Evaluation of urbanization effect on runoff volume by using Stormwater Management Model (Case Study: Zanjan City Watershed)

The concentration of human population in urban areas with urbanization and changing the face of the earth's natural has caused an increase in impervious surfaces and change in hydrological cycle. To evaluate the effect of urbanization on the runoff volume entering in urban drainage of Zanjan City, the trend of urbanization were processed by using Thematic Mapper images in IDRISI Selva and ArcGIS 9.3 software. Land use maps of the 1956, 2000 and 2012 were prepared. Analysis of hydrological and hydraulic behavior of urban development impact on the volume of runoff was carried out by using Stormwater Management Model (SWMM). Based on model calibration by observation of rainfall-runoff events, the results of calibration and verification have confirmed the accuracy of simulations. The trend of urbanization shows that urban area has been expanded in 2012 compared to 2000 and 1956, 22.59 and 923.88 percent and in 2000 compared to 1956, 543.06 percent, respectively. The results of SWMM model shows that urbanization and convert the land to impervious surfaces have caused an increase in the runoff volume, so that, runoff volume average has increased in 2012 compared to 2000 and 1956 64.45 and 698.58 percent and in 2000 compared to 1956, 376.91 percent, respectively.