In this research, the effect of the development of Mashhad city (in Iran) were investigated on the amount of runoff generated by the city and the capacity of the surface water collection system. The urban catchment of Mashhad city with a total area of 328 km2 was divided into 288 sub-catchments, 399 waterways, 398 nodes, and 5 outlets using GIS software. The pervious, impervious, residential, agricultural and street areas were then determined using the GIS software and the Google Earth and the Curve Number (CN) was calculated for each sub-catchment. Due to precipitation in urban catchments, the precipitation pattern is one of the important inputs to the flood simulation models. Three different methods of periodic block, uniform distribution and SCS II were used for selection of the suitable discharges. At the end, the SCS II method was selected. The results of modeling showed that in Mashhad city for the years 1941-2016, the peak flood in 2016 was 307 percent greater than the year 1941, 177 percent greater than the year 1986 and 259 percent greater than the year 1976. In addition, the results showed that the central, northern, and northeastern regions (downstream of the city) are flooded by the increasing the impervious surfaces and the insufficient capacity of the waterways.

Keywords