Simulated sediment flux during 1998 big-flood of the Yangtze (Changjiang) River, China

Abstract

The present study focuses on simulating sediment flux for 1998 big-flood with 60-year recurrent period in the Yangtze River catchment. On the basis of close correlation between discharge and sediment load recorded on the daily base of the past decades at a series of hydrological gauging stations located in the Yangtze River, the sediment rating curve of 1987/1988 was selected to simulate the annual and flood season sediment fluxes of 1998, when measured discharge was available in the most gauging stations. The result indicates that enormous sediment load was delivered downstream and to the estuary during the flood year. The simulated annual sediment flux was about 930 million-tonnes in the upper drainage basin, about 520 million-tonnes in the middle catchment and 720 million-tonnes in the lower drainage basin. These loads, respectively, approximate almost 1.9, 1.2, and 1.8 times those of the multiyearly sediment flux in the upper, middle and lower Yangtze catchments for the past decades. The result also indicates a unique pattern of sediment transport downstream through the drainage basin during the high flow season (early July to mid-September). While the upper Yangtze tributaries delivered about 580 million-tonnes of sediment downstream, the 3-Gorges valley added additional 270 million-tonnes. This totals about 850 million-tonnes that supplied the middle and lower Yangtze catchments, of which about 450 million-tonnes were silted in the middle catchments, immediately downstream of the exit of 3-Gorges. This amount is almost 6.5 times the normal flood season averaged over the last 50 years. High sediment load was also recorded in the river mouth area during the flood season, where 460 million-tonnes were delivered to the estuary and East China Sea, about 3.8 times that in a normal flood season. Intensifying human activity in the upper catchment is responsible for the large amount sediment sources delivered downstream and to the coastal region.