فهرست مطالب سعیده متش بیرانوند

The annual loss of soil in the world is about 75 billion tons. In Iran, soil erosion is one of the most important environmental problems, and in Iran's catchments, soil erosion increased by 800% between 1951 and 2002. The significant decrease in the performance of Iran's catchments due to a large amount of erosion indicates the increasing necessity of monitoring and following up on this destructive phenomenon. Dendrogeomorphology is a technique that has been very successful in describing and determining geomorphological processes. Dendrogeomorphology is a very flexible method to assess soil erosion and can be used as a data source to determine the reliability of data obtained from direct estimation techniques. The purpose of this research is to investigate the state of sheet erosion in the Nachi watershed using the dendrogeomorphology technique on the oak tree's protruding roots as the region's dominant species. Considering the limited nature of such studies in Iran and the very fragile situation of the studied area, and the risk of filling up the reservoir of Zrebar Lake, which is very important from the point of view of the environment, it is necessary to study the situation of sheet erosion and soil wastage and sediment trans.

In order to achieve the research objectives, after collecting and preparing the primary information, including written information, statistical data, maps, and pictures, a preliminary area survey was carried out, and sampling sites were selected. The samples were prepared according to the program, based on the status of the catchment (according to the land use of the catchment and the direction of the range, the desired work units were selected in places with exposed roots). Based on this, different samples were taken in two different forests, agriculture uses, and western, eastern, and southern directions. All the samples were prepared from the oak tree species, which is the absolute majority in the study area. Finally, 64 samples were selected from the collected samples that could analyze the growth rings' anatomy. Discs harvested from the roots were used to reveal the vegetative rings of the discs by polishing and cutting the surfaces. Using a sanding machine, it was gradually polished with different grades to clear the growth ring border. Then, the disks were measured in the laboratory to determine the first year of root emergence and to determine the width of vegetative rings using a Lin-Tab 5 device equipped with a binocular microscope and specialized T-Sap chronology software with an accuracy of 0.01 mm.

This research showed that in the Nachi catchment, surface soil erosion in agricultural use (average erosion rate 2.43 mm per year) compared to forest use (average erosion rate 0.6 mm per year) is about 4 times. The results of the statistical tests also showed that the type of land use affects the average annual surface erosion rate in the studied basin. Also, this study found that different geographical directions do not affect the average annual surface erosion rate of the Nachi catchment. Comparing erosion values in agricultural and forest use shows the importance of natural covers' protective and important role in preserving the soil and preventing its erosion and wastage. Various studies in the world and Iran have shown that in recent decades, there has been an increasing increase in land use changes, that these changes have the basis of increasing runoff and affecting the amount of soil loss, comparing erosion in the agricultural area with the forest area, showing the protective and important role of the covers. Natural and forests have a valuable role in preserving the soil and preventing erosion and wastage of soil.

The results of this research reveal the necessity of paying more attention to studies on the possibility of modification and change of land use in these areas. The change in land use and the negative effects caused by human interference are not only in the basin itself but also in places outside the occurrence of erosion in the form of accumulation on high-quality agricultural lands, pastures, water storage sources, and irrigated canals. Also, the creation of pollution by sediments and heavy metals and accompanying chemicals, especially the threat to the very fragile ecosystem of Zrebar Lake, is more evident today than ever before. It is suggested to use another method parallel to this method in future works to validate the obtained erosion rate. In future studies, sampling should also be done from the northern slopes for a more detailed investigation of the effect of the slope directions on soil erosion.

Channel location changes of the river is an important process in the river ecosystems and is a threat for human activities in flood plains. Exploring the how and why of these changes has an important role in predicting the process of future changes and channel migration order to manage the flood plain. On the other hand, human interventions such as sand removal from river bed, land use changes, river engineering projects, etc. cause changes in the pattern and direction of the river channel. Exploring the how and why of these changes has an important role in predicting the process of future changes and channel migration order to manage the flood plain. Each year, several significant and insignificant floods happen in Lavij River, which has led it face several lateral channel migration. The effects of this migration can be significant in the form of root exposure and Falling trees on canal margins, road demolition, agricultural land, stand bridges, etc.Lavage River basin area is 93 square kilometers of North Alborz independent basin located on the northern slopes of Alborz Range south of the city of Chamestan. This basin has a north-south direction and after leaving the mountainous area and crossing the agricultural lands and forest park Noor to the Caspian Sea. The Lavage Basin is bounded on the west and south by the Glendrud Basin and on the east by the Waz Basin. In this research, the evolution and lateral channel migration of Lavij River has been studied with the Dandrogeomorphology Technique.This study is a combination of field and laboratory methods that include field surveys and sampling, sample preparation and macroscopic measurements. After collecting baseline data from the study area, 4 intervals for field sampling Selected at each interval, were first mapped using river cross-sectional mapping and positioning of river channel geomorphic forms including active canal, abandoned canal, flood plain, point bars and terraces. In this method, the age of the trees in the flood plain, abandoned channels, terraces, point bars, and the location of surfaces in relation to each other are calculated; the lateral channel changes have been Reconstruction from the past until this day. Comparing the hydrology and chronology data of the present trees in different layers show that the channel migration occurred in the reach No 1 1374 and 1375, in the reach No 2 1 in almost at 1345 and 1346, and in the reach No 3 in almost at 1380. In the reach No 4, a significant incision occurred in the river bed and the major channel migration in the flood plain surface was in the left direction of the current. Basic channel migration is mainly related to flows that are less likely to occur, with longer return periods. study of the trees chronology data in the study area showed that the year of migration or abandonment at all intervals was not consistent with large floods with a long return period, but even in floods with a return period of less than 4 years. In the study area out of the 4 intervals studied in three intervals, the diversion of the river channel was caused by flood currents of less than 20 m3 / s,therefore flows with a return period of less than 4 years. But when such currents occur alongside transverse currents, the probability of shear and bank erosion is very high. That is, in subsequent years, larger discharges will manipulate the channel created in these floods until another severe flood occurs and lead to major migration in the stream and channel. In fact, exceptional discharges along with rare floods at the time of occurrence temporarily cause shorter and wider canals because geomorphic processes can respond to severe floods of several decades, river measurements (channel morphometry) will be reflecting stream history. The study of channel migration, with the chronology of alder trees in the study areas, showed that the major floods of the years 1345, 1346, 1374, 1375, 1376 and 1380 have extremely affected channel changes and the age of establishment of alder trees illustrates this.The floods of 1996 and 1997 have been recognized as an important event in the interval changes over the past few decades. These floods have led to the straight and narrowing of the channel (interval 1). These processes deepen the channel and bring the floodplain to a higher level. The geomorphic changes that occur will increase the amount of flow required to exit the channel and extend to the surface of the floodplain .

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.

One of the key issues of erosion and stability of the river is the beginning the movement of sediment particles. River sediment yield caused water turbidity, nutrients and pollution problems of water, buried in the water diversion facilities as well as filling the water storage lakes. Flow that will start moving particle, called the critical flow. The initial move threshold sediment particles has been investigated in several different methods, most important of which are the average critical velocity, critical shear stress and critical unit discharge. To investigate the stability of the Lavij river bed sediments in the city of Noor, according to river conditions used the critical shear stress and critical unit discharge methods. To determine initial move threshold sediment particles in the bed of the river were two cross-section of the river, two cross-section conditions were assessed. After that, the critical shear stress and critical unit discharge for four particle size D16, D50, D84 and D95 in each cross-section was calculated, and showed that in cross-section (1) in the bankfull discharge conditions all particles with sizes D16, D50, D84 and D95 begin to moving, and so in the bankfull discharge, sediment conditions will generally change. In cross-section (2) particles with a diameter D95 and the more it will be remain stable in the river bed, and other smaller particles of this size are starting to move. Due to further slope of the bed and width less active channel in the cross-section (1) has caused that all particles are unstable. Finally, the results from both methods were highly concordant, and this confirms that the use of these methods for stabilizes studies and sediment yield of river are appropriate.

Historically, Iran due to its specific political and geographical Political situation, Has witnessed suffering many natural and unnatural disasters. Hence, the practical and theoretical situation of passive defense against the crisis is very important in this extent. When an unexpected event occur, it will prevent the severe destruction of urban communities,if the positioning of new urban projects will be done using passive defense. Among the most important centers Disaster Management Support Centers is to provide operational and tactical fields, order to achieve prevention, preparedness and response in different crises. One of the notable instance before building Centers, survey and selection of appropriate location to establish the type of landuse. Thus, in this study, we attempted to localization of these Centers with Analytic Hierarchy Process (AHP) and Geographic Information System using the principles of passive defense in Tabriz. Finally, the raster maps were prepared to determining the preference of each location for the construction of these base. The purpose of locating are reducing vulnerability of Tabriz disaster management support centers of the crisis management against natural and abnormal hazards and preservation of effectiveness of these centers in Critical situations. Due to the time consuming process of localization, the extent of information and disability to use simultaneously all the factors affecting the localization, using of AHP method is one of the most comprehensive and easiest ways to locating of these bases. Finally, a raster plan is prepared that determine the Most appropriate and most risky areas to build this centers in metropolis of Tabriz, according to the principles of passive defense.

The dimensions, shapes and the patterns of natural rivers change according to their dynamic properties. These unavoidable changes cause the rivers imbalance and a new balance will be formed. The around lands will be affected by this dynamic and dangers such as instability of the bed. In this research we used chronological inference method to study Kashkan River morphology. Kashkan river is located in a region between Lorestan province and Gavmishan bridge in a reach of 25 kilometers. The aero photos of 1334, 1376, the sensing images of liss3 obtained from IRS P6 satellite in 1385 and the Geo Eye image of the land were digitized in Arc GIS software. In the second step geometrical parameters such as wave length, valley length, sinuosity, central angle and radius tangent on the river arch were calculated. Then these geometrical parameters were statistically analyzed and were compared in 4 stages. We Using HEC-RAS investigated flood zonetion as an important factor in river bed changes. The results of this study and comparing these parameters during the 4 reaches showed that in the abovementioned year's kashkan river pattern was meandering in the reaches of 1, 4 and 5 and also it was developed meandering form in the reaches of 2 and 3. Those river’s arcs which had the most changes in those years were located in the reaches of 2 and 3. At the end it was concluded that the geology factor and the river’s flood in the reaches of 2 and 3 were the most important factors in forming the bed’s changes and bank erosion. Topography factor was the most important factor in causing the most changes in the reaches of 2 and 3 which were located in floodplain.