Thermocline Thickness Changes On The Influence Of Density Flow Pattern

Although total volumes of fresh water resources are rich in China,they are unevenly distributed,the average per capita water is low,especially in the northern region,the lack of water resources is very prominent.The geographical environment in north China is special,especially in the Yellow River basin,storm runoff with high sand concentration is easy to form due to the loose soil and its scouring resistance.The thermal stratification occurs widely in reservoirs,the density currents can be formed when the inflow with high sand concentration enters into the reservoir,which influences the reservoir water quality.Lots of research has been carried out on the effects of inflow and stratification level on the density currents,but little has been reported on the effects of thickness of thermocline on the density currents.Using a physical model of stratified reservoir,the thicknesses of thermocline under various water depths were studied.Under strong and weak stratification levels,the varied inflow sand concentrations were chosen as 1.25 g/L?3.75 g/L?7.5g/L,the water depths were chosen as 45cm?50 cm?55cm?60cm?65cm?70cm,the generation and evolution processes of density currents were investigated,the separation depth of interflow,the hydraulic jump height,the depth of interflow,the distribution of sand concentration,and the sand discharge were analyzed under different conditions.Main conclusions are as followed:(1)In strongly-stratified reservoir waters,when the inflow sand concentrations were 1.25 g/L,3.75 g/L,7.5 g/L respectively,the vertical mixing was not obvious,the interface of clear and muddy waters was clear.When the thickness of thermocline was increased,the separation depth and thickness of interflow were all increased.The hydraulic jump was not obvious when the water depth was 45 cm,the hydraulic jump occurred if the water depth was more than 45 cm,and the height of hydraulic jump increased with the thickness of thermocline.If the water depths were low,the sand discharge capacity peaked at the water depth of 50 cm.If the water depths were high,the sand discharge capacity increased with the thickness of thermocline.(2)In weakly-stratified reservoir waters,when the inflow sand concentrations were 1.25 g/L,3.75 g/L,7.5 g/L respectively,the interflow propagated downwards with the running time,and penetrated the lower boundary of thermocline,vertical mixing was obvious,the interface of clear and muddy waters was not clear.When the thickness of thermocline was increased,the thickness of interflow and the height of hydraulic jump tended to increase,but the sand discharge capacity decreased.If the water depths were low,the separation depth of interflow increased with the thickness of thermocline.If the water depths were high,the separation depth of interflow decreased with the thickness of thermocline.(3)Comparing the parameters of density currents under strong and weak stratification levels,the stratification level mainly influenced the sand discharge capacity.under weakly-stratified conditions,the vertical mixing was strong,the deposited sand increased,and the sand discharge capacity obviously decreased.