QUAL2K model used in the water quality assessment of Qiantang River, China.

Qiantang River, a subwatershed of the Yangzi River, in China, is one of the main rivers in Zhejiang province. Because the Qiantang River is polluted as a result of urbanization and industrialization, its biochemical oxygen demand (BOD) concentration is increasing gradually, so that it is necessary to use versatile water quality models to assess the BOD concentration and make policies for pollution control. The QUAL2K model was applied to evaluate the spatial distribution of BOD in the Qiantang River. It was calibrated and validated using the data between 2000 and 2004 as a low-flow condition. Wastewater quantity, curtailed 25%, and a BOD level below 30.0 mg/L were simulated using this model. It was found that wastewater treatment is an effective method to reduce BOD content in the Qiantang River during a low-flow period. Also, the results suggest that BOD total maximum daily loads should be established to control pollution effectively. The QUAL2K model can provide the basic knowledge for water quality assessment in this area.