Abstract: Water diversion is one of the most common methods to improve water quality in city river network. However, there is no uniform standard or system to evaluate the diversion effect. With Jianggan District of Hangzhou City as a case study, we built a one-dimensional river network model to simulate the water quality in different diversion cases, and assessed the effect of water quality improvement through the rate of water quality improvement, the category change index and concentration change index. Results showed that increasing water quantity could improve the water quality of the city rivers, however, the efficiency decreased with the increase of water quantity. Moreover, the improvement of source water quality is a crucial factor which affects the diversion effect as it could apparently improve the water quality of river network, and the rate of improvement also increased with the improvement of the source water quality.

Key words: city river network, quantity of water diversion, water quality model, improvement rate of water quality, efficiency assessment