جستجوی مقالات مرتبط با کلیدواژه « رسوبگذاری » در نشریات گروه « آب و خاک »

One of the natural structures in rivers is mid-channel bar that is created due to shear stress decreasing and sediment deposition in the central part of river. Bifurcation and erosion are seen in rivers because of mid-channel bar existence. Also, energy loss is the other impact of mid bars that would intensify the deposition in rivers. Mid-channel bar is known as one of the most important aquatic habitats, so there is necessity to find more information on flow structures around it in operation processes and river restoration. In this research, the flow structures around mid-channel bars are assessed as laboratory study. Three mid-channel bars were made in the shape of rhombic, ellipse and lemniscate in this research. These shapes are common in natural alluvial rivers. This study was established in a laboratory flume by length of 9 meter, and width and height of 0.4 meter. The bed slope was fixed of 0.0007. This flume was located in the water and sediment research laboratory in Gorgan University of agricultural sciences and natural resources. Three-dimensional velocity of flow was collected using an electromagnetic current velocity sensor with a frequency of 30 Hz in 39 data points. The flow discharge was fixed as 4.5 liter per seconds using a frequency flow meter. The flow regime was subcritical and turbulent in all examinations. Findings showed that bar shapes have different impacts on flow structures and amounts of energy losses. Comparison between plots implied that there are similar conditions in elliptical and lemniscate shapes but a little different in rhombic case. The variation range of transverse velocity was between 0.4 to 1.6 times of average value for all shapes. According to the results, the existence of elliptical bar led to significant tolerance in longitudinal velocity in all axes (between 0.5 to 1.6 times the average in left and right axes and 0.2 to 1.4 times the average value in central line), but these tolerances were not significant for lemniscate and rhombic bars (between 0.8 to 1.2 times the average value in left and right axes and between 0.8 to 1.4 times the average value for central axis). The variation of vertical velocity in middle axis presented the maximum decrease before facing elliptical bar and similar conditions for this axis in facing with lemniscate bar, except that this decrease is started exactly at facing point here. In addition to the values of the velocity components, the direct effect of encountering bars should also be sought on the values of the flow energy as a cumulative indicator of the erosive power of the flow. A more detailed analysis of the graphs shows left that in the and right axes, encountering the elliptical bar has led to an increase in the relative energy of the current by 1.4 times the average, and after passing through the bar, the energy load has decreased to less than the average value. But in the middle axis, the presence of the bar reduced the relative energy of the flow to 0.6 average value and after passing through the bar, this component has an increasing trend. Exposure to the elliptical bar led to the greatest changes in the relative values of the triple velocity components, compared to the rhombic and lemniscate bars. Also, the changes in the total energy load caused by the presence of two rhombic and lemniscate bars are insignificant, but similar to the changes in all three velocity components, transverse, longitudinal, and vertical, the elliptical bar led to significant changes in the relative values of the total energy load along the channel.

One of the effective methods to reduce the kinetic energy downstream of hydraulic structures are the aprons. The horizontal aprons is one of these structures in the river that are often used downstream of stilling basins. At the time of execution, the apron and the riverbed are at the same level but when there is a flow in the boundary between the connection of the river bed and the aprons, scouring occurs, which causes the destruction of the apron and there is a possibility of destroying other water structures. In this research, using Flow 3D software, different scenarios were simulated for five Froude values of 0.32, 0.3, 0.25, 0.2, and 0.15, three Manning roughness coefficients of 0.025, 0.02, and 0.014 per particle diameter of 1.8 mm for horizontal aprons. In this numerical model, the graph of scouring depth changes in relation to Froude numbers in different roughness coefficients, the effect of Froude numbers on the location of the scour hole for different roughness coefficients of the horizontal aprons, the shear stress changes in relation to the length of the horizontal aprons with different roughness coefficients and different Froude numbers, as well as Erosion changes with respect to the length of the horizontal aprons were calculated with different roughness coefficients and different Froude numbers.

Due to the importance of the topic in the fluid transfer industry, the way of pipelines across the width and bed of the rivers has been considered especially in recent decades. In practice, the passage of pipelines through meandering rivers and river bends is unavoidable. In this research, local scouring of buried and semi-buried pipe in 90-degree mild bend under different scenarios was investigated. The results of this research can help the functioning of rivers and their interaction with structures in the river such as buried and semi-buried pipelines, predicting the amount of water washing around them and using its results in the design and placement of these pipelines.

The laboratory model on which the scenarios of this research are based includes an arc-shaped channel located in the hydraulic laboratory and physical models of the water science and engineering department of Razi University. In this arc-shaped flume, the length of the upstream span is 5.4 meters, the length of the downstream span is 4.5 meters, the inner radius is 1.6 meters, the outer radius is 2.1 meters, the height is 0.6 meters, and the floor width is 0.5 meters. In order to check the correct functioning of the physical model and to trust its results, an experiment was conducted without the presence of the pipe buried in the bend. In this experiment, the flow descent number equal to 0.32 and sediments with a uniform grain and a diameter of 0.85 mm and a thickness of 15 cm were placed in the flume bed. After conducting the test for 6 hours and not observing the movement of the bed load, the pump was finally turned off and after the complete drainage of the flume, the bed profile was measured.

The effect of the placement angle of the repeller pipe relative to the mild arc (θ) on the scouring pattern
The results showed that by placing the pipe in the repulsive state, the amount of scour after the pipe and under the pipe has increased compared to the attracting state. According to the placement angles, it was observed that in repulsive mode, with the increase of the placement angle of the pipe in the bend, the amount of scouring after and under the pipe has increased. The effect of the placement angle of the attracting pipe relative to the mild arc (θ) on the scouring pattern In the absorbant state, it was observed that by approaching the beginning of the arc and reducing the placement angle of the pipe due to the non-alignment of the flow direction with the pipe direction, the amount of scour after the pipe decreased, but the process of scouring under the pipe was observed as in the repulsive state.The effect of pipe placement depth on scouring pattern By increasing the depth of pipe placement, it was observed that the effect of the pipe on local erosion has decreased; Even in some simulation scenarios, the placement of the pipe in the depths with the ratio of the placement height to width of the channel of 0.06 buried pipe has no effect on the local erosion. It can be concluded that at depths equal to or greater than The ratio of placement depth to channel width is 0.06, the effect of local scouring caused by the buried and semi-buried pipe is minimal, and as a result, it causes the least damages.

The results showed that by placing the pipe in the repulsive state, the amount of scour after the pipe and under the pipe has increased compared to the attracting state. According to the placement angles, it was observed that in repulsive mode, with the increase of the placement angle of the pipe in the arch, the amount of scouring after and under the pipe has increased. However, in the absorbiant state, it was observed that by approaching the beginning of the arc and reducing the placement angle of the pipe due to the non-alignment of the flow direction with the direction of the pipe, the amount of scouring after the pipe decreased, but the process of scouring under the pipe was observed as in the repulsive state.

Longtime sediment routing and determining the location of sedimentation and erosion in rivers provide useful information for engineers to design hydraulic structures and river management. Therefore, in the present research a computer model was developed to simulate sediment movement in a river, in which after flow calculation at each time step, sediment continuity equation was solved numerically to predict bed change at the same time step. After model verification, using Meyer, Parker and Wilson equations for bed load prediction, bed variation of the river with 18.5 km length for 5 and 10 years was calculated. Also by numerical solution of 1-D depth average differential equation to calculate suspended load concentration the effect of suspended load on sedimentation and erosion pattern during 5-year simulation was investigated. The results showed that the erosion phenomenon was dominate pattern at the river reach. Also calculated volumes of sedimentation and erosion using the Wilson equation were more than those from the other relations. In addition the result showed with considering the effect of suspended load, variations and amounts of sedimentation and erosion were increased. Therefore, significant mistake would occur in prediction of sedimentation and erosion pattern in the mentioned river reach if the effect of suspended load was not considered.

Flood spreading system (FSS) is one of a variety of methods for artificial aquifer recharge. The system's main problem is sedimentation on the FSS area, which reduces its effectiveness for aquifer recharge. In this regard, satellite image change detection technique is a proper method for accurate sediment distribution pattern diagnosis with the FSS. A relevant study has been conducted by Sarreshtehdari (2005), where classified images of 1987 and 2001 were compared and revealed a sediment distribution pattern and variations. In the present study, which was conducted on Jarmeh FSS in the north of Khuzestan Province, sedimentation area and distribution pattern in several periods was determined by satellite image change detection technique.
The changes were detected for three periods: 1999 (FSS construction year) to 2000, 2000 to 2006 and 2006 to 2013. Change detection follows three main steps: 1- Data pre-processing including geometry and radiometry corrections 2- Selection of change detection method 3- Results accuracy assessment. In the data pre-processing step, image to image method was used for geometry correction and Dark Object Subtraction method was used for radiometry correction. Post-Classification comparison algorithm, change detection statistics method was selected for the present study. The method is capable of preparing a complete change matrix with details. Some indices including overall accuracy, Omission, Commission and kappa coefficient extracted from error matrix, were used to assess the accuracy of results. Maximum likelihood algorithm was selected and used for image classification. Also, Optimum Index Factor (OIF) was used to improve image color composite selection, for the preparation of training samples.
Based on the FSS area properties, three regions including sediments, disturbed and undisturbed terrains were separated on the FSS and the images were classified accordingly. Classification overall accuracy for 2000, 2006 and 2013 images was 78, 85 and 83%, respectively. The results of post-classification comparison algorithm by change detection statistics showed that, in the 2000 to 2006 period, sediment area increased from 8.5 to 27.5 ha. In 2006 to 2013, due to drought and the spread of flood on the FSS, the sediment area increased a little and reached 29.5 ha.
The results showed that, the sediment area was well extended in the first period. Proper amounts of precipitation and flooding on the one hand and no sediment initial surfaces on the other hand resulted in a good change detection. However, in the second period, the sediment area slightly decreased. Such a result is logically unexpected but drought in recent years and no flooding especially on the middle area of FSS, result in old sediment surfaces with different reflection properties. In this case, the classification algorithm was unable to enhance the entire sedimentation area. Hence, not only is there no reduction in sedimentation area, but the area slightly increased in the upper FSS for the second period.

One of the most important problems in determination of life expectancy of dams, are the rate and distribution of sediments in the reservoir. Mathematical models are recently used for simulation of the reservoir sedimentation rates and predicting life expectancy of the reservoir. These models are based on the analysis of governing equations of sediment transport, distribution, deposition and erosion. In this study, mathematical modeling of erosion and deposition of sediments in Satarkhan dam, has been studied using GSTARS 3.0 model. GSTARS mathematical model using stream tubes concept, has an ability to account for the longitudinal and lateral distribution of sediment deposition in the rivers and dams. For hydraulic and sediment calibration of this mathematical model, information of Satarkhan Dam and cross section between 1998 and 2009, have been used. Calibration results showed that Yang (1973) sediment transport equation had a good agreement with field data.

Dam construction on the rivers causes sediment accumulation behind them. Determination of quantity and quality of sediment deposition in reservoirs is important for their stability and operation. Area- reduction method is one of the empirical methods for reservoir sediment distribution. In this method, reservoir is divided to four types, based on its shape. Parameters are presented for each types of reservoir which is carried out based on sediment distribution. Determination of suitable parameters in operating reservoirs which have at least one period of hydrographic data, leads to increment of accuracy. The objective of this research is to determine the optimal parameters of empirical area reduction method in Karaj dam using Shuffled Complex Evolution algorithm. In this research, a computer model was developed based on area reduction method theory. Then optimization model was prepared using Shuffled Complex Evolution algorithm and these two models were combined and Simulation-Optimization model was developed. Simulation- Optimization model determined area reduction method parameters for Karaj dam so that the most compatibility occurs between computational and measured volumes. To determine optimal parameters values, objective function was defined as Root Mean Square Error (RMSE) calculation of actual values. Using prepared model, optimal parameters were obtained based on information in 1961 and hydrography in 1991. To verify simulation-optimization model, sediment distribution in 2007 was calculated using obtained optimal parameters by model and was compared to hydrographic values. Results showed that values of objective function were reduced up to 62% and 48% in calibration and verification periods, respectively. Then, sediment distributions of Karaj dam were predicted based on optimal parameters.

Estimation of the sediment load which a specific flow is capable to transport, is one of the main topics of sediment researches. Abhar Rood River is one of the major rivers in Zanjan province which plays a big role in the agriculture of the region. In the present research, HEC-RAS 4.1 model is utilized to simulate the sediment hydraulic in Abhar Rood River. For this purpose, 730 sections along 50 km of Abhar Rood have been prepared by using the DEM map of the river (map scale 1:4000) in Hec-GeoRas extension of ArcMap, thereafter it was used to introduce the river geometry information to Hec-RAS model. Also the discharge amount with 25 years return period has been calculated in HYFA model using the 33 years flooding discharge data which was measured at the Ghorveh hydrometric station and used to simulate hydraulic flow of the Abhar Rood River. After calibrating the model for hydraulic conditions of the river, sediment boundary condition and bed gradation have been defined in model. Thereafter the sediment transport capacity of the river was calculated by transport functions at total cross sections. The comparison between the achieved results and measured data shows that, the Yang equation has minimum error compared with other equations. Therefore Yang equation due to its acceptable results is recommended to recognize the sediment transport capacity potential. In addition, to investigate the erosion and sedimentation status of Abhar Rood River, Hjulstrum and Shields criteria have been utilized. The hydraulic condition of this river shows the erosion status at the whole crosses of the river.

With construction of storage dams، a large amount of sediments are accumulated behind them. Therefore، water released from the dam is so clear and possesses high sediment transport capacity، which causes the river erosion at downstream the dam. In this research، Polerood river morphological variations predicted in downstream of dam using mathematical models for a short period post dam construction. Then، results were compared with lack of dam existence manner. Results showed that، the presence of the dam causes more erosion in the river. Maximum erosion in presence and lack of the dam were 4. 7 and 3. 7 m، respectively. The maximum influence of the dam construction on river morphology is up to 10 km downstream from the dam axis. At far distances، river bed variations in both the presence and lack of the dam were the same and the intensity of these variations was very low. The most river variations occurred at early years and variations intensity reduced gradually. Results also showed that erosion and sedimentation in the river is balanced by the time and river will be arrived at a regime case.

Density of deposits is bounded on different variables e.g. physical properties of sediment particles, rate of deposit's layer compaction and type of reservoir operation. These criteria have uncertainty and so the specific weight of deposits has the same problem. In this paper, the effective factors that influence the density of deposits in the reservoirs had been classified and then the basic concept of Delta method was stated as one of the popular techniques for analysis of uncertainties. Further, the case of Kenny reservoir in the White River basin at northern Colorado was selected to determine the specific weight of deposits in the reservoir and the coefficient of variation. The results of this investigation indicate that in the case of Kenny Reservoir the density of deposits is 1267 ± 125.6 (Mean ± SD) kg/m3, and the coefficient of variation of specific weight for accumulated deposits equals 9.9% for the period of 15 years of reservoir operation.

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. The purpose of this study is to find out how these two factors could 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 two seconds intervals was used; undulations and tidal waves were sent to the mouth of the inlet simultaneously. By simulation، the morphology of the inlet changes in a way that with the passage of time reaches equilibrium; hence، there would be an ideal inlet. Also، by means of characteristic non-dimensionalHw/Ht، the dominant parameter in the inlet can be determined in the inlet. For calculation of morphological changes in inlet of estuary، first tidal fluctuations as a single parameter and then wave parameter separately considered، then two parameters together considered، the results show that for two cases، the morphological changes are the same

Dams are one of the most common structures to make a reservoir for water accumulation. Sediment deposition in reservoirs not only reduces the storage capacity of a reservoir but also decreases its useful life. Also¡ in many cases sedimentation creates problems for bottom outlets. In this study simulation of sediment deposition in Jiroft Reservoir is investigated with the aids of GSTARS3 model. At first the measured data of Jiroft Reservoir are used to calibrate the mathematical model. The Manning coefficient and the sediment transport equations are used for this proposed. After calibration¡ existing data are used for verification of the model. Finally¡ the time variation of reservoir volume is calculated. The results showed that the mean annual volume reduction of the reservoir is approximately equal to 1.27 percent of initial volume. Also¡ the trap efficiency of the reservoir is computed and it was equal to 87 percent.