Analysis On Evolution Process Of North Channel Of The Changjiang Estuary

There are three-order bifurcations and four outlets into the sea in the Changjiang Estuary, and the North Channel is the northern one of the second order bifurcations, it is one of the main channels into the sea. Because the North Channel is not the main channel into sea for the big shipping, there is a little study for the North Channel in the past 20 years. Several bathymetric maps of the North Channel since the 1970s were digitized and Digital Elevation Models of the various years were built with the method of Kriging. Then analysis for the changes of the cross sections, contours, thalwegs and volumes of river channel were made according to the DEM. On the basis of the former research, the process of the North Channel morphology was illustrated and the reason of the evolution was analyzed summarily. There are several cognitions after analyzing: 1. The change of the upper channel of the North Channel is correlated to change of the transverse slope caused by change of the flow resistance and the loose boundary conditions. 2. Liuxiao sand ridge in the main channel of the North Channel was formed of the sands cut from the Nanmen marginal bank of Chongming Island in the beginning of the 1980s. 3. There are three periods in the process of North Channel since the 1970s: (1) the period of instability (1972—1985); (2) the period of readjustment (1985-1996); (3) the period of relative stability (1996-now) . 4. A sand ridge was formed of the sands moved from the upper river channel and move downstream constantly in the recent years and the downstream segment of the North Channel changed into a multiple system channel 5. The process of the downstream channel is restricted by the process of the upstream channel, there is a lagging effect in the process of the upstream channel infecting the downstream channel. 6. The influence of the flood is important to the evolution of the regional North Channel. The resultsof this paper can offer scientific reference in the North Channel development and utilization.