جستجوی مقالات مرتبط با کلیدواژه "bank erosion" در نشریات گروه "جغرافیا"

Rivers in their path are always struggling with a phenomenon called erosion, which on the one hand causes many changes in the geometric shape of the river section, morphology and hydraulic characteristics of its flow, and on the other hand, it brings irreparable effects to the lands adjacent to the channel. One of the main sources of sediment production is the erosion of river banks. In this regard, investigating the amount of coastal erosion is one of the management strategies. The area under study is the banks of the Jajroud River, between Letian Dam and Mamlo Dam, with a total of seven sections. In this study, for the erosion of the river bank and estimation of the amount of sediment from the method or model of estimation of the bank and foot of the bank (BSTEM) in this model, the geometrical parameters of the channel (angle of the wall and height of the bank and the distance of the toe of the bank and its angle), the height of the layers And their species, flow information and vegetation cover and other side cover materials have been extracted and used. In this research, the depth of the flow in a spiral discharge mode and the flow duration of 12 hours were used to model the bank erosion. The model models the amount of bank destruction by calculating the shear stress and soil resistance. The results of the research showed that all sections except section 6 have high erosion. The difference in erosion values in different stages was mostly due to the type of bank sediments and bank slope angle. In terms of bank stability and safety factor (FS), the most unstable bank was in section 5 and the most stable bank was in section 6 of the river.

So much of the river sediment occurrs due to bank erosion. Understanding and predicting bank erosion is a vital requirement for river management. During  a  flood, river flow shear stress exceeds river bank materials shear strength and causes a meandering. To prevent a river accresion in a floodplain, it is necessary to understand the river and perform river management and organization operations, especially in erosion reaches. Bank erosion occurs commonly during a relatively long reaches of the river. Due to the high cost, stabilization practices are only possible locally. In order to reduce this phenomenon, it is necessary to create vegetation in river reaches. The Bank Stability and Toe Erosion (BSTEM) model is one of the most widely used models in the world in most river engineering projects developed by the National Sediment Laboratory in Oxford, Mississippi, USA. The BSTEM model was initiallly developed by Pallen Benkhead and Simon to investigate riverbank stability under vegetation and water conditions.Subsequently, in BESTEM model, various plant and hydraulic parameters such as slope patterns, roughness, angle, and pore water pressure are used. BSTEM is a bank erosion model that examines hydraulic processes, toe erosion and bank failure in soil homogeneous layers and is a suitable tool for determining riverbank conditions in order to protect river from streamflow erosion. A review of the research studies conducted in this regard showed that although the BSTEM model is a model with a long history and validity (based on numerous projects, articles and dissertations) and had been used in different countries and important rivers of the world to study the stability and bank erosion. In Iran, few studies have been done on the BSTEM model, which shows the need to conuct further studies for the purpose of validating this model. Therefore, this study was designed using the BSTEM model to investigate the stability of the river bank with respect to existing plant species in a section of the Bashar River in the city of Yasuj.

In this study, the Bank Stability and Toe Erosion (BSTEM) model has been used to investigate the stability of the reach of Bashar River in Kohgiluyeh and BoyerAhmad Province. This model is one of the most comprehensive models used for river engineering and management operations in the world, which besides stability, the failure rate, safety factor, erosion rate, sediment loading rate, and river accrestion rate are calculated. The appropriate reaches of the Bashar River for modeling, should have the same characteristics in terms of morphology, geology, land use and have a suitable length (300 meters). The study was condcuted by analyzing two parts: control (without cover, length = 300 meter) and experimental (with cover, length = 300 meter). Because of using the BSTEM model, it has been necessary to select several sections in the selected range. For this purpose, topographic maps and aerial photographs of the area were prepared. Then, with the help of these maps and Google Earth satellite images, a reach of the Bashar River was selected near the Darshahi region for modeling. Then, the selected reach was divided into two parts: control (without cover) and experimental (with cover) with the same length of 300 meters, and each part was divided into 3 sections of 100 meters. Shear strength of tree species was measured in cross-sections. The reserachers performed data comparison analysis with HEC-RAS software and BSTEM model.

The results of flood simulation in the HEC-RAS model in section 1 with cover reach and section 4 without cover reach showed that, in a 2-year flood, the average flow velocity in the middle of the cross section is 2.18 and 1.41 m/s, respectively (the estimated speed of the HEC-RAS model), and the flow height were 1.39 and 2.72 meters, respectively. The results of this study also showed that in terms of stability, there is a difference between sections with land cover (Fs <1) and no cover land (Fs <1). The results also pointed to the fact that the average width and volume of failure of the river bank in the no land cover section was 2.72 meters and 6280 cubic meters, respectively, and in the land cover section was 1.42 meters and 1686.33 cubic meters.

The results showed that in terms of stability, there is a significant difference between covered and no covered sections because of the safety factor, which confirmed the instability of the studied reach. Based on the results of uncovered sections, due to fact that their geometric condition are unstable, the need for river management operations intesifies. The results showed that for sections with vegetation, the safety factor is higher than one, which indicated the bank stability in the studied reach, while in sections of no cover, the river is unstable. Increasing tensile crack depth, and bank angle resulted in bank instability, and increasing river flow level, groundwater level and suction matrix can lead to bank stability. In order to prevent bank river erosion, cultivation and growth of plants that are compatible with the climate and the erosive conditions are necessary. Therefore, it is suggested that native plants and other various plant forms be used to prevent bank river erosion. In addition, comparative studies need to be performed on other species in order to determie the role of plant cover on river bank stability in other rivers.

The flow of water and rivers is the most important phenomenon in the crustal processes that not only plays a role in the overall appearance of the earth but also determines the form of human life on the planet. As a dynamic system, a river always changes its morphological location and characteristics according to time, geomorphic, geological-hydrological factors, and sometimes due to the human intervention. Bank erosion of rivers could cause a lot of damage to agricultural lands, buildings, riverside structures, roads, bridges, etc. every year. Inaddition, it could cause significant amounts of sediment to be transferred to dam reservoirs. The Haft Cheshmeh River basin is located in the Rozjerd region, in the northeast of Qazvin province and on the southern slope of Alborz. In the present study, the Haft Cheshmeh River in the area from Rozjerd to Shinqar villages has been studied for approximately 11 km. The pattern of the river in this sinusoidal range with an average curvature coefficient is 1.17.  

In order to obtain the required data, the Haft Cheshmeh River was divided into 4 sections and 10 cross-sections, and from these cross-sections, a cross-sectional profile of the channel was prepared during 7 field works. To investigate the erosion of the Haft Cheshmeh River using the near bank stress model (NBS), the estimation of the stress applied to the shore is related to the slope flow, in which seven methods can be used in accordance with the conditions of the region. According to the characteristics of the Haft Cheshmeh river, in this study, three methods of the ratio of the radius of curvature to the width of the bankfull (Rc/Wbkf), the ratio of the maximum depth of the near bank to the depth bankfull (dnb/dbkf), and the ratio of the shear stress of the near bank to the shear stress of the bankfull ) were used. After obtaining the data by field sampling and calculations, according to the measured parameters, the degree of lateral erosion in different classes was classified from very low to severe.  

To investigate the erosion of the Haft Cheshmeh River, the Near Bank Stress Model (NBS) was used. At the second level, which measures the ratio of the radius of curvature to the width of the bank, all sections, with the exception of cross-section 9, have severe erosion. Only in cross-section 9, very little erosion has been observed. At the fifth level, which is the ratio of the maximum depth of the near bank to the depth of the bankfull, low and very low erosion from the first to the eighth sections on both sides of the shore were observed. Only the ninth and tenth sections have high and severe erosion; however, even on the right bank of the tenth section, erosion is low. At the sixth level, which is the ratio of the shear stress of the near bank to the shear stress of the bankfull, the erosion has low and very low values in all cross-sections.  

The use of the ratio of the radius of curvature to the width of the bankfull is appropriate for a time when a narrow radius has the maximum effect on the bend of the river. Therefore, the results obtained from the cross-sections that were harvested at the site of the bend of the stream were consistent with the reality of the region and showed the instability of the sides. The results of the shear stress of the near bank to the shear stress of the bankfull did not correspond to reality. According to field observations and data obtained using the above-mentioned three methods, the ratio of the radius of curvature to the width of the bankfull is close to reality. Although the results of the near bank stress model show the erosive cross-sections with less intensity, if it is necessary to provide a quick and low-cost estimate of river intervals, it is reasonable to use the near bank stress model.   

Bank erosion is a severe problem to any fluvial system as it can generate up to 90% of the total sediment yield from a catchment It is also considered a hazard because it causes loss of lives and properties. The bank erosion and displacement of river planform change, each year, large areas of agricultural land and residential areas and coastal installation are exposed to destruction. The Haft Cheshmeh river located in the village of Razjard in Rudbar Alamut region ( Moaalem kelaye), northeast of Qazvin province‚ with longitude 50˚10ˈ14 and latitude 36˚ 20ˈ27, experiences severe bank erosion in several parts of its course.. This area located on the southern hillside of Alborz and south of Alamut in the mountainous area. The study area is on the southern hillside of Alborz in the Alamot section. The length of the studied route of the river is approximately 11 km and it flows near the villages of Razjerd‚ Rashteghon‚ Mianber and Shengher.

In this research were used from the topographic map (1:25000) of National Cartographic Center of IRAN (NCC) and Google images for the demarcation of the Haft Cheshmeh basin boundary and flow path of the river. Meander curve, vegetation cover, and other parameters of the bank have been measured from from Google images and field observations. In this study, the method Bank Erosion Vulnerability Zonation (BEVZ) has been used for investigate the factors affecting (rainfall erosivity, lithological factor, bank slope, meander index, river gradient, soil erosivity, vegetation cover, and anthropogenic impact ) the instability and bank erosion of Haft Cheshmeh river. After collecting data and using from available parameters, the reaches and cross sections are selected. The base on six parameters data, general weightage values have been assigned to each of them.. this model Interprets data by weighting variables and It is actually a proposed model based on GIS. Finally, it prepares a map of the river zoning according to the parameters mentioned. Based on this zoning, the severity of the vulnerability is divided into 5 categories: very high, high, medium, low and very low. At the end when all cross sections are scored‚ map of cross sections is prepared and zoned based on weights assigned to areas susceptible to instability and bank vulnerability.

The bank slope map of the study area indicates that the most of the river banks of the Haft Cheshmeh river belongs to the moderate to gentle category of slope. The right side of reach 10 is in Very steep category in terms of side slope. According to the results, In the case of the meander index, the first reach is in the meander class and the rest of the reaches have straight pattern. In the soil erodibility factor, most bank river were in the class very gentle to gentle. Also in the left bank of reach 1, the right and left bank of reach 8 are in very high class. In the lithology factor, all reaches belong to the moderate category and only The lower part of the side of the reach 8 belongs to the very high category. There are also bed samples of all reaches of river in the low category.The river gradient is considered as the triggering factor of river velocity that controls river erosion. Longitudinal slope at all reaches in Haft Cheshmeh river ranges from gentle to moderate category. Although in the height of 1710-1720 and 1700-1690 are in high category. In the vegetation parameter, most reaches are in scattered class and also reaches 4, 5 and 9 have high vegetation. In the human activities parameter, reaches 1-5 and 8.9 are in the medium category due to agricultural and garden land use. In reaches 6 and 9, human activity is in high category. According to the results, all reaches except reaches of 5 and 9 have received average score. All of these reaches had moderate erosion vulnerability. According to the scores obtained and field observations, reaches 1 to 4 had a lot of vegetation. Also the soil erosion parameter in these reaches is in the gentle category and the meander index has the lowest score. The right bank of reach 5 has a slow erosion rate‚ but the left bank of this reach is high erosion. Because there is an bend at reach 5 that causes the left bank slope to increase and despite much vegetation, erosion has increased and the roots of the trees on this bank also show a lot of protrusions. But on the right bank, the gravely point bar has caused the wall slope to decrease and the amount of shear stress applied to it is low. As a result, it is less vulnerable to erosion. The right and left bank of reach 9 are very vulnerable, because in field observations, was observed in upstream of this reach a sedimentary barrier that caused the flow path to change and Channel walls on both sides become steep. At this reach, shear stress is high and also human activities have the most score.

The results showed that most of reaches in Haft Cheshmeh river are in moderate condition in terms of susceptibility to erosion. But in 8 and 9 reaches, due to high human activity in the river, they were in the middle to high class in terms of risk. Also, in all reachs except reach 10, are in the middle to high class due to the sensitivity of the side materials to erosion. A study of erosion sensitivity at different reach of Haft Cheshmeh river showed that more erosion occurs in areas where there is no vegetation or vegetation is scattered‚ also it is more susceptible to erosion. This study showed that vegetation and bank protection plays a key role in riverbank sustainability in this region . Evaluation of erosion using Bank Erosion Vulnerability Zonation method showed that vegetation is a protective factor along the river and human activities and meander index are two driving factors in the development of vulnerability and erosion.

River bank erosion is a major management problem in alluvial corridors. Every year, structures and farmland Lavij riverbank are in risk of change the riverbed and bank erosion. Thus any operational and administrative facility on the edge of the river should be based on knowledge of future mobility river and prediction of erosion. In recent years the use of numerical modeling for determining channel mobility, and thus defining the extent of the erodible corridor have improved. In this paper was simulated Lavij river bank(reach 20m) using by bank stability and toe erosion model. The purpose of this simulation is to predict the regression of river bank and estimate the amount of sediment. For this purpose, the cross-section geometry data, discharge and flow data of the river, geotechnical data of forming layers and bank covering data enter the model. Model, for both the bankfull and peak discharge was simulated. The simulation results showed that river bank is unstable and undercutting and bank erosion is active. The recession and bank erosion, during the peak discharge was significantly higher than the current bankfull discharge. It also turned out, the bank recession in lower layers cohesionless sediments, mainly of gravel and cobble stone are far greater than the in upper adhesive layers. River bank erosion is a major management problem in alluvial corridors. Every year, structures and farmland Lavij riverbank are in risk of change the riverbed and bank erosion. Thus any operational and administrative facility on the edge of the river should be based on knowledge of future mobility river and prediction of erosion. In recent years the use of numerical modeling for determining channel mobility, and thus defining the extent of the erodible corridor have improved. In this paper was simulated Lavij river bank(reach 20m) using by bank stability and toe erosion model.

River channel change, bank erosion and bank sedimentation are natural process of alluvial rivers that cause destruction of agricultural lands and destroyed of structures around the river bank. The aim of this research is estimation of bank retrogression rate and bank erosion in Galali river (the reach between Galali and Shirvaneh village) due to assessment of changes and estimation of potential changes in frequency of bank failures (Safety Factor) and sediment load from the river bank in two different scenario and 12 hours and three reaches by BSTEM model. The big floods can be caused bank erosion in this river and this issue is so important because there are some dams have been constructed in downstream of this river so estimation of erosion and sediment load is very important. Results show that total eroded areas in first scenario are 0.244, 0.372 and 0.054 m2 in reaches 1, 2 and 3 and the total eroded areas in second scenario are 0.272, 0.1 and 0.054 in reaches 1, 2 and 3 respectively. According to bank stability and safety factor, all of three cross-sections are unstable in first scenario and safety factor is less that 1 but safety factor increase in second scenario so that safety factor is around 1 in reaches 1 and 2 and in reach 3 is more than 1. Therefore, by protection works on the erodible banks can be reduced the total volume of the sediment load from eroded bank.

There are seven methods for estimating NBS, which include: channel pattern and bar assessment, ratio of radius of curvature to bank-full width (Rc/Wbkf), ratio of pool slope to average water surface slope (Sp / S), ratio of pool slope to rifle slope (Sp/Srif), ratio of near-bank maximum depth to bank-full mean depth (dnb/dbkf), ratio of near-bank shear stress to bank-full shear stress (τnb/τbkf) and use of velocity profile/isovel/velocity gradients. In this article, three methods were selected for estimating Near Bank Stress (NBS); Rc/Wbkf, dnb/dbkf, τnb / τbkf and then according to these methods, the erosion of the Galali river banks were determined at different levels from very low to extreme. Results showed that in the method radius of curvature to bank-full width (Rc/Wbkf), the bank erosion was moderate to very low and in the method near-bank maximum depth to bank-full mean depth (dnb/dbkf) in most cross-sections, the bank erosion was low and in method near-bank shear stress to bank-full shear stress (tnb/tbkf) the bank erosion was very high. Also, curvature coefficient shows that the river is sinuosity in cross-sections 1, 2 and 3 and is a meandering river in cross-sections 4 and 5. Comparing the results and field observation shows that the method near-bank maximum depth to bank-full mean depth is acceptable. Finally, in the Galali river, results of near-bank maximum depth to bank-full mean depth (dnb/dbkf) for assessment of the bank erosion (NBS) is better than method radius of curvature to the bank-full width (Rc/Wbkf) and near-bank shear stress to bank-full shear stress (tnb/tbkf). The Galali river has low to moderate bank erosion potential. Also, the river is sinuosity in upstream and is meandering in downstream and according to field observation, bank erosion potential in downstream of the Galali river is more that upstream.

Kashkan River is one of the important and water logged tributaries of Karkheh River which collects waters of a vast area of ​​Lorestan province. This river at the south-west part of Poldokhtar in a region known as the Gel-Sefid River is joined to Seymare River and creates Karkheh River. Length of Kashkan river is about 270km، and the water basin area of this river at upstream of Kashkan - Poledokhtar station is 9400 km2. This river due to its morphological and meandering characteristics and even in some floodplain points is arterial. There exists the problem of side erosion and displacement of river plan. Since، finding the appropriate technical method requires the recognition of the river behavior and effective geometric and hydraulic factors on the erosion and sedimentation process، therefore in the present research، topographic maps and satellite images have been used for reviewing and studying the temporal variations of Kashkan river plan. For this purpose، through performing a field survey and comparison of the new and old plan of the river by GIS software، the variation of river was investigated during a 52 years period and critical periods waere identified. Also the meander characteristics of the river and development rate of meandering in the current status in 49 of river bends at the reach of 108 km، between Varpo; and Teymorabad were investigated. The results showed that 6% of bends are undeveloped، 51% are developed and 43% are more developed. Finally، with respect to the geometrical characteristics of the river and using empirical relationships، the rate of bank erosion at critical reach in the future was anticipated. The prediction results show that at، Upper Kalho and Chrkhstan، river will move 657 m. Also at Khatere، Doab، Dovale Bozorg and at upstream of Chame Pelk، its movement will be 1035m and 1297 m respectively to stabilize it naturally.

Ground water flow and skin is the most important phenomenon in the process streams are involved not only in the face of the whole earth, but also of the life of man on Earth can. Degradation of coastal erosion, lateral stability and continuity in Iran and around the world each year destroys fertilized agricultural lands around the river, coastal installations, bridges, and is General houses. This causes erosion at the river Chrdavl Chenareh in the range studied. During the course of the river in order to 5/1 km was selected and harvested field operations. After the TIN created using HEC-Geo RAS amendment to link the HEC-RAS model and software ArcGIS 50 provides a cross-section of the model is introduced and values of the Manning coefficient model was introduced. With the introduction of the geometrical characteristics of the river flow characteristics and the Manning coefficient model, HEC-RAS, characteristics of flood flows for return periods of 5, 25, 50, 100 and 200 are set and used to determine and identify areas susceptible to erosion and sedimentation rates Minimum and maximum shear stress and velocity across the range for different flood return period was determined. Finally, the bank erosion. The minimum shear stress for different flood return period equal to N / m ^ 2 12/7, which occurred on the left coast, so Left Coast Range Chenareh most vulnerable place for the deposition. Field visits the accuracy of the calculations and the results of recent research shows.

River channel change, such as bank erosion and accretion are natural processes in alluvial rivers. This paper aims to investigate migration and channel change plan form and effect on bank erosion and accretion done in Gamasiab River in Kermanshah Province. This study used aerial photography taken in 1955, 1969, 2003 and IRS satellite imagery of 2010 with a resolution of 5/8 m, aerial photographs were orthophoto in ARCMAP software based on 1/25000 topographic map. Shoreline was digitized and river was divided into 12 reaches. By comparing river in the sequence period investigated the positions have a change. Using the ARCMAP software to create polygons that represented the difference between two positions we calculated erosion and accretion separately for each side of the river. The area of bank accretion along the river had been 285.5 ha and from 1955 to 1969 this area had been 402.6 ha from 1969 to 2003 and the area of bank accretion was 112.9 ha from 2003 to 2010. Bank erosion had been 347 ha from 1955 to 1969, and this was been 414.17 ha from 1969 to 2003 and the area of bank erosion had been 138.2 ha from 2003 to 2010. Results show that the amount of bank erosion is more due to bank accretion in the Gamasiab River. Change and migration in river is the cause of the erosion. Some places in river show about 400 m of movement.