Water Quality Characteristics And Water Temperature Simulation Of A Canyon-shaped,Stratified,Source Water Reservoir

In order to study the seasonal thermal stratification,its water quality characteristics and the effects of meteorological and hydraulic conditions on the water temperature structure of the Heihe Jinpen Reservoir,the water temperature,dissolved oxygen,p H,conductivity,nitrogen and phosphorus nutrient were monitored continuously.Meanwhile,a 3-D water temperature model was established to simulate the thermal stratification based on the MIKE3 hydrodynamic module.The simulation results could provide the seasonal water temperature variation of the Heihe Jinpen Reservoir.The results showed that:(1)Heihe Jinpen Reservoir is a typical canyon-shaped,stratified reservoir,which shows a mixed single-cycle mixed pattern.From July to September,the reservoir forms a stable stratification,and the water quality stratified accordingly.From October to December,the thermal stratification weakened,and January to March is the mixing period,the water quality distribution is uniformed in the whole water body.(2)A 3-D water temperature model was established based on the MIKE3,simulation results of this model were verified by the field measured data.The simulation results could show the seasonal variations of the water temperature in Heihe Jinpen Reservoir.The maximum relative error between the calculated value and measured value was 5.4% while the mean relative error was 1.3%.(3)Effects of the meteorological and hydraulic conditions on the water temperature structure of Heihe Jinpen Reservoir was explored based on the 3-D water temperature model,results showed that while air temperature,solar shortwave radiation increased and inflow decreased,the potential energy value increased and the thermal stratification stability enhanced accordingly.On the contrary,the thermal stratification stability weakened.The simulations showed that higher air temperature could make the reservoir thermal stratification 15 days earlier and mixed time relatively 6 days longer.Meanwhile,the thermocline depth decreased to 1.62 m,thickness and gradient increased to 53.67 m and 0.46?/m respectively in the July.On the contrary,lower air temperature mak es the thermocline depth increased to 3.25 m,thickness and gradient decreased to 50.23 m and 0.24?/m respectively.A rise or drop in inflow temperature produced a corresponding rise or drop in hypolimnion temperature,while the thermocline had little variation.(4)The elevation change of outlet tunnel has significant influence on water temperature structure.That releasing water through a 10 m higher dam outlet tunnel caused 5m smaller thermocline thickness and 0.02?/m greater temperature gradient,while the thermocline thickness increased 5m and temperature gradient decreased 0.02?/m with a 10 m lower dam outlet tunnel inverse.Intake elevation changed produced thermocline varied accordingly,the whole water temperature in vertical decreased with the intake elevation increased while it increased inversely.The position of thermocline dropped with the intake elevation decreased,thermocline thickness increased and temperature gradient decreased accordingly,hypolimnion thickness decreased with the intake elevation decreased.(5)Compared the simulated water temperature with the measured value,the water-lifting aerator system could damage the thermal stratification effectively,which made the reservoir mixed two months earlier,formed a continuous mixing process in the natural state.Thus,good water quality could be maintained for a longer period.