Extended Abstract
Introduction
One of the hazards that is always associated with great human and financial losses is flood risk. Flood is one of the natural hazards in which human activities play an important role. In recent years, the increasing population trend has led to the development of residential areas towards the river banks, and this issue, along with land use changes and destruction of vegetation, has increased the probability and intensity of floods and the resulting damages. The increasing population trend and industrial development have led to the advancement of human societies towards the river banks and the concentration of economic activities in flood plains, and this factor has caused many urban areas to be exposed to flood risk and face billions in financial losses and human losses annually. Considering that flood risk is considered one of the challenges facing societies, it is very important to implement management measures, monitor and control land use changes, manage river courses, and identify areas prone to flooding. Different regions have different potentials for flooding, depending on the hydrogeomorphology and human factors. One of the areas at risk of flooding is the city of Nourabad in Lorestan province. The location of Nourabad city on the Badavar River and its topographic condition have made this city vulnerable to flooding, and for this reason, in recent years, including in April 2019, it has faced the risk of flooding. Given the importance of the issue, this study aims to identify areas prone to flooding and also areas flooded in Nourabad city during the April 2019 flood.
Materials and Methods
In this study, a 30-meter digital elevation model, Landsat 7 and 8 satellite images, and Sentinel 1 radar images were used as the most important research data. The most important research tools were ArcGIS (to prepare the desired maps and standardize the information layers), SuperDecisions (to implement the ANP model), ENVI (to prepare land use maps), IDRISI (to implement the WLC model), and Google Earth Engine (to identify flooded areas). Considering the subject and objectives, this study was conducted in several stages. In the first stage, six parameters of elevation, distance from the river, slope, slope direction, lithology, and land use of the region were used to identify flood-prone areas, as well as WLC and ANP models. In the second stage, Google Earth Engine and Sentinel 1 images were used to identify flooded areas. In the third stage, the results obtained from zoning methods and radar images were compared. In the fourth stage, in order to evaluate the trend of development of residential areas towards flood-prone areas, Landsat 7 and 8 satellite images from 2010 and 2020 were used.
Discussion and Results
The location of Nourabad city has caused this city to have a high flood potential. In this study, in order to identify areas vulnerable to flood risk, 6 parameters of height, distance from the river, slope, slope direction, land use and lithology were used. Based on the final map, the southern and central areas of Nourabad urban area have a high flood potential due to their low height and slope, as well as proximity to the river. Also, in this study, a map of the flooded areas in April 2019 was prepared using radar images and Google Earth Engine. Based on the prepared map, a large part of the Nourabad urban area, including its southern and central areas, is facing the risk of flooding. Also, the urban periphery areas, including the areas along the main river of this city, are facing flooding. According to the results obtained, there is a correspondence between the results obtained from zoning methods and radar images. Accordingly, using the parameters and methods used in this research, areas vulnerable to flood risk can be identified with high accuracy.
Conclusion
The results obtained from the WLC-ANP zoning method have shown that a large part of the urban area of ​​Nourabad, including its central and southern areas, has a high flood potential due to its low elevation and slope, as well as proximity to the main river. Also, the peripheral areas of Nourabad, which are located in the vicinity of the main river, also have a high flood potential. In this study, the status of the flooded areas during the flood of April 2019 was also evaluated using radar images. Based on the results obtained, a large part of the urban area of ​​Nourabad, including the central and southern areas of Nourabad, has faced flood risk. Comparing the results obtained from the zoning methods and radar images has shown the consistency of the results obtained; accordingly, it can be concluded that using the parameters and methods used in this study, areas vulnerable to flood risk can be identified with high accuracy. Also, in this study, the process of physical development of residential areas in Nourabad city towards flood-prone areas was evaluated, and based on the results, the area of ​​residential areas in the category with very high flood potential in the years 2000 and 2020 was about 1.3 and 1.9 square kilometers, respectively. According to the results, it can be concluded that in the process of physical development of residential areas in Nourabad city, the flood potential of this city has not been taken into account, and this has led to the development of residential areas towards vulnerable areas.