松花江干流中下游河型转化控制因素研究

Influences Affecting River Pattern Transformation in the Middle and Lower Reaches of Main Stream,Songhua River

河型转化机制研究对于分析河流沉积特征具有重要意义。以中国松花江干流中下游为研究对象,利用Google Earth和Arc GIS软件对河流形态参数进行精细测量,进而对不同河段河型发育特征及转化控制因素进行研究,结果表明:1)松花江干流中下游存在曲流河、辫状河和直流河3种类型,依据地貌特征、平面形态和弯曲度自上而下划分为3段,其中上段为低坡度背景下河流逐渐加宽且植被密度逐渐降低的曲辫共存型河流,中A段为低坡度背景下河流较宽且植被密度高的简单辫状河,中B段为高坡度背景下河流宽度集中且植被密度低的直流河,下段为高坡度背景下河流宽度频繁变化的复杂辫状河;2)曲流河向辫状河转化控制因素为植被密度降低引起的堤岸抗侵蚀能力减弱,辫状河向直流河转化控制因素为河流被两侧山谷夹持且伴随坡度陡增造成河流下蚀能力增强,直流河向辫状河转化控制因素为支流注入导致流量和输沙量增大;3)建立了松花江干流中下游3种河型转化模式,上段为渐变曲—辫转化,中段为突变辫—直转化,下段为突变直—辫转化。

The study of river pattern transformation mechanisms is highly significant in the analysis of river sedimen⁃tary deposits.The middle and lower reaches of the Songhua River main stream were the object of this study.Google Earth and Arc GIS software were used to carefully measure the morphological parameters of the river,and the riverpattern growth and the influences leading to changes in the two reaches were then investigated.The study showed the following.(1)Three river types occur in these regions:meandering,braided and straight river zones.These were di⁃vided into three sections from upstream to downstream according to their geomorphic features,plane morphology and sinuosity.The upper section of the river is a coexisting meandering-braided river that has gradually widened and grad⁃ually reduced the density of the vegetation on a slight sloping background.The middle section‘A’is a wide,simple braided river with high vegetation density on a low slope.The middle section‘B’is straight and relatively narrow,with low vegetation density on a steeply sloping background.The lower section is a complex braided river in steeply sloping ground;its width changes frequently.(2)The main cause of transformation from a meandering river to a braided river is the erosion resistance of the banks due to the decrease in vegetation density.The factor influencing transformation from braided to straight river is the enhancement of downwards erosion resulting from the“clamping”effect of the steeply sloping terrain.The final transformation from straight river to braided river is due to the increased water and sediment discharge from tributaries.(3)Three river pattern transformation models were established for the middle and lower reaches of the river,a gradual change from meandering to braided stream in the upper section;abrupt change from braided to straight in the middle section;and abrupt change from straight to braided in the lower section.