Small catchment division in the typical karst landform areas：A case study of Jinsha county, Guizhou

Prevention and control of soil and water loss and desertification in China are normally implemented on a small catchment as a unit basis. However, scientific study on the division of a small catchment in karst area has seldom been done. Jinsha county is located in a typical karst area in Guizhou, with various types of landform. This research was commenced on the work of digitization and DEM generation with the topographic map of Jinsha sheets on a scale of 1∶50,000. After that, the hydrological analysis module of GIS was used to automatically extract the small catchments, to merge the micro-catchments and in the meantime validate the basin boundaries from which 338 small catchments were finally extracted by the system. Result shows that the sizes of the small catchments fall in a range of between 3 km2 and 10 km2，accounting for 79.29% of the total small catchments. Within the range of integrity, and slope, and other three small catchment types, small catchment types in the study area is dominated by complete type of catchment. Most of the catchment boundaries can meet the requirements. In the areas with peak forest, peak cluster and karst depression, the boundaries do not exactly cross the top of the mountain or hill saddle. Due to the complexity of local drainage network, automatically extracted small catchments are not in accordance with the reality, which have to be manually modified.