Effects Of Typical Meteorological Events On The Hydrodynamics,Water Temperature And Algal Bloom In Xiangxi River

Since the initial impounding of Three Gorges Reservoir?TGR?in2003,the tributaries of TGR burst into varying degrees of algae bloom.It is well known that outbreaks of blooms are closely related to meteorological conditions,flow conditions,water temperature conditions,sufficient nutrients and light.In order to analyze the influence of typical meteorological processes on the water temperature and bloom of the Xiangxi Bay?XXB?,the paper takes the XXB of TGR as the research object and carries out tracking and monitoring of rainfall and wind processes from July to August in 2019.The paper used the inertial dissipation method to calculate the characteristics of the turbulent flow near the surface of the XXB;and analyzed the influence of the meteorological process on the turbulent flow near the surface of the XXB based on turbulent flow characteristics;and analyzed the influence of water temperature from the aspects of heat flux and hydrodynamic;finally,based on the data of a monitoring process of algae bloom,the paper analyzed the impact of meteorological process on bloom from a small scale.The main conclusions of the research include:?1?From 2003 to 2016,the daily rainfall of the Xingshan Hydrological Station in the XXR Basin was between 0-160 mm and the annual rainfall was between 700-1400 mm.The rainfall levels were mostly moderate and light rain.Obvious mutation.The average daily wind speed of XXR in 2003-2016 is between 0-7m/s,of which the average daily wind speed in 2003-2008 is concentrated between 0-1m/s;the average daily wind speed in 2009-2016 is concentrated in 1-Between 2m/s,the average daily wind speed showed an overall upward trend,and after the Three Gorges Reservoir first impounded to the normal water level of 175 m at the end of the flood season in 2009,the wind speed increased significantly.?2?The high-frequency flow velocity data obtained by the ADV observation must undergo signal inspection,filtering,and denoising.The unprocessed data is not suitable for calculation of water flow characteristics and turbulence characteristics.From August 3 to August 18,the turbulent kinetic energy and dissipation rate of the surface layer of XXB varied from 4?10^-6-1.3?10^-3m²/s² and 1.1?10^-9-4.7?10^-5W/kg.The monitoring results show that the meteorological process enhances the surface wind and wave current is the main contributor for the enhancement of near surface turbulence.The intensity of the wind and waves on the surface of XXB is significantly increased during the wind,which promotes the intensity of the turbulence of the near surface water.During the rain,the wind and waves are suppressed by the rainfall,and the increase of the turbulence of the near surface water is not as obvious as that of the wind process.?3?Latent heat flux and net long-wave radiation flux are the two main heat loss terms in the water-gas interface heat flux.Long-wave net radiation flux is dominant,short-wave radiation flux is the heat source term,and sensible heat flux is related to heat flux.Very little contribution.The short-wave radiation flux and the increase in latent heat flux during the wind blowing cause the water body to radiate heat and the water surface temperature decreases,but it does not drive large-scale vertical convection,which promotes the water below the surface layer under the joint action of advection heat exchange and heat exchange of the lower water body.As the temperature rises,the water temperature of the water column gradually tends to be evenly distributed.According to the turbulent scale of the MoninObuhov turbulence,it can be seen that the wind-induced turbulent mixing is the main mixing method of the water during the wind;the short-wave radiation flux reduction during rainfall is the heat release of the water body The decrease in temperature drives vertical convection,and under the combined effect of advection heat transfer and bottom layer heat exchange,the water temperature of the water column gradually tends to be evenly distributed.According to the Moning-Obhov turbulence scale,it can be seen that the wind and rain to shear turbulent mixing and convective turbulent mixing during rainfall The combined action promotes the mixing of water.?4?The algae bloom is mainly affected by the depth of the mixed layer.The sudden drop of the mixed layer will be beneficial to the rapid proliferation of phytoplankton in the true light layer.In the Xiangxi River,the size of the wind has a significant effect on the strength of the bloom.When the wind speed is less than 7m/s,the wind speed increases,which is beneficial to the use of nutrient pulses caused by turbulent algae,which promotes the increase of the strength of the bloom and the larger volume.Cyanobacteria and diatoms are more likely to use nutrient pulses;when the wind speed is greater than 7m/s,algae migration and growth are affected by high-intensity turbulence,thereby suppressing the increase in bloom intensity.