عنوان مقاله [English]
Rivers are among the most dynamic natural systems that any intrusion and occupation in them is associated with a negative reaction of the river in the form of floods, erosion, bed changes and so on. In this study, Kordan river due to its special geographical, ecological and ecotourism location is highly exposed to adverse human interventions such as severe harvesting of materials, agricultural and industrial activities, implementation of development projects in the riverbed, villa construction and encroachment on the river There are tourist activities, each of which has been very effective in changing the balance of the river. Since the life of this river affects groundwater nutrition, agricultural activities and climate adjustment of Hashtgerd plain, so its maintenance and optimal use is essential. In this study, the role of human factors in the imbalance of the Kordan River using Satellite images and HEC-RAS software have been studied. In many projects, only HEC-RAS software and hydrometric data have been used to simulate floods. The advantage of this research is the combined use of satellite images. The effect of land use change around the river as a result of human activities such as harvesting materials and its role in creating floods and changes in cross-sectional profiles in the Kordan River using HEC-RAS software. Therefore, in this study, in addition to flood simulation The role of human factors in creating imbalances and changes in the bed of the Kordan River was investigated. The main required data include Landsat 7 and 8 and Sentinel 2 satellite maps with an accuracy of 30 and 10 meters, respectively, from 1999 to 2021, Kordan River 1: 2000 topographic maps, hydrometric data and river boundary conditions. In order to calculate the maximum instantaneous flow rate with different return periods, the completed and extended annual maximum instantaneous flow rate of hydrometric stations in the region, including Deh Soomeh, Fashand and Najmabad stations, has been used for a statistical period of 40 years. Also, Pearson type 3 distribution was found to be suitable for fitting data from statistical distributions. Based on the results obtained from satellite maps for 22 years, it was found that a large part of the land around the river has been converted into industrial units and residential areas as a result of land use changes. For example, the area of industrial units located around the river has increased from 59 hectares to 466 hectares (nearly 8 times), which is related to the expansion and construction of mammoth factories, Persia and asphalt production plants, crushers and New Jersey products. . Also, about 60 hectares of the main bed and floodplain of the river have been reduced. In the continuation of the work, using HEC-RAS software, floods with a return period of 2 to 1000 years were simulated. According to the results, the maximum depth The flow is related to the area of sand holes before the old Hashtgerd road bridge. Regarding the speed, the railway bridge with a flow rate of 9 meters per second has the highest speed in the study area. The results of flood distribution show that in case of floods with a return period of 2 to 5 years, there is no danger to the lands and structures around the river, but in case of floods with a return period of 10, 25, 50, 100, 200 , 500 and 1000 years, 8, 17, 25, 32, 41, 53 and 64 hectares of residential, industrial and barren lands around the river, respectively, will be exposed to floods and will be submerged. Also, the width of flood zones for the return period of 2 to 10 years was 278 meters, 25 to 100 years 355 meters and 200 to 1000 years 473 meters. The area before the bridge is the old Hashtgerd road. From the results obtained according to the method called the Australian Standard, it can be seen that in 2 to 10 year floods, most of the study area is located in the category of safe or low risk areas and only at the exit of bridges in the path to The reason for the high flow velocity mentioned at 4 m / s is the critical situation. Regarding the return periods of 25 to 100, catastrophic and critical points are like the return periods of 2 to 10 years, with the difference that the area between the Tehran-Qazvin highway bridge to the old Hashtgerd road is in a very high danger class. Results It is different in terms of periods from 200 to 1000 years. Also, the entire area between the Tehran-Qazvin highway bridge to the old Hashtgerd road will be in the category of high to critical and catastrophic areas.