滨江平原的形成模式是江—湖、洲—陆转化——以长江武汉段武昌北部为例

Formation model of riverside plains in Wuhan reach of the Yangtze River:River-lake and island-land interaction transformations in northern Wuchang

长江武汉城区段呈SSW—NNE向从城市中心流过.两岸滨江平原是武汉城市的黄金地段.分布于汉阳和武昌沿岸的滨江平原,平面形状似弓形分布于晚更新世岗地与长江之间.研究发现,其形成经历了江—洲—湖—陆的转变过程,是长江中的沙洲并岸的产物.本文以武昌北滨江平原为例,对其形成过程进行了解析.长江武汉蛇山—青山段在明代江面十分开阔,左岸相对平直,因受汉江三角洲影响岸线微向江突出;右岸弯曲呈抛物线形,边界大致在现沙湖南岸—沙湖港—青山港一线.河道中沙洲发育,河型为多分汊河道.至清代中期后,沙洲先后向右岸移动,多沙洲不断聚合,河道呈东西两支分汊,西汊道为主河道.右汊道被先后靠岸的沙洲分隔为余家湖、沙湖、白杨湖等串珠状湖泊,并不断萎缩.到1899年因自然和人为作用,右汊入口被堵,沙洲与右岸陆地相联,滨江平原形成.余家湖消失,白杨湖萎缩成现在的青山港,沙湖与长江脱离成为独立湖.其河道地貌演化与滨江平原的形成过程可归结为:多沙洲分汊河道—单沙洲分汊河道与沙洲夹湖—沙洲成陆与顺直单河道.该研究对长江中下游类同地貌环境江段滨江平原形成具有启示意义。

Yangtze River runs across Wuhan city’s central area along the direction of SSW-NNE.The riverside plains of Wuhan have always been considered as the city’s prime locations.These plains are distributed along the riverbanks between the Pleistocene low hilly region and Yangtze River.In this study,we have discovered that the formation of riverside plains in this area are product of incorporated by sand bars into former riverbanks,experiencing four mainly multi-transportation stages:river-central bar-lakeland.We analyzed the formation factors of the northern Wuchang Plain as a classic case.By consulting the geographic maps,we found that Sheshan-Qingshan reach of Yangtze River was much wider with asymmetric banks in Ming Dynasty(1368 AD to 1644 AD),the left bank line had straighter curvature,slightly bulging into the river under affect by Hanjiang River Delta.The right bank line,however,had a parabolic shape and outline stretching along the modern southern bank of Lake Shahu,via Shahu harbor to Qingshan harbor.Multiple channel branches and sand bars developed on the Yangtze River.Until mid-Qing Dynasty,the sand bars constantly shifted towards the right bank and fused together to divide the river channel into two branches,the main drainage branch was to the west,the right branch was clogged and separated by fusing sand bars into bead-like lakes,including Lake Yujiahu,Lake Shahu and Lake Baijiahu.In the 1899 AD,causing by natural and human activities,the entrance of right branch had been blocked,the sand bars incorporated with the right bank and formed the modern riverside plain.The Lake Yujiahu disappeared,the Lake Baiyang shrunk into modern Qingshan harbor,the Lake Shahu became interior lake during the same period.Hence,the evolution of river channel and riverside plains can result into the following model:Multiple River channel branches with multiple sand bars-Dual River channel branches with single sand bar and lakes-Single straight wide river channel with sandy banks.Our study can provide rewarding insights for studying formation process of similar stretches of Yangtze Rivers riverside plains along the middle and lower reaches of Yangtze River.