Estimation of Urban Imperviousness and its Impacts on Flashfloods in Gazipaşa, Turkey

Abstract

The paper examines flooding issues under rapid urbanization in Gazipasa city during the past seven years 2013-2019. The Storm Water Management Model (SWMM) integrated with the satellite images representing temporal variation in the land use and land cover (LULC) characteristics of the city were used to determine the variation in the runoff generation capacity, flood volume, and associated risks. The Google Earth software together with GIS technology were utilized to create and handle spatial data required for SWMM simulation. Standard design storm intensity derived from the local intensity-duration-frequency curves was used as the stationary input parameter for SWMM simulation in both the past and current LULC conditions. The comparison between LULC maps showed that the extent of urban imperviousness area has been approximately increased by 80% in average. The SWMM simulations showed the peak flood value of 51.3 m³/sec and 61.4 m³/sec for the year 2013 and 2019, respectively. Moreover, under the same design storm, Rational Method has been applied and 39 m³/sec of peak flow rate has been calculated by disregarding the urbanization activity. The results indicate that the LULC variation during the past seven years resulted in almost 20% (18%) increase in peak flow (flood volume).