Research Of Catchment Profile Spectrum On Northern Shaanxi Loess Plateau, China

Catchment is one of the basic geographic units on Loess Plateau. Study on Loess Plateau catchment geomorphological configuration is of great significance to further research on catchment erosion and conservation of soil and water. It is also of great benefit to the exploration of landform evolution.Topographic profile is proved can be effectively reflect regional landform feature. Previous research using'Catchment Boundary Profile Spectrum'to study the character of landform. Rather than focusing on the local topographic characters, the method take the catchment structure into account, therefore, it can reflect the landform feature in macro-scale.Three main kinds of feature line, catchment boundary line, Loess shoulder line, and valley line, exist widely on the Loess Plateau, China. They are used to respectively depict inter-gully area geomorphy, divided line of inter-gully area and slope-gully area, and bottom-gully area geomorphy. The interrelationship between these three feature lines can reflect the inner characteristics of the catchment, like topographic feature, erosion feature, and evolution feature. However, previous research works merely on using catchment boundary line, named Catchment Boundary Profile Spectrum (CBPS), to depict macro characteristics of loess landform and its spatial distribution pattern. Little attention is paid on the syntagmatic relation of different feature lines, and its role on terrain analysis. The objective of this research is to investigate how to deal these three feature line, catchment boundary, Loess shoulder line, and valley line, as a whole, named Catchment Profile Spectrum (CPS), and then use it to further study the drainage area geomorphology on Loess Plateau.Primary works and contributions of this thesis are summarized as follows:1. Concept of Catchment Profile Spectrum (CPS) is given. Automatic extraction of three loess feature lines, catchment boundary line, loess shoulder line and gully line, is carried out with DEM data. The three feature lines were integrated based on feature points, corresponding segments of lines between feature points are then projected together.2. On the basis of morphological characteristics and relationship of catchment profile lines, quantified parameters about catchment terrain and development are constructed, and their calculation methods based on DEM are proposed. Among these parameters, parameters about catchment terrain contains Fluctuating Frequency, Fluctuating Amplitude, Average Slope and Density of shoulder-line, parameters about catchment development contains approximation in plain between catchment Boundary line and shoulder-line, approximation in elevation between catchment Boundary line and shoulder-line, erosion ratio of starting point and ending point, gradient ratio of main gully and elevation ratio of positive area and negative area.3. In the research, nine periods small watershed models are selected as the test data for the study of time series characteristics, while 48 geomorphologic units distributing from south to north of Loess Plateau in northern Shaanxi are selected as the test data for the study of spatial distribution characteristics. The scale of DEM of small watershed models is 1:20, while that of geomorphologic units is 1:10,000. Based on DEM, CPS quantified parameters are calculated and analyzed. The result shows, parameters about catchment terrain can effectively reflect terrain relief, terrain slope and terrain fragmentation, and parameters about catchment development can reflect catchment erosion and catchment development from different aspect. Moreover, catchment erosion and development of different geomorphologic units distributing north of Loess Plateau is much more complex than that of nine periods small watershed model, due to it is influenced by more factors, such as soil type and ground vegetation.Catchment Boundary Profile Spectrum is useful to reflect morphological character of Loess Plateau. However, it can only depict the positive landform. Catchment Profile Spectrum works as an extension of CBPS, it can not only reflect the macro characteristics of loess landform, but also work very effective on reveals the internal character of the catchment. It is useful to further study the erosion law on Loess Plateau and its evolution feature.