# Analysis of Long-Term Water Level Variation in Dongting Lake, China

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area and Data

^{11}m

^{3}[17], 37% and 55% of the inlet comes from three outlets and from four rivers, respectively [35].Together with Poyang lake, it is one of two large lakes still linked with the Yangtze River. Dongting Lake is also an important international wetland, with a capacity of more than 1.7 × 10

^{10}m

^{3}[36]. The wetland helps regulate flooding in the Yangtze River as well as the local climate and serves as a water source for industry, agriculture, domestic use and entertainment. The inflows and the water level at the outlet have an important impact on the evolution of the lake. Because Chenglingji station is located at the confluence of the Yangtze and the outlet of Dongting Lake (see Figure 1) and the small longitudinal slopes of the lake’s bathymetry and water level, water level changes at Chenglingji station can reflect changes in all of Dongting Lake’s water level, although the intense unsteady flow states in the four tributaries and the hybrid river networks linked to Jinjiang may briefly cause some temporary changes along the thalweg of Dongting Lake. Therefore, for this study, we selected daily water level data at the Chenglingji station from 1961 to 2014, as measured by Changjiang Water Resources Commission.

#### 2.2. Methodology

#### 2.3. Determining the Hydrological Variables

## 3. Results of Water Level Variation at Dongting Lake

#### 3.1. The Results of Lake Water Level from 1961 to 2014

#### 3.2. The Results of Lake Water Levels from 1981 to 2014

#### 3.3. Comparisons of Water Levels between Three Time Periods

## 4. Impacted Factors Analysis for the Water Level Variations

#### 4.1. Impacted Factors Identification and Analysis for the Inter-Annual Variations of Water Level

^{3}/s and 2200 m

^{3}/s of flow discharge at Yichang and Luoshan, respectively. Among them, flow increment of 1200 m

^{3}/s at Luoshan may be mainly produced by early larger rainfall and the releasing flow from dams in the four rivers at the start of flood season (April–June); (3) In early flood season from April to June, additional flow discharge from reservoir releasing for flood control will increase the flow discharge at some degree, especially on the stations at the downstream of TGR in Yangtze main channel; (4) At the end of the flood season, there is an obvious reduction in flow discharge because of the rapid water storage by the large dams. The comparison between the shapes for inter-annual variations at three sub-periods can explain qualitatively the possible combination effects driven by the net rainfall variation from climate changes and dams’ operation at some degree. However, only using combined in situ data, it is not easy to evaluate the effects caused by the operations of dams separately and quantitatively. Therefore, in subsequent sub-section, a refined numerical modeling is applied to further identify the water level and flow discharge variation linked to the operation of TGR and GZB.

#### 4.2. Quantitive Identification on the Hydrological Variation Linked to TGD and GZB

^{3}/s and 1500 m

^{3}/s, respectively; (2) Because of flood detention by reservoirs, there is some reduction during the flooding peaks usually from July to August; (3) At the end of flood from the mid of September to November, in order to guarantee the enough hydropower generation in dry season, the inflows storage by a reservoir will obviously decrease outflow from the reservoir. For example, the reduced flow discharge at Yichang station was 20,000 m

^{3}/s on 25 September 2011; (4) In general, the operations of TGR and GZB make the flood period earlier than before. Compared to the flow discharge at Yichang, the discharge process at Luoshan, located about 400 km downstream of Yichang, showed the similar variation trend with smaller variation magnitudes because of hydrodynamic attenuation in the Jingjiang–Dongting systems and flow mixture with inflows from four rivers and three outlets (Figure 8b). The discharge variation in Luoshan will cause a similar variation in the water level at Luoshan and Chenglingji station (Figure 8c,d).

#### 4.3. Relationships between the Hydrological Processes and Net Rainfall around the Dongting Lake Region

## 5. Discussion

#### 5.1. The Analysis on Water Level Changing Trend

#### 5.2. Identification on the Hydrological Variation Linked to TGR and GZB

#### 5.3. Further Evaluation on the Hydrological Variation Linked to Anthropogenic and Climate Factors

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

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**Figure 1.**Diagram of the river–lake system in the Dongting Lake. Note: (1) F1, Shimen station at Lishui River; F2, Taoyuan station at Yuanjiang River; F3, Taojiang station at Zishui River; F4, Xiangtan station at Xiangjiang River. Inflow from Four rivers is equal to summarization of F1–F4; (2) T1, Xinjiangkou station at west Songzi River; T2, Shadaoguan station at east Songzi River; T3, Mituosi station at Hudu River; T4, Guanjiapu station at west Ouchi River; T5, Kangjiagang station at east Ouchi River. The inflow from three outlets of Jingjiang is equal to summarization inflow of T1–T5; (3) West, South, and East in Dongting Lake region mean West, South, and East Dongting Lakes.

**Figure 2.**Trends for WLM, WL, and WLm from 1961 to 2014 (note: the black dotted line denotes the linear trend of water levels).

**Figure 3.**The changes in hydrological variables (RA and Cv) from 1961 to 2014 (note: the black dotted line denotes the linear trend of hydrological variables).

**Figure 4.**Trends for WLM, WL, and WLm from 1981 to 2014 (note: the black dotted line denotes the linear trend in water level).

**Figure 5.**The changes in hydrological variables (RA and Cv) from 1981 to 2014 (note: the black dotted line denotes the linear trend of hydrological variables).

**Figure 7.**Inter-annual variations in flow discharge during three sub-periods (1961–1980, 1981–2002, and 2003–2014). (note:

**a**–

**f**is the variations of Yicheng discharge, Luoshan discharge, Dongting inflow, Four Rivers inflow, Three outlets inflow, and Chenglingji outflow, respectively).

**Figure 8.**Water level and discharge comparison with and without operation of TGP and GZB. (note:

**a**,

**b**, and

**e**is the discharge comparison at Yicheng, Luoshan, and Chenglingji, respectively;

**c**and

**d**is the water level comparison at Luoshan and Chenglingji , respectively).

**Figure 9.**Inner annual water level variation during 2003–2014 at Chenglingji with and without the operation of TGR and GZB.

**Figure 11.**Comparison between total inflow from four rivers and net rainfall induced inflow around Dongting Lake.

**Table 1.**The hydrological variables abbreviations and their measurement units used in this manuscript.

Number | Variable | Definition | Unit |
---|---|---|---|

1 | WLM | Annual maximum lake water level | m |

2 | WL | Annual mean lake water level | m |

3 | WLm | Annual minimum lake water level | m |

4 | RA | Range between maximum and minimum water level | m |

5 | Cv | Coefficient of variation | % |

6 | JAN | Monthly lake water level in January | m |

7 | FEB | Monthly lake water level in February | m |

8 | MAR | Monthly lake water level in March | m |

9 | APR | Monthly lake water level in April | m |

10 | MAY | Monthly lake water level in May | m |

11 | JUN | Monthly lake water level in June | m |

12 | JUL | Monthly lake water level in July | m |

13 | AUG | Monthly lake water level in August | m |

14 | SEP | Monthly lake water level in September | m |

15 | OCT | Monthly lake water level in October | m |

16 | NOV | Monthly lake water level in November | m |

17 | DEC | Monthly lake water level in December | m |

Variable | Z (MK Test) | Sen’s Slope (cm/year) |
---|---|---|

WL | 2.1 ^{★} | 1.65 |

WLM | 0.6 | 0.90 |

WLm | 2.5 ^{★} | 4.58 |

RA | −2.3 ^{★} | −0.37 |

Cv | −3.5 ^{★} | |

JAN | 4.1 ^{★} | 3.53 |

FEB | 3.5 ^{★} | 3.07 |

MAR | 2.9 ^{★} | 4.29 |

APR | 1.6 | |

MAY | 0.6 | |

JUN | 2.1 ^{★} | 2.68 |

JUL | 0.8 | |

AUG | 1.3 | |

SEP | −0.1 | |

OCT | −1.7 | |

NOV | −1.4 | |

DEC | 1.5 |

^{★}are significant at >95% confidence level. Positive values indicate increasing trends, and negative values indicate decreasing trends.

Variable | Z (MK Test) | Sen’s Slope (cm/year) |
---|---|---|

WL | −1.0 | −0.79 |

WLM | −0.7 | −2.27 |

WLm | 2.6 ^{★} | 2.56 |

RA | −1.3 | |

SD | −0.7 | |

Cv | −0.6 | |

HR | −1.5 | |

JAN | 2.3 ^{★} | 2.62 |

FEB | 0.8 | |

MAR | 0.3 | |

APR | −0.9 | |

MAY | 1.7 | |

JUN | 0.8 | |

JUL | −0.5 | |

AUG | 0.0 | |

SEP | −0.9 | |

OCT | −3.8 ^{★} | −9.39 |

NOV | −1.8 | |

DEC | −0.7 |

^{★}are significant at >95% confidence level (positive values indicate increasing trends, and negative values indicate decreasing trends).

Parameters | Element | Sum of Squares | df | Mean Square | F | p Value |
---|---|---|---|---|---|---|

1 | Months | 346.08 | 11 | 31.46 | 9.71 | 4.18 × 10^{−6} |

Sub-periods | 0.61 | 2 | 0.31 | 0.09 | 0.91 | |

2 | Months | 349.04 | 11 | 31.73 | 9.66 | 4.36 × 10^{−6} |

Sub-periods | 0.75 | 2 | 0.38 | 0.11 | 0.89 |

**Table 5.**The mean water level for all sub-periods and percentage changes from the first sub-period to the two subsequent sub-periods.

1961–1980 | 1981–2002 | 2003–2014 | 1981–1999 | 2000–2014 | |||||
---|---|---|---|---|---|---|---|---|---|

Mean (m) | Mean (m) | % | Mean (m) | % | Mean (m) | % | Mean (m) | % | |

WLM | 31.72 | 32.76 | 3.29 | 31.66 | −0.19 | 32.85 | 3.56 | 31.77 | 0.16 |

WL | 24.44 | 25.32 | 3.58 | 24.91 | 1.91 | 25.30 | 3.52 | 25.02 | 2.37 |

WLm | 18.45 | 19.81 | 7.38 | 20.28 | 9.92 | 19.73 | 6.94 | 20.29 | 9.97 |

JAN | 19.34 | 20.75 | 7.29 | 21.18 | 9.52 | 20.73 | 7.16 | 21.13 | 9.26 |

FEB | 19.23 | 20.90 | 8.68 | 21.21 | 10.30 | 20.89 | 8.66 | 21.15 | 10.00 |

MAR | 20.22 | 22.06 | 9.10 | 22.46 | 11.08 | 21.98 | 8.69 | 22.48 | 11.20 |

APR | 22.87 | 24.07 | 5.25 | 23.60 | 3.18 | 24.10 | 5.37 | 23.65 | 3.42 |

MAY | 26.23 | 25.88 | −1.33 | 26.13 | −0.36 | 25.76 | −1.79 | 26.23 | 0.00 |

JUN | 27.14 | 27.94 | 2.95 | 28.09 | 3.48 | 27.84 | 2.58 | 28.19 | 3.85 |

JUL | 29.77 | 30.85 | 3.63 | 29.84 | 0.23 | 30.97 | 4.03 | 29.89 | 0.41 |

AUG | 28.59 | 29.70 | 3.88 | 29.02 | 1.51 | 29.77 | 4.13 | 29.06 | 1.66 |

SEP | 28.24 | 28.83 | 2.09 | 27.99 | −0.88 | 28.87 | 2.23 | 28.11 | −0.45 |

OCT | 26.87 | 26.87 | 0.00 | 24.80 | −7.69 | 26.90 | 0.12 | 25.18 | −6.30 |

NOV | 23.90 | 24.19 | 1.21 | 23.22 | −2.84 | 24.08 | 0.76 | 23.55 | −1.48 |

DEC | 20.93 | 21.78 | 4.06 | 21.40 | 2.23 | 21.71 | 3.71 | 21.56 | 3.00 |

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**MDPI and ACS Style**

Han, Q.; Zhang, S.; Huang, G.; Zhang, R.
Analysis of Long-Term Water Level Variation in Dongting Lake, China. *Water* **2016**, *8*, 306.
https://doi.org/10.3390/w8070306

**AMA Style**

Han Q, Zhang S, Huang G, Zhang R.
Analysis of Long-Term Water Level Variation in Dongting Lake, China. *Water*. 2016; 8(7):306.
https://doi.org/10.3390/w8070306

**Chicago/Turabian Style**

Han, Qiaoqian, Shuanghu Zhang, Guoxian Huang, and Rui Zhang.
2016. "Analysis of Long-Term Water Level Variation in Dongting Lake, China" *Water* 8, no. 7: 306.
https://doi.org/10.3390/w8070306