中文摘要：

：沟道等级结构与顺序结构都可看作是沟道拓扑结构，在黄土高原小流域坝系规划研究中，往往需要将Horton—Strahler的沟道分级模型与较长沟道优先的顺序编码模型进行整合。该文提出一个沟道结构假说，即在黄土高原小流域尺度上，存在一个最小集水面积与最短沟道长度的适宜取值区间，使得基于DEM提取的沟道网络上任意节点对应的较长沟道作为主沟道，其Horton—Strahler沟道等级不低于汇入支流。搜集的黄土高原丘陵沟壑区多个副区的一些典型小流域数据有效验证了上述假说，从而为实现整合等级结构与顺序结构的沟道编码模型的进一步研究提供理论基础。

英文摘要：

The network rank structure is a kind of network topological structures,as well as the network order structure. In the research on silt-dam planning of small watershed on the Loess Plateau, it is essential that the Horton-Strahler rank model and the longer-channel-flrst order model were integrated. There has not yet been a geographic theory that could support it. In this paper, a hypothesis on network structure is presented based on theoretical geomorphology analysis. It is that, in small watershed scale on the Loess Plateau, there should be a couple of suitable intervals on critical source area （CSA） and minimum source channel length （MSCL） that can make the mainstream＇s Horton-Strahler rank value of arbitrary node in the network no less than the tributary＇s. The mainstream is defined as the channel that from the outlet to the starting point along the longest ravine. The node is defined as the confluence point which two channels converge. In this research, nine sample watersheds distributed over the Hilly Areas of the Loess Plateau were gathered up which could verify this network structure hypothesis,which provides theoretical foundation on integrating rank and order structure in network codification.