Circulation Pattern Succesions And Environmental Consequences Of Xiangxi Bay In Flood Season

In the flood season,the water level of the Three Gorges Reservoir area fluctuated frequently due to flood control operations,and the hydrodynamics and water environment of tributary reservoir bays have undergone tremendous changes.In order to gain an in-depth understanding of the frequent evolution of hydrodynamic forces in tributary reservoir bays during the flood season and its response mechanism to the external environment,In this paper,based on the CE-QUAL-W2 model and fluid mechanics theory,the continuous numerical simulation of the hydrodynamic water temperature of the Xiangxi River Bay in flood season.The hydrodynamic process of the Xiangxi River Bay in the flood season is analyzed to clarify the driving mechanism of the change of the water environment factors of the Bay Bay caused by the hydrodynamic force of the Xiangxi River Bay.(1)By collating a large number of measured data(2015-2018),the grid boundary conditions of the CE-QUAL-W2 hydrodynamic model of the Xiangxi River Bay in the flood season are established.By calibrating and verifying the sensitivity parameters of the model,a model that can accurately reflect the actual situation of hydrodynamic water temperature of Xiangxi River is obtained.Verification of water temperature and flow rate was carried out.The water temperature verification effect is better.Except for the upstream XX09,the absolute average error of XX01 and XX06 are both less than 1 ?,which is within the acceptable range.The simulation effect of XX01 is the best,AME is within 0.5 ?.The flow rate is verified by comparing the measured flow rate and the simulated flow rate in the 2015-2018 flood season,Select the flow velocity chart of the longitudinal section of the Xiangxi River during the 2015-2018 flood season for verification,.From June 16,2017 to July 24,2017,the Xiangxi River was tracked and monitored,and the vertical flow rate at point XX05 was monitored day by day.The vertical flow rate of XX05 during this period was selected for comparative verification.Looking at the flow rate comprehensively,it is better to verify.(2)Based on the ten classic circulation models and fluid mechanics theory of the Xiangxi River,the in-situ observation and numerical simulation of the Xiangxi River Reservoir Bay circulation model during the 2015 to 2018 flood season were re-identified and defined.Seven types of circulation patterns and intermediate states of flood seasons are defined,which provides a more intuitive display of the continuity study of subsequent circulation evolution processes in flood seasons.Through the analysis of the measured and simulated data,combined with the seven circulation evolution models and the intermediate state of evolution,three kinds of evolution processes that frequently occur in the flood season are summarized: the circulation evolution process of the middle and upper layer reverse irrigation evolves into the surface layer reverse irrigation;the middle and upper layer reverse irrigation evolves into the middle and lower layer Circulation evolution process of reverse irrigation;the middle and lower layers of reverse irrigation evolved into the cyclic circulation evolution of surface reverse irrigation.Since the upper reaches of the Xiangxi River and the reservoir bay in the flood season are all low-temperature inflows,the upstream of the flood seasons all show downhill inflows.(3)Based on the calculation results of the CE-QUAL-W2 hydrodynamic model and the inductive definitions of the three types of circulation evolution in the flood season,the analysis of different indicators characterizing the stratification structure of the water body is carried out.In the two circulation evolution processes where middle and upper layer reverse irrigation evolves into surface layer reverse irrigation and middle and lower layer reverse irrigation evolves into surface layer reverse irrigation,the middle and upper layer water body is mixed strongly.Significantly increased.The turbulent kinetic energy of the reservoir bay showed an overall increasing trend when the mid-upper-layer reverse irrigation evolved into the middle-lower-layer reverse irrigation,and the middle-lower layer of water was mixed more strongly.By analyzing the hydrodynamic parameters,it can be found that the two types of circulation evolution,which is the evolution of the upper and lower backflow into the surface,and the lower and middle backflow into the surface,are more conducive to changing the stratified structure and hydrodynamic characteristics of the water body;The circulation evolution process from upper-middle-level upside-down to middle-lower-level backflow has little effect on the original conformation structure and hydrodynamic characteristics of the water body,and the water environment is relatively stable.(4)In the two circulation evolution processes where middle and upper layer reverse irrigation evolves into surface layer reverse irrigation and middle and lower layer reverse irrigation evolves into surface layer reverse irrigation,The surface water body is greatly affected by the reverse irrigation flow,which strengthens the water body disturbance,destroys the water body stability,and weakens the water temperature stratification in the upper and middle reservoir bays.The reduced depth of the mixed layer is not conducive to the growth of some algae,resulting in a decrease in the concentration of chlorophyll a.In the flood season,the upper and lower layers of the Xiangxi Bay evolved into the middle and lower layers of reverse circulation.During the circulation evolution,the surface water temperature was not affected by the reverse irrigation,the water temperature was strongly stratified,and the depth of the mixed layer was reduced,which was beneficial to the outbreak of blooms.The risk of bloom is greater,leading to an increase in chlorophyll a concentration.