عنوان مقاله [English]
In the last decade, the use of fractal analysis to quantitatively describe the geomorphological and hydrological watersheds has increased and the main purpose of most of these studies is to find a mathematical relationship between the geomorphological characteristics of the basin and issues such as erodibility of formations and segregation of geological units. Alimoradi et al. (2015), in calculating the fractal dimension of geological formations and examining its relationship with the sensitivity of formations, showed that there is a significant relationship between fractal number and the sensitivity of basin formations to erosion. Barzegari Dehj et al. (2019) in comparing the dimensionless index of drainage network density and fractal dimension of drainage network in the separation of lithological units of Taft watershed, Yazd, concluded that the drainage network density technique compared to the fractal dimension of drainage network technique in identifying and Separation of geological units of the region has provided excellent results. Donadio et al. (2014) compared three rivers from a fractal point of view of the hydrographic model and concluded that the relationship between tectonics and erosion is very high with the fractal dimension number. Hui et al. (2017) in examining the relationship between fractal dimension of drainage network and evolutionary stages of erosion of China Yellow Basin showed that fractal values of drainage network have a positive and linear relationship with sediment delivery and runoff values of the basin.
Alvand mountain massif of Hamedan is located in the division of tectonic units of Iran in the structural zone of Sanandaj-Sirjan, which extends parallel to the Zagros rotation. The purpose of this study is to determine the fractal dimension of the drainage network and to investigate its relationship with geomorphological patterns and the sensitivity of geological landslides to erosion in the northern slopes of Alvand Hamedan. In this study, four geological units including granite, chlorite hornfels, marl limestone and sterolized schist were first selected using Google Earth software, geological map of the area and satellite images and field visits. Then, in each geological unit, 2 plots of 2*2 km were determined and their fractal dimensions were calculated using Fractalyse software. After calculating the fractal dimension and determining the sensitivity of each formation, the relationship between the fractal dimension and the formations was investigated by Pearson test and the correlation value.
Results and Discussion
The results showed that the highest amount of fractal dimension is related to chlorinated Hornfels Formation with 1.33, marl limestone 1.31, sterolized schist 1.27 and Alvand granite 1.22, respectively. Examination of the coefficient and deviation angle data in each of the geological units shows that these values are somewhat high in the fractal dimension technique of the drainage network. So that the deflection angle is 1.909 in sterolized schist, 1.555 in granite, 1.528 in Hornfels and 1.171 in marl limestone. Studies show that the computational values of the fractal dimension of the drainage network are very good and in the amount of 0.99 and indicate the good performance of the fractal dimension technique for identifying and separating the geological units of the region. Due to the proximity of the coefficient of determination in the fractal dimension technique of drainage network density to 1, low deflection angle and proximity of its computational figures to zero, the fractal dimension technique of drainage network is the best and most appropriate technique for separating geological units in the study area. Studies show that in formations with more sensitivity than resistant formations, more changes occur in drainage density and their fractal dimension is more. Regression analysis of fractal dimension values and numerical index of abrasion resistance of the studied formations shows that the value of R2 is equal to -0.835 and shows a high correlation and significant relationship between the fractal dimension and the numerical index of erosion resistance and indicates that As the strength of formations increases, their fractal dimension decreases.
The results showed that the fractal dimension technique of drainage density is the best and most appropriate technique for identifying and separating the geological units of the study area. Studies show that in formations with more sensitivity than resistant formations, more changes occur in drainage density and their fractal dimension is more. The results of Pearson test and the correlation value (-0.828) of the data indicate that there is a significant and inverse relationship between the strength of formations and their fractal dimension, ie with increasing the resistance of formations to erosion, their fractal dimension decreases and Therefore, drainage density is also low. The results of ANOVA statistical analysis show the significance of the whole model, the relationship and the effect of the two variables of sensitivity of the formations and their fractal dimension at the level of 0.000 significant and in reverse. Therefore, according to the acceptable results, using this technique, the type of formations and their sensitivity to erosion can be separated and examined with acceptable accuracy.