جستجوی مقالات مرتبط با کلیدواژه « بعد فراکتال » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Introduction and Goal:

Understanding the role and influencing factors of soil erosion is crucial for effective management and recognition of erodible land areas. Watershed management is one of the most sensitive and complex types of resource and production management. The fractal dimension can be used to examine the complexity of data and simplify complex natural phenomena. This tool enables generating fractal patterns to assess the morphological behavior and power of watersheds. This research focused on the connection and interplay between the morphological characteristics of the watershed and the fractal dimension in the creation of runoff and sediment.

In this research, the necessary data were obtained from the statistics of the country in the water measuring and observation stations of the watershed. The base maps were utilized to determine the watershed characteristics. The calculation of the fractal characteristics was done in Fractalyse 2.4 software by utilizing the box counting method. The factor analysis method was used to identify 85 features related to watershed. In this research, for further analysis, the size of annual runoff and sediment was investigated using different return periods. Therefore, 5 different scenarios were considered based on the homogeneity of the watershed, climatic characteristics, physical and morphological characteristics of the watershed, physical and climatic characteristics simultaneously, and fractal characteristics of the watershed. The correlation between estimated irrigation and sediment size (with different return periods) and different morphological features was also carried out.

The results of the factor analysis technique showed that among the 85 parameters related to the watershed, 18 are the effective parameters of the area, the slope area is 8-12 and 12-20%, the area of the east slope in 9 directions, the length of the 100-m level lines in the watershed, the total length of the stream , the concentration time base Kirpich method, elevation difference, fractal of 200-m level lines, deviation from the moisture standard, temperature difference, average slope, net slope of the main stream, average temperature, average moisture, average precipitation, elongation coefficient and fractal of the basin environment. Also, the fractal dimension of the 200-m horizontal lines and the fractal dimension of the watershed environment were able to significantly explain the overall changes in discharge and sedimentation. This finding explained well the role of fractal characteristics in the relationship between irrigation and sedimentation.

Conclusions and Suggestion:

Based on the results of this research, it was found that almost all the effective factors in estimating discharge and sedimentation in large watersheds are summarized in the area and fractal of the watershed environment, and these two features justify the most changes in discharge and sedimentation. Therefore, with the reduction of the area of ​​watersheds, the role of other factors such as the direction of the slope, the net slope of the waterway, etc., is more evident in explaining the changes, and it can be said that dividing large watersheds into smaller watersheds is the best measure to control the erosion and runoff of watersheds. Implementing watershed management measures in these small sub-watersheds is the next step. The reduction of watershed area in most relationships is sufficient to justify up to 70% of sediment changes. This research findings should be utilized by users and beneficiaries to implement watershed development and management programs.

This research focused on studying the morphometric characteristics, topographic threshold of gullies and their relationships, dominant process of gully initiation and development stages as well, in agricultural and rangeland land uses. Also, morphometric characteristics of 120 gullies including top width, bottom width and headcut height and surface characteristics of gullies contributing area including vegetation, rock fragment and bare soil by 1 m2 plot and soil samples from top soil and gullies wall were collected in semi-arid part of Ilam Province. Results showed that top width–depth ratio of gullies in cropland and rangeland is 2.1 and 1.5, respectively that widening and deepening has more important role in gully growth. Top width-length ratios are 0.41 and 0.57 in croplands and rangelands, respectively that shows rangeland gullies are more elongated. Negative exponential relationship between those ratios and slope shows the effect of topographic factors especially slope on final shape of gullies. Bottom width-top width ratio in croplands and rangelands is about 0.33 and 0.3, respectively and cross section shapes are trapezoidal and V shape. Results showed that slope describes 16 percent of cross sections area variation and lateral growth of gullies in croplands and rangelands and describes 84 and 73 percent of gully volume variation. Effective factors on gully volume are sand content in top soil, land use and slope. Studied gullies in both land uses have mean fractal dimension of 1.08 and has linear growth with length and power growth with volume of gully. Power of Hack law in studied gullies in croplands and rangelands gullies are 0.5 and 0.54, respectively.

Many natural phenomena have many variables that make it difficult to find relationships between them using common mathematical methods. This problem, along with the impossibility of measuring all elements of nature, has led to a major evolution in the way of understanding and explaining phenomena. In this way, one can use the fractal geometry with the theory that many natural phenomena are order in the chaos. Each element of nature is represented as a fractal geometry number. In fact, fractal geometry is a quantitative tool for studying the geomorphology of drainage networks and modeling many complex natural phenomena. Since geological variables have a profound effect on the nature and activity of the drainage networks. In this study, the role of lithology and geological formations is studied to quantify the drainage networks and used fractal dimension to indicate sensitivity to erosion of the formations of this area.

The present study consists of four main sections. The first section is the collection of maps and data. In this section, geological maps of 1:100000 areas were provided and selected from the geological formations of Yazd- Ardakan basin, three geological formations of Kahar, Granit and Taft. Sensitivity to erosion of these formations was studied in this area using PSIAC, Feyznia and Selby methods. In second section, fractal dimension is estimated in 30 plots of 1 × 1 km2, three geological formations of Kahar, Granite and Taft. In each geological formation, fractal dimension was calculated by box counting method using Fractalyse software and the number of plots required in each formation was determined using Graphical method. In the third section of this study, morphometric indices were calculated including drainage density, number of ranks, average length of rank and rank frequency. In the final section, uncertainty analysis of fractal dimension efficiency was studied in classification and separation of geological formations. In most studies in the field of fractal dimension, the uncertainty of this method is not considered. As a result, their findings do not have enough accuracy to generalize to natural phenomena. Therefore, in this study, uncertainty of fractal dimension efficiency was investigated in 30 plots of 1 × 1 km2 that were excluded from other study sections for testing this method.

The mean fractal dimension of 1.149 represents Taft formation, the mean fractal dimension of 1.161, is Granite formation and the amount of 1.207 is Kahar formation. The highest fractal dimension was calculated in Kahar formation (1.279) and the lowest in Taft formation (1.046). In addition, the correlation coefficient is 99%. The results also indicated a significant and meaningful relationship between fractal dimensions of drainage networks and morphometric properties. In this paper, a positive relationship is observed between morphometric parameters and fractal dimension, so that the greatest correlation coefficient is found between the fractal dimension and the drainage density (0.99). The results of uncertainty analysis of fractal dimension showed which fractal dimension in the geological formation of Kahar with 90% has a steady trend and in two geological formations of Taft and Granite, this amount is about 70%. Therefore, fractal dimension in the drainage network identification of the Kahar formation is more powerful than two other granite and Taft formations.

The drainage networks are the most prominent landscapes on earth that are the basis of many hydrological and geomorphological models. Due to the geomorphological characteristics of the region, the drainage network shows its own fractal properties that are saved as code in it. In fact, drainage networks are fractal phenomena with fractal behavior. In this study, the fractal dimension and morphometric properties of the drainage network were used to analyze the sensitivity to erosion of the geological formations of this area. PSIAC and Feyznia methods did not perform well in separating the sensitivity to erosion of Taft and granite formation, and they are unable to distinguish between these two formations. So, using the Selby method, six effective factors were investigated on the resistance and sensitivity of formations to erosion (Schmidt Rebound Hardness, weathering, distance between joints, direction of the joints relative to the slope, the width and connection of the joints) in Taft and Granite formations. The study of these factors leads to field visits and spends a lot of time and cost. As the results of the resistance to erosion of formations were shown by Selby method, Granite formation has less resistance to Taft formation. Due to the climatic conditions in this area, Granit formation is susceptible to weathering. Extreme weathering acts as arenization process. In fact, fractal dimension in three geological formations of the study area is well showed the difference in resistance to erosion of both Taft and Granite formations. The results of this study showed that fractal dimension allows for a quick and accurate analysis of the erosion characteristics and sensitivity to erosion of the formations of this area.

Every phenomena in the nature, despite the complexity of the subject, has certain rules and regulations. River pattern and behavior as one of the most complex natural phenomena to this is not an exception. Depending on geomorphologic, climatic, topographic and erosive conditions, the waterways exhibit different patterns and behaviors. One of the parameters which can be achieved using the complexity of the pattern of the form of phenomena is fractal geometry. The purpose of this study is to calculate and compare the fractal dimension of hydrographic networks in Ilam watersheds, which were extracted from 50 m DEM and SRTM satellite data. Hydrographic networks that were derived from SRTM data with a precision of more than 5 meters are mapped by using Google Earth images. For this purpose, 12 watersheds were first selected in Ilam province (Ema, Tang-e-Sazbon, Doiraj, Holylan, Nazarabad, Chamgahs, Kolm, Siagav, Jafarabad, Chaviz, Jezman and Vargach) and after determining the units of 25 square kilometers in each of the areas and drawing and completing the drainage network patterns in the studied areas, their fractal dimension were calculated using Fractalys software. The results showed that the calculation and comparison of fractal dimension with visual methods is correct if the compared fields have the same area, and the accuracy and scale of the drawing of hydrographic networks is also the same. On the other hand, the drainage network drafted on Google Earth with a precision of more than five meters compared to the corresponding waterway network with a precision of 50m DEM in 5 × 5 square kilometers (25 square kilometers), has a very high accuracy. Also, the minimum fractal dimension before the modification of hydrographic networks is for Ema watershed (1/042) and the maximum amount is for Tang-e-Sazbon watershed (1,424). However, after the modification of hydrographic networks and calculating fractal dimension, the lowest fractal dimension is for Chaviz watershed (1.1) and the highest amount is for Nazarabad (1.49).

In this study, the relationship between the gully formation and some soil properties, climatic factors, land use and slope was investigated in Dareshahr Township in Ilam Province, Iran. Toward this attempt, 18 axial, digitated and frontal gullies were recognized. The soil samples were taken from the top and subsoil in the gully bank. The climatic, land use and slope information were obtained using Dareshahr Climatic Station and available maps, respectively. The relationship between gully erosion frequency and slope as well as land use was then studied using ANOVA and the most important factor was ultimately recognized by using principle component and regression analyses. The results of the study have shown that most numbers of gullies were formed in areas with slope less than 10% and land uses had no significant effect on gully formation. Besides that, the percentage of clay and sand as well as calcium content were found to be as most affective soil factors on gully formation. Among climatic factors, the rainfall depth and average intensity played important role in gully initiation. The results extracted from discriminate analysis also proved that the depth of rain is the most affective factor in gully formation in the study area.