پهنه‌بندی مخاطرات زیست محیطی حوضه آبریز ویرمونی استان گیلان

Introduction
Environmental hazards, both natural and human, are threatening and capable of harming the human physical and social environment. This damage not only occurs during the occurrence, but is also likely in the long term Environmental hazards are caused by three factors: nature, human and technology The increase in the world's population from three billion people in 1960 to 7.6 billion people a year and the possibility of its increase to 11 billion people in 2050 is one of the reasons for the pressure on nature and the occurrence of hazards Every year many natural hazards and disasters occur in our country, therefore, today it is time for the planners and policy makers of the society to accept that there are always strange events in nature and to predict the possibility of their occurrence in their plans and programs so that when they occur with the volume to face less problems. In other words, knowing the risks is important to reduce them, more important is that people and societies accept the reality of the existence of risks. The frequency and spread of calamities caused by natural hazards has increased In most cases, natural disasters cause severe financial and human losses and disrupt economic and social activities.
Methodology
Virmoni catchment area is located between 48°43° to 48°50° east longitude and 38°21° to 38° north latitude. This basin is one of the large sub-basins of Talash and rivers in the northwest of Gilan, which originates from the western heights of Astara city (Mount Espinas) at an altitude of 1300 meters and passes through the village of Laton and after passing through the villages of Laton , Turk Mahalle, Awad Ler, Sayadler, Jibreel Mahalle, Sheikh Mahalle, Amir Mahalle and Bijarbin closes at zero altitude near the village of Virmoni, and the branch continues past the middle of Astara city and finally empties its water flow into the Caspian Sea. do The studied basin is limited to Lundville basin from the south, Bezoune basin from the southeast, Caspian sea from the east, Astrachai and Azerbaijan Republic in the north, and Astrachai basin in the west. Its direction is first southwest-northeast and after the exit of the basin in the mountain (the place where the basin closes) it has a general west-east direction. The area of its small water basin at the point of entering the plain is 45 square kilometers, the length of its main branch is 13 kilometers and its shape is elongated, and the average annual volume of the river flow at the point of entering the plain is 28 and 47 million square meters at the Astara station. The water flow of this river has been under investigation and control since 1364, and its power source is the annual rainfall of the area in the rainy season and the melting of the snow in the highlands in the hot season. In (Figure 1) the geographical location of Virmoni watershed is presented.
Discussion
General Geology of Talash: This mountain range with a north-south (N-S) trend is basically an anticline, which has a north-south axis, the eastern slope has a steep slope and the western slope has a relatively gentle slope. The border of this mountain range with the Caspian sea basin is probably a fault (Astara fault). Talash mountain range is divided into two major parts under the main divisions of Tektunuk: Eastern zone and Western zone. It may be possible to imagine the Noor fault as the boundary of these two zones, as the deposits of the eastern part of the fault are mainly formed from a large amount of clastic sediments along with volcanic activities related to the Late Cretaceous and Paleocene times, and have created anticlines and transgressions in the north-south direction. In its core, in the area of Khutbah Sera, they have found a complex of metamorphosis. Therefore, the oldest rock unit includes metamorphic rocks belonging to the Precambrian, and formations belonging to the Jurassic and Cretaceous, such as limestone, sandy limestone, and pyroclastic rocks of the Cretaceous and Paleogene, including sandstone, conglomerate, gray shales, tuffs, andesitic flows. Agglomerate tuff and basalt and sand and silt sediments along with gypsum and salt layers are outcropped in the west of Astara. There are no limestones that can feed the underground water table of the plain in the region, and only in the headwaters of some rivers, there are Cretaceous limestone formations in the form of silty limestones and sand with many joints and cracks, which play an essential role in the formation of the river's base discharge.
Conclusion
The current research is under the title of zoning the potential of natural hazards in the Virmoni catchment basin, which during the past seasons has investigated the performance of various natural and human factors influencing the occurrence of natural hazards and the effect of these hazards on the environment and finally preparing a zoning map of the potential of occurrence. According to the results obtained in the topographic section, the area under study is located in the extreme north-west of Talash mountains, and it consists of two parts, the foothills and the plains, and the topographical factors that are effective in the mass movements of this area are the slope, direction and height. According to the studies conducted in the climate section, based on the climate coefficient calculated by Dumarten and Amberget methods for the selected station, this region is located in a very humid climate. In terms of rainfall, it is one of the regions that benefit from the highest rainfall in the country. The effects caused by this type of weather due to excessive rainfall have caused the soil of this region to increase the adhesion and adhesion of its particles and grains to each other, and the penetration of water due to heavy rainfall and increased water pressure has caused Slope movements, especially landslides in the slopes, and the occurrence of heavy rainfall for several days also cause floods. According to the vegetation department studies, the majority of the area is of dense forest vegetation type. This factor prevents landslides to a large extent despite the availability of other natural conditions, but in case of land use change, the conditions for landslides occur. Landslides occur after heavy and continuous rains. The geomorphological studies of the region show that, after the stabilization of the structural geomorphology of the region and the creation of the current complications at the beginning of the Quaternary, the dominant phenomenon in the region, apart from the change of the Caspian Sea bed level during the glacial and interglacial periods, is probably chemical weathering with great intensity. has been high Because considering the current climate (Astara synoptic station) where the rainfall is more than 1368 mm, the average annual temperature is 15.9 degrees Celsius, good conditions are provided for chemical weathering; Especially since the number of frosty days in the region is very few. The evidence in the region indicates that the region follows the Caspian system. According to the climatic information of Astara, based on Peltier's morphogenic model, the weathering system will be of medium chemical type with weak ice performance. In such a system, river morphogenesis is intense, mass movement is moderate, and wind morphogenesis is very weak. However, human intervention in changing the environment and manipulating the unevenness has accelerated the occurrence of the normal phenomena of geomorphology, i.e. the process of morphogenesis. In general, the most important results obtained in understanding the risk factors are as follows: The most important factor in the creation of fine surface materials and clays and silts is chemical erosion caused by rain on rocks. The rocks in which the most landslides have occurred are mostly volcanic igneous rocks with volcanic lava, cataglomera and shale with their surface materials such as clay, marl and silt. The lack of proper drainage of the underground waters that are located on the upper level and the infiltration of sewage water on top of some slopes, which increase the water pressure between the holes of the rocks and the surface materials of the slopes, cause an increase in the number of landslides and damages caused by it Will be Another cause of mass movements is the abandonment of agricultural terraces on the slopes in the foothills of the region. The lack of agricultural activity on them blocks the spaces between the stones and drainage is not done well, and in fact, heavy and consecutive rains, water accumulates and cannot penetrate, brings the range to the limit of plasticity and flow. Investigating issues related to the geomorphology and geology of the region revealed that most of the slopes of the basin slope towards the east. Mainly in the slopes between 15-30 degrees due to chemical erosion, abundance of water and fine and soft surface materials (thick-layered soils), the ground for potential and actual slope movements is high.