Does water diversion project deteriorate the water quality of reservoir and downstream? A case-study in Danjiangkou reservoir

In response to water deficiency in Northern China, a scheme called the Middle Route Project was devised under the South-to-North Water Transfer Division to divert water from the Han River, the biggest tributary of the Yangtze River, to supply two provinces (Henan and Hebei) and two municipalities (Beijing and Tianjin) in the north. The minimum water qualityindex (WQImin) based on four water quality parameters and Mann-Kendall test methods were applied to determine the status of overall water quality inDanjiangkou reservoir (DKR) and downstream of Han River before and after the water intake (from 2006 to 2018). Results show that pH, dissolved oxygen, chemical oxygen demand, and ammonia nitrogen of water showed similar seasonal trends at the reservoir center, intaking place and downstream of Han River. According to WQImin index, the water quality status of most water samples at reservoir and downstream remained at good. After water diversion, water quality did not significantly differ from the status before intake at reservoir center. However, water quality was improved at intaking place and downstream. Inter-basin water diversion from reservoir did not deteriorate the local and downstream water quality, or significantly reduce the downstream flow discharge before it pours into Yangtze River. This study can inform other regions with serious water crises that both water diversion and local water quality can be preserved with appropriate environmental managements. •WQImin showed that the water quality status of most water samples at Danjiangkou Reservoir remained at good.•Water quality improved at intaking place and downstream during both dry and wet seasons.•Both water diversion and local water quality can be preserved with appropriate environmental managements.