Impact of flood events on water quality of the Biliuhe reservoir

The frequency of ex tr eme floo ds is increasing due to t he impact of g lo bal climate chang e. Reser voirs, as an important water co nser vancy project , suffer ed fr om serious w ater qualit y problems during flo od ev ents in the river basin. This study too k the Biliuhe r eser vo ir as an example and analysed the water quality data befo re and after seven flo od events since the dam w as co nstr ucted. T he r esults show ed that floo ds could w eaken the thermal str atification o f the Biliuhe reser voir and influence the vert ical distribution of disso lv ed ox yg en. Flood ev ents had gr eat impacts o n water quality v ariables of hex avalent chrom ium, coli2 fo rm bacteria, permang anate index , ammonia and t otal phospho rus, w hich had incr eased aft er the floo d event. In terms of spatial distribut ions, the concentr ation of po llutants at the entr ance section of t he r eser vo ir w as gr eater than the fr ont of the dam. T he topog raphic characteristics o f the Biliuhe r eser voir could w eaken the impact of floo d density flow o n the w ater quality in fro nt of the dam. T he assessment results indicated that the w ater qualit y gr ade of the r eser voir become w orse after the flood, but it meet the env iro nmental quality standards for surface water. The po llutants ent ering the reserv oir during f loo ds mainly come fr om the no n2point so ur ce pollution in the Biliuhe r eser vo ir basin. The countermeasur es such as contro lling non2point so ur ce po llutants, intercept ion at the entr ance o f the reservo ir, reasonable r egulation during flo ods pro cess could alleviate the im pact of floo d e2 v ents on the wat er quality o f the Biliuhe r eservo ir.

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