Effect of the Three Gorges Dam Project on flood control in the Dongting Lake area, China, in a 1998-type flood

To evaluate the protective effect of the Three Gorges Dam Project (TGP) against flooding in the middle region of the Changjiang River basin, we applied an integrated watershed hydrological model using gauged daily precipitation data for 1998, when the second largest flood of the last century occurred in the basin. From the results simulated by applying the daily average discharge rate controlled by each of the upper limit values of 40,000, 45,000, 50,000, and 55,000 m3/s as the safety discharge in the downstream reach, we were unable to find any clear reduction effect on the water level during the flood period, not only in Dongting Lake, but also in the Changjiang mainstream, when the upper discharge limit exceeded 50,000 m3/s. When an upper discharge limit of 40,000 m3/s was used, although a flood protection effect was clearly exhibited in both the mainstream and the lake, the simulated storage volume of the TGP reservoir markedly exceeded the total flood control volume (221.5 × 108 m3) at the inflow peak. These results suggest that the TGP would not work efficiently for decreasing flood damage in the Dongting Lake area in the event of another 1998-type flood without other countermeasures to control the increased water level in the lake.