The assimilative capacity of Qiantang River watershed, China

The Qiantang River, located in Zhejiang Province, China, is a major water supplier to a highly populated region for multiple uses. With economic development, the received pollutants exceeded its assimilative capacity, leading to algal blooms or fish kills. This study was an up‐to‐date evaluation of the assimilative capacity of the Qiantang River, investigating the influence of stream flow. A confidence of 75 and 90% of instream flows were selected as the design flows, while the traditional one‐dimensional point discharge model and QUAL2K model were used to analyse biochemical oxygen demand (BOD) assimilative capacity. The results showed that the assimilative capacity of 75% confidence instream flow was larger than that of 90% confidence. The assimilative capacity based on QUAL2K model considered almost all rates of BOD gain and loss, which were larger than that of one‐dimensional point discharge model. The total amount of BOD discharged into Qiantang River was 17 1283 t·a⁻¹ in 2004. Under 75 and 90% confidence river flow conditions, the calculated total BOD reduction percentage of the whole river was 38.2 and 55.9%, respectively. Furthermore, the results were used as criteria for developing a BOD total maximum daily load (TMDL) in order to achieve the sustainable use of water resources derived from Qiantang River watershed. Copyright © 2012 CIWEM.