جستجوی مقالات مرتبط با کلیدواژه "رسوبگذاری" در نشریات گروه "آبخیزداری، بیابان، محیط زیست، مرتع"

The removal of alluvial deposits from the riverbeds causes changes in the balance of the rivers. These changes are not limited to extraction and harvesting, but the miles appear higher and lower. Due to the rapid growth of industrial activities, urbanization and related developments, demand for sand has increased over the past few decades worldwide, especially in developing countries. In the present study, the HEC-RAS5.0.6 model was used to simulate the sediment flow of Allah Ramhormoz River and the hydrometric statistics of the junction stations as the upstream boundary conditions and the hydrometric statistics Meshrageh of the station as the lower boundary conditions in the 44 years old(1352-1396), transverse sections of the river, which were taken in year 87, longitudinal profile of the river, aggregate of the bed material was introduced into the model. The results of this study showed that the Ichres-White sedimentation transfer function with R2 equaled 0.87 best results have given. Also, the study of erosion and sedimentation in the river showed that from the beginning of the Allah River range to the intersection of Allah River and Zard River with an equivalent of 165 thousand cubic meters per year, the best area for harvesting.

Intakes are structures that are used to divert water from a river or canal. Optimizing the performance of intakes and increasing the inflow to the intake, while controlling the sediment bed of the canal in terms of erosion and sedimentation has been one of the topics of water engineering. The use of spur dikes is effective in modifying the flow pattern, controlling erosion and transferring sediment to the intake. The purpose of this study is to use spur dikes to increase the inflow to the lateral intake, in a way that causes the least turbulence, erosion and sedimentation.

In order to perform the experiments, a rectangular channel with a length of 15 meters and a width of 1.5 meters with a fixed slope was used as the main channel. Lateral intake is a rectangular canal with a width of 0.6 and a length of 5 meters at an angle of 90 degrees to the main canal, at a distance of 10 meters from the beginning of the main canal. The model without spur dike was considered as a control model and in other models, the spur dike is located upstream of the intake, upstream in front of the intake, downstream in front of the intake and also as a series of spur dike upstream and in front of the intake. The laboratory models were modeled in FLOW-3D software and calibrated based on laboratory results and data.

Examination of laboratory results showed that the condition of the spur dike at the downstream and in front of the intake has the best scouring results and branching ratio and increase of 66 and 41% at 40 and 60 liters per second, respectively, for branching flow ratio Shown to the control model. According to the results of laboratory models, the model was selected as the best model and modeled numerically with the location of the spur dike in the downstream and in front of the lateral intake (the position of No. 4). Validation of the results of numerical and laboratory models in the hydraulic values ​​of water flow points (R2=0.95) and the number of bed points (R2=0.74) showed that the acceptable accuracy of the numerical model and analysis performed by Flow3D software. Then, first by changing the distance and then by changing the length of the spur dike in the position of No. 4, the numerical model was examined and the best distance of the spur dike, a distance of 58% of the width of the intake and the best length of the spur dike, a length of 30% of the channel width The original was calculated.

This study showed that the use of spur dike downstream and in front of the intake in appropriate dimensions can not only increase the ratio of inlet flow to the intake, but also reduce the scouring of the canal bed, as a result of the use of these spur dike in lateral intake of canals And rivers are recommended.

Seasonal floodwater has been kept in the lands by using watershed projects so that it penetrates into underground beds, but this case causes different influences on graining, permeability, underground water and vegetation. Three sections were chosen as experiment sites to measure soil changes of watershed projects in Nodoushan watershed area of Yazd province. Seven permeability experiments with double cylinder inside every section and three experiments in the control group were performed. Along with each of these experiments, one sample was collected from 0.5 meter of the surface soil and graining experiment was performed on it. The significance of permeability was investigated by the use of non-parametric Mann-Whitney test and Kolmogorov–Smirnov test. The results show that permeability in Sadrabad, Nodoushan and Alaviyeh in control group were 4.92, 3.52 and 5.89 cm/ hr, respectively. After some periods of dewatering they were reduced 94 percent, 89 percent and 92 percent, respectively. And finally reached to 0.28, 0.37 and 0.47, respectively. Also, the average diameter of the particles decreased about 90 percent. The results of experiments showed that the decrease of permeability was significant in the level of 95 percent.

Evaluation of mining methods and the volume of the bed and flood plain sand and gravel mining show that many problems will be created due to geometry and naturally changing of rivers, increasing of the flood power and environmental and ecological dangers. Hence, applying correct management on river sand and gravel mining can create many positive effects. In this research, the effect of locating of the consequent river bed material mining pits on their sedimentation is investigated in order mining management via an experimental study. Results indicated that, there is no perceptible effect on the infilling and migration velocity of the upstream pit by increasing the distance between the pits up to 16 times the flow depth. Also, mining near the wall of the channel (20% width of the channel) leads to decrease infilling volume up to 25% and decreases migration velocity of the upper edge of the upstream pit up to 37%. By increasing of the distance between the pits, infilling of downstream pit is decreased, but it depends on the distance between the downstream pit and the wall. When the distance between the pits doubles, migration velocity of the downstream pit decreases up to 70%. If the mining is located at the center of the channel and the pits are in close proximity, it creates more suitable condition due to the infilling and migration for upstream and downstream pits.

Soil erosion is a serious threat to human life. This calls not only for appropriate methods of assessing soil erosion and sedimentation levels but also for the implementation of soil conservation practices. Fallout radionuclides (FRN) such as beryllium-7 (7Be), lead-210 (210Pbex), and cesium-137 (137Cs) have been used as soil redistribution tracers in various studies. The present review aims to investigate the suitability of plutonium 239+240 (239 + 240Pu) radioisotopes as a new tracers for the assessment of soil redistribution rates. Plutonium isotopes are present in the environment mainly due to nuclear activities including nuclear weapon tests and nuclear power plants (NPP). Among them, the 239+240Pu isotopes offer such advantages as long half-lives, availability, relatively easier determination using highly sensitive techniques, and uniformity of their values at reference sites. Application of plutonium isotopes as soil redistribution tracers was first investigated in 1978.However, relatively few practical attempts have been eversince made to exploit the full potential of Pu isotopes as efficient and reliable tools for soil redistribution assessment compared to other existing techniques.

This research was aimed to investigate Hirmand River morphology alterations through the estimation of suspended loads transported by floods. The sediment samples were collected and suspended loads were estimated. The alterations of sediment load along Sistan reach was investigated, spatially and temporally. The suitable reaches for sedimentation inspected through   the high resolution Satellite imageries of Spot-5 (with the spatial resolution of 2.5-5 m). Through the geo-referencing of aerial photos and satellite images in GIS environment, the changes of river width, meander angel, and sinuosity index were estimated during the last 50 years. The t-student test was employed to assess the changes of river width during time. Results showed that the average suspended sediment load of Sistan River was 32 grL-1 and approximately 7.3 million tones sediment load entered to the study reach. According to the results, the river width has been changed, significantly. The river width in 2016 has been decreased by 0.33 of that in 1965 and 73% of the river has no capacity for flow transport and shows a high density of suspended load. This study established that the hydrology parameters (sediment and flood), biologic and slope changes are the main causes of sediment load and the changes of river morphology from a disorganized sinusoidal meanders to limited meanders. During the period  of 1965-2016 the pattern of flow changed from meander to the sinusoidal. The average angel of river from 287.94 changed to 295.26 degree. The average of sinusoidal index changed from 1.39 to 1.18 and the average of flooding bed width from 160.79 m changed to 41.32 m in 2016.

Introduction Water erosion is one of the most important factors in land degradation in large parts of Iran destroying fertile soils and agricultural land. The impact of soil erosion and related sediments decreases significantly water quality and reservoir capacity. Especially in semiarid areas like in the Menderjan watershed in the west Isfahan province sheet and rill erosion contributes to the sediment dynamics in a significant way. Particularly, sheet and rill erosion processes and related forms and features are very common in this region. Hence, this study is aimed at identifying and quantifying the major erosion process dynamics. Therefore, we applied an integrated approach combining the USPED and RUSLE models with data mining, remote sensing, and GIS methods.
Materials and methods The study area is Menderjan watershed locating at east Isfahan and has an area of about 21,100 hectares. In this study, the USPED and RUSLE was used. The USPED model is based on the assumption that soil erosion depends on the detachment capacity and the sediment transport capacity of surface runoff. However, the USPED models do not consider the sediment yields from gullies, stream banks, and stream bed erosion. In the USPED model erosion and deposition (ED) are computed as the change in sediment flow in the direction of flow.
ED=d×(T×cosa)/ dx d×(T×sina) /dy
Where a is the aspect of the terrain surface, dx, dy is the grid resolution, and T is the sediment flow at transport capacity. ED can be positive, indicating soil deposition, or negative, indicating soil erosion. Transport capacity (A) is expressed as: A=R×K×C×P×L m×(sin S) n
Where A: Average yearly soil erosion (t ha-1 y-1), R: yearly rainfall erosivity factor (MJ mm ha-1 year-1h-1), K: the soil edibility factor, LS: Slope Length and Steepness factor, C: cover management factor and P: Support Practice Factor, S is the slope, L is the upslope contributing area, and m and n are constants. For prevailing rill erosion m = 1.6, n = 1.3, while for prevailing sheet erosion, m = n = 1. The USPED and RUSLE model was applied using Arcmap10. In this study, the Landsat satellite images 8 (OLI) and rainfall data, soil properties and digital elevation model (DEM) were used, and GIS plays a major role in preparing thematic layers and estimating soil erosion.
Result The range of obtained R factor values range was from 82 to 118 MJ mm/ ha h year. The average values for the Menderjan watershed amount to 265.2 MJ mm/ ha year-1. According to the soil laboratory analysis soil texture is dominated by silt clay loam and clay loam and thus is highly susceptible to soil erosion. The amount of organic matter in all samples was 2 %. Soil organic matter reduces the erodibility of soil. In many arid and semiarid areas soil organic matter is low due to scarce vegetation, and hence, soil is more susceptible to erosion. The annual average soil erodibility of this basin 0.04 (t h MJ-1 mm-1). The amount of topography for RUSLE varies from 0.001 to 16.7 and USPED varies 0.01 to 30 Support Practice Factor of the study area is variable from 0.1 to 1 and C factor value varies was 0.2 to 0.5. According to result more than 35 % of the area is affected by high to very high erosion and deposition process intensities. The stable areas and low erosion and deposition zones cover about 15 % of the area. However, some of the mapped and predicted sheet and rill processes are located in the stable and low intensity soil erosion classes. The extreme values are characterized by steep slopes in ridge positions in the northern and southern parts of the watershed.
Discussion and Conclusions During recent years, the role of water erosion as one of the land degradation factors in arid and semi-arid areas of large parts of Iran has increased. In our study we applied a combined approach using the RUSLE and USPED models rill/inter-rill (sheet) erosion processes, and deposition processes. To the knowledge of the authors, this is the first attempt integrating different erosion processes and deposition dynamics in Iran. In the study area soil loss is concentrated especially in the abandoned bare land areas. The protection of bare soil to reduce soil loss should be ensured by appropriate cultivations. According to the results a large part of severe erosion occurs in the steep areas in the north and southwest of the study area. Agricultural cultivations may change the land cover, leading to poorer vegetation cover or bare land, especially after harvest and thus increase erosion processes and land degradation. Thus, control of soil erosion targeted to the area not only reduces direct costs of soil erosion; however, it also it diminishes the implementation costs of control operations for decreasing soil erosion.

Investigations show that in some cases the distance between check dams are decreased due to wrong ultimate slope. In this Study، a survey and investigation implemented on Gush and Bahreh catchments، Kartian، Kameh and Dasht watersheds which are located on upstream of Kardeh، Torogh، Shahid Yaghubi and Golestan dams، respectively. In this way، longitudinal section profile، ultimate slope، location، distances and height of dames with acceptable performance about upstream ultimate slope has been measured. Meanwhile، characteristics related to bed aggregates has been sampled and determined. Then، with the measure of dimensions regarding the ultimate slope، some equations which were based on primary slope of river direction has been developed. Our investigations claim that unsuitable design in ultimate slope had been lead decreasing the distances between dams; consequently، some of upstream weirs had been buried under sediments. To wrap it up، we have to argue that definition of distance between dams based on the measured ultimate slope could result 25. 4 percent descend in expenses of all studies weirs and dams construction and protection.

Inlets play an important role in controlling sediment movement and its distribution in coastal areas. Therefore, recognizing effective factors in the hydro-dynamicity of inlets known as transmission process and determining the geometry and formation of inlets are of paramount importance. The undulations of water and tidal waves are among the major factors shaping an inlet. Breaking of wave in shallow water in the mouth of inlets causes the formation of long shore current and sand transport in this area. Also tidal currents and waves play an important role in the change of morphology of both sides of inlets. The purpose of this study is to find out how these two factors can interactively affect the sediment. To this end, a coastal basin that is connected to the open sea through a mouth is simulated in Mike 21/3 software. For this simulation, a 10*50 meter un-structured triangular flexible mesh in a finite difference model at one second intervals was used; undulations and tidal waves were sent to the mouth of the inlet at varying heights. Simultaneously simulation results show that by simulation of flow and sedimentation patterns interactively change the morphology of the inlet so that with the passage of time it reaches equilibrium; hence, there would be an ideal inlet. Also, by means of characteristic non-dimension H_w/H_t, the dominated parameter can be determined in the inlet.

In the network of floodwater spreading and artificial recharge system, deposition is the main obstacle of infiltration water in the soil and reaching of water to the groundwater. Soil infiltration reduction depends on suspended material, the infiltration rate, soil physical characteristics and quality of the floodwater spreading. Fine-grained sediment enters into the network during the flood; reduce the efficiency of these projects and in long time of operation to actually lose its effectiveness. The main objective of this study is the effect of sediment deposited on the variation of infiltration rate by the floodwater spreading. In this study, double rings with triangular surface soil infiltration rate were used and the relevant data were entered into the Excel software. The analysis and comparison of the effects of the floodwater spreading on soil infiltration rate in comparison to control was evaluated using the statistical method of factorial completely randomized design. The effects of floodwater spreading on soil infiltration rate were evaluated using the statistics factorial method in completely design. Duncan mean comparison test was applied to compare rate of infiltration on spreading area with ditches between them. It is necessary to mention that the control values in the first year were compared with the results of reminder years. In general, the analysis of variances show the difference between rates of infiltration in depth of soil is significant at level %5 but the level signiticant for floodwater is %1. There is no significant difference for interaction of these two factors.

Sedimentation is one of the most important problems in watershed management. The characteristics of geological formations are the most basic factors which have an important role in sediment yield. There are several methods for sediment estimation، but sediment transport equations and formulas have been developed for special conditions which may not represent all conditions. Therefore to find out which method is suitable for a specific river، it is required to compare each method with the measured data. The purpose of this research is to evaluate efficiency of different methods of sediment discharge estimation in Jagin River at Panhan hydrometric station. The methods of modified Einstein، Engelund-Hansen، Yang، Habibi and Van Rijn are used in this investigation. The required data was collected from Water Regional Organization of Hormozgan Province. The sediment yield is estimated based on concentration of collected samples of floodwater. Then، the collected data were checked and corrected. The conclusion shows that the modified Einstein method is the most suitable method for sediment estimation in the study area.

The phenomenon of sedimentation in dam reservoirs is the most important threatening factor in huge investment of capitals in hydraulic projects. Uncertainty analysis for each phenomenon shows the real view of its parameters and creates real understanding of the effective factors on the phenomenon. In this research, to estimate the volume of sediments in reservoir, using hydrometric and sediment data of Karaj River from 1961 to 2003, factors affecting sediment transportation and a model considering non-uniform sediment sizes. Then by using Monte Carlo simulation method and statistical input parameters, effective factors on sediment volume in reservoir, random input parameters and Latin square sampling method, some samples were obtained. At the end, the uncertainty of each parameter was introduced using statistical characteristics. The Results from uncertainty of annual sediment of reservoirs, expressed as coefficient of variations, was introduced as 56% Sensitivity analysis showed that annual mean flow rate and sediment rate were the most important factors in estimation of reservoir sediment volume.

Dare- Gap River in the north of Booshehr province of Iran, in the reach of study, has a meandering pattern. Most of the arcs are left wise in the reach of study that caused to increase water level during flood events through the city. To solve this problem, it was supposed, if the arcs are omitted by making three cutoffs in designed path, river slope, flow velocity and also river erosion potential will increase. Then the average of annual erosion, aggradation and also the maximum depth of erosion and aggradation for designed flood were studied for two paths; existing path and artificial path, by using MIKE 11 model. Results showed that the maximum erosion for annual flows occured in two reaches with bridges in them. The amount of erosion in Kamarbandi Bridge was more than Main Bridge. And also deeper erosion was observed in the designed path than existing path. In the Dare- Gap River in the kamarbadni Bridge, results of the maximum depth of erosion and aggradation in the case of designed flood (100- years Flood) showedthat the maximum erosion in the designed path and for former path, was 0.65 and 0.78 meters, respectively.