黄河源同德盆地刺状水系初步研究

A preliminary study on spinulose stream networks in the Tongde Basin of the Yellow River source

在野外调查、实地测量和DEM特征统计的基础上,从形态特征、发育环境和形成机制三个方面介绍了青海黄河源同德盆地出现的一种独特水系,它是在广泛覆盖厚层河相沉积物和风成黄土的平缓宽谷上,由干流下切带动支流溯源冲刷逐渐形成的一系列近平行排列的细短支流,以非对称方式近直角入汇深切干流的水系格局,因支流形似针刺,称之为刺状水系。刺状支流、简单的河道等级结构以及干支流非同期发育都是刺状水系区别于其它水系的显著特征。初步认为刺状水系的发育有两个基本条件,一是有覆盖厚层黄土和河相沉积物的平坦宽谷,二是由干流深切引发的大规模溯源侵蚀。由于历史上青藏高原的不均匀抬升,古同德地区成为沉积盆地,接受了大量的河相沉积和风成黄土。然而,随着共和运动以来青藏高原的不断隆升,古黄河切穿龙羊峡,与盆地内的古水系连通,沉积区转变为易侵蚀区,河流快速下切,支流广泛发育,逐渐形成现今的刺状水系。

Based on field work,remote sensing interpretation and DEM geomorphic analysis,this research introduces a unique stream networks found in the Tongde Basin within the Yellow River source.The stream networks,named spinulose stream networks for its tiny branches,was developed in flat broad valleys covered by deep fluvial sediments and loess where a series of narrow and short branches merge into deeply incised mainstream in parallel at nearly right angles.Spinulose branches,simple ordering river structure and asynchronous development of mainstream and tributaries are the three features making this kind of stream networks different from others.This preliminary study suggests that two preconditions are needed for the development of spinulose stream networks.One is gentle valley or basin covered by deep loess and sediments,the other is adequate retrogressive erosion caused by deep incision of mainstream.Historically,ancient Tongde area became a fault basin and received great amount of fluvial sediments and loess because of the uneven uplift of Tibetan Plateau.However,with the ancient Yellow River incising through the Longyangxia Gorge and connecting with inner stream networks owing to the sustained plateau uplift since the Gonghe movement,the sedimentary basin was transformed into easily erosion area where inner rivers incised rapidly.Gradually,the spinulose stream networks formed.