جستجوی مقالات مرتبط با کلیدواژه « فرسایش » در نشریات گروه « محیط زیست »

One of the significant issues in hydraulic engineering is reducing erosion in rivers by using groynes to preserve soil. The purpose of this study is to investigate numerically the groynes' presence on the sedimentary flow parameters using FLOW-3D software. For this purpose, groynes were examined at angles 30°, 60°, and 90° under 10 scenarios in various discharge and hydraulic conditions. Here, the mesh block with dimensions of 5 mm was chosen as the optimal mesh block for simulating models. In addition, Large Eddy Simulation (LES) turbulence model was used for simulations. In the scenarios where two blades are used scouring is observed in the first blade, while the sedimentation phenomenon was observed in the groyne after the first groyne in the direction of the flow. In the two blades with a distance of 0.60 m from each other, 48 mm erosion occurred. The highest amount of scour is related to the arched groyne (LLeft-Q285) with 45 mm. Discharges have an increased effect on scouring, so by comparing the scenarios with one groyne (I-Q285, I-Q200, and I-Q350), the lowest amount is with the value of 5.5mm corresponding to I-Q200. The insufficient erosion in the angled groynes corresponds to the smaller angle scenario.

Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.Desertification asone of the most important of environmental threats in the present century,is one of the main obstacles to meeting the needs of the inhabitants of arid and semi-arid areas.better understanding of desertification severity and determining the most effective factors on it are the first steps to de-desertification. For this purpose, the severity of the Jiroft plain to desertification was investigated using IMDPA method on the basis of geological and geomorphological criteria. Firstly work unit map was created using geology, land use map, Landsat 8 satellite imagery and Google Earth data. In each unit the "slope", "land use" and "erodibility" indices scored and combined with each other by calculating geometric mean of indices, finally the map of desertification hazard was generated in GIS10.3 software. The results of this study showed that Jiroft plain was classified in moderate class (II) of desertification hazard. Accordinglyalthoughin the Jiroft plain the geological and geomorphological factors have moderate intensity on desertification but it can be turning a risk to an environmental crisis by unsustainable use of lands and natural resources. According to findings, it can be concluded that the management strategies and landuse activities in Jiroft Plain needs to consider the spatial planning.

In order to plan and recognize the destructive condition of the watershed, it is indispensable to know the extent of erosion and sedimentation produced from each basin. In this study, the soil erosion and sediment estimation of the Khorkhoreh basin using Sediment Rating Curves were investigated. By integrating geological and geomorphological layers in GIS and removing polygons under 6 ha, 24 working units and 68 sub-basins were attained. To identify the erosion type through field visits, the Bureau of Land Management (BLM) scoring was carried out in each work unit. Using the sediment curve, the amount of total suspended load in the basin was obtained as 2990 ton/yr. With the calculations performed, the amount of specific sediment yield in the Khorkhoreh basin was found to be 25.3 ton/km2. All types of erosion were seen in the portions of the basin, while most of the basin area belongs to the “sensitive” and “very sensitive” to erosion classes. Examination of erosion types showed that in most of the basin’s working units, all types of erosion such as Sheet erosion, Rill erosion, Gully erosion, Channel erosion, and Stream Bank erosion can be observed.

Gully erosion is an important and major process of land destruction and is considered one of the most important sources of erosion and sediment production in the country. The purpose of this research was to determine the effect of saturated lime solution (SLS) in reducing the growth rate of gullies. After locating two active gullies with similar physiographic and soil characteristics in one of the gully areas of Tehran province and recording the physiographic and soil characteristics, one was considered as a control and the other as a treatment. The effect of volume of SLS and curing time in improving the uniaxial strength of gully soil was investigated and tested. To inject SLS, a strip pond was created around the gully and the optimal volume of SLS was discharged on the surface of the pond. Then, in six-month periods, the length and volume growth of gullies were measured and the results were compared with each other. The results of the effect of the volume of SLS on the uniaxial strength of gully soil during constant curing time showed that the maximum increase in soil strength by 420% of the control sample was obtained by injecting 40 times the volume of soil porosity. The results of the study of the effect of curing time on the soil strength showed the maximum increase in the 60-day curing period and as much as 400%. Also, the stabilized gully had a 58% decrease in longitudinal growth and an 83% decrease in volume growth.

Due to the complexity of hydraulic and sedimentary problems in rivers, it is not possible to solve the equations analytically, so numerical methods are used. In the present study, the HEC-RAS 5.0.3 model was used to simulate the sediment flow of the Khondab River. For this purpose, using the topographic map of the route, DEM and TIN of the River route with a scale of 1: 2000, in the HEC-GeoRAS extension package in ArcMap software, 200 sections along 5 km of the river were prepared. Relevant information was inserted to introduce the river geometry to the model. The flow rate was calculated with 25-, 50- and 100-year return periods and was used for river hydraulic simulation. Quasi-volatile flow conditions, boundary conditions and granulation of riverbed materials were introduced to the model. Using sediment transport estimation relationships, river sediment transport capacity was calculated. The results showed that the Mir-Peter and Müller relationship with 26% error is closer to the observed sediment values ​​than the other relationships. Moreover, the study of erosion and sedimentation status of the river using Hjulstrom and Shields criteria showed that a part of the sections of this river is in erosion status and another part is being sedimenting.

During the intensive flood in 1384, the floodplains in east Azerbayjan were waterlogged for a period of 1 month. The aim of the study was to assess the effect of the flood on the level of contamination of the soils in this region. For this purpose, 20 soil samples were collected from the area immediately after the flood event from the upper (0–30 cm) soil layer together with four samples from the 30–60 cm depth layer.  The analysis included basic physico-chemical soil properties, contents of Cd, Ni, Pb, Cu, and Zn metals. The concentrations of identified metals at all the samples were below the acceptable limits for agriculture use. The results show that this flooding episode in “clean” agricultural area had no immediate negative impact on the soils properties (organic matter percent, acidity, and nitrogen content) and did not result in excessive soil contamination.

Nowadays, the assessment of erosion value and sedimentation yeild in the watersheds is one of the fundamental issues in water resources management and environmental assessment. In recent years, the use of experimental methods have been developed due to lack of the sediment data. In this paper, using MPSIAC model, erosion value and sediment yield of Shazand basin (one of the Sub-basin of Saveh Dam) assessed and compared with a hydrometery method. For this purpose, using Landsat and IRS satellite images and Geographic Information System (GIS) with an accuracy of 10 × 10 m, the various parameters required to simulate by MPSIAC model applied to ArcGIS 10.2 and ENVI 5.1 software. Then, using this model the sediment yield and erosion zoning of Shazand basin are obtained as zoning maps. Following, the results of the annual sediment from the studied stations (Poledoab, Toureh, Azna and Bazaneh) were compared with the results of hydrometric method. The results show MPSIAC model with hydrometry method have a good accordance with together in which Poledoab, Toureh and Shazand stations with 95.4%, 77.7%, 95.05% of accordance, respectively. According to the study, MPSIAC model to estimate maximum annual sediment and erosion zoning is acceptable accuracy.

Soil erosion is a phenomenon that leads to destruction and loss of valuable soil, especially under accelerated conditions. As the life of human societies requires water and soil, variety of biological and mechanical operations are practiced in order to prevent soil erosion and water loss, runoff control, and to improve the soil vegetative coverage. In order to evaluate the role of biological and mechanical watershed management projects on the erosion and sediments of Chehel Gazi Watershed, Sanandaj, the erosion and sediment of the watershed was determined using MPSIAC Model after identifying the performed operations. Then using paired T-test method, the impact of watershed practices on decreasing erosion and sediment was investigated. The results showed that specific sediment of watershed has decreased from 2.7 to 2.5 ton/hectare. Moreover, the level of higher sediment classes decreased and level of lower sediment classes increased. The statistical analyses showed that there is a significant difference between sedimentation before and after the watershed management project.

Forest roads are important components of forest management units and involving special roles in wood transporting and the other forest uses such as hunting, tourism, etc. One of the most important problems due to forest roads developing is increasing erosion of different forms of soils around roads, sediment yield resulting of vegetation destroy, ruining of soil structure, increasing run off velocity and instability of slope.
In this research, sediment due to existence forest roads was estimated in a part of Experimental Forest Station of Tarbiat Modares University using of SEDMODEL and GIS. In this model effective factors consist of geology, road, slope, precipitation, vegetation cover and drainage network.
Findings: Created erosion resulting of this road network was estimated about 1576.4 ton/year without considering SEDMODEL. This amount was estimated about 140.7 ton/year with considering SEDMODEL on basis distance of waterway.
Discussion and Results showed that the share of roads sediment yield is about 1.33 percent of watershed exit, but roads includes 0.017 percent of watershed areas. Paying attention to the covered areas by roads in watershed, the amounts of sediment yield is 78 equal of sediment yield average in watershed area.

So far, many studies have been done to design reshaping berm breakwaters (RBB) that mostly have provided the effect of individual parameter on structure stability. Accordingly, the presentation of systematic optimal geometrical design of RBB is necessary. In this research, a generic program is presented to determine the optimal geometrical structure of RBB based on administrative costs. So, initially, the methodology were proposed to determine the breakwater optimal dimensions based on calculated berm recession from empirical formulae of previous studies and the cost of extraction and transportation of the materials from JAHAD and TOUSEH mines. The nominal diameter of stone blocks and the berm height from sea bed were selected as a decision variable based on sensitivity analysis. The results of implementation of the proposed structure using random search algorithm represent a significant reduction in costs of breakwaters construction compared to non-optimal values of decision variables. Based on the resulting optimal values, were determined the optimal percentages of extraction from miscellaneous mines with lowest extraction and transportation costs. The results indicated that the minimum cost is obtained if the values of nominal diameter of stone blocks and the berm height from sea be are equal to 0.82 and 4.9 meters, respectively. Therefore, the optimal width of berm recession was determined equivalent to 17.77 meters. Also, in order to achieve an optimal economic plan, the breakwaters constituent materials in JAHAD and TOUSEH mines must have 63.37 percentage with gradation of 1-2.5 tons and 61.71 percentage with gradation of 0.3-1.5 tons, respectively.

During the intensive flood in 1384, the floodplains in east Azerbayjan were waterlogged for a periodof 1 month. The aim of the study was to assess the effect of the flood on the level of contamination ofthe soils in this region. For this purpose, 20 soil samples were collected from the area immediatelyafter the flood event from the upper (0–30 cm) soil layer together with four samples from the 30–60-cm depth layer. The analysis included basic physicochemical soil properties, contents of Cd, Ni, Pb,Cu, and Zn metals. The concentrations of identified metals at all the samples were below theacceptable limits for agriculture use. The results show that this flooding episode in “clean” agriculturalarea had no immediate negative impact on the soils properties (organic matter percent, acidity, andnitrogen content) and did not result in excessive soil contamination.