Study On Temperature Of Water Released By Selective Withdrawal From Large Reservoirs

A large area of backwater field is formed after a reservoir is built. Because ofradiation of the sunlight and physical chemistry characteristics of water, anenvironment which totally different from original river is formed, the character of thetemperature in reservoir is obviously distributed of seasonal stratification. Thetraditional bottom withdrawal from reservoir, especially the large reservoir, makes thetemperature of downstream lower than original water temperature, and thelower-temperature water will do harm to corps; suppress growth and propagation ofaquatic life; lengthen the time of released turbidity water. So more and more peoplepay high attention to the problems of lower-temperature water released, strengtheningthe study of low temperature of water released from large reservoirs. Selectivewithdrawal is a valid method to reduce the negative effect of lower-temperature waterreleased from the intake to the environment in downstream reach.This paper mainly composed of two parts: first, study the variation law of watertemperature released by selective withdrawal in large reservoirs used for hydropowerintake, use the simulation method, based on Nuozhadu Hydropower station, discussthe relationship among the water temperature distribution, the height of the stoploggate and the temperature of water released; second, study the variation law of watertemperature released by selective withdrawal in large reservoirs used for ecologicalenvironment, use the simulation method, based on Glen Canyon Dam, discuss therelationship among the water temperature distribution, the withdrawal elevation andthe temperature of water released. Finally summarize the regular conclusions of watertemperature released by selective withdrawal in large reservoirs, the results providethe theoretical basis for selective withdrawal in large reservoirs. The main contentsand conclusions of the study are as followed:(1) A comprehensive summary of temperature distribution and selectivewithdrawal in reservoirs was made. Aim at temperature distribution in reservoir,introduced the methods for defining, predicting and simulating the structure of watertemperature. Aim at selective withdrawal, introduced the types of selectivewithdrawal, and summaried the results from two aspects: model test and numericalsimulation.(2) This paper made an comprehensive introduction of the three-dimensional numerical model—Environmental Fluid Dynamics Code（EFDC）. Based on EFDC,the3-D numerical model simulating the temperature of water released was established.The model was calibrated and validated by the model test of water temperaturereleased from Nuozhadu hydropower station and the field data of water temperaturereleased from Glen Canyon Dam, and be proved that the model could better adapt tothe complex topographical condition of reservoir in front of the intakes, accuratelysimulated the temperature of water released from different types of selectivewithdrawal intake.(3) Aim at stoplog gate withdrawal, take Nuozhadu hydropower station as anexample, simulated the water temperature released of different stoplog gate schemefor three typical years. Studied the variation law of water temperature released bystoplog gate withdrawal, got the relationship among the water temperature distribution,height of the stoplog gate and the temperature of water released. Simulated the watertemperature released of different single unit discharge and combined opening turbine,discussed the effect of single unit discharge and combined opening turbine on watertemperature released.(4) Aim at multi-level withdrawal, take the Glen Canyon Dam as an example,simulated the water temperature released from surface intake and bottom intake.Study the variation law of water temperature released by multi-level withdrawal, getthe relationship amoung the water temperature distribution, withdrawal elevation andthe temperature of water released. Simulated the water temperature released ofdifferent single unit discharge and combined opening intake, discussed the effect ofdifferent single unit discharge and combined opening intake on water temperaturereleased.