DEM-based River Network Characteristics Of The Loess Region

With the development and the popularization of the GIS (Geographic InformationSystem), productions of digital terrain have been widely used in kinds of fields gradually. Asfar as we know, the research and the operating methods of earth sciences, especially terrainanalysis and hydrological analysis, has transferred from paper topographic map, manuallyvisual interpretation and hand painted to volume-produce of digital terrain analysis outputwith higher efficiency and precision.Generally, it has been the trend to adopt DEMs in the drainage characteristics analysis. Inthis thesis, comprehensive methods of digitized contour line of topographical map, TIN, andextractive technique of grid are compared in the river network extraction. And DEM basedmethod is finally decided as the main research method. With the help of functions of ArcGIS9.3, the extraction of river network of different study area is realized.Modern technology of GIS is taken as the experimental platform, the newest digitalproduct of National Geographic Foundation Database is adopted, with the help of GIS, thedetailed information about DEMs is obtained, including their resolution and structure. Afterthe systematic analysis, the special resolution of15m is selected as the optimum resolution ofDEMs. Subsequently, the15m resolution is used in generation of the irregular TIN based onthe original digital contour lines, and then regular DEM grid is generated from the TIN wheninterpolation technique used. Forth more, the theory and process are elaborated on how toextract the river network based on the D8arithmetic. During the extracting process, the trendanalysis between the threshold of flow accumulation and the drainage density is adopted todetermine the threshold. At last, the flow accumulations with the ultimate threshold aredetermined with the help of Flint. Finally, the distribution and classification of extractive rivernetwork are analyzed, and the relationship between the geomorphology, the slope and theriver network is analyzed too, the fractal dimension of river system is calculated.The results of the thesis show that the river network systems of the loess region aremainly belong to the tree-shape structure and fan-shape structure. They are distributed at thevalley, tableland in the hilly and gully region. The result of fractal dimension shows that mostparts of the loess region are in prime of landform development. The general characteristics is:the fragmented earth's surface has been eroded seriously, and the river side is seriously erodedtoo, therefore further measurement should be taken to prevent the loss of soil and water.