جستجوی مقالات مرتبط با کلیدواژه "تراکم زهکشی" در نشریات گروه "جغرافیا"

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.

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.

The public opinion is that in the landform-topographic study, the drainage system, and the drainage pattern, by using geomorphic indicators one could assess the performance of active tectonics (Maghsoudi et al., 2011). This is true if we do not consider the primary structure of the earth, rock type, and local factors determining the microclimate (Abedini et al., 2015; Jafari and Barati, 2018). Considering these factors, the results question the geomorphic indicators. In this paper, the researchers study the role of various factors in the drainage asymmetric index of 117 sub-basins in the Alvand mountainous of Hamadan. A subject not considered in the drainage asymmetry index of areas such as the Alvand mass of Hamadan is the shape of the magma lies between the sedimentary layers at the time of cooling. In relation to the drainage symmetry index, this paper tries to study the physical properties and the effect of local factors in the watersheds of the Alvand Hamedan Batholith. Although the drainage networks asymmetry of is analyzed with morpho-tectonic indices, the basic land structure, lithological and erosion properties can also affect the asymmetry of the basin.

For this purpose, parameters of the dominant slope, average slope, average height, the area of the right and left of the river, main river .length, river airy length total length of the rivers, distance of the source of the dividing line, and rock types in different parts of sub-basins were determined. These parameters were used in calculation and analyses of Gravelius coefficients (compactness coefficient), elongation ratio, drainage density and asymmetry index. For the phenomenological investigation of the drainage network index status, with the help of topographical maps 1: 50000, the outlet point of the Alvand Batholith sub-basin was identified in the mountainous area. Accordingly, 13 sub-basins were classified in the Alvand Batholith. Class B subclasses are located inside the subclasses of class A and subclasses of class C are located inside class B subclasses. To separate sub-basins in each of the 13 sub-basins, the longest river was considered as the main river. All the streams connected to it are separated as subclasses of Class B. In the next step, the main river basin in the sub-basins of class B was also determined and the rivers entering it were designated as the sub-class C. Accordingly, a total of 117 sub-basins was identified.

 In order to investigate the factors affecting the asymmetry index (tectonics, lithology, microclimate and physiography's characteristics of sub-basins); at first the status of sub-basin rock was studied. The largest area lies in the cordierite-Gabbro Stone (15.4%), and the smallest area lies in the Granite- Schist- Gabbro and cordierite-Gabbro (0.69%) groups. Investigating the elongation coefficient the sub-basins in which the dominant stone is granite shows a very low elongation ratio of these sub-basins. They lie in a group that is less elongated than the rest of the sub-basins in other rocks. In terms of the Gravelius coefficient, it can be said that the more symmetrical the basins tend to be circular in shape, as the mean Gravelius coefficient of the stable sub-basins for the asymmetric index is 3.35 vs. 2.64 in the relatively stable sub-basins, which fully confirms this point. The ratio of bifurcation of unstable sub-basins is very high, and according to the rocky area, the drainage density in the unstable sub-basins is inversely related to the slope of the basin.

In general, sub-basins of the northeast slopes are more asymmetrical than sub-basins in the southwest slopes, which it can be due to the zhizman form of the Alvand Batholith, the differences in the physiographic properties, and finally the dominant sub-basin rocks. In the wider sub-basins of the slope and the varying direction of slope, are vectors that can have a significant effect on the drainage network asymmetry. The further elongation ratio of drainage of the basin with low drainage density, in granite rock, affects the drainage network asymmetry of the basin. Investigating the conditions of slope values in different classes of the asymmetric index in sub-basins other than granite rocks indicates that the difference between the value of the left and right slopes of rivers is not a significant effect in the basin asymmetry. By decreasing the sub-basins area, the effect of direction and slope value, elongation ratio and bifurcation coefficient on asymmetric basins decreases. The study of the Gravelius coefficient indicates that the shape of the more stable sub-basins is closer to the circular shape. The bifurcation ratio of most unstable sub-basins is very high. The drainage densities of unstable sub-basins have an inverse relationship to the basin slope. The difference between the rock types on the left and right and the river's position on the boundary between the two rocks have an important role in the basins asymmetry.

The Hydrographic network system is a function of lithological factors (hardness, permeability, quality and quantity of joints and gaps), and structural agents (the status of stretching and slope of the layers, the presence or absence of faults, etc.). Therefore, the characteristics of the waterways (flow, density, type and shape) are a function of the status of the rock and the roughness of each region. In this study, four geological formations including alvand granite, chlorite hornfels, marl limestone and screw styrite were selected. In each formation, a 2 km 2-kilometer plot was installed randomly-systematically in each formation, and to investigate the drainage network of The Australian method and a better comparison of the fractal dimension are also used. Also, in order to study the erosion of rocks and their role in damaging the northwestern formations of Alvand Mountain, microscopic sections were performed with sampling of granite, schist and hornfels rocks. The erodibility map was prepared and compared with the results of fractal dimension and drainage network. In this study, in first 4 geology formation that including Alvan granite, Cordierite hornfels, marly limestone and Staurolite schist was selected and then each zone of geology formation, set a plot with the size of 2*2 km as randomly and extract drainage network of each formation and then the fractal dimension of them were be calculated. Comparison of fractal dimension showed that maximum and minimum of fractal dimension related to Cordierite hornfels and Alvan granite with 1.33 and 1.22, respectively. On the other hand, the result showed that graphical and mathematical fractal dimension in 4 geology formation, have correlation coefficient upper 99 percent. The results showed that with increasing fractal dimension, with the parameter drainage, erosion of geological formations increases. The results from the mineralogical study of microscopic sections show that granite rocks are less erodible than schist, hornfels and lime and marn against erosion.

Drainage density is an important hydrogeomorphologic indicator in determining activity quality of processes of overland run-off, flood intensity, soil erosion and sedimentation load in the basin. Drainage density was defined as the ratio of the total length of streams in a watershed over its contributing area. It describes the degree of drainage network development and was recognized by many authors to be significantly effective on the formation of flood flows. Drainage density is higher in arid areas with sparse vegetation cover. The higher the drainage density, the lower the infiltration and the faster the movement of the surface flow. The structure of watershed topography depends to a large extent on the interaction between slope and channel processes. The applicability of these relatively simple summaries, however, needs to be examined carefully. It is still uncertain how the development of drainage systems with time affects the relation of drainage density with lithology, slope, aspect and elevation. The Behrestagh watershed is a sub-basin of Haraz River basin where in varied geological and topographic conditions and the many overland flow cause soil erosion and destruction of pastures and gardens of the area. This study examines the relationship of drainage density with Geology and topography factors for Behrestagh watershed.
The Behrestagh watershed lies between the latitudes of 35° 56΄ N to 35° 59΄ N and longitudes of 52° 16΄ E to 52° 22΄ E. The main stream in the area is Haraz River. Topographic elevations in the study area vary between 1172 to 3548 m. Here, in order to examine drainage density in the studied area, map of the watershed’s streams was prepared first using GIS and Digital Elevation Model (DEM) of that area. Then, effective Geology and topographical properties including lithology, elevation, slope and aspect was considered and classified in ArcGIS environment and finally were overlaid with the streams as a dependent variable. Accordingly, sum of streams length per unit of each factor was calculated and drainage density was obtained. Data were analyzed in SPSS 20. Moreover, collected data were described using descriptive statistics (tables, charts, abundance distribution, mean and standard deviation). Data analysis was performed using one-way ANOVA to obtain differences with other studied variables.
Discussion of In this study, data analysis was performed using one-way ANOVA to obtain differences with studied variables. Results of the statistical test indicated that the relationship of lithology and slope with drainage density in the considered area was significant at .95 and .99 level of confidence, respectively. The relationship of drainage density with elevation and aspect was not significant, as well. The results showed that the most drainage density of the area was observed in elevation lower than 1400 meters (average density of 8.24). Also, the cretaceous melaphyre formation (km) with average density of 8.79 and the slope class of 20 -30 percent showed an average density of 10.7 and the western aspect (domain direction) indicated an average of 5.57.
To determine the geology and topography factors influencing drainage density, data layers of lithology, slope, aspect and elevation were analyzed through overlaying the dispersion map of the watershed’s streams. The results showed that cretaceous melaphyre formation, elevation below 1400 meters, slope of 20-30 percent and the west aspect are sensitive to streams. Also, results indicated a significant relationship between lithology and slope with drainage density in the considered area and slope was found to be the most important topography factor affecting drainage density. Therefore can used from these variables to assess erosion intensity and its control.

Drainage density is one of the parameters that can be considered as an indicator of erosion rate. This study analysed the relation between drainage density and soil erosion in five watersheds in Iran. The drainage density was measured using satellite images, aerial photos, and topographic maps by Geographic Information Systems (GIS) technologies. MPSIAC model was employed in a GIS environment to create soil erosion maps using data from meteorological stations, soil surveys, topographic maps, satellite images and results of other relevant studies. Then the correlation between drainage density and erosion rate was measured. T.The results indicate that the relationship between these two factors improved when the types of sheet erosion, mechanical erosion and mass erosion was ignored because these types of erosion were not mainly influenced by the power of runoff. There was a high correlation between drainage density and erosion in most of the watersheds. Finally a significant relationship was seen between drainage density and erosion in all watersheds. Based on the results obtained, the present method for distinguishing soil erosion was effective and can be used for operational erosion monitoring in other watersheds with the same climate characteristics in Iran.