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

Nowadays the dust phenomenon is one of the biggest environmental problems in the world, causing major damage to sectors such as industry, transportation, agriculture, tourism and human health each year. The dust storm, which commonly occurs in arid and semi-arid regions such as the central and southern parts of Iran, carries a large amount of dust and reduces daily human activities and horizontal visibility. According to the World Meteorological Organization (WMO), when the wind speed exceeds 15 meters per second and a large amount of dust enters the atmosphere so that the horizontal visibility reaches less than 1000 meters, dust storms are reported. The creation of dust is caused by natural and man-made factors, the human component of which is mainly a response to changes in soil cover and land use. One of the objectives of the present study is to monitor the location and source of dust (origin and destination of dust) and the movement of dust storms and streams/trajectories containing dust.

In this study, meteorological data including temperature, relative humidity, rainfall, evaporation, wind speed and number of dusty days from 3 meteorological stations of Qom province were obtained from Meteorological Organization and analyzed. Also in this study, to determine the potential dust sources by the maximum likelihood and minimum distances classification methods was done to determine the land use and soil type of different areas with Landsat images. This process was completed using time series images of Qom province in 30 years, from 1989 to 2019 with 5-year steps and monitoring the changes of this period with in 11 different classes. Next, according to the recorded dust data (horizontal visibility) at Shokouhieh/Qom Meteorological Station showing the occurrence of dust storms as defined by the World Meteorological Organization, backward tracking of air trajectories using the HYSPLIT meteorological model. The backward trajectory, if it is close to the surface of the earth and the area potentially capable of spreading dust from the surface into the air, can be considered as the source of the dust phenomenon.

The results identified 30 areas with different soils and cover as the source of dust. There were 20 spots of bare land, 5 spots of salt land and 5 spots of sandy land. The main sources of dust storms studied in this province are located in the eastern half of the province adjacent to the Namak Lake and the Dasht-e Lut. In the final part of the present study, meteorological data that directly report the occurrence of dust storms were first analyzed. Then, based on the recorded data and some restrictive conditions, the target dates that the dust storm defined by the World Meteorological Organization at that time were selected. Codes w=06 and w=07 are related to the dust phenomenon, and both codes are used in this study. One of the innovations of this research is the combined view of soil cover and land use in the study area and also the investigation of dust events.

The results of HYSPLIT model show that the main sources of dust events studied in this study are from neighboring eastern regions such as Semnan. These storms are ultimately considered as a domestic dust event. About 15 percent of the total dust storm events in the studied dates are likely to have been foreign dust. These events are mainly of foreign source and have been imported from western and southwestern Iran countries such as Iraq, Saudi Arabia and perhaps Syria and are modeled as foreign dust and generally considered as sever dust storms.

This research was conducted to evaluate the effect of land use changes on the land quality under deforestation in semi-arid regions. Soil quality of the top layer (0-15 cm) was compared for two land uses. The results show that the organic matter (OM), aggregate stability (AS) and dispersible clay (DC) were changed from 1.19, 2.22, and 2.4% in oak forest to 0.67, 2.08, and 22.8% in deforestation area, due to land use change. These results showed a severe decrease in soil quality due to deforestation. Aggregate stability was decreased and dispersible clay was increased due to deforestration. In addition, the canopy cover and soil organic matter were reduced. With increasing the DC, it was increased the soil surface crust and accelerate the splash erosion. Bulk density increased, since the OM decreased. Also, the percentages of gravel, sand, coarse and fine silt changed from 6.3, 56, 12.6, and 5.4% to 35.6, 64.3, 14.6, and 2.5%, respectively, due to deforestration. Direct sunlight and higher soil heat, especially in hot seasons, accelerated the volatilization of soil nitrogen and despite the addition of nitrogen fertilizers to the farmland, the amount of nitrogen in the farmland decreased. Data analysis by PCA method showed that the different factors affect the varimax due to land use changes. Deforestation was the main factor changing the soil characteristics and seriously reducing the land quality. Land use change not only does not benefit the production of more food, but also destroys the quality of the land, causing floods and increasing sediment from these areas.

Increasing attention to environmental issues in the management of rivers, causese the development of research in the field of hydraulic parameters and sediment transport in the rivers. Vegetation in many rivers, has a significant impact on the flow hydraulic, morphology and sediment transport processes. Understanding the hydraulics of flow in a compound channel with vegetated floodplains is very important for determining the stage-discharge curve and for supporting the management of fluvial processes. There are few models within CFD codes that conceptually or physically represent the hydrodynamic impact of a vegetation canopy on the velocity field and conveyance characteristics within an estuarine or riverine system. The present research investigates the numerical and experimental modelling aspects of flow in compound channels with vegetated floodplain, emphasis to the suspended sediment transport. This study, has proposed a method for predicting the depth-averaged velocity in compound channels with vegetated floodplains, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation (RANS) with a term included to account the effects of vegetation. Two dimensional advection-diffusion equation were used to calculate the dispersion coefficients and sedimentation rate, this equation were solved by using a finite volume method. The vegetation is modeled via an additional term in the momentum equation to account for the additional drag force. The method includes the effects of bed friction, drag force, lateral turbulence and secondary flows, via four coefficients f, CD, λ & Γ respectively. This model is able to estimate the velocity distribution in channels with different dimensions, different vegetation densities. This model is able to estimate the velocity distribution in channels with different dimensions, different vegetation densities. The wake interference model given by Nepf (1999) is used to estimate the bulk drag coefficient. Modified forms of the Colebrook–White equation can be used to calculate a local friction factor in compound channels with vegetated floodplains. Several eddy viscosity models have been used in the literature to predict transverse momentum exchange in the mixing layer. Once velocity profile is obtained, the dispersion coefficient is evaluated and the remarkable role of vegetation is shown. Both the velocity profile and the dispersion coefficient have been validated using our new experimental results. The model was applied in inverse mode to estimate the model parameters that quantified eddy viscosity coefficient, secondary flow, longitudinal dispersion, transverse dispersion and filtration in the experiments. In addition, the Elder’s and Neph’s relationships also calibrated to calculate the Longitudinal and transverse dispersion coefficients. A Levenberg-Marquardt algorithm was used to find the values of the model parameters that minimized the sum-of-squared differences between measured and modeled velocities and particle concentrations. Experiments performed in a flume of the Hydraulic laboratory. The experimental channel is employed in this investigation was 10 m long × 0.3 m wide and 0.6 m deep. The channel has a simple rectangular cross section; however, this was modified by using Plexiglas sheeting to produce an asymmetrical compound shape. The artificial stems were PVC rods of 5 mm outside diameter, arranged in staggered grid. The model substance used as suspended load was silica of mean particle diameter around 7µm and density 2143 kg/m3. Silica suspensions were injected to produce fully mixed inflow concentrations of about 6 g/l. In general, two series of experiments have been done in this study. In The first series of experiments the depth averaged velocity were measured, the second series have been conducted to estimate the rate of sedimentation. Depth averaged velocity measured by using micro-propeller and pitot tubes. Results showed that the use of constant coefficient of 0.0683 for eddy viscosity coefficient have not a significant impact on depth averaged velocity. The error about 1% have been observed between results of numerical modeling and experimental data, when the relationships 0.417δρgS0 HDr and 0.62δρgS0HDr have been used for secondary flow coefficients, to the main channel and floodplain, respectively. Results showed that dispersion coefficient in vegetated channels increased cross the main channel compared to no vegetated case, due to the gradient of velocity. Sedimentation rate coefficients calibrated by comparing the experimental and numerical sedimentation rate. The numerical model underestimates the experimental data about 8%. Experimental data of Zong(2011) were used to verification of numerical model, the results showed that the modified model overestimates the data with 22% difference. The results show that the quasi 2D model reproduces a reasonable simulation of the flow field and sediment transport in compound channels with vegetated floodplains.

The simulation of nitrate and sodium transport was done in native soil and soil treatment by vermicompost under three irrigation flow rates in saturation and unsaturation states. For this purpose, 12 columns with 20 cm length and 5.9 cm diameter chopped of PVC pipes were used that soil layer in column was 10 cm. All of columns saturated at 24 hours, and leaching was immediately done with distilled water at 24 hours, too. Next, the solution consist of 1mMol KNO3 and 25.42 mg in 1 liter distilled water injected to soil columns with three different water flow rates during 570 minutes, and the nitrate and sodium concentrations were measured in effluent solutions at specified time intervals. The Advection-Dispersion model was used for simulating of solute transport, and dispersivity and distribution coefficients of nitrate and sodium were determined by inverse method. Sodium breakthrough in native soil and soil treatment with vermicompost condition occurred at 280 and 160 minutes under saturated condition with flow rate 0.0704 cm/min, 330 and 200 minutes under unsaturated condition with flow rate 0.0477 cm/min, but sodium breakthrough did not occurred in unsaturated condition with flow rate 0.0208 cm/min. Nitrate breakthrough in native soil with flow rates 0.0704, 0.0477 and 0.0208 cm/min occurred in 50, 80 and 120 minutes, and become maximum in 120, 200 and 270 minutes. Nitrate breakthrough in soil treatment with vermicompost in flow rates 0.0704, 0.0477 and 0.0208 cm/min occurred in 30, 40 and 80 minutes, and become maximum in 80, 120 and 240 minutes. The results showed the breakthrough times of nitrate and sodium and time of maximum concentration of nitrate were decreased by application of vermicompost and increasing soil water flow rate. The results of modeling showed dispersivity and distribution coefficients were increased by using of vermicompost and decreasing soil water flow rate.

Applicability of rockfill dams which has been made from large rock materials for purpose of flood detention reduces over the time because of siltation of pore system with sediment contained basin outflow. Since some of structures which were built with large rock materials should convey suspended sediment contained flows therefore routing process of these type flows have been investigated. The investigation around advection and dispersion of sediments particles through the large porous media usually is being done with breakthrough curve. This investigation is usually common for pollutants in rivers, sewer system and fine porous media. Previous researchers used from various techniques like numerical solving, parameter estimation and exact solution for solving of above mentioned problems. But unfortunately any general inquiry about suspended sediments was not accomplished yet. The exit breakthrough curves in many cases are asymmetrical and have Skewness in their falling limbs. Therefore some researchers after collecting the series of field data have discovered it and have presented a new model named transient storage model. Some investigators by considering Asymmetry in exit breakthrough curve have joined first order mass transfer equation with ADE equations and have extracted exact solutions with various primary and boundary conditions. The important criterion in this regard is to use them in similar primary and boundary conditions. Therefore in many cases the investigators are using from temporal and spatial moment technique according to experimental data series. By emphasis to above mentioned criteria and as regards to this fact that any coherent research in the investigation of behavior of suspended sediments through the large porous media were not accomplished yet therefore in this research tried to focus on it.
In this research by creating a laboratory model of large porous media and employing suspended sediment particles, tried to acquire an experimental data series in order to investigate longitudinal convection and dispersion phenomenon of suspended sediments through the large porous media. In this investigation by application of 2 media diameters, 4 inflow discharges and different hydraulic gradients over the media, the breakthrough curves of suspended sediments were extracted. The BC curves were extracted with water sampling from media end and then the samples have been passed from filter paper and dried. The concentration-time graphs were extracted after weighting of dried sediment particles. Also by using of parameter estimation technique for classical advection dispersion equation and temporal moments method, the longitudinal dispersion coefficients were extracted.
The results showed that due to the inherent properties of exit breakthrough curve, the temporal moments method has a better estimation accuracy rather than classical advection dispersion equation. Additionally by dimensional analysis method a relationship has been acquired for estimation of longitudinal dispersion coefficient with average relative error of 30% which is reliable in sediment transport studies. Furthermore, the results of analysis of BC curves exhibited that the curve has an Asymmetric limbs in rising and falling stages which this observation is because of temporary storage of sediments and gradual release of them through the downstream flow.

Generally soil preferential flow occurs through soil macropores. These flows can transport a large amount of water and any type of pollutant to groundwater in a short time. This issue causes the water and soil pollution and in terms of environmental and health, affect the lives of animal and human. In this study the movement of water in preferential routes in the soil was investigated using a physical model. Also this movement was evaluated using Kinematic–Dispersive Wave (KDW) model which is a second degree non-linear partial differential equation and optimization of its coefficients. At first, the model coefficients were obtained using Particle Swarm Optimization (PSO) method. After that, the model was validated using experimental observation of rainfall hydrograph which was passed through the preferential routes of physical model and was recorded from the bottom of soil column. The results showed that the numerical model has very good agreement with experimental observations, and this prediction is better in lower rainfall intensity. Since dispersive mechanism was applied in this model and the effect of dispersive is disappeared graduatly with increase of input rainfall intensity, this effect in lower velocities causes the model to predict much better the observation. Consequently, this model can be a way to predict the preferential water flow and contaminant in soil to be eligible to make a reasonable decision in environmental management planning.

An Accurate estimation of contaminant transport parameters is one of the most important steps for simulation of contaminant transport in porous media. In this work, the mean pore water velocity and the dispersion coefficient in three kinds of saturated porous media were estimated and their dispersivity variations with scale were investigated. The values of the mean pore water velocity and the dispersion coefficient were obtained by fitting the analytical solution of advection-dispersion equation to experimental breakthrough curves by using software CXTFIT2.1. The required data were collected by conducting tracer tests on a sand tank of internal dimensions 250 ×10 ×60 cm3. The tests were conducted in three kinds of porous media (homogeneous sandy soil, randomly heterogeneous sandy soil and natural heterogeneous sandy soil) under three hydraulic gradients 0.017, 0.025 and 0.034. The results showed that the dispersivities of each three porous media at each three hydraulic gradients increased with scale. Also, it was observed that with increasing the heterogeneity degree, the dispersivity variations with scale increased. Under hydraulic gradient 0.017, the dispersivity of the homogenous porous medium increased as a nonlinear function and in two other hydraulic gradients, its variations followed the linear functions. In the studied heterogeneous porous media, under hydraulic gradient 0.017, the dispersivity variations were erratic. However, in two other hydraulic gradients, its variations were as a power function or an exponential function. Therefore, in general, in a homogeneous aquifer and under high hydraulic gradients and in a heterogeneous aquifer, one can approximate the variations of the dispersivity using a linear function and a power function or an exponential function, respectively.

In this research, the effect of calcium carbonate, existing in natural environments, on removal, advection and dispersion of cadmium using batch reactor experiments, is studied. The results showed that 99.2% of Cadmium with initial concentration of 1.5 ppm will be removed by CaCo3 with concentration of 330 ppm. Regarding to high ability of CaCo3 in cadmium sorption and the existence of CaCo3 in soils and waters, one can conclude that CaCo3 has a great influence on self purification of natural environments and it must be considered in heavy metal transport transformation modeling. Firstly, by increasing salinity in the range of natural condition, sorption will decreased very fast but after the salinity of 2500 S/cm, the amount of this reduction will decrease. At last, the amount of sorption could be decreased by 50%. Investigation of Langmuir and Freundlich isotherms showed that the governing isotherm for cadmium sorption to CaCo3 on the basis of current data is Freundlich. Furthermore, comparing the linear and nonlinear methods in estimating Freundlich parameters show that the non linear sum of square of errors 0.3 of linear method. So it is better to use non linear method in estimation of parameters.

A detailed description of the behavior of cohesive fine-grained sediments is a very complicated task. Simulation of cohesive sediment movement has been successfully treated in the past using the macroscopic properties of the water-sediment system. In this study, a 1-Dimensional equation of cohesive sediment has been proposed for deposition term and dispersion coefficient of mass transfer equation. This equation has been solved by Control Volume method and calibrated with laboratory data. The tests have been done in a flume with 0.3m diameter, the slope 0.00008, discharge between 3~5.7 liter per second and the concentration of 4~8 gram per liter. The model shows that the dispersion coefficient is a function of Reynolds number and rate of velocity to shear velocity.