عنوان مقاله [English]
Floods are one of the most destructive and most frequent natural disasters. In this regard, flood risk zoning is one of the most effective methods for managing and mitigating the effects of floods. In this study, the spatial and risk assessment of flood events at the surface of Ghorichai watershed in Ardabil province was investigated. In this regard, 10 measures affecting the flood event were applied. These criteria include elevation, slope, slope orientation, convexity, geological formations, drainage density, curve number (CN), waterway distance, land use and vegetation. In the meantime, the ground slope variable with a weight of 0.26 (excluding network analysis process model) plays a major role in identifying high risk flood zones. Two fuzzy logic models and a network analysis process (GIS) were used to integrate and overlap the aforementioned subject layers in order to prepare a flood risk zoning map. Flood hazard zoning of the Ghorichai watershed showed that about 18% of the studied watershed area was located in high and very high risk classes. Flood risk in the basins of the main valleys and downstream lands of the study basin due to Geomorphometric reasons such as formation and development of flood plains, low relative elevation, concave terrain, and rapid upstream runoff of the event potential. It is high. In addition, relocation of residential areas downstream of the basin has increased the risk of flooding in these areas.
Flooding is called the dangerous increase in the flow of a river or a flood. This phenomenon has a long history in human history and is one of the most damaging and destructive natural events. Old towns are usually formed alongside rivers due to easier access to water; they are therefore affected by floods, causing casualties. Floods occur when water flows out of rivers, streams and canals, in other words leaving its natural channel. We see an event when the canal or river is completely filled with water and enters the floodplains and areas where people live. In the present study, the risk of flooding in the Ghorichai watershed is investigated. Due to the large extent of the semi-arid climate and the presence of numerous settlements in the region, it is important to assess the importance of flood risk assessment and zoning in the Ghorichai catchment area. This is especially important in the presence of large human settlements, extensive agricultural lands and conservation of water and soil resources. Therefore, flood risk zoning at the basin level of the study is one of the essential steps in the management of flood risk mitigation and management measures.
Material and Method
The present study investigates the risk of flooding in the Ghorichai watershed. This basin is located in Ardebil province within the administrative districts of Nair, Ardebil and Kosar. Much of this basin is located in the Nair area. The study area is located at 48 degrees 2 minutes to 48 degrees 31 minutes east longitude and 37 degrees 46 minutes 38 degrees 11 minutes north latitude in mathematical position. The basin has an area of about 824 km2 and an area of about 240 km. In this study, the following data and tools were used to analyzed flood risk in the Ghorichai catchment: 1: 50000 area topographic maps, 1 scale geological maps : 100000 including Ardebil and Givi Sheets, 1: 250000 Scale Soil Map, Digital Elevation Model (DEM) for ALOS - PALSAR Satellite Area with 12.5 m Resolution, Sentinel2 Satellite Images with 10 m spatial resolution and meteorological and climatic data including Ardabil synoptic station data and rain gauge station data located within the watershed. Two models of fuzzy logic and network analysis process (ANP) in the framework of Geographic Information System (GIS) were used to model flood risk in the Ghorichai catchment area.
Discussion and Result
The final layer resulting from the composition and overlap of the subject layer indicates the potential for flood risk at the Ghorichai watershed. The resulting map was classified into five classes of very low, low, medium, high and very high flood risk. According to the flood risk zoning map of the Ghorichai catchment, it can be stated that approximately 49 km2 of the catchment area is in a very high flood risk class, covering about 5.9% of the catchment area. In addition, more than 101 km2 or about 12% of the study area is in high risk class. Most of these high-risk areas are adjacent to either side of the basin's main waterways or floodplains adjacent to them. This can be attributed to a number of reasons, such as the smoothness or slowness of these areas (and thus the possibility of easier spreading and spreading floods), the existence of a valley extended by the flood plain below it. , Counts the crossing of the Ghorichai River through these zones and the low altitude of these zones.
In this study, in order to map the flood hazard in the Ghorichai catchment area, 10 factors influencing flood event were applied. These criteria can be divided into three main categories: geomorphological criteria including altitude, slope, slope direction, ground convexity and geological formations; hydrological criteria including drainage density variables, curve number (CN) and distance from the waterway. And land cover criteria including land use and vegetation (NDVI). To integrate and overlap the research thematic layers with the aim of mapping flood risk zoning at the Ghorichai watershed, we use two models of fuzzy logic and ANP in the form of GIS. There was action. In this regard, all subject layers affecting flood occurrence were applied with different fuzzy functions, in the range between 0 and 1 standard and having the same units. Then all relevant subject layers were combined with the weights obtained from the ANP model. Flood hazard zoning of the Quriichai watershed showed that about 18% of the studied watershed area was located in high and very high risk classes.