Flood zoning of Bandar Abbas city and evaluation of the development trend of residential areas towards flood areas

Extended abstract   1- Introduction An examination of the number of floods in recent years shows that floods are no longer a rare sudden disaster, but a growing phenomenon that, at any given time, causes a lot of damage, including life and death. As a result of interference in natural environments, the presence of multiple structures, and the lack of appropriate measures to protect these environments, flood conditions are provided. Also, with the rapid growth of urban development and the creation and development of infrastructure, floods in urban areas have become more and more severe. In our country, especially in the southern regions of the country, due to climatic conditions, floods are frequent and harmful. The growing trend of floods in recent years suggests that most of the countrychr('39')s southern cities are at risk of flooding. According to studies, about 40 large and small floods occur in different parts of the country every year. Experimental and managerial experience of different countries shows that the first step in reducing the harmful effects of floods is to identify flooding areas and zoning of these areas in terms of flood risk so that based on the results obtained with integrated management. And comprehensive urban planning prevented the harmful effects of urban floods as much as possible. This study aims at identifying potential flood areas of Bandar Abbas and Bandar Abbas strategic city using GIS, and adapting this map to the development plan of residential areas obtained from LCM model in remote sensing of satellite images as well as determining the flood risk areas. 2-Materials and methods In this study, two steps have been taken to achieve the desired goals. In the first stage, using five height parameters, slope, land-use, lithology, and river mile have been used as effective parameters in identifying flood-prone areas. After preparing the information layers for each parameter, the layers are standardized using fuzzy logic. After standardizing the layers, a hierarchical analysis model (AHP) was used to weight the layers. After determining the weight of each layer, in the ArcGIS environment, the weight obtained is applied to that layer, and finally, using fuzzy gamma, the information layers are combined, and the final map of flood-prone areas is prepared. In the second phase, satellite imagery from the 1990s, 2000s, 2010, and 2019 was used to assess the development of residential areas to prone to flood-prone areas. After preparing the images, in the ENVI software, first the necessary pre-processing on the images, including radiometric and atmospheric studies, has been done, and then by using the maximum probability method, land-use maps of the study area related to the 1990s, 2000s, prepared in 2010 and 2019, were presented. After preparing the land use maps, IDRISI software and the LCM (Land Change Modeler) software were used to evaluate the trend of land-use change in residential areas. 3-Discussion and results Evaluation of the final results of flood-prone areas indicates that a large part of the study area has a high flood-rising potential, so based on the results, the class has a very high potential for floods, 88 km2 (equivalent to 28.7% of the study area). The study area includes mainly areas close to the river, low-slope, and low-lying areas. Also, the class with a very low potential for flooding includes 24 km2 (equivalent to 7.8% of the study area) of the study area, which mainly includes the highlands and the northern slope of the study area. In addition, the results of the assessment of land-use changes indicate that land-use has undergone many changes during the study period, and the use of residential areas has increased. Assessing the trend of changes, shows that the increasing trend of use of residential areas has been due to population growth and construction development. The decrease in the use of vegetation and water area is also due to the development of the use of residential areas, which has caused the destruction of vegetation and the progress towards the coast. Also, the trend of changes in the use of weak pastures and salt marshes has been affected by the development of residential areas and climate change. 4-Conclusion The results indicate that the study area has a high potential for flooding, so that about 170 km2 of the study area (equivalent to 55% of the study area) have a high and very high flood potential these areas mainly include low-slope and low-lying areas of the urban area and the suburbs of Bandar Abbas. Therefore, in terms of used parameters, the city of Bandar Abbas has a high potential for flooding. Also, in this research, the trend of land-use changes and residential areas of the study area has been evaluated. According to the results, the use of residential areas (including residential areas and man-made areas) has grown so much that in 1990, this area was 32.2 km2, which in 2000 to 42.9, and in 2010 it increased to 55.7 km2 and in 2019 to 77.4 km2. Assessing the spatial trend of land use changes indicates that a large part of the residential area has moved to areas prone to flooding. According to the results, in 1990, 14.2 km2 of residential areas were located on the potential floor of many floods, which in 2000 to 16.4, in 2010 to 21.9 and in 2019, it has increased to 28.1 km2. Therefore, it can be said that in recent years, a large part of the residential areas has moved to flood-prone areas.