Abstract: In the study of urban waterlogging simulation, the division of catchment areas is a very important link. At the same time, the fine division of catchment areas of large-scale plain cities is also a technical difficulty that researchers jointly study. Aiming at the problems of the existing classification methods based on DEM flow analysis that cannot correctly reflect the complex terrain and flow directions of actual cities, this paper proposes a fine watershed classification method that takes into account land types and flow directions and is suitable for large-scale plain cities. First, starting from the city's natural topography and main rivers, the first-level macro-scale division is carried out. and then the second-level meso-scale division is realized based on the city's main and secondary arterial roads, main canals and pipe networks. Finally, on the basis of the second division, the flow direction the land type is divided into a fine three-level subcatchment micro-scale. This paper selects the 30 km² core main urban area of Dongying City for verification and analysis. The research results show that the classification results are consistent with the actual feature types and real flow directions. This method has good applicability to large-scale plain cities.

Key words: catchment, plain cities, surface type, modified DEM, classification