عنوان مقاله [English]
Morphological Assessment will be necessary to understand the current situation and the potential for possible river changes in the future. Natural factors such as floods, soil erosion, landslides and human factors such as land use change and sand removal from the riverbed affect the morphology. River systems have always been of interest to humans as one of the most vital elements of the Earth's surface. Humans also change the face of the earth by changing their use, destroying natural resources, plowing the land in the direction of the slope, planting trees in the riverbeds. Any Manipulation into the riverbed will change the process of erosion and sedimentation along the river. Understanding the characteristics of flow and sediment is the basis for evaluating the behavior of rivers and deciding on engineering activities. Therefore, it is necessary to obtain the necessary information on how they work before starting engineering projects for rivers.
Data and Method
In this study, geological maps at a scale of 1: 100000 of the Geological Organization, topographic maps at a scale of 1: 50,000 digits of the Geographical Organization of the Armed Forces, Landsat satellite images, 2020 April, November 1995, Climatic data Temperature and precipitation (1399-1374) of Lorestan Meteorological Organization and Digital elevation model of 30 meters has been used. Arc GIS software was used for spatial analysis and ENVI software was used for processing satellite images. The normalized water difference index is the first index of water extraction in images and remote sensing data. In this indicator, two green and infrared bands are used. Positive values of this index indicate water and negative values indicate phenomena other than water. Researchers have proposed different methods for studying changes in river channels. The transect method is used to evaluate changes and displacements in river channels. In this method, lines with specific distances on both sides of the river route are drawn as baselines. These lines are constant for the time periods studied. River channel displacements relative to these lines are quantified. To further evaluate the Kahman River canal, the canal migration rate method was used. The Kahman river Canal was divided into two areas, mountainous areas and plain and agricultural areas, based on topography and land use.
Results and Discussion
To calculate the area to the right and left of the transects, the Kahman river channel was cut separately with a transect layer in 1995 and 2020. Calculation of changes in the area of transects shows that about 185.85 hectares of land adjacent to the Kahman river (1995-1999) have been eroded. On average, about 7.43 hectares of these lands have been destroyed annually. The maximum value of this index in transect 30 is calculated at 8.27 hectares. In order to better understand the changes and dynamics of the Kahman river Canal, the migration rate index (Rm) was also used. First, two fixed lines were drawn around the Kahman river channel. The area between the two was calculated using Arc GIS software functions. The average migration rate of Kahman river (1399-1374) was 2.51 meters per year. The lowest level of this index occurred in Trasket 49 at 0.18 meters per year. The mountain factor and stabilization operations along the river have been the most important reasons for its control and stabilization. The highest rate of migration occurred in transects 4, 32 and 30 at 4.80, 5.5 and 6.12, respectively. Shortcuts and land use changes have been the main reasons for the high rate of duct migration in these transects. The largest amount of lateral changes in the Kahman river route occurred in parts of the plain and agricultural areas, including transects 30 to 35. The most important factor was the high lateral changes of the Kahman river route in the plain area due to the high erosion of the coastal and floodplain materials. Most of the constituents of the bed and banks of the Kahman river in these periods are from fine to coarse sands.
Duct migration rate index showed that the average displacement of Kahman river canal (1374-1399) was 2.51 meters per year. The lowest value of this index was 0.18 meters per year and the maximum value was 6.12 meters per year. Calculation of changes in the area of transects showed that about 185.85 hectares of land adjacent to the Kahman River (1374-1399) has been destroyed. On average, about 7.43 hectares of these lands are lost every year. In the mountainous area, the effects of the mountains were the most important factor in determining the morphological changes of the Kahman River channel. The presence of erodible materials along the Kahman River in the plains and agricultural areas has increased the lateral migration of meanders and the width of the valley and floodplains adjacent to the river has increased significantly. Therefore, it can be said that the Kahman River has had more geometric changes in the plains and agricultural lands.