Water Temperature Simulation Of A Stratified Source Water Reservoir And Optimal Operation Of Water-lifting Aerator System.

Jinpen Reservoir is a canyon-shaped source water reservoir with a deep water depth and stable thermal stratification.Based on the combination of numerical simulation,in-situ water quality monitoring and laboratory test,a study was carried out on Jinpen Reservoir.This research was mainly focused on the dynamic characteristics of thermal stratification and water quality;A 3-D water temperature model which suitable for Jinpen Reservoir was established to explore the influence factors of thermal stratification;The effect of destratification and oxygenation and destratification efficiency of water-lifting aerator system were studied,and the optimal scheme for system operation was proposed.The main research results and conclusions were as follows:(1)The dynamic characteristics of thermal stratification and water quality in Jinpen Reservoir were further explored.Jinpen Reservoir had a single mixed mode with a long stratification period and short mixing period.The height of anaerobic water layer was nearly 20 m at bottom in May.The rainstorm runoff could supplement dissolved oxygen to the water,but it did not break the thermal stratification.After the runoff,the bottom water would return to the anaerobic state.Long-term anaerobic condition aggravated the endogenous pollution,the maximum monthly average concentration of total nitrogen,total phosphorus,iron and manganese exceeded 2.2 times,1.52 times,3 times and 3.2 times of the standard limits of class III,respectively.(2)A 3-D water temperature model was established which suitable for Jinpen Reservoir,and the main influencing factors of thermal stratification were ascertained.The 3-D water temperature model was established based on MIKE 3.Combining the measured bathymetry,the grids were divided using a Sigma/ z-level method which was better adapted to the changes of bathymetry to improve the simulation accuracy.Based on the measured water temperature,the parameters of turbulence equations and heat budget equations were calibrated,and the model was verified.Combined with the meteorological and hydrological data from 2004 to 2016,the influences of different meteorological and hydrological on the thermal stratification of Jinpen Reservoir were simulated.Results showed that high inflow,low water level,low air temperature,low radiation,low inflow water temperature and deep withdrawal could reduce the thermal stratification stability the existence time of thermocline,thus reduce the risk of seasonal water quality deterioration caused by stratification.Inflow volume,water level and air temperature were the main factors affecting thermal stratification.Deep withdrawal could promote water mixing in autumn,and combined with water level control was a kind of scheme for reservoir operation.(3)The effect of destratification and oxygenation of water-lifting aerator system was studied,and the calculation method of destratification efficiency was established.Based on the 3-D water temperature model,the changes of thermal stratification under natural state during the system operation were simulated.Compared with the measured data,results showed that the system operation could effectively weaken thermal stratification and promote water mixing.The oxygenation effect was very obvious,the bottom anaerobic layer disappeared at the end of system operation and dissolved oxygen supersaturated area emerged.The calculation method of destratification efficiency was established,calculation results showed that compared with other technologies,the water-lifting aerator had higher destratification efficiency and wider scope of application.(4)The scheme for optimizing operation was put forward.Based on the destratification and oxygenation function of water-lifting aerator,and taking into account the main influencing factors of thermal stratification in different seasons,the optimization scheme for system operation at different periods was put forward.In spring,system operation was mainly focused on the anaerobic problem and reduced surface water temperature to prevent algal blooms.In summer,system operation was mainly for algae control bottom anaerobic problems after rainstorm runoff.In autumn,system operation was mainly for destratification,and achieved the effective connection between artificial force mixing and natural mixing to improve water quality continuously.The scheme covered each period of stratification which could provide scientific and reasonable guidance for system operation.