Document Type : پژوهشی
Authors
1 Assistant Professor, School of Earth Scinecs, Shahid Beheshti University, Tehran
2 Associate Professor, School of Earth Scinecs, Shahid Beheshti University, Tehran
3 MSc in Geomorphology, School of Earth Scinecs, Shahid Beheshti University, Tehran
Abstract
1-Introduction
One of the methods used in river surveys is river classification. The main aim of the classification of the river is simplify the processes of hydrology and sedimentation, and ultimately predict river behavior. So far, rivers have been categorized from different perspectives and the basics of these categories are including topography, slope, flow discharge, river age, and pattern in the plan. The first classification Recognized by Davis in 1899. Davis classified the rivers according to their evolution and modification into three groups of young, mature, and old. Leopold and Welman (1957) divided the form of alluvial rivers based on the sinuosity coefficient and the ratio of width to Depth into three straight, meandering and braided groups. A descriptive classification by Shumm (1963) presented based on two factors of river stability and sediment transport. The objectives of this research are to identify the factors affecting the bank erosion of the Kaleybarchai River, identifying the damages incurred in the construction and banks of the river, runoff and preventing possible floods. In this research, the river classification system is based on the Rosgen method, which is presented by the American researcher Rosgen (1994) to the river engineering community. The Rosgen method is the most complete and comprehensive method provided so far and includes many of the
features of previous systems. Rivers are living beings that constantly change their beds and banks, and this causes the river to undergo major changes over time. In addition, human activities, such as the utilization of riverine material and river modification, will cause the river to be moved.
2-Methodology
To evaluate the classification of the flow pattern in the Kaleybarchai River, the Rosgen model has been used at levels I, II, III. A reach of 3 km between the two villages of Pazhagh and Gheshlag was determined, and then 8 cross sections were selected in this reach. To simulate the river and extract the required parameters from geological maps, topography, land use and ARC GIS software was used. After determining the river reaches, based on field observations and topographic maps, classification in level I and level II were carried out in 8 cross-sections at the Kaleybarchai River, which are based on the slope, curvature coefficient, bankfull width, mean flood plain depth, flood plain width and bed material.
3-Results
After crossing the river route with field observations and then analyzing data and general calculations, 8 cross sections from the entire river course were extracted in all of the studied river and all the parameters required for classification and geometrical identification of the channel wrer calculated.
In order to obtain the average size of channel material, 16 samples were taken at river in different reaches and were analzed in the laboratory (Table 2). According to the obtained data, the highest percentage of particles along the river were average sand with 26.6% and cobble up to 14.7%, which were evaluated for the Rosgen classification, according to the results, the total of river is in groups B and C.
To determine the channel type at level I, after obtaining the slope of the Kaleybarchai River in the study area, four sections of the river were in type B and four sections in type C.
4-Discussion and conclusion
Based on morphological indices, sediment content and flow conditions, two different types of channels including B and C were identified in the study area and evaluated level according to the Rosgen in level I, II and III.
Morphological study of type B in relation to the evaluation of the correspondence and efficiency of the Rosgen model showed that their dominant morphology consisted of narrow valleys with relatively low widths and moderate slopes and relatively stable banks. Type C has meandering and high sinuosity, valleys with floodplain and point bars in low slope.
The high instability of the river bed in the reaches of 3, 5, 7, is a threat to the agriculture land land and surrounding buildings. Due to the fact that the braided rivers are not stable and the flow and position of the sedimentary islands and the width of this rivers are constantly changing, it is necessary to manage and organize the operations in this section with regard to the morphological variables and Flow conditions. The results of the Kaleybarchai River assessment based on the Rasgen classification system at level I, II and III showed that the Rosgen system present good the patterns of the channel in the Kaleybarchai River and, consequently, the effective parameters in the classification and separation of the channels. In this way, there are differences in the quantities and the parameters due to the specific conditions of the factors affecting in the locality.
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