In this paper, the sinks, the steep slope areas, and locally flat areas, and junction sites of reach are extracted using spatial analysis in Geographical Information System (GIS) and hydrology analysis, based on study area Panxi river basin in Chongqing main city. The junction sites of reaches are directly determined as key sites of flood discharges. Overlaying other factors, three ranks of key areas of flood discharge are recognized based on times of presence in the same location. The first-level key areas with the biggest possibility of forming waterlogging account for only 0.01% of the total basin area, and distribute mainly in the reservoir peripheral mountain area, and distribute discretely in the low population density areas. The second-level key areas with lower risk account for 0.77% of the total basin area, and distribute mainly in upstream areas and downstream areas of Jiulong Lake, as well as in the middle of Panxi rive basin (Nanqiao temple district), in which urban residential areas are compactly distributed. The third-level key areas with the smallest risk account for about 28.66% of the total basin area, and distribute widespread over the entire basin. Key sites and key areas provide the guidance for the improvement project of urban sewerage pipe network, and serve as the first step for the distributional hydrology model simulation.
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