In recent years, the flow of the Yellow River has often beeninterrupted, which has resulted in exposure of channel bars and point bars, and even extensive exposure of the riverbed. Consequently, a large number of rill marks have developed. They are diverse in morphology. According to the hydrodynamic types of their formation, they can be grouped into 6 categories, i. e. the wave-eroded, backwash, seepage, rain-eroded, water-drainage and runoff rill marks. Morphologically, they can be divided into more than ten types: the linear, tooth-shaped, comb-shaped, fence-like, ear-like, braided, branched, leaf-like, flower-like, root-like, dendritic, net-like, radial etc. Their cross sections include the broad-u type (the width/depth ratio is over 2, and may reach 10－20), U-type (width/depth ratio from 1 to 2), V-type, Ω-type and (-type. Their occurrences may be attributed to the variations in composition, grain-size, color, fabric and morphology. They have 5 scales: the micro-scale (length and width within 1 cm), small-scale (length and width within 10 cm), medium-scale (length and width ranging from 10－100cm), large-scale (length and width 1－5 m) and giant- scale (length or width over 5 m).  相似文献