Floods in urban areas are a significant concern for government authorities. Proper estimation of urban floods is essential for any city’s storm water drainage planning and land use development. The frequent flood events in Chennai City, Tamil Nadu, require accurate estimation of urban runoff for better planning. In the present study, Chennai City is divided into a few watersheds using satellite imageries in QGIS software. A contour map and digital elevation models are developed and used for delineation of watersheds. 10 to 20 recent years of daily rainfall data of various stations within the study area are used to arrive probable maximum precipitation (PMP) based on various return periods. Probable maximum precipitation amounts for various return periods have arrived and used for analysis. Soil Conservation Service-Curve number (SCS-CN) method is used to calculate runoff depth. The runoff depth obtained from SCS-CN method is converted into a probable stagnation depth of floodwater for various magnitude of rainfalls. The study shows that the stagnation depth of water within the area under completely restricted flow due to blockage of water paths within the study area. The depth can be considered for better planning of storm water design and fixing maximum flood level for culvert and bridge deck levels.