Parametric Sensitivity Analysis Of The Water Quality Seasonal Variation Simulation In The Three Gorges Reservoir Area

Sensitivity analysis is a primary approach used in water quality models to identify important parameters which control the response in the model,allowing a reduction of parameters incorporated in the model.Based on the related literature about the sensitivity analysis of dynamic models an ecological dynamic model was established and verified to identify the sensitivity of parameters in the model with the local method(Perturbation method)and global methods(Sobol' sensitivity analysis)in Caotang River and the distribution rules of chlorophyll and nutrient in the river is conclude.The main research results are as follows:(1)The concentration of the chlorophyll in the water is higher in autumn and spring and the chlorophyll is distributed in the surface of water body.Research found that there is some correlation between the blooms and the distribution of nutrients or dissolved oxygen in the water.But it is not a single or stable correlation and the result shows the reasons of blooms are randomness and complexity.(2)A simple water quality model is established which belong to box-type model in this study.The model includes the water ecological and material exchange.The model was verified by setting the full year chlorophyll concentration in the water as an example and the simulation result is acceptable and reasonable except the results of March and May which have a larger error.(3)The local and global methods are used to research the sensitivity of parameters in the model which the concentrations of chlorophyll and dissolved oxygen are the objective functions of the model.The results of the sensitivity analysis are different in both methods.The level and variation of sensitivity result are both different which show that the interaction between parameters is not negligible.(4)The sensitivity result of the same parameter is different when the model result comes to the different objective function in both local and global methods.The sensitivity of same parameter in same objective function would change at different times.The sensitivity of parameters are different with each other when the objective function is different in the model which show that the specific parameters need to be analyzed when the model need to be calibrated.(5)The parameters ananlysis results show that growth rate,mortality rate and respiration rate of phytoplankton are directly related to the growth process of the phytoplankton.The parameters such as illumination and water temperature also do a big affect to the output of the model which should be given priority in parameter ratesetting.(6)The correlation between the sensitivity of parameters and the seasonal variation of the ecological elements in the water body is analyzed.The result shows that the correlation is different and the results are segmented into positive and negative.The correlations are also different even it comes to the same parameter and ecological element when the results under the different objective function which can provide general directions for the adjustment of parameters in the modle.