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The Three Gorges area of the Yangtze River located between the Sichuan Basin and the Jianghanplain is a highly dissected mountainous area which geomorphology is very complex.Composedmainly of high mountains and mid-altitudes mountains, the Three Gorges area present landscapeis a conjugation of the eroding action of rivers running down the Daba Mountains and thedifferent anticlines and the resistance of the lithology to these actions.
Through the analysis of the morphometric properties of the drainage basin it is possible to shed alight on the always-evolving landscape of the area.The area of the Three Gorges is occupied byriver of different sizes that feature 3 types of drainage patterns: dendritic drainage patterns at thefoot of the Huangling anticlines and the low altitude rivers, parallel drainage pattern at thenorthern part of the area west of the Wu Gorge, and trellis drainage pattern at the southern part ofthe area.Those drainage patterns show the effect of the control of lithology and structure in theinitiation and development of rivers.If the dendritic drainage pattern is the result of normalevolution on granitic rocks, the parallel drainage pattern shows the development of rivers in thedifferent synclines and their interconnections later through drainage piracy.The rivers whileinitiating followed the slope of the Daba Mountains, which is N-S.Therefore, all the riversflowing to the Yangtze from the north at their initiation have an N-S orientation that they stillhave.Eroding upwards, they integrated progressively the different drainage basins oriented W-E.
The Southern area, which does not show this pattern of succession of anticlines and synclines,developed normally by headwater erosion.In this section of the area, neo-tectonics seems tohave been very important.The southeastern region as analyzed in this thesis is characterized bytectonic uplift that had as result the integration to the Yangtze Rivers system of tributaries,which used to belong to the Qingjiang River.
One of the results of the impact of the structure on the development of the rivers is the presenceof numerous gorges in the area.The Yangtze River and its tributaries, while growing cut throughthe different anticlines and wherever a river crosses an anticline in the area, a gorge is found.Therefore the gorges are the natural consequences of the river trying to overcome the control ofstructure during their evolution.The speed of the cutting of the gorges is sustained also by thefact that the anticlines have been uplifting as shown by the results of basin asymmetry analysisand the analysis of mountain front sinuosity. The uplift of the southern part has also a consequence on the course of the Yangtze River first byintegrating rivers from the Qingjiang River second by pushing the course of the Yangtzenorthwards as attested by the short length of the last order of the stream flowing to the Yangtzefrom the north.
One of the important questions to be resolved in this thesis was the formation of the YangtzeRiver in the Area.To do so, it was first necessary to set the former divides of the rivers, whichconnected to form the Yangtze River.From the analysis of drainage patterns, the differentmorphometry of the rivers, this drainage divide seems to be the Hengshixi anticline.This area isthe demarcation line of the three drainage pattern found in the area.The analysis of thehypsometric curves shows that this area is much younger than the Huangling area and the Chongqing area.The angle of the different rivers is large evidence that shows that the capture ofthe rivers that became the present day Changjiang is at the Wu Gorge.The large rivers of thenorthern area have an angle of incidence to the Yangtze River opposite to the effect of the forceof Coriolis, and also to all the other rivers of the area.This is evidence that they used to flowwest, while all those in the eastern part of the area follow the incidence of the force of Coriolisand all flow in the same direction as the flow of the Yangtze River.The Guandu River shows noangle of connection to the Yangtze River and seems to prolong the Yangtze River towards theheadwaters on the highest altitudes of the Hengshixi anticline.Therefore the conclusion caneasily been made.The Daning River at the western mouth of the Wu gorge and the Guandu Riverat the eastern mouth are just the remnant of the two rivers, which later formed the Yangtze.
Those two rivers, as shown in the results used to flows in the synclines between the Qiyueshanand the Hengshixi anticline, and in the east of the Hengshixi anticline.The tributaries of the tworivers eroding head wards on the Hengshixi anticlines made the capture.The resultant form is theelbow of capture of a "Z" form seen nowadays at the Wu gorge.