Abstract:In recent years, with the development of urbanization, the scale of infrastructure construction is expanding day by day. The layout of bridges and culverts in the road design process needs to meet the flood control requirements. The hydrological computation of bridge and culvert must be done before a structure is designed, which is one of basic parameters to determine the bridge span and culvert aperture. The important basic work before the hydrological computation of bridge and culvert is the on-site flood investigation to obtain the catchment area of the basin. The catchment area is generally outlined on the measured topographic map according to the watershed, but it is difficult to obtain a large proportion of topographic maps during the project process, especially in the early scheme phase. The satellite map on the Internet is one of the resources for reference. By utilizing Global Mapper software, combined with a municipal road project, the catchment area of the basin is calculated. By using the rainstorm organon in Handbook for Calculation of Rainstorm and Flood in Small and Medium Basins of Sichuan Province, the rainstorm flow is calculated, and the cross-flow section of a bridge span is rechecked.