An Investigation on the Effect of Physical Development of Darab city on the Flood in the City

Most of the citiesof arid an d semi-arid regions have been built on alluvial fans. These cities are subjected to flood. By intervening in stream natural trend, increasing impermeable surfaces, changing the slope, assembly and concentration of flood-ways, shortening the time of basin concentration and blocking flood-ways; through city constructions, urban development causes an increase in flood incident. Darab city has been built on Tang Katoye alluvial fan. One of the main problems of this city, urban floods and flooded streets in the rain and damage to the facility each year, the city will enter This research aims to investigate Darab city,s physical development and it,s effect on the flood occurrence. To do so, trend of Darab development was examined, using aerial photographs and the map of city land use in three stages(1335, 1363, 1390), then the relation of city physical development with increase of flood occurrence was defined using the method of American soil conservation (SCS). The results of the research show that from first to second stage, city,s physical development growth by four percent, while it would result in increase of surface run-off by 7 percent, and from second to third stage, it has had a growth of 33 percent, that resulted in 23 percent increase in surface run-off.