Data Mining-Based Characteristics Of Flow And Sediment Transport In Qiantang Estuary

The Qiantang River estuary is the most representative estuary with strong tide, because of it's strong tide, tidal bore and the tempestuously change of erosion-deposit on the river bed. It is always an important basic work of estuary treatments and protection that researching and using the hydraulic characteristics of water and sediment movement at the Qiantang River estuary. The hydraulic characteristics aforementioned are developed by methods, such as analysis of field data, numerical model and physical model and a series of achievements are obtained basing on the past studies. Recently, the modern data analysis technologies, such as gray theory, neural network, fractal theory and wavelet analysis, provide a new approaching methods and thinking for the studies on hydraulic characteristics.In this paper, the characteristics of run off of the Qiantang estuary, bore, sediment-moving incipient velocity, sedimentation velocity of fine sediment, the sediment carrying capacity of tide and riverbed scouring-siltation are discussed by new data analysis technologies, wavelet analysis, neural network and the combination of the later two methods, theoretical analysis and experimental research, basing on the past studies. And it also provides a technological support for the Qiantang River estuary treatment and important wading water management projects. The mainly work contents are as below:(1) The model for predicting the height of tidal bore basing on neural network. According to complex non-linear relationship between the tidal height of the Qiantang bore, sediment-moving incipient velocity, flocculation and sedimentation velocity of fine sediment and sediment carrying capacity of tide and their influence factors, a predicting model is established by RBF (Radial Basis Function) basing on identifying the major influence factors and improving the representativeness of learning sample. The comparison of the simulated results with the observation data shows that the model has good generalization ability and it is successfully adopted to quantitatively analyze the contributions of each influence factor.(2)Study on hydrodynamic force and long-periodic feature of riverbed scouring-siltation by wavelet analysis. In accordance with the non-stationary hydrological time series and topographical data, the wavelet method was adopted to analyze the periodic feature and the trend of the runoff in the Qiantang estuary. The complex Morlet function, whose basic characteristic is discussed, is selected to transform the standardized time-series of the annual runoff discharge. Basing on the distribution of module and real of wavelet transform coefficients and wavelet variance, the prominent period of the annual runoff discharge in the Qiantang River estuary is 21 years approximately, and it is predicted that the trend of the annual flow is in the low flow period till 2010, and then the annual discharge is increase. According to the prominent period, the long-term evolution model of water and sediment movement at the Qiantang River estuary is proposed.(3)Study on response of height of tidal bore to influence factors and regulation works. Based on qualitatively analyzing influence factors, the model for predicting the height of tidal bore at Yanguan is established by using BP neural network. The comparison of the simulated results with the observation data shows that the model has good generalization ability. Combining the theory of orthogonal experiment design, the major affecting factors such as tide, runoff and river topography are quantitatively analyzed. It is found that the height of tidal bore is positively related to the tide, and negatively related to the river topography. The height of tidal bore is positively related to the runoff when the discharge is less than 7000m3/s. However they are negative correlation relationship if the discharge is greater than 7000m3/s. Then the model is used in a case to study on the effect of large-scale reclamation and regulation works on the tidal bore in the Qiantang estuary. The influence extent to the bore height at Yanguan is quantitatively analyzed under different hydrodynamic and river-bed condition. The results show that the bore height decreased by 0.17m after reclamation under straight alignment of river course, and increased by 0.39m under curved alignment of river course.(4) Study on empirical formula of incipient velocity of fine sediment, sedimentation velocity, sediment carrying capacity of tide. Basing on Large amounts of field data and experimental results, the empirical formulas are established by dimensional analysis and multiple regression analysis, which adapt the flow characteristics of Qiantang River estuary. Comparison with the field data and experimental results, it indicates that computation results by the formulas have a good agreement and application extent. In this paper, a method for deciding incipient velocity of sediment and sediment carrying capacity of tide through a non-stationary flow and sediment process is established.(5)Study on prediction model for riverbed volume by wavelet analysis and neural network. Due to the change of riverbed volume has characteristics of tendency, periodicity, randomness, a prediction model for riverbed volume of the Qiantang River estuary is established by using the technologies of wavelet analysis and neural network. Comparison with the field data, the model reaches 97.5% and 88.2% accuracy rate in fitting and testing process and 0.90 and 0.71 coefficient of determination, respectively. The computation results are acceptable and it provides a feasible technical solution for riverbed volume prediction.