| Estuary is located at the interfaces between ocean and river. Under the circumstance of global change and human activities becoming greater, the research of self-adjustment of estuary and channel to human activities is theoretically important. The total area of land reclamation on tidal flat in the North Branch of Yangtse estuary was 939.83 km2 for recent 50 years from 1956 to 2005. So study of self-adjustment of North Branch to land reclamation on tidal flat can provide important scientific basis for its sustainable development and protection of both the tidal flat and the channel. A set of nautical charts of Yangtse estuary from 1915 are digitized using GIS. Combined with measured data, river width, flow depth, width-depth ratio, section area, channel-fill volume, B.M. coefficient , channel gradient are calculated to characterize the self-adjustment of north branch channel to tidal flat. The results show that:(1) The sediment in upper channel is composed of coarse particle including fine particle. The sediment in lower channel is composed of fine particle including coarse particle. The gradient of middle channel is largestest and lower channel is smallest. It is corresponding to sediment diameter. B.M. coefficient increases from middle to lower of channel,the same as the vertical stability . (2) From 1915 to 2005, 15.9 billion m3 of sediment was deposited in channel, coastalline moved northward for 3 to 4km, maximum channel sedimentation height was 8 to 9m and narrowed for 5.75km, the decrement of sectional area reached 75 pecent and width-depth ratio changed from 25.3 of 1970 to 18.4 of 2005.A From 1915 to 1958, 3.7 billion m3 of sediments was deposited in channel, coastaline moved northward for 2km, channel deposited for 0.9m and narrowed for 1.45km, the maximum decrement of sectional area reached 97.8 pecent and width-depth ratio was 22.2. Channel morphology of eastern Touxinggang to Lianxinggang changed from straight to braided. The main influencing factors was flood current not runoff. Section configuration of Qinglonggang changed from W-shape to V-shape and Jiukuanghe changed from W-shape to U-shape. Sand bars swinged from Qinglonggang to Maojiagang.B From 1958 to 1991, 9.5 billion m~3 of sediment was deposited and the channel had severe sedimentation because of large-scale land reclamation on tidal flat. The coastaline moved northward for 1.3km, channel deposited for 1.4m and narrowed for 1.56km, width-depth ratio decreased from 22.2 to 21.1. Section configuration of Jiangxinsha changed from W to V and Qinglonggang recovered to W as Jiukuanghe. Sand bars swinged to river reach of Jiukuanghe to Denggangang. C From 1991 to 2005, 2.7billion m3 of sediment was deposited in channel, coastaline moved northward for 0.5km, channel deposited for 0.6m and narrowed for 0.82km, width-depth ratio decreased from 22.1 to 18.4. Section configuration of Qinglonggang and eastern Jiukuanghe changed from W to V and eastern Touxinggang changed from W toU. Sand bars swinged to river reach of Qinglonggang to Linggaoyan.(3) The land reclamation on the tidal flat around the North Branch is typical human activity of estuary. The self-adjustment of North Branch channel features as, tidal level ascends, the width-depth ratio decreases, channel morphology changes from wandering to braided and straight, sectional form has variation process from W to U and V, sand bars swings up and down, stability improves and the effect of flood current is obvious. The whole channel tends to be narrowing and depositing although the situation of widening and erosion appeared.In order to sustainably use tidal flat, my suggestion is to make land reclamation east to Santiaogang. It can improve channel morphology and decrease flood tide flow to 50 percent. Then North Branch can paly important role as drainage channel and will not disappear naturally.
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