.**Monthly variation of RT averaged over the entire Bay. Red lines denote medians of RT in the month, blue rectangles denote the first and third quartiles, dashed lines denote the upper and lower whiskers, and red crosses denote the outliers.

**Figure 13.**The observed water temperature difference between ZB and the Yangtze River. Positive value indicates that ZB temperature is higher than the Yangtze River. Negative value indicates that ZR temperature is lower than the Yangtze River.

Case | Tributary Discharge | Yangtze River Discharge | Local Winds | Baroclinic Forcing |
---|---|---|---|---|

0 | Yes | Yes | Yes | Yes |

1 | 0.5 times | Yes | Yes | Yes |

2 | Yes | 0.5 times | Yes | Yes |

3 | Yes | Yes | No | Yes |

4 | Yes | Yes | Yes | No |

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**MDPI and ACS Style**

Cheng, Y.; Mu, Z.; Wang, H.; Zhao, F.; Li, Y.; Lin, L.
Water Residence Time in a Typical Tributary Bay of the Three Gorges Reservoir. *Water* **2019**, *11*, 1585.
https://doi.org/10.3390/w11081585

**AMA Style**

Cheng Y, Mu Z, Wang H, Zhao F, Li Y, Lin L.
Water Residence Time in a Typical Tributary Bay of the Three Gorges Reservoir. *Water*. 2019; 11(8):1585.
https://doi.org/10.3390/w11081585

**Chicago/Turabian Style**

Cheng, Yao, Zheng Mu, Haiyan Wang, Fengxia Zhao, Yu Li, and Lei Lin.
2019. "Water Residence Time in a Typical Tributary Bay of the Three Gorges Reservoir" *Water* 11, no. 8: 1585.
https://doi.org/10.3390/w11081585