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 center dot 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.