Sayed Naeim Emami; Hamidreza Peyrowan
Abstract
Marls are one of the main causes of sediment production and subsequent soil erosion in watersheds. Researchs shows that there is a close relationship between the rate of marls sediment yield and their physical and chemical characteristics. With the aim of determining the expansion of marly formations ...
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Marls are one of the main causes of sediment production and subsequent soil erosion in watersheds. Researchs shows that there is a close relationship between the rate of marls sediment yield and their physical and chemical characteristics. With the aim of determining the expansion of marly formations and a quantitative assessment of the mentioned indices role on the sediment yield of marls in Chaharmahal and Bakhtiari Province, a comprehensive study was conducted and its outstanding results are presented in this study. After identifying and separating the marly formations in Chaharmahal and Bakhtiari Province and performing systematic sampling, necessary physical and chemical experiments were performed and the results were analyzed using statistical methods. Then, using a rainfall simulator, the sediment production rate of each marly stratigraphic units was measured in the field. Results showed that about 1073.95 Km2 (equal to 6.5%) of province rocks has devoted to marly lithological units. On the basis of analyses, Razak, Pabdeh, Hormoz, Mishan and Gurpi formations with mean of 96.34, 94.41, 87.1, 76.17 and 33 grm-2 are the most sensitive marly formations, respectively. Sediment yield is directly related to silt amounts, total lime, active lime, exchangable sodium and reverse related to clay amounts. The presence of Kaolinite and Illite clay minerals is one of the intensifying factors in sedimen yeild in marly formations.
Shahriar Sobh Zahedi; Ramin Naghdi; Mohammad Reza Gharibreza; Ali Salehi; Ghavamoddin Zahedi Amiri
Abstract
The method employed in this study was based on experimental research and field study. In this method, the stored radiocesium of the forest region which was supposed to be converted into Poplar plantation has been compared with the stored radiocesium of the reference region. 11 core samples were taken ...
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The method employed in this study was based on experimental research and field study. In this method, the stored radiocesium of the forest region which was supposed to be converted into Poplar plantation has been compared with the stored radiocesium of the reference region. 11 core samples were taken from reference region and then 7 core samples were selected from the transect which was a part of Poplar plantation that were taken by topographic characteristics in a depth of 25 centimeters, Having prepared the core samples according to the IAEA, they were packaged into the special Gama spectrometer containers. After that the amount of radiocesium of all samples has been measured by Bq kg-1 scale. The findings revealed that the amount of radiocesium in reference region was computed as 5894.1. Bq m-2 y-1. In the present study, soil loss rate during transect was estimated using proportional conversion models and mass balance I and II of 18.70, 22.72 and 18.64 ton / ha, respectively. These values were obtained for slope of 10-20%, canopy cover of 25% and clay loam soil under 1000 mm precipitation. This study recommended mass balance model II for estimation of erosion in changed land use areas and concluded that forest land use change to plantation due to reduction of long soil cover and plantation management by removing other seedlings and herbaceous cover increased the rate of soil erosion occurs. This process for many years has caused the erosion rate to exceed and has caused the loss of 0.1 cm of soil per year.
Davoud Nikkami
Abstract
Using erosion plots is a way to research on soil erosion and conservation that with different dimensions, which are constructed in the natural arenas or in laboratories. Mistakes and false conclusions are common task that should be avoided when sampling runoff and sediment from the tanks of these plots. ...
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Using erosion plots is a way to research on soil erosion and conservation that with different dimensions, which are constructed in the natural arenas or in laboratories. Mistakes and false conclusions are common task that should be avoided when sampling runoff and sediment from the tanks of these plots. A few researches have been done on the ways of sampling from these tanks and reducing the errors. In this study, the accuracy of sampling was investigated by placing a bucket in the tank and using bottle sampling. For this purpose, two 220 liter tanks were used. In the first tank located at the upper level, concentrations of sediment were prepared for five, 10 and 20 grL-1 and the mixture of runoff and sediment was transferred to the second tank. Coarse particles were trapped by a bucket of twenty liters placed underneath the importer tube in the second tank. The contents of the bucket were weighed in the laboratory after drying. Also, sampling of the second tank contents was carried out after mixing the solution and using one-liter bottles in three replications per each concentration. Sampling was also done without placing the bucket as a witness. The significance of the effect of concentrations on the error value was defined by analysis of variance through a random block design scheme. Results demonstrated that there was a significant difference between the concentrations obtained in the experiment with bucket and without bucket at a level of one percent. Without using bucket, the amount of errors were 63.13, 78.40 and 73.97 percent for 5, 10 and 20 gr.L-1 concentrations, respectively and with using bucket they were 15.90, 15.07 and 4.83 percent. The mean errors in all concentrations were 71.83 and 11.93 percent without and with using buckets, respectively.
Saeed Nabipay Lashkarian; Mahmood Arabkhedri; Samad Shadfar
Abstract
Accelerated soil erosion and the production and transfer of large amounts of sediment are considered as one of the most important issues in many parts of Iran. Having enough knowledge on soil erosion and sediment production as well as identification of critical areas are necessary in order to reduce ...
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Accelerated soil erosion and the production and transfer of large amounts of sediment are considered as one of the most important issues in many parts of Iran. Having enough knowledge on soil erosion and sediment production as well as identification of critical areas are necessary in order to reduce the adverse effects of this problem through soil and water conservation measures. Due to lack of gauge stations in the outlets’ of small watersheds, empirical models are considered as the proper tools for estimating soil erosion and sedimentation. One of these methods which was developed based on Meditranean sediment data, is the Factorial Scoring Model (FSM). Towards this, the main objective of this research is to compare estimated vs. observed sediment yields in some selected regions of Iran. For this purpose, 58 small chatchments equipped by reservoirs in their outlets were selected in Semnan, Central, Isfahan, Chaharmahal and Bakhtiari, West Azarbaijan, Lorestan, Fars, Golestan and Khorasan Razavi Provinces. The comparison of the results showed that all estimates of the original model (before calibration) are several times bigger than observed values obtained by surveying (0.44 to 459.44 t.km-2.y-1). In order to correct the model coefficients for Iran, calibration was performed in two scenarios; once using all data and in the second secenario after allocating data into three geographic regions, which in both cases resulted in significant improvement of estimates. The Nash‐Sutcliffe Efficiency coefficient for all catchments was 0.39, and for Central, Zagros and Northeast regions were 51.1, 0.66 and 0.78, respectively. Based on obtained findings, the application of original FSM must be avoided in study areas. Instead, we strongly recommend using calibrated models based on observational values for different geographic regions.
Raziyeh Motamedi; Mahmood Azari; Reza Monsefi
Abstract
Landscape is one of the main factors influencing hydrological processes of the watershed. Changes in structure and spatial pattern of land use play important role in surface runoff and sediment yield. Determining the relationship between landscape patterns and hydrological processes can be used as an ...
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Landscape is one of the main factors influencing hydrological processes of the watershed. Changes in structure and spatial pattern of land use play important role in surface runoff and sediment yield. Determining the relationship between landscape patterns and hydrological processes can be used as an indicator of watershed soil erosion and sediment yield. Therefore, due to the problems in field measurement of sediment yield, its estimation using landscape properties and land use pattern is an appropriate alternative for current estimation methods. The purpose of this research is to determine the relationship between watershed sediment yield and landscape metrics in the selected sub-watersheds of Golestan Province. To this end, suspended sediment concentration data for all hydrometric stations of the studied province were obtained from the relevant resources and appropriate sub-watersheds were selected. Then, using the land use map of Golestan Province, 15 landscape metrics related to sediment yield were determined for different land uses by Fragstats 4.2 software. In order to determine the relationship between watershed sediment yield and landscape metrics, a partial least squares regression was used which combines the methods of principal component analysis and multiple linear regression. The relative importance of landscape metrics was determined through examining the values of Variable Importance for the Projection (VIP) and Regression Coefficients (RCs). The results of this study indicated that the watershed sediment yield is densely associated with land use patterns. The main indices in reducing sediment yield were the Largest Patch Index (LPI), the average of the nearest neighbor distance (ENN-MN) and the average of perimeter-area ratio (PARA –MN) with values of VIPs of 1.296, 1.184 and 1.747, and regression coefficients of -0.014, -0.039, and -0.002, respectively. The main indices in incrising sediment yield were Landscape Shape Index (LSI) and mean patch size (AREA-MN) with regression coefficients of 0.020 and 0.017, respectively. The landscape characteristics in watersheds could account for as much as 71% of the variation in sediment yield of watershed. The results of study showed that the landscape characteristics can be used for watershed sediment yield modeling.
Leila Gholami; Ataollah Kavian; Abdulvahed Khaledi Darvishan; Azame Alipour; Zahra Besarand
Abstract
Determination of time to runoff and runoff volume in watershed response management against rainfall are the key parameters in watershed system management. Among different factors of effect on time to runoff and runoff volume, the rainfall intensity is one of the most important factors. In this study, ...
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Determination of time to runoff and runoff volume in watershed response management against rainfall are the key parameters in watershed system management. Among different factors of effect on time to runoff and runoff volume, the rainfall intensity is one of the most important factors. In this study, the effect of rainfall pattern on variables of time to runoff, runoff volume and coefficient was studied under simulated rainfall in the southeastern Noshahr city, Mazandaran province. To achieve the study purposes, four rainfall patterns, each with three changes in rainfall intensity (I: Low-Medium-High, II: Low-High-Low, III: High-Medium-Low, IV; High-Low-High) were simulated. Then, the time to runoff, runoff volume and runoff coefficient were measured for each rainfall pattern. The measured data were analyzed in Excel and SPSS 23 softwares to determine the relationship between the rainfall pattern and variables of time to runoff, runoff volume and runoff coefficient. The results showed that there was a significant difference (P≤0.05) in variables time to runoff, runoff volume and runoff coefficient resulted rainfall patterns. Also the results showed that, in all of rainfall patterns between mean amounts were the significant differences on time to runoff, runoff volume and runoff coefficient in level of 99 percent. The results showed that the rainfall pattern I had the longest time to runoff and rainfall pattern III had the largest amounts of runoff volume and runoff coefficient. The average time to runoff in rainfall patterns of I, II, III was 5.90, 4.24, 0.71 and 1.25 min, respectively. Also, the average runoff coefficient in rainfall patterns of I, II, III and IV measured 30.03, 49.63, 88.82 and 75.16 percent, respectively.
Asghar Azizian; Amir Samadi
Abstract
River bed materials are of great importance in construction works as one of the most valuable resources due to their economical costs and ease of extraction. This has caused the rivers to be subjected to profound changes due to excessive, improper and non-standard harvesting by effective activities ...
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River bed materials are of great importance in construction works as one of the most valuable resources due to their economical costs and ease of extraction. This has caused the rivers to be subjected to profound changes due to excessive, improper and non-standard harvesting by effective activities of human apart from their natural changes. Hence, replacement of river resources with other resources such as mountain mines can be considered as an essential way to protect the rivers. Considering the importance of this issue, the present study has evaluated the potential of sediment production and delivery in Qaen and Ferdows’ rivers sub-basins using a combination of GIS and geomorphological models. The results obtained from the studied basins indicated that the geomorphologic models are capable of identifying areas susceptible to sediment production. According to calculations performed by the geomorphologic model, the southern and south-western parts of Ferdows and northern parts of Qaen Basins in Southern Khorasan Province have good potential for harvesting. Moreover, sediment quality assessment showed that most of materials in these areas are coarse grains and therefore require far less processing.
Reza Kordian Hamedani; Saeed Azadi; Safar Marofi; Abdollah Taheri Tizro
Abstract
Erosion is always a major concern for farmers, engineers and policy makers due to economic and environmental impacts. Slope is one of the most important indicators on soil erosion, therefore, the aim of this study is investigation of slope steepness and its aspect on sediment and surface runoff on Gonbad ...
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Erosion is always a major concern for farmers, engineers and policy makers due to economic and environmental impacts. Slope is one of the most important indicators on soil erosion, therefore, the aim of this study is investigation of slope steepness and its aspect on sediment and surface runoff on Gonbad Watershed located in Hamadan, Iran. To this regard, three standard experimental plots installed at southern, northern, and eastern aspects of the basin. The plot dimensions were 1.8×24 meters installed in the relatively uniform slope with different values. Runoff and its sediments were collected in spatial containers. 16 rainfall events (2010-2013) were sampled. Effect of slope steepness, its aspect as well as their interactions were analysed using a factorial experiment by SAS 9.4 software. Results indicated significant roles of slope, its aspect and their interactions in surface runoff volume. Based on the results, small slope has carried out slope steepness significantly on runoff rate, that have more significant effect on smallest steep compared to higher steepness. This is because of land use and vegetating cover and also higher average infiltration rate as well as the recent soil moisture content on the high steep. This is important to note that the slope steepness have not significant effect on runoff sediment rate. The aspect also has significant effect just on 6.25% of the events. The interaction of slope steepness and its aspect also was significant on 18.75% of the events.
Ramyar Aliramayee; Abdulvahed Khaledi Darvishan; Mahmood Arabkhedri
Abstract
Various factors such as rainfall intensity and slope affect hydrological processes such as infiltration and runoff. Study on rainfed soils is very important because of intense degradation and sensitive ecosystem. The present research was conducted to investigate the effect of rainfall intensity and slope ...
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Various factors such as rainfall intensity and slope affect hydrological processes such as infiltration and runoff. Study on rainfed soils is very important because of intense degradation and sensitive ecosystem. The present research was conducted to investigate the effect of rainfall intensity and slope gradient on infiltration and surface runoff using rainfall simulator in rainfed lands of Kalaleh region, Golestan Province. To achieve the study purposes, four rainfall events with the intensities of 33, 64, 80 and 110 mm hr-1 and duration of 15 min were simulated. Three slope gradients of 6, 12 and 25% were selected and infiltration and surface runoff were measured in four 25×25 cm2 plots. The results showed that the infiltration average rate and runoff average coefficient were increased with increasing rainfall intensity and slope gradient. The main and interaction effects of rainfall intensity and slope gradient on infiltration and surface runoff were significant (p≤0.01). The results of subgroups of rainfall intensity and slope gradient using Duncan test showed that two turning points in hydrological response of plot are distinguishable, one between rainfall intensities of 64 and 80 mm hr-1 and another between slope gradients of 12 and 25%. In other words, at the rainfall intensity more than about 70 mm hr-1 and the slope gradient more than about 15%, average infiltration rate and average runoff coefficient were significantly decreased and increased, respectively. These results emphasized on land use management via avoiding change from rangeland to rainfed land especially when the slope is more than 15%. Agricultural and land cover management was also emphasized especially in high rainfall intensities (more than 70 mm h-1).
Leila Gholami
Abstract
In severely eroded areas, especially steep slopes, establishment of vegetation cover is not possible. The application of organic and inorganic amendments can therefore improve the conditions leading to establish vegetation cover through playing an effective role in runoff control. Accordingly, in the ...
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In severely eroded areas, especially steep slopes, establishment of vegetation cover is not possible. The application of organic and inorganic amendments can therefore improve the conditions leading to establish vegetation cover through playing an effective role in runoff control. Accordingly, in the present study, woodchips as a soil organic amendment was applied to control runoff variables including time to runoff, runoff volume and coefficient. For this purpose, three levels of woodchips treatment of 0.5, 1.0 and 1.5 kgm-2 were used in three replications at in 1 m2- plot scale. The plots were located in 30% slope in accordance with field conditions under simulated rainfall of 60 mmh-1 and duration of 15 min. The results showed that application of woodchips in 0.5, 1.0 and 1.5 kgm-2, time to runoff increased 97.50, 192.38 and 203.31%, respectively. The runoff volume decreased 35.23, 55.11 and 60.43% and runoff coefficient also decreased 42.43, 67.40 and 72.14% in three levels of woodchips treatments, respectively. The results of GLM showed that woodchips treatment had a significant increasing effect on time to runoff (p≤0.01) as well as a significant decreasing effect on runoff volume and coefficient (p≤0.05). The application of woodchips as a conservation treatment on the soil surface showed that this amendment can be used for runoff control especially where large quantities of woodchips are simply available.
Saeed Najafi; Seyed Hamidreza Sadeghi; Tobias Heckmann
Abstract
Comprehensive watershed management programs need to take into account the sediment and related process in sediment management paradigm. Whilst, the dominant processes on sediment yield has not been considered in watershed scale yet. Accordingly, sediment connectivity is an emerging concept in sediment ...
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Comprehensive watershed management programs need to take into account the sediment and related process in sediment management paradigm. Whilst, the dominant processes on sediment yield has not been considered in watershed scale yet. Accordingly, sediment connectivity is an emerging concept in sediment management that has been accounted in recent years to investigate the sediment transfer from different sections of watersheds. Sediment connectivity is defined as the integrated transfer of sediment across all possible sources to all potential sinks in a system over the continuum of detachment, transport and deposition processes. The structural connectivity is therefore a concept derived from sediment connectivity which investigates potential of sediment particles displacement across a watershed on the base of anatomy of watershed's system. Naturally, identifying sectors with similar sediment connectivity patterns support applying similar and integrated sediment control mitigation strategies. The present research was planned to investigate the structural sediment connectivity in Taham Watershed in Zanjan Province for year 2014. To calculate the structural sediment connectivity, the Digital Elevation Model (DEM) and C Factor layers were used and the results were assessed according to field observations and surveying in several times. The results of the validity of the structural sediment connectivity map showed there were acceptable agreement between Field Index of Connectivity (FIC) and Index of Connectivity (IC). In addition, IC map with respective max, min and mean values of 1.02, -8.24 and -5.95, showed 32 percent of the study area had a high structural sediment connectivity that generally have been dispersed in western parts of the study area. Regarding to rapid appraisal and being low cost of IC calculation as well as identification of primary sediment sources, the structural sediment connectivity is a very useful concept for sediment management of watersheds of Iran.
Elnaz Azartaj; Ali rasoulzadeh; Ali Asghari
Abstract
Soil and water are the most valuable national resources. Unfortunately in recent decade, due to land use change and vegetation cover degradation, most of the rainfall changed into runoff and in addition to loss of this vital resource, causes abundant loss of life and property by creating enormous floods. ...
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Soil and water are the most valuable national resources. Unfortunately in recent decade, due to land use change and vegetation cover degradation, most of the rainfall changed into runoff and in addition to loss of this vital resource, causes abundant loss of life and property by creating enormous floods. The aim of this study is to assess the effect of land use change from range land to agriculture with different percent of vegetation cover on runoff and soil erosion. For this purpose, three types of land use included preserved range land with 100 percent of vegetation cover; range land with 50 percent of vegetation cover and agricultural land (range land changed to agriculture) were identified in the study area. Then, in each land use, three slopes were determined (10, 15 and 24%). This study was carried out split plot experiment based on completely randomized design. In each land use and slope, runoff and erosion were measured in plots randomly using rainfall simulator with 1.5 mm.min-1 intensity and 15 min duration with 3 replicates. Results showed that the maximum of runoff, sediment mass and sediment density were in the range land changed to agriculture with 24% slope and the minimum of them were in the preserved range land with 10% slope. Also the results showed that the change of range lands to agricultures increase runoff 5 times. In the other hand, with increasing slope from 10 percent to 24 percent, runoff increased 1.7 times. Runoff coefficient was determined for 3 land uses and 3 slopes level. The maximum and minimum runoff coefficient were found 0.72 and 0.06 for the range land changed to agriculture with 24% slope and preserved range land with 10% slope, respectively.
Salman Mirzaee; Shoja Ghorbani Dashtaki; Jahangard Mohammadi; Hossein Asadi; Farokh Asadzadeh
Abstract
Understanding the spatial distribution and variability of erodibility and soil properties is essential for planning of water conservation methods, controlling of flood and runoff and managing of soil erosion or watershed. Selecting and using appropriate interpolation techniques for soil properties and ...
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Understanding the spatial distribution and variability of erodibility and soil properties is essential for planning of water conservation methods, controlling of flood and runoff and managing of soil erosion or watershed. Selecting and using appropriate interpolation techniques for soil properties and erodibility mapping by erosion models such as WEPP is essential. The objective of this study was regionalization of interrill erodibility and effective factors like clay, organic matter and lime using kriging and cokriging and remote sensing data (Landsat 7). For this purpose, 100 soil samples were selected randomly from 0-15 cm depth of Selin watershed in Kaleibar region of East Azerbaijan. Interrill erodibility of WEPP model and some soil properties as clay, organic matter and lime were measured. Correlation analysis between soil properties and digital number (DN) ETM+ image showed that clay, organic matter, lime and interrill erodibility had the highest correlation with DN of Band 7, 1, 1 and 3 ETM+ image (−0.406, -0.431, 0.291 and 0.299), respectively. Therefore, the DN of these bands used as auxiliary data for cokriging estimator. The spherical model was fitted the best model to calculate variogram of interrill erodibility, clay, organic matter and lime. No significant difference were noted between kriging and cokriging despite using remote sensing data as auxiliary data. This can be attributed no strong correlation between interrill erodibility, clay, organic matter and lime and remote sensing data.
Mohsen Zabihi; Seyed Hamidreza Sadeghi; Mehdi Vafakhah
Abstract
Soil erosion as a threatening phenomenon for the world population is mostly the result of the combined effects of unsuitable land use and climatic factors. Among climatic factors, rainfall is considered as one of the main causes of soil erosion and therefore detailed study of the different properties ...
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Soil erosion as a threatening phenomenon for the world population is mostly the result of the combined effects of unsuitable land use and climatic factors. Among climatic factors, rainfall is considered as one of the main causes of soil erosion and therefore detailed study of the different properties of rainfall such as rainfall erosivity is necessary. However, investigation of spatial variability of rainfall erosivity factor at different scales at national level has been less considered. Therefore, the present study aimed to investigate the spatial variability of rainfall erosivity factor in Universal Soil Loss Equation (USLE) for monthly, seasonal and annual scales in Iran. Towards this attempt, the amounts of rainfall erosivity factor were calculated through calculation of kinetic energy and maximum 30-minute intensity over 12,000 showers occurred at 70 stations in the study period of 20 years (1984-2004) in Iran. The spatial patterns of temporal variation were also in different time scales. According to the results, existing stations in the south west and north of the country had the first priority of annual rainfall erosivity factor hazard. The west and south west stations and south east stations had also the highest and the lowest seasonal and monthly risk rainfall erosivity factor, respectively. Also, results showed Tangpich in Khuzistan, Anzali in Giulan and Poleshalo in Khuzistan had the maximum rainfall erosivity factor whereas Bande Enherafi in Semnan, Tabas in South Khorasan and Bam in Kerman Provinces had the minimum annual rainfall erosivity factor hazard country wide. The average annual rainfall erosivity factor in the country was ultimately obtained 14.13 tm.ha-1.cm.h-1.
Mehdi Bashari; Hamid Reza Moradi; Mir Masoud Kheirkhah3; Majid Jafari Khaledi
Abstract
Study of soil erosion without simplification of experimental conditions is difficult and sometimes impossible. Soil clay content has significant relationships with soil aggregates stability and infiltration, that these relationships in various clay contents may be positive or negative. Many properties ...
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Study of soil erosion without simplification of experimental conditions is difficult and sometimes impossible. Soil clay content has significant relationships with soil aggregates stability and infiltration, that these relationships in various clay contents may be positive or negative. Many properties of soil in successive rainfalls can be changed and also affect on runoff and sediment production. Hence, this study attempted to investigate the effect of soil clay content on runoff and sediment production during successive rainfalls under rainfall simulator using erosion plots and eliminates the effects of the overlapping factors. To achieve these aims, 1.5 m2 erosion plots containing soil without clay, combined with 0, 10, 20, 30, 40 and 50 percent of clay soil in three replications, respectively (totally 18 plots) and then were subjected to two successive runs under 70 mmh-1 rainfall intensity for 30 minutes and 24-hours intervals. Sampling and measuring the volume of runoff during rainfall was done each 2.5 minutes. Based on observed data, the amounts of observed sediment in the second runs were 1.5 to 2 times higher than those found in first runs (with a total average of 9/2 and 15/0 grams per liter, respectively for first and second runs), but amounts of runoff in 0 and 10 percent of clay soil mixtures were higher in first runs (2613 and 2045 volumes in milliliters, respectively), whereas for the other mixtures, runoff volume in second runs were higher (2694, 2677, 2315 and 2752 volumes in milliliters for 20, 30, 40 and 50 percent of clay mixtures, respectively). Finally, the statistical analysis showed that in both successive runs in all mentioned soils containing various clay soil mixtures, runoff and sediment values were different significantly (p<0.01). The results showed that there are significant temporal variations within soil properties and also soil clay content has great effects on the quality and quantity of soil erosion process.
Mehdi Bashari; Hamid Reza Moradi; Mir Masuod Kheirkhah; Majid Jafari Khaledi
Abstract
Soils containing rock fragments are covering major parts of land surfaces. Physical and chemical properties of soil are affected by rock fragments as they also affect on the hydrological and erosional processes. So far, many studies have shown the effect of surface rock fragments on soil erosion and ...
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Soils containing rock fragments are covering major parts of land surfaces. Physical and chemical properties of soil are affected by rock fragments as they also affect on the hydrological and erosional processes. So far, many studies have shown the effect of surface rock fragments on soil erosion and runoff. Sediment production is a complex and ambiguous process and a notice to these effects is necessity. Hence this study examines the soil erosion reactions in different impermeable coverage of rocks with erosion plots and rainfall simulator. For this purpose, plots were covered with 0, 5, 10, 15, 20 and 25 percent of rocks, respectively. The results of sediment sampling and measuring the volume of runoff during 30 minutes of rainfall with an intensity of 70 mm/h were analyzed and the results showed that increasing of rock fragment coverage had no effect on runoff volume. But, the amount of sediment increased significantly (p<0/05) in soils containing rock fragments compared to soils without rock fragments. Although, results did not show a linear relationship between sediment values and rock fragment coverage percentage. The highest value of runoff and sediment concentrations observed in soils containing 10 and 20 percent of rock fragment coverage in comparison to other treatments. Finally, by increasing of surface rock fragments to 25 percent, the value of runoff and sediment decreased significantly. The results of this study confirmed the threshold levels in surface rock fragments to increase runoff and sediment values and also their dual roles at different levels.
Saeed Nabipay Lashkarian; Seyed Ali Asghar Hashemi; Samad Shadfar
Abstract
Erosion and sedimentation are main challenges in Iran, which cause the reduction of soil quality and quantity. Soil conservation and watershed management activities should be implemented to reduce the impact of these phenomena. Therefore, the knowledge of critical area is necessary through the learning ...
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Erosion and sedimentation are main challenges in Iran, which cause the reduction of soil quality and quantity. Soil conservation and watershed management activities should be implemented to reduce the impact of these phenomena. Therefore, the knowledge of critical area is necessary through the learning the amount of sedimentation and erosion. Because of lack of sediment measurement stations in more watershed outlets in Iran and insufficient data, empirical models are proper tools for data layers generation. Factorial Scoring Model (FSM) is one of the experimental models which has been recently developed out of the country. The main objective of this research is to compare sediment yield estimated by FSM model and observed values. So, in order to evaluate the model, nine small dams of 10 years old with no overflows were selected from in Semnan province. For modeling sediment yield, topography, lithology, gully, catchment shape and vegetation cover of related catchments were studied and required data layers were prepared and scoring indexes were given and finally, the calibrated model was presented. Estimated model values were then compared with measured values. Results showed that main model equation does not have sufficient efficiency. Also, results demonstrated that calibrated FSM model has conformity with observed sediment values at 84 percent.
Majid Mahmoodabadi; Elham Sirjani
Abstract
Soil erosion is a dynamic process with high variability in sediment size distribution. Dynamic recognition of sediment size distribution is as a base for modeling of soil erodibility and movement of nutrients, pollutants and fine particles in consequence of erosion. This study focused on sediment transport ...
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Soil erosion is a dynamic process with high variability in sediment size distribution. Dynamic recognition of sediment size distribution is as a base for modeling of soil erodibility and movement of nutrients, pollutants and fine particles in consequence of erosion. This study focused on sediment transport mechanisms due to sheet erosion on two different soils (cropland and sandy) using flume experiment. The experiment was performed applying different flume slopes (1.5 and 2 %) and flow rates (75, 100, 125, 150, 175 and 200 ml/s). The result showed that hydraulic condition as well as soil type, played an important role in selective transport of sediment particles so that, in the sediment size distribution of cropland soil two peaks were observed. For the first (fine particles with size of 0.042 mm), the dominant transport mechanism was attributed to suspension- saltation, while for the second peak (large particles with diameter of 1.5 mm), bed load was known as the main transport mechanism. Moreover, increasing stream power, the selectivity of fine particles declined therefore, both fine and large particles were transported by the flow. For sandy soil, only one peak for the range of 0.109 to 0.175 mm was observed. In this soil, saltation was the main mechanism in transporting sediment. Increasing flow rate, the frequency of particles smaller than 0.015 diminished, whereas particles larger than 0.218 mm increased. For both soils at higher stream powers, the relative importance of transport as suspension and bed load decreased and increased, respectively. The findings of this research reveal that sediment size distribution and also transport mechanisms depend on hydraulic condition such as slope and flow rate.
Seyed Hamid Reza Sadeghi; Bahar Salavati; Abdolrasoul Telvari
Volume 2, Issue 2 , July 2010, , Pages 111-115
Abstract
Population ever increasing and consequent demands in recent decade have encouraged farmers to utilize unsuitable and marginal lands such as forests and ranges for agricultural purposes. However, these lands have high soil erosion potential and low productivity and their proper management is therefore ...
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Population ever increasing and consequent demands in recent decade have encouraged farmers to utilize unsuitable and marginal lands such as forests and ranges for agricultural purposes. However, these lands have high soil erosion potential and low productivity and their proper management is therefore a vital task. In the present study, the land use areas have been evaluated in Garan watershed in Kordistan Province, Iran, from 1995 to 2002 by using three digitized images and corresponding changes have been then assessed. The effects of land use changes on changing annual runoff were ultimately evaluated with the help of moving average and hydrological regime analyses. The results of the study revealed that the variation in water discharge thoroughly followed the annual rainfall oscillation which itself affected land allocation to different land uses.
Mohammad Shabani
Volume 1, Issue 4 , February 2010, , Pages 240-247
Abstract
Estimation of soil erosion and sediment yield in a river is a difficult task and several methods have been suggested for its estimation. One the new methods in river engineering and suspended sediment estimation is application of artificial neural networks which uses the same algorithm of human brain ...
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Estimation of soil erosion and sediment yield in a river is a difficult task and several methods have been suggested for its estimation. One the new methods in river engineering and suspended sediment estimation is application of artificial neural networks which uses the same algorithm of human brain to find out the internal relation between data based on the training process. The objective of current study is to explore the capability of artificial neural networks method for estimation of daily suspended sediment in Kharestan watershed located in the northwest of Fars province, Iran. The study of efficiency is based on the comparison of neural network with regression models. For this purpose, 22 years of water and sediment discharge data of Shoor Kharestan River were considered and tested for outliers. Then the estimation was done based on neural networks and linear regression method (sediment rating curve) and were compared based on RMSE, MAE and R2. The results showed that estimation of neural network is more accurate than that of linear regression (sediment rating curve). The estimations of RMSE, MAE and R2 for neural networks method was 19.27, 12.14 and 0.98 respectively while these values for linear regression were 36.84, 20.75 and 0.74 which showed the lower errors of neural networks method compared with linear regression.
