Masoumeh Rajabi; Shahram Roostaei; Bahareh Akbari
Volume 6, Issue 20 , December 2019, , Pages 21-40
Abstract
1- IntroductionRiver morphology is the science of knowing the river system regarding general shape and form, dimensions and hydraulic geometry, direction and longitudinal profile of the bed, and the process and quality of its changes. The river plan is divided into three classes of direct, braided (multi-branch) ...
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1- IntroductionRiver morphology is the science of knowing the river system regarding general shape and form, dimensions and hydraulic geometry, direction and longitudinal profile of the bed, and the process and quality of its changes. The river plan is divided into three classes of direct, braided (multi-branch) and meandering river in terms of the morphological structure of the river, among which the meandering pattern has attracted the most attention due to its abundance in nature. In order to describe the pattern of the meandering streams, a number of geometric parameters related to the river plan have been defined. By analyzing the frequency and magnitude of these characteristics along the river and at different times, the river changes in the temporal and spatial dimension can be examined. These parameters Such as the length of the pontoon, the width of the pontoon, the width of the river and the length of the river. The purpose of this study is to examine the characteristics and patterns of the Aji Chai River. These parameters are such as the length of meander, the width of meander, river width, and the length of the river. The purpose of this study is to examine the characteristics and pattern of the Aji Chai Rivers’ meanders. 2- MethodologyThe study area was part of Aji-Chay River (Bakhshayesh to Khajeh) with an approximate length of 50 km, located in the northeast of Tabriz. The following materials are used in this study:1) Topographic map of 1:50000 and 1:250000 scales were used to examine the morphology of the study area,2)Geological maps of 1:250000 and 1:100000 scales for the analysis of geological and tectonic characteristics of the study area and 3)Using Landsat-8 and Google Earth satellite images and the ArcGIS, Excel, Autocad softwares.The study area was divided into three reaches. Some circles fitted to the meanders in the AutoCAD environment and the geometric characteristics such as wavelength, arc length, and radius of curvature of the circle, which is tangent to the river path, were measured to calculate the curvature coefficient (S = c / v) and the central angle (c/Rπ = ϴ 180). Then specification of each of the circles of the same samples was obtained and then in the EXCEL software, a plot of the samples was drawn. 3- ResultsDue to the long-range of the study area, the intended path was divided into three reaches. In terms of the central angle index in the first reach, the most frequent central angle was 62.5%, which is related to developed meander pattern. In the second reach, the highest frequency of central angle with 56% was related to the developed meandered pattern. In the third reach also the most frequent central angle was related to the developed meander pattern with a frequency of 57.5%. By comparing the three studied reaches in terms of the central angle index in general, it is concluded that all three reaches have a meandering pattern, in particular, a developed one, so that the average of all three reaches (the first reach 110.2, the second 118.2, and the third 123.1, respectively) are in the developed meandering pattern category (85-158). In each of three reaches, the most frequent central angle belongs to the developed meandering pattern.The average curvature coefficient of the reaches, calculated by dividing the sum of frequencies in each reach by the total number of samples of each reach, is as follows: in the first reach, the average curvature coefficient was 1.18 which is in the range of 1-06 – 1.25 showing a sinusoidal pattern. In the second reach, the average curvature coefficient is 1.30, which is in 1.25-2 range, also has a meandering pattern. In the third reach, the average is 1.26, which is the same as the second average in the range 1.25-2 and the pattern is meandering. In general, the pattern of flow in the first reach was sinusoidal and with the increase of arches in the second reach, it changed to the meandering pattern. In the third reach, although, there was a minor reduction trend was, it retained the meandering pattern. 4- Discussion and conclusionBased on the results from the morphometric indices, including the central angle and curvature coefficient in the studied area, the total mean of the central angle in the three reaches is 126.1 degrees, which is in the range of 85-158, showing the developed meandering pattern in the river morphology.The mean curvature coefficient in the three studied reaches is 1.25, which is in range 1.25-2, takes the meandering pattern in terms of curvature coefficient, so the studied river has a meandering to developed meandering patterns.The findings of the study indicate that the study area has a nearly uniform and smooth slope, and considering the fact that the existence of a gradient is a significant factor affecting the development of the developed arcs and meander formation, as a result, in determining the river pattern and morphology of the study area, the topography factor had the first priority.Due to the fact that erodible formations cover most of the area, the factor of lateral erosion in low-slope areas has been effective in the warping of the river path due to the presence of loose and erodible sediments.
Shahram Roostaei; Samad Azimirad; Davood Mokhtari; Seyed Asadollah Hejazi; Mojtaba Yamani
Volume 5, Issue 16 , December 2018, , Pages 119-138
Abstract
Abstract
Introduction
Saymarreh landslide is one of the known largest landslides in the world that is located in the southwest of Iran. The purpose of this study was to compare the characteristics and geomorphological influences of this landslide with the largest landslides of the world. Saymarreh ...
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Abstract
Introduction
Saymarreh landslide is one of the known largest landslides in the world that is located in the southwest of Iran. The purpose of this study was to compare the characteristics and geomorphological influences of this landslide with the largest landslides of the world. Saymarreh landslide is one of those large landslides that have undergone significant geomorphological, historical, and cultural changes during the Holocene era. The evolutionary trend of this landslide is highly complicated; in fact, it is one of the most important characteristics of large landslides. This landslide formed several dam lakes, and their formation were frequently repeated. However, it is not clear that whether the formation and evolution of the lakes were due to the river erosion sequences or the repetition of Saymarreh landslide.
Methodology
A large number of researchers believe that Saymarreh landslide is the largest landslide in the world, but some researchers do not believe so and introduce other landslides as the largest ones. Thus, by performing detailed investigations into the region, the geomorphic features of this landslide and its evolution was probed. To achieve this goal, ETM2002 satellite images, IRS of PAN and LISS III satellite images of 2004 and 2006, topographic maps, geological maps of SRTM DEM, and ArcGIS software were employed. The research method was empirical and it was based on the analysis of the field data. In this regard, the process of the landslide formation, its causes and morphometric characteristics in three classes of slide area, mass movement and displacement parameters along with deposited materials in Saymarreh Dam lakes were studied.
Result
The results relevant to the morphometry of the landslide indicated that various factors were involved in the occurrence of Saymarreh landslide. Among these factors, undercutting of the Asmari limestone layers made by Saymarreh and Kashkan Rivers, particularly in front of the landslide, was the most important cause of the landslide occurrence. The landslide had formed a large lake behind the slide mass and had formed sequential terraces due to repeated slides. The results of the morphometry of the lake, particularly through the estimation of its water (45.642 Gm3) and sediment volume (23.422 Gm3), and comparison of the time taken for filling of the water volume (19.8 years) with the time required for deposition of the whole sediment volume (1888 years) showed that the sediments have not been deposited only during one stabile period of the lake and the lake has been renewed at least at several stages. As a result, the reoccurrence of Saymarreh landslide at several times led to the obstruction of the Saymarreh River. Stratigraphy studies on the lake sediments and the age of its terraces clearly implied the renewal of the lake at least at 4 stages. The sequences of the lake terraces and other evidences confirmed the different scales of the reoccurrence of the large Saymarreh landslide.
Discussion and conclusion
This landslide obstructed the Saymarreh and Kashkan rivers and led to the formation a large lake in that region. The lake depleted after destructing the landslide mass, and there was a change in the direction of the Kashkan River.
The main triggering factor for this landslide was undercutting of Saymarreh and Kashkan rivers. Other factors included the direction and the angle of the slope, steep structural slopes, and gravity. The results obtained from the morphometry of Saymarreh Lake and stratigraphy of the lake sediments demonstrateed that Saymarreh landslide had been reactive several times and led to formation of the lake at several stages.
Tohid Rahimpour; Shahram Roostaei; Mahsa Nakhostinrouhi
Volume 4, Issue 13 , March 2018, , Pages 1-20
Abstract
Introduction A landslide is a natural phenomenon that often occurs because of falling down or seamless and quick movements of volumes of sediment along the slope. It has such speed and extent that it may influence tens or hundreds of cubic meters of rock and soil together. This phenomenon causes a lot ...
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Introduction A landslide is a natural phenomenon that often occurs because of falling down or seamless and quick movements of volumes of sediment along the slope. It has such speed and extent that it may influence tens or hundreds of cubic meters of rock and soil together. This phenomenon causes a lot of economic damages to forests and their growth, farmlands, gas and power transmission lines, mines, engineering structures, and buildings. One of the best ways to prevent these damages is preparing a landslide hazard map. Methodology The method used for zoning the Sardool Chay Basin is the Analytical Hierarchy Process. This is one of the most comprehensive multi-criteria decision methods, which was first presented in 1980 by Thomas L. Saati. This method is based on weighing each pair of variables with each other. AHP method consists of three main steps including (1) creating an Analytical Hierarchy, (2) comparing pairs of elements in it, and (3) weighing the criteria. The main feature of this method is the use of expert opinions. In AHP,n paired factors are compared with each other and more weight is given to the layer that has the maximum impact on the target set. The paired comparison of a scale, based on1 to 9, for its two components' relative weighing is hierarchical. Discussion In this study, the landslide hazard zonation was used in the Sardool Chaycatchment in order to identify areas with landslide incidence potential. The main factors contributing to the landslide occurrence in this case study consisted of geology, land use, slope, aspect, rainfall, altitude, distance from faults, and distance from stream. Their layers were prepared in ArcGIS software. An Analytical Hierarchy Process in Expert Choice software was used for paired comparisons of criteria and calculation of final weight. The results indicated that the geology criterion, which weighed 0.343, and the slope criterion, which weighed 0.215, had the most influences on landslide occurrence. Conclusion Landslide is one of the most common environmental hazards in mountainous areas of the northwest of Iran. Factors such as slope, rainfall, lithology, and earthquakes can trigger them. One of the best ways to deal with this phenomenon, before the implementation of any project, is the zonation mapping of the area. This study was based on the Sardool Chay catchment, located in Khalkhal, the southern part of Ardabil Province. To this end, 8 factors including geology, land use, slope, aspect, rainfall, altitude, distance from faults, and distance from stream were used. The weighting factors and the Analytical Hierarchy Process (AHP), and the Expert Choice software were used. The results classified the basin into five areas including very high risk of landslides (65 km²), high risk (144 km²), medium risk (202 km²), low risk (142 km²), and very low risk (120 km²). In addition, it indicated that the landslide risk of the Sardool Chay catchment is medium. Comparing the landslide zonation map and points of distribution suggests that the AHP can be a good method of weighing the criteria involved in the happening of the landslide.
