عنوان مقاله [English]
Among the types of environmental hazards, flood is one of the most destructive natural disasters that causes a lot of damage (Yousef et al., 2011). Floods are a common natural disaster in Iran after an earthquake that endangers human life. Every year, terrible floods occur in the northern cities of Iran, such as the provinces of Mazandaran, Gilan and Golestan. Due to the occurrence of these floods, the places with the highest potential for floods (sensitive areas) should be identified before planning by flood sensitivity maps (Bobek et al., 2012) to the loss of life and property (Kurgalas and Karatazas, 2015). In case of excessive rainfall, especially in the form of showers due to the uneven conditions and vegetation of the region, most of it becomes runoff and after a short time flows as a flood and causes a lot of damage. The increasing trend of floods in recent years indicates that most parts of the country are exposed to periodic and destructive floods and the extent of flood damage and loss of life and property has increased, which is one of the reasons for the frequent recurrence of this phenomenon in the result is a disturbance of the hydrological and ecological balance (Miller et al., 1990) such as urbanization (along rivers), climate change (Tehrani et al., A 2015; Kjildson, 2010) and deforestation (Branastirt, 2003).
The research method is applied based on the purpose and descriptive and analytical in nature. The method of data collection is based on library, field, spatial data of the study area and questionnaires. First, the study area is determined and the identification of the basin and the status of the factors are considered. In flood zoning, many factors must be considered, each of which is of varying degrees of importance, but due to the limitations that existed in the preparation of some layers and the limitations due to their length. There is a model process, the use of multiple layers of information causes excessive complexity of the model, cost and long time in model analysis and processing (Mousavi et al., 2016). Therefore, according to these limitations and previous experiences, the factors that have had the greatest impact on the occurrence of floods in the Gorganrood basin and are more in line with our models have been selected. In this study, 11 effective parameters in flood zoning including slope, slope direction, altitude, geology, rainfall, distance from waterway and river, distance from roads, distance from residential areas, drainage density, NDVI index (cover density) and runoff coefficient (including land use, soil texture, soil hydrological group, curve number, surface maintenance and annual runoff height) were prepared and classified. After identifying the effective layers, the steps of the research method are as follows:
Results and Discussion
Table 14 also shows the area of each flood susceptibility class. As it is known, 40% of Gorganrood basin per hectare has a very high and high sensitivity and as about 41% of the basin has a low and very low sensitivity to floods. Therefore, the results indicate a high risk of flooding in the Gorganrood watershed.
The results of this study with the results of Amir Ahmadi et al. (2011) in the city of Neishabour who concluded that among these effective factors in floods, the distance from the river and thewater way has the highest weight and impact and also the study of Sheikh et al. (2015) in Malaysia, agree that soil type has the least impact on floods. According to the final map, the high-risk areas are mainly located in the flat and sloping areas located in the north and northwest of the study area, and the closer we get to the steep and mountainous areas, the greater the flood potential in the basin is reduced.
Although slope is one of the most important factors in the occurrence of floods, it has the lowest weight in this study; This is because this research focuses on flood damage, not the factors that contribute to the flood itself. In other words, although the slope plays a role in causing floods, but the most damage has occurred in low-slope areas, because in these areas the water velocity decreases and flood accumulation occurs, and this is the case with the areas with the most damage due to the flood observed in it, it is coordinated. Also, Fernández and Lutz (2010) consider flood slope and poor maintenance of drainage canals as the most important causes of floods by preparing a flood risk map in two cities of Argentina. Other researchers have also considered other parameters important in the occurrence of floods, including Sani (2008) by examining the factors affecting the occurrence of floods in rivers in Nigeria and concluded that the annual rainfall has the highest weight and land cover the lowest weight and they have an impact on the occurrence of floods. Morley et al. (2012) examined the flood potential of the Arno River in Italy and concluded that urban development areas are more vulnerable to flooding.
The results of the final flood risk map in Gorganrood basin show the fact that 19.97% of the basin has a very high risk situation, 19.98% has a high risk situation, 19.98% has a medium risk situation, 20.07% has a low risk situation, 20% have a very low risk of flooding. Therefore, the results indicate the high capacity of the basin in terms of flood risk, so there are many areas with high and high risk, which need protection and watershed management measures (such as: prevention of soil erosion and destruction, reducing water sediment load, reducing the speed and intensity of runoff flow, increasing flood concentration time, creating opportunities for water infiltration in the lower layers of the basin and feeding the aquifers, planting plants suitable for the geographical conditions of the slopes and rehabilitating rangelands and creating green spaces in the basin.