Geomorphology
mehdi feyzolahpour
Abstract
Glacier cirques show the characteristics of past glaciers and climates. In this research, the analysis of 39 glacial cirques in the catchment area of Jajrud River was done. For this purpose, Arc GIS software and Google Earth images were used. The parameters of length, width, height of the top of the ...
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Glacier cirques show the characteristics of past glaciers and climates. In this research, the analysis of 39 glacial cirques in the catchment area of Jajrud River was done. For this purpose, Arc GIS software and Google Earth images were used. The parameters of length, width, height of the top of the circus, height of the floor of the cirques , area, perimeter, ratio of length to width, ratio of length to height of floor and ratio of width to height of floor were used to check the morphometry of cirques. For each of the morphometric parameters, statistical factors of coefficient of variation, standard deviation, average, maximum and minimum were calculated and estimated in Excel. Then R2 values or coefficient of determination were estimated for each of the parameters and a scatter diagram was drawn. Finally, the correlation matrix was estimated using the Pearson correlation coefficient for all factors. The highest abundance of cirques is located in the southwest direction. The maximum height of the cirques is 3800 meters and belongs to the geographical direction of the south.The highest correlations between length and width parameters were observed at the rate of 0.9936. The results show that the cirques in the north-facing slopes have a lower height. This indicates the high nutrition of these cirques and their significant volume in the Pleistocene period. Investigations showed that more developed cirques have more area, less height and less length to width ratio than less developed cirques .
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.
Ebrahim Beheshti Javid; Fariba Esfandiyari Darabad; Shahram Rostei
Volume 5, Issue 16 , December 2018, , Pages 177-197
Abstract
Abstract
Introduction
Geomorphometry is the science of quantitative land-surface analysis (Pike, 1995, 2000a; Raseman et al., 2004). It is an interdisciplinary field that has evolved from mathematics, the Earth sciences, and most recently computer sciences (Pike et al, 2008, 3). It is ...
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Abstract
Introduction
Geomorphometry is the science of quantitative land-surface analysis (Pike, 1995, 2000a; Raseman et al., 2004). It is an interdisciplinary field that has evolved from mathematics, the Earth sciences, and most recently computer sciences (Pike et al, 2008, 3). It is well to keep in mind the two overarching modes of geomorphometric analysis first distinguished by Evans (1972) as specific, addressing discrete surface features (i.e. Landforms), and general, treating the continuous land surface. The morphometry of landforms per se, with or without the use of digital data, is more correctly considered part of the quantitative geomorphology (Thorn, 1988; Scheidegger, 1991; Leopold et al., 1995; Rhoads &Thorn, 1996). The shape of terrain, i.e. landforms, influences flow of surface water, transport of sediments, and soil production, and determines climate on local and regional scales. Furthermore, natural phenomena like vegetation are directly influenced by landform patterns and their relative position across the landscape (Blaszczynski 1997; Blaschke & Strobl, 2003).
The Earth’s surface is structured into landforms as a result of the cumulative influence of geomorphic, geological, hydrological, ecological, and soil forming processes that have acted on over time. Landforms define boundary conditions for processes operative in the fields of geomorphology, hydrology, ecology, pedology and others (Dikau, 1989; Dikau et al., 1995; Pike, 1995, 2000a; Dehn et al., 2001). In this study, using MRS algorithms and Ecognition software, landforms in the northern slopes of Mount Sabalan have been extracted and the effects of Landform morphometry on its hydrology have been investigated
Methodology
The semi-automated methods refer to the automatic procedures of extracting a landform based-process. This is mainly relying on unsupervised isodata classification, pixel-based classification (supervised /subpixel classifier based on training material), the analysis of digital elevation models (DEM), algorithms, hydrological modelling, and object oriented analysis (Nabil and Moawad, 2014:42).
In this study object-oriented methods and Ecognition software were used for the classification and the extraction of landforms. The object-oriented classification was used as an alternative to traditional pixel-based classifications, to cluster grid cells into homogeneous objects, which can be classified as geomorphological features (Seijmonsbergen, 2012). In addition, the DEM and its derivation (Slope, Profile and plan curvatures, maximum and minimum curvatures), were used in order to extract landforms. Then, using fuzzy logic method, the landform, land use, NDVI index , precipitation, density of river, and lithology layers were Overlaid and the potential flooding area was obtained.
Results and Discussion
In the object-oriented method, determining the scale parameter is a very important factor in the separation of different objects in an image. Scale parameter is a crucial threshold that determines the maximum allowed heterogeneity for segmentation and has a direct influence on the size of the objects to be obtained. The scale parameter, after a trial and error process, is recognized to be within a particular range (Gerçek, 2010:115). A novel method that was introduced by Dragut et al. (2010) and the ‘Estimation of Scale Parameter (ESP) that built on the idea of ‘Local Variance’ (LV) were employed to obtain the optimum scale out of a range of scales. By interpreting thresholds and prominent peaks in the ROC-LV graph, characteristic scales relative to data properties at the scene level could be found. This curve in 100 scale level was produced for the study area by using the ESP software and with respect to curve, the scale of 25 was selected for the segmentation. After segmentation, using the morphometric differences between the landforms, the landforms were extracted. After this stage, the landforms along with three layers of NDVI index, land use, and lithology was fuzzy. Finally, using gamma 0.8, they were combined and the zoning map of the potential flooding was estimated. Flood zoning map was classified into 5 classes and the percentage of each zone risk was calculated in each landform.
Conclusion
In this research, using an object-oriented model, landforms were extracted as plain, peak, pit, ridge, channel, nose, shoulder slope, hollow shoulder, spur, planar slope, hollow, spur foot slope, and hollow foot. An assessment of the effect of landforms on the hydrology of the area revealed that three landforms of hollow, shoulder and planar slope which were respectively 67.3%, 62.9%, and 53.2% had the greatest impact on flooding and their area were zoned as high and very high flooding. On the other hand, plain and pit landforms were zoned in the form of low and very low flooding areas.
