Inexact Chance-Constrained Waste-Load Allocation Model for Water Quality Management of Xiangxihe River

In this study, an inexact chance-constrained waste-load allocation (ICWA) model is proposed for supporting river quality management under uncertainty that is capable of addressing uncertainties expressed as intervals and probability distributions as well as analyzing the reliability of satisfying (or the risk of violating) various constraints. The ICWA model is then applied to water quality management of the Xiangxihe River in the Three Gorges Reservoir Region, which faces severe water quality problems due to point and nonpoint source pollution. The results demonstrate that higher biological oxygen demand (BOD) discharge amounts are observed at the Baishahe chemical plant and Gufu wastewater treatment plant. Moreover, total phosphorus discharges into the river come mainly from point sources, particularly the chemical plants and phosphorus mining companies. For nonpoint sources, crop farming generates large amounts of total phosphorus and total nitrogen. Tradeoffs between economic benefits and system-failure risks are also examined. Alternatives can be obtained from different combinations of decision variables within their lower and upper bounds, which are valuable for decision makers, who need to develop the desired regional economic plans while satisfying environmental requirements.