|关键词: 云梦泽 荆江三角洲 面状堆积 垂向堆积 河流纵剖面 历史变迁
|Historical evolution of Yunmeng marsh and Jingjiang Delta
Jing jiang River-bed Expertmental Station, Water Resources Committee of Chang Jiang River, shashi 434002
|On the basis of comprehensive research on the information of geology, geomorphology, channel hydrography, meteorology, historical documents and archaeology of Yunmeng Marsh and Jingjiang Delta, some conclusions are obtained as follows: (1) The Yunmeng Marsh was formed at the end of late pleistocene ice age, when the sea level was declining draniatically resulting in the cutdown of the river-bed of the Changjiang River.As the climate went warmer in the postglacial stage, the gradual rise of sea ievel made the gradient of the Changjiang River more gentle, the sedinientation against the stream took place and the river level began to rise.When the flood breached the bank after the original channel was mandated, the Yunmeng Marsh was formed in the Jingjiang River (middle reach of the Changjiang River) area.The early marsh limited mainly in the abandoned river valley, when constant deposits in the Changjiang River accumulated 0n the lower lands, the marsh was enlarged.The marsh was vast with lands and shallow water interlocked, including the areas of Changjiang River, Hanshui River and part of the Dong ring Lake, (2) The Jingjiang Delta experienced three changes in history;the delta was a part of the developing Yunmeng marsh till Tang and Song dynasties;of the developing Jingjiang bend plain till the end of Qing Dynasty;of the developing Dong ting.Lake delta since the early 19th century.It was concluded that the migration of the Jingjiang Delta showed sume gradient southward.(3) The evolution of the Jingjiang Delta has proved some characteristics of stages.The early delta was thin due to plane accretion on a big area.while later vertical accretion along the diversion channels increased its thick ness.The depocemer position of sediments was the main factor affecting the delta's evolution.urhers were the neutectonic muvement and human activities such as dike building, etc.(1) The developmein and migraduii of Jingjiang Delta in history led Co the dramacic rising of flood level in Dungting Lake and Jianghan plains.Beginning from Pleistocene, the first rising period was from pustglacier age tu some 5000 years ago while the second in the late Ming or early Qing dynasties. Nowadays because of many discharge diversions of the Changjiang River, a great quantity of sediniems depusited to the south of Dungting Lake,the lake bed rose ajid the surface area shrank gradually.Were some programs and counter-measures not employed.the third rising period of fluucl level would Come to reality in no time,which would make the flood control of the two lake plains more difficult to deal with.
|Key words: Yumneng Marsh Jingjiang Delta plane accretiun vertical accretion lungtidutional section of river hisrurical evolution