Reserch On The Influence Of Different Hydrodynamic Circulation Patterns Succesion Process And Algal Bloom Of Xiangxi Bay

Since the three Gorges Reservoir was impounded,the water environmental conditions of the reservoir area have changed,the eutrophication of the tributary bay water body,the frequent occurrence of algae problem,the slow down of the water flow velocity of the main tributaries in the reservoir area,and the change of the hydrodynamic condition are the important reasons.Xiangxi Bay is a typical first grade tributary of the three Gorges Reservoir.Algae erupts every year,and the water environment problem is prominent reason,which has been widely concerned by all walks of life and many scholars.Based on the CE-QUAL-W2,a mesh encrypted Xiangxi Bay model is constructed in this paper.The grid boundary conditions are established by sorting out a large number of measured data from 2010 to 2015,and the sensitivity parameters of the model are determined and verified.A model which can accurately reflect the actual situation of the dynamic water quality of Xiangxi Bay is obtained.By simulating the circulation model for many years,the dynamic succession process of the typical circulation model and its hydrodynamic water quality characteristics are analyzed,and the causes of the typical process and its influence on algal bloom is sensitive dynamic parameters are explored.The influence of typical process on algal bloom is analyzed.The main points and conclusions are as follows:(1)The CE-QUAL-W2 hydrodynamic water quality grid encryption model of Xiangxi Bay Bay of the three Gorges Reservoir is established.The relative error of the water level and storage capacity curve of the encrypted grid model is only 0.022.The hydrodynamic sensitivity parameters are determined,and the model hydrodynamic module can accurately simulate the water temperature structure of the reservoir bay.The spatial longitudinal velocity distribution reflects the stratified and heterogenous flow characteristics of Xiangxi Bay Kuwan water body.The model water quality module can simulate the chlorophyll a concentration,which is an important reference index of algal bloom risk.It can accurately reflect the change of chlorophyll a concentration.(2)In this paper,the in situ observation and numerical simulation of the circulation model in Xiangxi Bay from 2010 to 2015 are identified and defined.Eight typical circulation models are summarized,including the flow pattern,the water temperature structure,the retention time of the water body,and the vertical eddy current viscosity coefficient of the water body.The turbulent kinetic energy iso-hydrodynamic parameter angle represents the shape of the circulation model in the reservoir bay.This study explains the water temperature of the typical backflow mode in the lower reaches of the reservoir bay.The main reason for the different backflow modes is the difference of the water temperature among the main tributaries.When the water temperature of the main stream is higher than that of the surface water of the tributary water,the water temperature of the main stream enters the tributary with the surface inversion,for example,the water temperature of the main stream from June 27 to July 3,2010 is 0.37? higher than that of the tributary.The water temperature of the main stream between August 5 and August 19,2015 is always between the surface and middle layers of the tributary bay.(3)The variation of circulation model in Xiangxi Bay is mainly influenced by the variation of water temperature at the lower boundary of Xiangxi Bay.In 2010,the variation process of water temperature at the lower boundary is divided into three water temperature processes: water temperature warming period(March 11-July 13),water temperature fluctuation period(July).14-8 October,water temperature cooling period(October 9-December 31).In the period of water temperature rising from 11.2 ? to 24.6 ?,the water temperature of Xiangxi Bay only produces surface and upper layer backwater,and the circulation model is more complex in the period of water temperature fluctuation,when the water temperature of the main stream keeps rising,When the water temperature of the main stream suddenly decreases,the circulation model is transformed from the surface or the upper layer to the middle or lower layer,and the water temperature decreases from 23.8 ? to 16.6 ? during the cooling period of water temperature.The circulation model of Xiangxi Bay is mainly middle and lower layer inverted irrigation or bottom inverted irrigation.(4)The influence of the dynamic succession process of the circulation model on the water metamorphosis.With the change of the water temperature in the lower boundary,the circulation model changes correspondingly,but when the circulation model is converted from the middle and lower layers to the surface or upper layer,the concentration of chlorophyll a changes from increasing to decreasing.The highest point appeared around the inflection point of water temperature on August 9,with a value of 110.1mg / m3.When the circulation model changed from the surface to the lower layer,the concentration of chlorophyll a in the middle and lower reaches gradually increased,and the concentration of chlorophyll a in the middle and lower reaches gradually increased,and the concentration of chlorophyll a in the middle and lower reaches increased gradually.When the water temperature at the lower boundary increases,the circulation model changes from the middle and lower layers to the surface or the upper layer,the concentration of chlorophyll a decreases,and algal bloom disappears in time.Further eliminated the risk of algal bloom outbreak.