تأثیر تغییر مقاطع عرضی بر طغیان و ظرفیت انتقال رسوب رودخانه آبشینه همدان

The effect Transition sections change on flood And sediment transport capacity Abshineh River of Hamedan

Abstract
The use of river engineering models in flood simulation and sediment transport is a common use in hydraulic flow. The purpose of this study was to simulate the effect of geometric geometric deformation of the Hamedan Aqueduct Ridge on flow processes and sediment transport during different return periods using SMADA software and HEC-RAS model. The results of the HEC-RAS model show that the flow of sediment can not flood the river bed and its sides in a transverse section from a distance of twelve kilometers downstream to the transverse section near the dam, so the danger to the river boundary areas in It will not be. But at a crossroads of eight kilometers downstream of the basin, the amount of discharge and sediment discharge is high at this level and river engineering must be organized to prevent accumulation of sediments and river floods.
Key words: Morphology, erosion and sedimentation, HEC-RAS, Abshinehh

Introduction
The flow of water in the river is a dynamic phenomenon that is constantly changing and displacing. Various mathematical relations such as HEC-6, HEC-RAS, SSIM, MIKE21, GSTAR, FLUVIAL are used to understand the phenomenon of riverbed displacement and displacement. Using the sediment transport equations and different methods for calculating particle velocity in the HEC-RAS model, river bed transformation can be studied and predicted. The results of the studies show that the sediment transport equations are not very sensitive to the particle velocity calculation in modeling the shape of the river bed shape, and the major difference in the results depends on the type of sediment transport equation used.The purpose of this study is to study the effect of changes in the section of the Abshineh River on the processes governing sediment transport capacity and the determination of flood sections using the HEC-RAS model, so that it can be used to control flood, sedimentation and seismicity Made

Material and Methods
The study area
The catchment area of Ekbatan Dam is located in the south-east of Hamedan city and is one of the sub-basins of the Ghare-Chay River, located in the southwest of Alvand Mountain. Abshineh River is one of the most important sections of the Gharacheh watershed which flows from the northern slopes of Alvand Sarcheshmeh Mountain and enters the dam of Ekbatan-e Hamadan. The river's regime is under a semi-humid semi-humid climate of snowy, rainy and permanent mountains. The average annual rainfall is 312.9 mm and the average annual temperature is 11.3 ° C.
Research Methodology
In order to simulate the effect of geometric geometric deformation of Abshineh River transverse sections on flow and sediment flow processes, we first selected 6 cross sections of the river, and by sampling the sides and soil mechanics tests, particle diameter and bed gravel, then the maximum discharge Moments with different return periods were calculated using the SMADA software and introduced into the HEC-RAS model for hydraulic simulation of the river. and in Finally, the effect of section changes on the flow velocity, transfer capacity and sediment accumulation were analyzed and evaluated.



Results and discussion
The study of discharge and sediment showed that runoff had the most effect on river morphology, which, with the process of erosion and sedimentation, changed transversely. Also due to the size of the particle diameter of the river, the erosion process, the velocity of the water and the slope, the transverse sections of the upper hand V formed and in which the bottleneck was observed. While in the middle sections due to the erosion and sedimentation process, the transverse sections of the river in the shape of U and at the end of the path, due to the presence of Ekbatan Dam and the process of accumulation, have been subjected to a change in morphology. Studies show that runoff has the most impact on river morphology and the amount of sediment transport capacity is directly related to the flow velocity, which increases the flow capacity of the sediment transport, and vice versa. . The results of the model simulated simulation during the 50-year return period show that the flow rate can not flood the riverbed and the sides of the river at a distance of twelve kilometers below the bottom of the dam, resulting in a danger to the areas The boundary of the river and its lands will not be followed. But at the crossroads, located eight kilometers downstream of the basin, the discharge rate and sediment discharge from this section are high. This causes accumulation of sediments and flooding of the river in these places. And can cover the boundaries of the river.
Conclusion
Nowday The study of the effect of river cross-sectional changes on the processes governing sediment transport capacity and the determination of flood sections using the HEC-RAS model has been considered by water resource planners and planners. The results showed that the transverse sections of the V-shaped arm and the middle sections were changed to U-shape. In addition, at the end of the Abshineh River, the cross section has been transformed into tensile form. The most important reasons for changing the morphology of the transverse sections of the Abshineh River include the difference in bedding and surface changes, depth and speed of water flow, and erosion and sedimentation. The results of the HEC-RAS model showed that the river is not capable of flooding from its bed at a cross-section of twelve kilometers downstream to the transverse section near the dam. But at a crossroads of eight kilometers downstream, the amount of discharge flowing from this section is high and with accumulation of sediments in this range, the bed will rise and the river flood will occur. Therefore, it is necessary at this point to manage and organize river engineering and engineering.