Stagnant water environmental management in urban river networks: An integrated risk analysis involving hydraulic potential dissipation

Abstract

Rapid urbanization has led to water stagnation by temporal and spatial imbalances of the hydrodynamics in urban river networks, which further entails environmental risks to drinking and recreational water supplies. The establishment of a succinct hydraulic potential dissipation (HPD) index to indicate the spatiotemporal stagnant water environmental risks quickly and intuitively is of vital significance to urban river networks with complicated water regimes and diversified water diversion measures. On this basis, an integrated stagnant water environmental risk analysis model (ISWERA) was established by coupling the process-based model and stochastic process to comprehensively and accurately assess risks, which has been calibrated and validated against the real data of 11 monitoring stations from May 3 to May 11 in 2017 and November 28 to December 10 in 2020, respectively. To represent the rationality of stagnant water environmental risks assessment using HPD, ISWERA was used to evaluate the temporal- and spatial-varying stagnant water environmental risk intensity and probability of 270 water diversion schemes formed by the combination of water diversion duration, flow, route, and potential in the Changzhou urban river network along the Yangtze River. For time-varying results, it revealed that cumulative risk intensity was reduced by nearly 15%, and risk probability was significantly reduced by nearly 50% with the increase of diversion duration to 5 days in general. For spatial-varying results, most of the rivers reached the low-risk grade under the optimized diversion duration, flow, route, and potential. While the rivers adjacent to densely populated areas still presented a moderate-risk state. The positive correlation was significant between HPD and stagnant water environmental risk intensity and probability results, with R2 = 0.86 and 0.74 respectively. When the HPD of upstream channels are below 63.4%, 74.1%, and 57.7% and the downstream HPD of S1 to T1, S2 to T2, S2 to T3, and S3 to T4 are below 40.6%, 32.9%, 22.4%, and 19.1%, respectively, the stagnant water environmental risk is lower. Arguably, this study could provide a scientific reference and foundation for water environmental management of similar urban stagnant water systems.