The Changjiang river is rich in sediment supply which exerts an important influence on development of the Changjiang delta, evolution of shoals and channels in the estuary, realignment and utilization of the estuary. Trend analysis and period analysis on the sediment transport series at Datong Station state that an obvious decrease trend has emerged in the annual series of sediment transport at Datong Station although the sediment discharge at Yichang Station and the annual runoff series at Datong Station have little change trend. The situation is mainly related to shoaling of Dongting Lake, Poyang Lake and other lakes. The sediment-producing region is mostly located in the upper reach and sediment-producing effect of upper, middle and lower reaches is obviously different, so that sediment transporting situation is responded with runoff discharge only about 30% of years in the series. As for monthly distribution of sediment discharge, some 87.7% of suspension loads are discharged through the Datong section from May to Octorber. In addition, the matching status of sediment discharge between flood and dry seasons is preliminarily analyzed in the paper.
Based on the analysis of the observation we organized in August of 2000 off the Changjiag mouth,we found for the first time that there exists upwelling phenomenon at Lusi fish ground.The upwelling can bring the colder water and nutrient from the lower layer to the upper layer,and has an important effect on the environment and ecosystem.In order to understand the dynamic mechanism of the upwelling phenomenon,we used a three-dimension high resolution turbulent closure circulation model in spherical coordinates based on the modified ECOM_si model to study this upwelling.The calculated domain includes the East China Sea,Yellow Sea and Bohai Sea,and the real coastline and water depth were considered.In the case of considering all dynamic factors (water volume flux at the open boundaries,density gradient forcing and wind stress),the numerical model reconstructed successfully the upwelling phenomenon which is fairly consistent with the observations.The numerical experiments show that the dynamic mechanism of the upwelling is mainly produced by the baroclinic effect that is induced by the mixing between fresh water from the Changjiang River and the saline water.The wind stress has a little effect on it,and the water volume flux at open boundaries has no effect on it.The combination force of the slop of bottom with the baroclinic effect and wind stress makes the upwelling stronger.
This paper gives a solution to the problem of estimating coeffcients of index model in a time series. The kernel estimate method and the average derivative method are employed. Under the data being β-mixing depentent,the asymptotic normality of the estimator are established.