جستجوی مقالات مرتبط با کلیدواژه "پیچان رود" در نشریات گروه "جغرافیا"

Geomorphology of the river, a term used to check the river system. Zohreh river is one of the rivers in Khuzestan that consisted from 2 arm Fahlian and Kheyrabad it flow to Persian gulf at the end of Hendijan flat. To accomplish this study topographic maps, remote sensing data, including: Landsat satellite images, Landsat TM and ETM + collected from the Geological Survey of America (Earth Explorer), aerial photographs taken in 1334 of National Geography Organization is used. Next, aerial photos of 1334 as the base image and satellite image of Landsat 8 (2015) were selected as the data terminal. The future direction of the river in 2030 (1409) is plotted and compared with other periods. In this interval is 2 Meander complained. The findings suggest that during the period under review trends in three periods studied are quite different in the river, so in terms of reducing the length, intervals 7, experiences the lowest decline while interval 2 experience biggest decline in three visits. In terms of increasing the length, intervals 7, experiences the lowest increase and intervals 8, had the largest increase. The findings indicate that during the three periods under review, the river changes in the periods studied are quite different. The results show that in 1955 10 cases of amputation has occurred in the river channel and along the river has become 3,653 km shorter. Even though at intervals of 1 to 5 we except villages along the way, there is no human factor; But in the interval of 6 industries are seen. Interval 7 in the northern part of the land is under irrigated agriculture. But in the southern part are bare. In the interval of 8, lands under the tide, and asphalt and dirt roads are important feature.

River 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.

The 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.

Due 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.

Based 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.

Rivers are considered as one of the main sources of water and energy supply for humans, due to their special effects on human life and the formation of different civilizations. Therefore, their behavior should be considered. Flood flow is very complicated in natural rivers, especially in Meanderi Rivers. Therefore, the present research uses a numerical model to evaluate river floods characterized as different return periods of 10 and 50 years. The study area is located on the Kor River. In this study, the geometry model and a numerical mesh system were calculated by taking advantage of topographic surveys and the required parameters for running CCHE2D were collected through filed works.
The CCHE2D model, a two-dimensional hydrodynamic model of flow and sediment transportation for unsteady flows, is able to simulate and analyze sediment transportation flows and morphological processes. It contains two parts: 1- CCHE-MESH generation for meshing the studied area
2- CCHE-GUI for applying the resulted mesh to simulate flow and sediment.
Finally, the model outputs including flow depth were obtained for the considered river reach in different return periods. In this study, using the numerical model CCHE2D, changes in the depth of the water in two return periods of 10 and 50 years in different sections of the river route were obtained and the diagram of these changes was one of the outputs of the model. Discussion and Conclusion: Study shows discharges with different return periods. In the Meander range of the study area, centrifugal force gradient flow of flow on the center and cross slope caused at the level of the water was so high, but the water level in the upper arch cross external and internal were decreasing. This phenomenon caused peripheral gradient pressure within the cross section which resulted in an imbalance of the local effect between the centrifugal force and gradient pressure flow, the secondary flow forms in the transverse section.
Once flooding occurs in the river (50-year return period), water level exceeds the main river channel and enters the surrounding floodplains. Under such circumstances, due to the differences between flood plains roughness and the main channel, flow rate (velocity) on flood plain is much slower than the main channel. Consequently, such difference leads to some shear layers in crossing points of the main channel and floodplain in the entrance, resulting in greater water turbulence. The comparison of the water flow velocity in different reach sections indicated that the highest water velocity was related to the first meander so that in return periods of 10 and 50 years it respectively reached 2.7 m/s and 3 m/s. The results of the study confirmed the applicability of the numerical model to predict river changes using flow parameters. Therefore, it can be said that the present numerical model is capable of analyzing the river changes in the wind tunnel channels in a desirable manner.

River pattern variations are one of the most important river engineering issues. In order to achieve this goal, using field observations, a 1: 1000 topographic map was prepared and extracted using Landsat and Google Earth satellite images in the GIS environment of the studied areas. By digitizing the river route in AutoCAD, the geometric parameters of the river (central angle, relative radius, plan shape, torsional coefficient) were calculated on the images. The results indicated that in Azad River, the winding river at 40% relative has a radius of more than 3.5. In 30% relative radius bends in river is 1.5 to 3.5. In addition, about 30 percent of the stress concentration around the inner corners is the main river. According to the findings, the probability of serious and significant changes in the period of study, Azad River is small. Intervals that are unstable are likely to need special attention in the context of their privacy be determined. Among the intervals, there are nine critical intervals that include intervals of 58,56,47,41,29,26,24,20,18. Therefore, it is necessary to determine the bed boundaries.

One of the main topics of geomorphology and river management science is river channels morphology that with its help can be found useful information about geometry, form the substrate, longitudinal profiles, cross sections, deformation and displacement them over time. The measure of these indexes represents the real performance of stream channels. In this research, studied the rate of change and displacement of meanders of Chelchay-Narmab river from 1961 to 2013 by using aerial photographs and Google earth images to access the current situation and future movement and forecast of displacement this river meanders. To achieve this aim, measured the situation of river plan and geometric indices as the channel length, the number of meanders, the sinuosity, the central angle, the radius of curvature of meanders and channel width in GIS and AutoCAD in four separate reaches and compared with each other. The results showed that during the period under review, dropped the average for more morphometric parameters of the river. For example the river channel length of 6200 meters, Sinuosity 3.0, the number of meander loops 31, the average central angle of 1.4 degrees and an average channel width of 9 m is reduced. Also the study of change process in four reaches showed that the changes and trends in reaches were different. In reach 1 to reach 3, the most geometric parameter values were decreased while in fourth reach the values were increased. Factors influencing these changes can be discharge, land slope, soil type and land use types within the river cited. With respect to the maximum number of meanders too developed in reach of 4 and in the vicinity of Gonbad Kavoos, the highest risk areas was in this reach.

An important characteristic of river is channel form and meandering rivers for active forms. Dams as barriers to water and sediment flow can create discontinuities in fluvial geomorphological conditions. The objectives of this paper are to assess the effects of reservoir on the meandering river morphology. The Gorgan River catchment is located in the southern part of Golestan province with a total area of 11,380 km2. This river is originated from the Alborz Mountains into Caspian Sea. A reach of the river, 44 km long, that is examined in this research is situated in middle Gorgan River, between Gonbad Kaboos city and Digjeh. The construction of reservoir and changes in land use is effective on the main activities that potentially impact water regime, sediment transport and fluvial dynamics in the Gorgan River.
The data of the flow discharge and suspended sediment load of Gorgan River are available in 1973- 2015 at the Ghazaghli gauge station (73 km downstream from the Golestan reservoir Dam). The hydrological analysis was divided into two periods: before dam construction (1973-2001) and after dam construction (2001-2015). Sediment rating curves were created by daily mean suspended sediment discharge and daily mean water discharges by a power function. The fluvial changes have been measured using aerial photographs of 1967 at a scale of 1:20,000, Landsat satellite images (Landsat TM) 2001 and Google Earth images, 2015. The river was digitized from photographs and satellite images, after they were geographically referenced with the help of ArcGIS 10.2. Meander morphology was described based on some of form parameters such as wavelength, amplitude and radius of curvature, and bank width of the channel. Lateral migration and channel activity was analyzed as geomorphic activity. The normality hypothesis was studied for each parameter and conducted with the Kolmogorov–Smirnov test. If the normality test was not rejected, an ANOVA test was applied. If the normality hypothesis was rejected, the Kruskal–Wallis test was used. In all cases, the significance level assumed was α=0.05, as a threshold for rejecting the null hypothesis. The spatial distribution for these parameters was analyzed in order to change downstream the channel. Thus, the correlation coefficient of Spearman was calculated.
During the pre-dam period (1967–2001), mean discharge below the dam was 14 m3 s-1. These values were 10.5 m3 s-1 after the dam was constructed (2001-2015). Power regression between suspended sediment discharge and water discharge data shows that suspended sediment load is reduced to 50 % after dam construction. The values of wavelength and amplitude show minor differences in the three records and do not show significant differences. The radius of curvature, the length in 1967 (124.7 m) was reduced in 2001 (100.6 m) and 2015 (103 m). The dispersion values show significant differences, with a maximum in 1967 and reductions in 2001 and 2015. Bank width shows significant variations in the three records. In 1967 and 2001, it reached the values of 31 and 33 m, respectively. This is decreased to 15.7 m in 2015(-50% from 1967). Thus, bank width loses half of its value in the pre-dam. In pre-dam period (1977-2001) channel lateral migration was reached 39.3 m and in post-dam (2001-2015) the displacement was recorded to 22.2m. The channel activity during the time period 1967–2015 reached 0.65 m/y. The ratio between radius of curvature and the bank width (Rc/W) is changed from 4.14 in 1967 to 3.04 in 2001 and 7.48 in 2015. These results have indicated that migration capacity is decreased. The stability state shows the spatial distribution of the values. There is no significant relationship between landuse and lateral migration.
After construction of the three dams, upstream flow discharge is reduced (26%) and mean width of river is reduced (50%) from 2001 to 2015. Suspended sediment discharge has decreased (50%) after the construction of dams. Wavelength and amplitude do not show significant differences throughout the time period. The ratio Rc / Wb doubles from 1967 to 2015. The results show that geomorphological activity is decreased and a static equilibrium was obtained

The purposes of this study are investigation of Shahr Chai river patterns, its stability and subsequently changes in the period of 2000-2013. For this purpose were used Landsat images, topography, geological maps and hydrological data. For study of river pattern and its changes was used Sinuosity and Meander Central Angle Indexes. Also for study of river stability was used by shear stress ýand RBS indexes. Results indicated that river pattern changes are very low. River stability analysis indicated that totalý shear stress rate is higher than critical shear stress. Results show that potential of river is high for creating of morphological changes in costal interval but decreasing of river flow has been caused that river changes be in lowest amount possible.

The Path of meandering rivers is indicator Morphological characteristics this rivers. This path is not straight and has major bends with different geometric characteristics, and sometimes the same. In recent years, Fractal geometry used to explain the route that has dimensions 1-2. The aim of this study is investigation of meandering pattern the Germi Chay River by geomorphology methods and Fractal analysis. For this purpose, Germi Chay River divided tow intervals. Then geometry pattern of this river determined by Central Angel and Sinuosity Ratio indexes in each intervals. In next stage, Fractal dimension determined using Fractal geometry for intervals. Results indicated Germi Chay River is a meandering river and there is a direct relation between Fractal dimension and parameters of Central Angel and Sinuosity Ratio in this river. Therefore Fractal dimension such other methods of river pattern identifying can be entered in morphology models of meandering rivers.

Predictions of total and even partial changes in rivers patterns are as the most essential issues related to rivers geomorphology. In this regarding, a lot of researches have been done by geomorphologists. This research has explored Kordan River aqueduct morphology changes in bights areas of Afkaneh cone surface. Kordan river is the one which has been affected by various factors and has changed a lot so that this changes has impressed on components an human activity around the river and on side erosion and channel. The research method is on analytical and time comparison method by which direct and indirect observations, maps and images are used, to the drainage characteristics in the two study periods. In this research topographic maps at 1:25000 scale and photogrammetry at 1:55000 and 1:40000 scale of studied region was used. Beside these, to exploit sack changes some software application such as Arc GIS , Excel and SPSS were applied. Research results show that river side changes in 37 to 165m are varied in river different parts that in average, river has gotten eroded 31583.4 m2 in 44 years that annual erosion amount has been 718.8 m2. It can be predicted for further 20 years that probably right side of the river will get eroded 14415 m2 in average. In 1999, developed and non-developed bights were added to river area, and high developed bights have been reduced from river than 1955. According to Leopold and Wolman index, bend coefficient more than 1.5 has bight pattern, therefore in studied bight parts of Kordan river 90% of bows has had evolved bight pattern in 1955 and this amount has arrived to 81% in 1999. Regarding to calculation, it can be concluded that bights had been increased from 1955 to 1999 but their sharpness were decreased.

Meanders are typical geomorphologic forms that in the southern coast are of the Due to the availability of environmental conditions. Those landforms have Strong spatial variations، Influenced by the dynamics of rivers and deltas gentle slope in a small interval. In this research was tried with using of remote sensing and survey field data، is Calculated and analyzed Mond river bed morphologic change over a period of 57 years at five time intervals (1955، 19855، 1994، 2000، and 2012). The results were showed Mond river bed morphologic change was very high، over 1955 to 2012، So that the 5/3 km displacement substrate was observed the estuary nearly. The length of river bed was 51. 45 Km in 1955، while in 2012 is achieve to 39. 87 Km and this change is caused sinuosity reduce، Mond river is changed of meander form to wave formation. Spatial compare of river bed was showed 42. 52 square kilometers have been added to the left side while this amount was calculated on the right side kilometers 33. 8. Moreover is reduced 7. 66 square kilometers from the left side and the right side is 4. 42 square kilometers. Surface delta gentel slope was caused velocity of the water and placing sediment in river bed، vegetation in river bed and side is caused trapping sediment and dams in the river. Also human is reduced sediment input with action such as dam’s construction in Mond basin، make of Bridge and protective pads on the bottom of the bed and the water transfer to the shrimp site. The result can significantly help to authorities and organizations related to environmental management.

Meanders، as a interesting water flow patterns in nature، is giving dynamic to courses of rivers. Creation of curvature on courses of rivers is give enough energy for migrate active channel on floodplain. This migration is main reason for many geomorphology in events is floodplains and at final is changing the floodplain pattern. These changing is created many problems for man-made structures that is constructed at bank or on courses of rivers. Aji-Chay River، as a typical meander is migrate on floodplain by creation curvature on its course (is situated at 37° 58′ to 38° 07′ N and from 46° 15′ to 47 °45′ W). In this article is analyzed and estimated migration rate، migration potential and time of migration، by use of experimental methods، by satellite and areal images In this study rely on parameters of meanders، as bind and width of river corridor is estimated by use of W methods and ∆t، R/W calculation، in order to investigation on capability of rivers for movement. In this study also is estimated time of active channel migration on floodplain by use of valid methods. The results of this study show that active channel of Aji-Chay repeatedly movement on floodplain in during time and because these movement and changing and bank erosion، is flatten the floodplain. In part of Aji-Chay course time period for completed a cycle of migration is from 1 to over 5 years. This period is vary in many parts of river course. The results of this study also suggested that sinuosity rate at length of Aji-Chay course is changed in during time and old race of water flow is evidence these changes.

Karun River with a length of about 890 Km is considered as a main river in the country. In this paper، types of Karun’s screws regarding to the geometric factors of radius of curvature and chord length were identified by fitting circles with the arcs of the river’s axis. River’s arcs were classified into simple and compound screws. Then، by formation of the database consist of topographic maps (1:50000)، Landsat satellite images of 1973 and IRS images of 2006، multi-time images were processed in ERMapper and GIS to determine the rate of meanders variations in a 51- years interval and finally map of changes was drawn. The results illustrated that from 149 meanders which exist in region، 21 meanders have changed from simple to compound and vice versa. Most of variations are related to the change of simple meander into compound meander. In some regions changes in river’s pattern were identified، so that 7 meanders have changed from simple pattern into arterial pattern. Another significant change is observable in the end of the Karun’s route (Bahmanshir River) which is related to the increasing of the 2 new meanders in the meandric route of the River.

Most of water structures and land uses being rivers or in rivers banks are somehow influencing morphological changes in rivers. Therefore survey of this phenomenon is considered as the most important part of studies projects and land uses. In this study part of the Aji Chay River has been studied between Khaje and Vanier with about 22 km length. The main aim of this study is indicating trend of morphological changes in the river, in 52-years period using the geometric parameters of the channel such as arc length, along the river valley and radius of the river circle tangent arc in the form of models the curvature coefficient and the central angle. For this purpose river path from satellite image IRS sensor Pan and aerial photos for years 1956-1995 and 1995-2008 in the ArcGIS environment in two intervals and two periods were digitized and calculated. Causes of changes using the topographic maps 1:50000 and geological 1:100000, hydrological data and field methods were investigated. Results show that 1) river on average in both periods and in both interval of their arch curvature is reduced. So that the central angle in the first interval of 137 to 100 degrees and the second interval of 160 to 148 degrees and curvature coefficient in the first range of 1/133 to 1/15 and the second period from 1/48 to 1/27 is reached. Also numbers of arcs in the years 2008 to year 1956 have increased making the year 2008 the first range number of arcs of 11 to 51 and the second interval of 19 to 86. No observed meander-like and horseshoe (oxbow) pattern on the river exists. Morphological changes of AjiChay River in the timeframe and location studied have been affected by natural factors such as loss of power of flow due to reduction of annual average water discharge and sediment, accumulation of sediment and erosion.

World''s coastlines are the most dynamic natural environments and diverse extraordinary and unique processes are active in this area. One of results of these processes is the formation and evolution of alluvial fans and delta. The studied areas include Hormoz Strait coastal، Shour، Jalaby and Hassan-Langi river delta; which in the form of a strip with a varying width covers the areas from the change line of the mountain slope dominating the coastal plain to the sea coastline. Strip of coastal plain was made by sediments that were transported by rivers of northern plain mountain basins and the Hormozgan Zagros Mountains and were deposited on the surface of the plain. According to previous studies، Hormoz Strait coastal plain has been created by geological structure effect and delta depositional. The geology structural effect plays the most significant role in the development of the coastal plain. To achieve results، according to research findings and from the perspective of risk area deltas surfaces has been zoned based on the dynamics of river and sea water movements. Analyses to achieve results were mainly based on indirect observations obtained from satellite images and direct observation carried out by detailed field studies and sampling of sediment from sections of river in coastal and surfaces of deltas and profiles created with the help of statistical methods and geomorphologic models that were considered as conceptual tools. To sum up، first، instability of the delta regions surface affected by the meandering movements and their instability resulted from the change in river paths were analyzed and investigated and their distribution are shown in the satellite images and maps.

Meanders are active landforms and usually are formed in the path of low slope channel of the rivers. These features are very unstable, because of river dynamic influence and little slope of deltas and are evolved in relatively short time intervals and sometimes they are changed the direction of channel. In this research, the changes of Jagin River channel at the level of Makran coastal plain has been studied. The existing evidences indicate that meanders movement and the bed changes of this river to other areas of Iran are significantly considerable. Geomorphological and hydrodynamic features of the direction of this river including low delta slope, particle sediments, overflowing the river and tectonic factors are considered as main unstable factors of Jagin River channel. The main aim of current research is study the influencing variations in the changes of this river. Method of study is comparing the river meander developments and changing the direction of river from 1971 to 2004 within a period of about fifty years. Topography and geological maps, satellite images and aerial photographs are of the most important research tools for studying time and place changes and meander development of Jagin River. For studying the slope and other morphometric data of region, the drawing of longitudinal profiles have been used. The situation the position of meanders has been controlled with field survey and through GPS and simultaneously, sampling has been conducted for analyzing the sediment logical impacts. The conclusions demonstrate that the abundance and development of meanders and changing the direction of Jagin River depends on low slope of Jagin delta and the particle of sediment texture.

River as a dynamic system can change its location and morphological characteristics based on time, geomorphologic, geological, hydrological and sometimes due to human intervention. By exact examining and identifying of these factors can obtained correct behavior of river and realized its natural reactions and possible changes. Thus the goal of this paper is reviews the role of geomorphologic and geologic factors on the geometry of the river bed and showing cause of curvature in the interval of plain and mountain. In this research, the study area is Qezel Owzan River in 47 º 48 to 48 º 27 N and 37 º 12 to 37 º 25 E. high Length of river and its pass from erodible and Marn formation has been caused increasing River sediment load and also the formation of bed geometry is indifferent at various intervals.