Figure 1

Location and geological map of Lake East Dongting"

Figure 2

An example of how to measure the Changjiang River’s effect on its tributary lake, East Dongting (Lake ED). The QChangjiang in the legend is the runoff volume of the Changjiang River (m3/s), HLake is the water level of Lake ED (m), QLake is the discharge volume of Lake ED (m3/s). When runoff of the Changjiang River is in the 21,500-27,500 m3/s range, 15,500-21,500 m3/s range, and 9500-15,500 m3/s range, the rating curves of Lake ED fit well (R2=0.82, 0.86, 0.80, respectively) and are nearly parallel with each other. As noted, when the runoff of the Changjiang River decreases with a step interval of 6000 m3/s from 27,500 m3/s to 9500 m3/s, the lake water level drops by h1 (in the maximum river runoff range) and h2 m (in the minimum river runoff range) at equal lake discharge. Hence, we interpreted the distances, for example, h1 and h2, as the impact of the Changjiang River on the water level of Lake ED during specific hydrologic conditions."

Figure 3

Water level changes within Lake East Dongting during 1980-2014"

Figure 4

The effect of the Changjiang River on Lake East Dongting (Lake ED) at various runoff magnitudes. (a) The rating curves of Lake ED in various categories separated by the interval limitations of the Changjiang River runoff. The QChangjiang in the legend is the discharge of the Changjiang River (m3/s). (b) The spacing between adjacent lake rating curves, interpreted as the effect of the Changjiang River to Lake ED, at corresponding Changjiang River runoff magnitudes."

Figure 5

Comparison of the Changjiang River runoff in all four seasons between 1980-2002 and 2003-2014. (a), (b), (c) and (d) are the box plots illustrating the daily mean runoff of the Changjiang River in summer, autumn, winter and spring, respectively."

Figure 6

Comparison of the predicted Changjiang River component influences and the observed lake water level variations in all four seasons between 1980-2002 and 2003-2014"

Figure 7

Channel profile changes near the Chenglingji hydrologic station at the outlet of Lake East Dongting"

Table 1

Key parameters of linear trend analysis for the total inflow of Lake East Dongting from its four tributary rivers"

Figure 8

Variations of water levels in the reservoir of The Three Gorges Dam (using the situation in 2007 as an example)"