6. Conclusions
Through comparative analysis of the water area of Poyang Lake in the
past 42 years, draw these conclusions:
1. During the 1977 to 2021 flood season, lake water areas at
−9.14km2/a have a significant downward trend. In the
dry season, the lake water area showed a significant downward trend with
the rate of −17.52km2/a. The change point years of
flood season water area are 2005 and dry season water is 2003.
2. Lake runoff, sediment, and precipitation significantly correlate with
flood season water area. In the dry season, the sediment significantly
correlates with the water area.
3. The analysis of satellite imagery confirms that in flood season,
there is a direct correlation between the change of water area and the
change of net outflow of the lake, and the net outflow is affected by
river-lake interaction. Poyang lake is a classical river-connected drain
lake. Flood or drought events in the mainstream of the Yangtze River
will affect the blocking or reversing of the Yangtze River on the Poyang
lake estuary, which affects the change of net outflow of the lake
bringing the changes in water area.
4. In the dry season, based on the analysis of image and land use, the
sediment deposition at the elevation of the estuarine entrance lake
lakebed is raised, especially at the Ganjiang river estuary, affecting
the water body shape. Meanwhile, after 2000, the TGD water impoundment
operation at the end of the flood season on the upper Yangtze river
affected the runoff of the lower reaches of the Yangtze River. That
impaired the river lake interaction, made the area of Poyang Lake shrink
in advance, made the water area shrank in advance, and affected the
water area in the dry season.
Results show that the variation of water area in Poyang Lake is not only
affected by the runoff of the Poyang Lake basin but also by the runoff
of the Yangtze River main stream and the sediment inside the Poyang Lake
basin.
The downside does not consider the groundwater’s effect. Therefore, the
water resource utilization in the Poyang Lake basin needs to consider
the changes in the lake basin and the runoff outside the basin.