Geomorphology
Masoumeh Rajabi; shahram roostaei; Mohsen Barzkar
Abstract
Introduction Rivers are one of the best geomorphic landscapes in which the connection between the system of forces and the forms of unevenness can be clearly understood (Chorley et al., 2000: 163). Various sites, especially sedimentology, are important. Zab River is one of the most water-rich rivers ...
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Introduction Rivers are one of the best geomorphic landscapes in which the connection between the system of forces and the forms of unevenness can be clearly understood (Chorley et al., 2000: 163). Various sites, especially sedimentology, are important. Zab River is one of the most water-rich rivers in the country, which due to the high discharge, causes a lot of damage annually due to floods on agricultural lands located in the river. This river, by changing its course in the bed and creating erosion along the bed, exposes the lands around the bed to destruction, and considering that the farmers of the region use the river water for agriculture, it is of great economic importance for them.Therefore, it is necessary to classify and determine the boundaries of the riverbed and thus understand the existing processes and morphological knowledge of it. Therefore, it is necessary to classify and determine the boundaries of the riverbed and, as a result, to understand the existing processes and its morphological knowledge. Data and Method River classification according to Rosegan method: Rosegan classification is divided into four levels: In this research, for the morphological classification of Zab river, first by scrolling along the study area, an almost uniform set of geomorphic units is identified. Then, using GPS in three paths upstream, middle and downstream of the study area were segmented. After intercepting the river route and then entering the required data into the WMS9.1 and HEC-RAS software environment and executing the hydrological model, the geometric properties of 24 transverse sections of the total sections in all intervals The studied route was extracted and all the parameters required for classification and geometry of the duct in those intervals were calculated. To determine the overflow discharge of the intervals, the discharge with different return periods obtained from the relationship between Fuller and smada software with The prepared sections were given to HEC-RAS software and then based on one of the methods to determine the full cross section (level at which the ratio of width to depth to depth in an orthogonal device is minimized) the overflow flow is determined Took. Accordingly, in each cross section of the curve, the ratio of width to depth of flow versus depth for each section was plotted and the minimum point on the curve was selected as the discharge of the full section. After determining this discharge in each transverse section, using frequency analysis, the full section discharge has been determined for the whole river. Finally, by introducing flow characteristics, geometric characteristics and manning coefficient of each section in HEC-RAS software, flow simulation was performed and data related to cross-sections and water surface profiles including width to depth ratio, indentation index Bed, cross-sectional area in overflow, overflow width, maximum depth, flood plain width and water level slope, etc. were calculated. The implementation steps of the HEC-RAS model are shown in Figure 2. Results and Discussion According to field and laboratory studies, Zab River is in the alluvial group in terms of classification based on the type of bed sediments (rocky and alluvial). In summer, due to dehydration, fine-grained sediments are placed on coarse-grained sediments, as a result of which sand particles get stuck between the sand particles and cause the bed to solidify. These sediments are sandy but in winter Due to the flood, fine particles are displaced along with the flood and large particles remain at the bottom of the bed, so the type of sediments on the bottom of the Zab River are sandy. To obtain the average size of duct material, 15 samples were taken along the river at different distances and granulated in the laboratory. Due to the fact that the intervals 4 in the upstream and 11 in the middle part of the studied route have a mixed bed of irregular rapids or erosion basins and the bed (profile) and sides are relatively stable and have a limited sediment transport system with type B Roses are compatible. Also, moderate roughness and narrow valleys with a gradual slope are other reasons for confirming this claim. Intervals 1, 2, 3, 4, 5 upstream, 10, 12, 13, 14 in the middle and 17, 20, 21, 22, 23, and 24 downstream of the studied route with respect to stability They and their sediment load and limited transport are Type C compliant. The predominant morphological feature of these areas is wide valleys with alluvial terraces associated with the flood plain, which are again the characteristics of this type. Section 18 is located in the downstream part of the studied route in type D, which is witnessed by the following reasons. The river is arterial in this area and rock fragments are rarely seen in the bed. The ducts also have erodible edges and high suction load. The morphological appearance of most areas has this type of wide valleys with alluvial and clovial cones. Interval 12 is located in the middle part of the studied route in type E. Here the ducts show significant sinusitis and the ratio of width to depth is low. The river is stable in this area and one of the reasons is the development in the floodplain with dense grass cover on the vertical shore of the duct. The predominant morphological feature of this section is the type of wide valleys with grasslands. Conclusion The characteristics of these intervals indicate their conformity with the Rosgen model. High instability of the riverbed in the range of intervals of types C and D is a threat to agricultural lands and surrounding structures. The results of evaluating the stability conditions of the intervals of the study area in the third level of Rozgan showed that in the upstream path of the study area, the intervals of 2, 5, and 8 intervals have more stable conditions at a good level than other intervals. Flow conditions in the intervals 1, 3, 6, 7 are at the intermediate level and in the interval 4 are at the weak level, which have more unstable conditions. In the intermediate path, the range 11 is better and more stable, and the 10, 12, 13, and 15 ranges are at the intermediate level, which is less stable. In the downstream direction, the studied areas are intervals 19, 21 and 22 at a good level and with more stable conditions, intervals 18, 20, 23 and 24 at a medium level and range 17 at a weak level and instability conditions. The results of Zab River evaluation based on Rozgan classification system at levels two and three showed that the canal patterns in Zab River and consequently the effective parameters in classifying and separating the canals are consistent with Rozgan system. However, there are differences in the values and parameters that are due to specific conditions of local influencing factors. However, the Rozgan system is responsible for the morphological knowledge of the Zab River and similar fluvial systems. کرد. Therefore, this model has the ability to quantitatively predict the geomorphism of the Zab River and rivers with similar conditions.
Geomorphology
Somayeh Soltani-Gerdefaramarzi; Somayeh Asgari Varzideh; Mehdi Tazeh
Abstract
River morphology is the science of knowing the river system in terms of general shape, dimensions and characteristics of hydraulic geometry, the direction and longitudinal profile of the bed, as well as the mechanism of its changes. Morphological study is needed to understand the current conditions and ...
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River morphology is the science of knowing the river system in terms of general shape, dimensions and characteristics of hydraulic geometry, the direction and longitudinal profile of the bed, as well as the mechanism of its changes. Morphological study is needed to understand the current conditions and the potential for future river changes in the future, and perhaps it is only that it is possible to predict the natural behavior of the river in relation to natural changes or actions arising from the implementation of various river engineering projects. Most of the water structures such as dams, bridges and pumping stations are located in the margins of rivers that can be affected by changes in river morphology. Application of remote sensing images and Geographical Information Systems (GIS) can be effective to achieve a more accurate analysis. Today, land use change, vegetation cover and morphological changes of rivers in River Engineering Sciences are of great importance using remote sensing and GIS techniques. Yamani and Sharafi (2012) showed that morphological changes and erosion of the Herrud River from the upstream downstream has decreased. Also, the geological and lithological structures of the bed and river bank are the most important factors in the stability of the bed. Yousefi et al. (2013). In order to investigate the changes of some Meander parameters in the Karun River using Landsat satellite images, morphological parameters of 20 Meanders were determined in an interval of 128 km length of Karun River after the preparation of a land use map for each period. Rashidi et al. (2016) studied geomorphologic changes of the Karoon River bed and its causes from 1334 to 1391. The results indicate significant changes in river morphology including latitudes, meanders, and sedimentary islands due to the decrease in the discharge, the construction of multiple bridges along the path, geological factors and vegetation. The study of past research shows that the study of river morphology in other countries has also been of great importance. Clerici et al. (2015) examined the morphological changes of the Taro River in Italy over the last two centuries and showed that human beings have made the most of the changes for agricultural and industrial purposes, the construction of multiple bridges and casualization. According to the research, the main issue of this research is to investigate the changes in the Gamasiab River, which in recent years has threatened the communication paths, landscapes and, in summary, human structures along the river banks. Therefore, the objective is to study the variation of the morphology of the Gamasiab river from the point of view of the central radius and angle, and the number of archs during the 1990-2013 period, and the extent of the development of the piers.
Mohammadhosein Razaeemoghadam; Adel Mohammadifar; Khalil Valizadeh
Volume 17, Issue 44 , September 2013, , Pages 161-178
Abstract
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 AjiChayRiver has been studied between ...
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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 AjiChayRiver 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 AjiChayRiver 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.
