Sustainable Improvement of Water Quality in Urban River Network by Rotating Overflow Weir—Case Study of Changzhou City in China

Abstract

Water diversion is a practical and commonly used approach to improve the water quality of rivers in urban plains in China. This paper researches using rotating overflow weirs as the primary engineering solution to facilitate water diversion and improve the water quality of the river network in urban plain area of Changzhou, including hydrodynamic modeling, field tests, and application. The water diversion scheme, including clean water source, water transfer paths, quantity, and rate, was designed based on its current terrain and river systems. The Yangtze River was selected as a high-quality water source, and its two tributaries were utilized as clean water paths. Four rotating overflow weirs were proposed to create three stages of hydraulic gradient. Clean water can flow naturally and orderly in the researched urban river network without pumps. The required clean headwater level and clean water distributions were modeled hydrodynamically. Four temporary weirs were constructed at design locations to conduct field tests. And the water diversion scheme and its water quality improvement had been verified by field tests. Afterward, four permanent rotating overflow weirs were built. Currently, the monitoring results show the design water transfer scheme reaches expectations. The flow velocity in most rivers has been increased to 7cm/s from standstill in Changzhou's main urban plain area. The composite water quality of 93% river cross-sections monitored has been improved from Class V to Class â…¢ and all have been improved to Class IV and above.