Spatial analysis of flooded and flood-prone areas and it’s hazards in Nourabad city of Lorestan

Introduction
Today, environmental hazards and coping with them are among the most important concerns of researchers in the field of environmental planning and crisis management. Meanwhile, the flood phenomenon is one of the most dangerous natural disasters that should be given special attention in crisis management. Floods are considered to be one of the most destructive risks that can cause great damage, so that according to the International Danger Database, floods along with earthquakes and droughts have caused the highest loss of life and property. In Iran, in recent years, floods have caused a lot of damage to various areas, especially urban areas, including the floods of April 2019 that many cities, including cities of Golestan province, Lorestan and it covered Khuzestan and caused extensive destruction and great damage to these cities., According to the Lorestan governor's office, the damage caused by the floods in April 2019 was more than 100,000 billion IRRtomans, and 15 people lost their lives due to the floods. Meanwhile, Nourabad city has also suffered a lot of damage, including the destruction of 5,000 residential units and 16,000 hectares of agricultural and garden lands. Also in Nouoorabad city, floods have destroyed part of residential areas and infrastructure. Due to the fact that the city of Noorabad has a high potential for flooding and in April 2019 has faced the risk of floods, in this study, flood-identified areas as well as flood-prone areas in the urban area of Noourabad have been identified.
Materials and Methods
In this study, in order to identify flooded areas and areas prone to floods, a digital model of 5 m height, 1: 50,000 topographic map, Sentinel 1 radar images, information about Dubai river discharge, and river roughness coefficient were used as research data. ARCGIS, HEC-RAS and SNAP software are also considered as research tools. In this study, after collecting data and information, the work was done in 4 steps. In the first stage, using Sentinel 1 radar images, the flooded areas were identified in April 2009. For this purpose, Sentinel 1 radar images related to before and after the flood were used. In the second stage, field visits have been used in order to adapt and validate the results obtained through radar images. In fact, after the flood, in order to identify the flooded areas through field visits, the direct observation method was used during the flood, the interview and also the review of the available evidence. In the third step, using the HEC-RAS model, flood-prone areas are identified. In the fourth step, the results obtained from the previous steps and the extent of their compliance are evaluated.
Discussion and results
The results of the assessment of flooded areas using radar images indicate that due to the flood in April 2009, many parts of Noourabad city with an area of 0.562 km have been flooded, the northern parts of the city, according to the confluence of the river Gachineh and Badavard have the highest flooding area. AlsoIn addition, in this research, after conducting field visits, the final limit of flooded areas in Nouorabad urban area has been determined, the area of which is 1.212 km. According to the results of field visits, the areas adjacent to Gachineh and Badavard rivers have been flooded, with the highest level of vulnerability to flooding in the downstream areas of Gachineh River, including the surrounding areas of the municipality, as well as areas adjacent to Badavard River. It has been from other areas. In this study, after identifying the flooded areas, using the HEC-RAS method, the areas prone to flooding for different return periods have been identified. , 10, 25, 50 and 100 years old are 0.149, 0.256, 0.564, 0.953 and 1.544 km², respectively.
Conclusion
The results obtained through the HER-RAS model indicate that the flood covers a larger part of the city. In fact, since the 100-year return period has been used to compare, the area of the floodplain obtained through the HEC-RAS model, with 1.542 km², is wider than the flooded areas identified by radar images. And field visits. Also, the area of flooded areas prepared by radar images (0.562 km²) is less than the area obtained by other methods, which can be attributed to the flooding on the day of imaging. Evaluating and comparing the results obtained through different methods indicates that the results are consistent, in fact, the areas identified in field visits as flooded areas, In radar images, it has also been identified as a flooded area, and these areas are considered to be flood-prone areas based on the results of the HEC-RAS method, so the results are consistent. The overall results of the study indicate that the city of Nouorabad has a high potential for flooding and many of its residential areas, including areas close to the outlet of the Gachineh River, are prone to flooding.