Impacts of flood events in coarse sediment-producing areas on channel siltation and fluvial process of the lower Yellow River

The method of multiple regression is used to analyze the influences of flood events from the coarse sediment producing areas on the channel siltation and fluvial process of the lower Yellow River based on the flood events from 1950 to 1985. The results showed that the flood events from the coarse sediment producing areas carry larger amounts of sediment load and coarser particle sizes than from other source areas, which increases deposition in the lower river channel. And there exist good correlations between channel siltation of the lower reaches of the Yellow River and the coming water and sediment of flood events from the coarse sediment producing areas. Through these correlations, the amounts of sediment deposition in the lower river channel could be roughly estimated based on the runoff and sediment load of flood events from the coarse sediment producing areas. The sediment deposition caused the fluvial process. There exists a complex response of channel form change to the coming water and sediment load of flood events from the coarse sediment producing areas. When the sediment concentration is smaller than 200kg/m(3), the ratio between wide-depth ratio after flood and wide-depth ratio before flood((B/h)(a)/(B/h)(b)) Will increase with the increase of the maximum sediment concentration; when the sediment concentration is near 200kg/m(3), (B/h)(a)/(B/h)(b) reaches the maximum value; and when the sediment concentration reaches the limits of hyperconcentrated flow, (B/h)(a)/(B/h)(b) will decrease with the increase of the maximum sediment concentration. Generally, flood events from the coarse sediment producing areas made channel form of the lower Yellow River deeper and narrower, but a large amount of sediment deposition simultaneously occurs. So, the impacts of flood events from the coarse sediment producing areas on the channel of the lower Yellow River are lessened.