The Effect of Urban Development on Urban Flood Runoff (Case Study: Mashhad, Iran)

Abstract

In this research, the effects of the development of Mashhad city (in Iran) on the amount of runoff generated were investigated. The urban catchment of this 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 Google Earth. The Curve Number (CN) was calculated for each sub-catchment. Three different methods of periodic block, uniform distribution and SCS (CN) II were used for selection of the storm discharges. Finally, the SCS (CN) II method was selected. The results of the modelling showed that the peak of flood in 2016 was 307, 259 and 177% greater than the years 1941, 1976 and 1986, respectively. In addition, the results showed that the central, northern, and northeastern regions (downstream of the city) were flooded due to the increase of the impervious surfaces and the insufficient capacity of the channels.