Water Residence Time in a Typical Tributary Bay of the Three Gorges Reservoir

Yao Cheng,Yu Li,Haiyan Wang,Fengxia Zhao,Zheng Mu,Lei Lin

doi:10.3390/w11081585

Abstract

Tributary bays of the Three Gorges Reservoir (TGR) are suffering from environmental problems, e.g., eutrophication and algae bloom, which could be related to the limited water exchange capacity of the tributary bays. To understand and quantify the water exchange capacity of a tributary bay, this study investigated the water residence time (RT) in a typical tributary bay of TGR, i.e., the Zhuyi Bay (ZB), using numerical simulation and the adjoint method to obtain the RT. The results show that RT of ZB with an annual mean of 16.7 days increases from the bay mouth to the bay top where the maximum can reach 50 days. There is a significant seasonal variation in RT, with higher RT (average 20 days) in spring and autumn and lower RT (average < 5 days) in the summer. The sensitivity experiments show that the TGR water level regulation has a strong influence on RT. The increase in the water level could increase RT of ZB to some extent. Density currents induced by the temperature difference between the mainstream and tributaries play an important role in the water exchange of ZB, while the impacts of the river discharges and winds on RT are insignificant.

Highlights

The fate of chemical and biological species in aquatic systems is determined by the combination of transport and species-specific transformations [1]
The simulated velocity shows a pattern of density current where the velocity boundary thefurther fast gravity waveusing speed, the simulated water is highly with model forand
To understand the water exchange capacity of the tributary bay of Three Gorges Reservoir (TGR), this study investigated the spatiotemporal variation in residence time (RT) in one of typical tributary bay of TGR, i.e., Zhuyi Bay (ZB), using the numerical simulation and the adjoint method for obtaining RT

Summary

Introduction

The fate of chemical and biological species in aquatic systems is determined by the combination of (passive) transport and species-specific transformations [1]. Processes controlling planktonic biomass and contaminant distributions in semi-enclosed bodies are linked to the water transport timescales. The water transport timescales can be adapted to quantify the water exchange capacity of semi-enclosed water systems and quantify the transport rate of contaminants that are taking place in both the dissolved and adsorbed phases [5,6]. There are several defined transport timescales, namely (1) the flushing time, (2) the age, (3) the residence time (RT), and (4) the exposure time. The exposure time which is a concept extension of RT is defined as the cumulative time spent by the particle in the control domain, irrespective of its possible excursions out of ω [7,8,9,10,11].

Results

Discussion

Conclusion