The significant water level reduction by the TGD's impoundment in the late flood season from September to October also accelerated the recession of the mainstream river and resulted in an earlier dry season in the Middle Yangtze. The lowering rate of daily water level increased significantly in the first half period of water storing from mid-September to mid-October (Figure 6). Specifically, the lowering rates in the main stream increased from 0.065 m/d to 0.123 m/d at Luoshan, from 0.067 m/d to 0.115 m/d at Hankou, and from 0.047 m/d to 0.080 m/d at Datong. Both Dongting and Poyang lakes had a fast lowering rate. They increased from 0.058 to 0.114 m/d at Chenglingji in Dongting Lake and from 0.063 m 0.105 m at Hukou in Poyang Lake (Table 2). In general, the lowering rates have almost doubled the natural rates due to the TGD's impoundment.
Table 2
Changes in the Yangtze River recession caused by the Three Gorges Dam
| Lowering rate of water level (m/d) | Low flow | |||
|---|---|---|---|---|
| Stations | Measured rate with the TGD | Restored rate without the TGD | Characteristic low water level (CLWL) (m) | Preceding days of its first appearing date of CLWL |
| Luoshan | 0.123 | 0.065 | 22.83 | 20 |
| Hankou | 0.115 | 0.067 | 18.26 | 16 |
| Datong | 0.080 | 0.047 | 7.93 | 12 |
| Chenglingji | 0.114 | 0.058 | 23.87 | 34 |
| Hukou | 0.105 | 0.063 | 11.94 | 13 |
| Lowering rate of water level (m/d) | Low flow | |||
|---|---|---|---|---|
| Stations | Measured rate with the TGD | Restored rate without the TGD | Characteristic low water level (CLWL) (m) | Preceding days of its first appearing date of CLWL |
| Luoshan | 0.123 | 0.065 | 22.83 | 20 |
| Hankou | 0.115 | 0.067 | 18.26 | 16 |
| Datong | 0.080 | 0.047 | 7.93 | 12 |
| Chenglingji | 0.114 | 0.058 | 23.87 | 34 |
| Hukou | 0.105 | 0.063 | 11.94 | 13 |
Figure 6
The earlier lowering of water level in late flood season due to the TGD's impoundment. The measured (with the TGD) and restored (without the TGD) water levels clearly show the rapid and earlier drawdown of the Middle Yangtze River.