Analysis on general variation of water quality in Chongqing reach after impoundment of Three Gorges Reservoir

Through statistical analysis on water quality monitoring data of main monitored sections in the Three Gorges reservoir from 2003 to 2009,the general water quality of the reservoir before and after impoundment is evaluated with single factor method and the change characteristics of water quality is reflected through the ratio of monthly water quality classification to annual water quality classification.The analysis results show that if fecal coliform is not considered,in general,the water quality in Chongqing reach was good,the water quality classification of most monitored sections was III or better,TN,CODmn and petroleum of a few sections in individual month and year exceeded the standard seriously;the ratio of III water classification of the main stem of Yangtze River rangeed between 58.9% and 80.56% during 2003 to 2009 and had a gentle increase tendency,and it ranged between 80.3% and 96.96% in the tributaries during 2004 to 2009 in a gentle variation tendency.In the 6 years after impoundment,the water quality in the reservoir had an improvement tendency.