The Effects of Impermeable Surfaces on the Flooding Possibility in Zarrin- Shahr, Isfahan Municipal Watershed

Flood is one of the most destructive natural disasters causing a great damage to natural resources. Changing the land uses, converting the urban lands and rising the impregnability of surfaces have changed the hydrological regime of urban watersheds in such a way that most of the rainfall turns into the runoff. This research seeks to use Santa Barbara urban hydrography in the environment of Storm water Management and Design Aid (SMADA) to study the effects of land use changes and the impermeable surfacesʹ arise in the flooding possibility of municipal watershed Zarrin Shahr in Isfahan province in Iran. To analyze the achievement data, the required maps of the area were first prepared by Arc-GIS software. Then, the preparation process of annual and maximally 24-hour rainfall data was undertaken by the help of the synoptic situation of Zarrin Shahr. All the parameters required for the above mentioned model such as concentration time, design rain and curve number (CN) were studied and determined. Then, the hydrographic simulation of the flood was done in the environment of SMADA. Two stations, namely Pol Kalleh in the west and Lenj in the east of the watershed were studied. As the results indicate, changing the green urban environment in the residential areas causes a considerable increase in maximum floodwater discharge. The impacts of this land use change are greater on the flooding possibility of the area studied in low return periods.