Author(s): Baiyinbaoligao; Fengran Xu; Xingru Chen; Tong Chang
Keywords: Sediment flushing; Sediment concentration; Dissolved oxygen; Yellow River Carp; Mortality
Abstract: Dam sediment flushing can help mitigating reservoir sedimentation and restoring river consecutive sediment transportation. But high concentrated sediment flow and water quality degradation may cause adverse effects on downstream fish. During sediment flushing of the Xiaolangdi Reservoir in the Yellow River, dead fish were usually observed in downstream river reach. Explains for the phenomenon were studied by field survey and laboratory experiments. In the process of sediment flushing in 2010, high concentrated sediment flow destroyed downstream river habitat. Investigation showed 11 fish species from 5 families and 5 orders were affected by the lethal sediment concentration. 7 laboratory experiments were carried out with Yellow River Carp (Cyprinus carpio) exposed in water body with suspended sediment concentration ranging from 16 to 182 kg/m3. Influences of sediment concentration, dissolved oxygen (DO) and exposure duration on mortality were analyzed. It could be demonstrated, by variation process of sediment concentration and DO from field and laboratory study, that high concentrated fine sediment flow, which caused the clogging of fish gills, and DO decline were 2 crucial reasons for fish mortality. When the sediment content was higher than 80 kg/m3, the dissolved oxygen concentration fell below 2 mg/L, which was a lower limit for fish living requirements. In this circumstance, fish went to death in a short period caused by hypoxia. While sediment content was lower than 60 kg/m3, by survey and experience, there were no dead fish in downstream river reach. There is a direct correlation between DO and sediment concentration downstream of the reservoir during sediment flushing period, which means that DO would decrease with the increase of sediment concentration. Thus, it was discussed and concluded that environmental friendly dam regulation method should be carried out considering sediment concentration and duration of dam flushing to relieve adverse effects on downstream fish.