Assessing and predicting water quality of outflow under water levefluctuation of the three gorges reservoir, china

Abstract

The Three Gorges Reservoir (TGR) has made a significant contribution to social and economic development and has vast effects on the aquatic environment. However, reservoirs can also pro-duce a negative impact on the environment. The Three Gorges Dam (TGD) started operation since 2003. TGR operates at a low water level for 145 m during flood season while the water level rises to 175 m during the non-flood season. Water level is an essential hydrological parameter impacting water quality. Continuous and periodical water level change makes the changes of water quality in reservoirs more complicated. This study examined water quality changes in the main channel outflow of the Yangtze River after (TGD) completion and analyzed its relationship with water level fluctuation (WLF). Results showed that water quality indicators (DO, CODMn, and NH3 –N) had cycli-cal changes for hydrological scheduling control, and water quality indicators at different water levels had significant differences, which reflected the response of water quality to reservoir scheduling. According to water quality index, TGR water quality was best at high water level and stayed worst at low water level. Predicting outcomes of the Auto-Regressive Integrated Moving Average model showed water quality would still keep a good level in the future. A comprehensive understanding of temporal variability in water quality and evaluation result will be helpful in investigating water quality at a high precision time for water management.