جستجوی مقالات مرتبط با کلیدواژه « sediment yield » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

 The soil erosion is one of the effective factors in reducing agricultural production and threatening food security, in which the soil fertile layer is destroyed. The risk of soil erosion is different depending on the watershed topography, soil characteristics, conditions of local weather, land use and methods of land management, which the land use change can be exacerbated. Land use changes are one of the important factors in changing hydrological flow and soil erosion. As a result of land use change and vegetation destruction, a large part of the rainfall has turned into runoff, which in addition to soil loss and sediment production, causes a lot of financial and human losses caused by floods. Therefore, the knowledge from erosion process in different time periods can help in determination of the distribution pattern of erosion and its effects over time. So that, the decision-makers, while monitoring and evaluating the conducted measures about the soil and water conservation take the appropriate decisions for the current and future conditions of watersheds. Therefore, in the present study, the effects of land use change on soil erosion have been evaluated using the RUSLE model in Chardavel watershed of Ilam province for the years 2005 and 2020.

 In the present study, the effective factors in the Revised Universal Soil Loss Equation were prepared in the form of raster layer. These factors include the rainfall erosivity, length and degree of slope, vegetation management, soil erodibility and conservation operations. The factor of rainfall erosivity was calculated for each of the stations inside and outside the watershed and the erosivity layer was prepared in the GIS environment, by using the Inverse Distance Weighting method. For the length and degree of slope were used from the digital elevation model map and cumulative flow map. The layer of soil erodibility was obtained using the soil texture map. The NDVI index was calculated using Landsat 8 of OLI sensor (2020) and satellite images of five ETM Landsat satellite images (2005) and using bands of 4 and 5 (for Landsat 8) and bands of 3 and 4 (for Landsat 5) in the remote sensing software, and then, the management factor was obtained in years of 2005 and 2020. In order to obtain the factor of conservation operation, the land use map was used for years of 2005 and 2020, and according to each land use was determined the its conservation value. In the next step, the amount of annual soil loss was estimated by multiplying these layers in the GIS environment. Finally, to determine the amount of erosion in each of land uses, the layers of erosion and land use placed on top of each other to the years of 2005 and 2020.

 The results showed that the rainfall erosivity was from 220.5 to 309.8 MJ mm ha-1 h-1, the length and degree of slope were 0 – 403.7 at the pixel level, the vegetation management was 0.16 - 0.57 (in year of 2005) and 0.18 - 0.61 (in year of 2020), the soil erodibility was 0.03 - 0.06 t. ha h ha-1 MJ-1 mm-1 and protection operation was 0-1 for both years of 2005 and 2020. The average erosion was 13.23 t ha-1. year-1 for year of 2005 and this value was 20.13 t ha-1 year-1 for year of 2020. The barren land uses due to the lack of vegetation produces the highest amount of erosion, so that its amount has increased years of 2003 to 2005 from 0.65 to 3.8 t, and residential areas due to the presence insulation, asphalt and proper drainage have the more role of transferring runoff. In agricultural areas, it has been exposed to erosion during this period due to not following the principles of proper cultivation and usage of proper tools.

 Considering the extensive effects of soil erosion on various aspects of human life, its continuous monitoring and evaluation can help to make the right decisions to confronting with this crisis. In the present study, the RUSLE model was used to investigate the effects of land use change on soil erosion for the years of 2005 and 2020 in Chardavol watershed. In general, the results showed that the erosion amount has increased in the studied watershed from 2005 to 2020, which it indicates that there is the dangerous situation for the watershed in the future. Therefore, it is suggested to use soil and water conservation operations, especially in the steep areas and also in the upstream areas of the watershed. Also, according to the change of land use in Chardavol watershed, the measurements should be taken for soil and water conservation in areas with high erosion potential. It also seems that the adoption of appropriate laws to prevent land use change can help reduce soil erosion.  But, because the most important part of the watershed are its residents, these laws should be in such a way that while attracting people's participation and satisfaction, it guarantees their stable income. Therefore, the development of management scenarios in the region will help natural resource managers in prioritizing and usage of appropriate management methods in controlling soil erosion in high-risk areas of Chardavol watershed.

The response of water balance components as indicators of hydrological performance to stimuli such as land use change is of strategic importance. In this study, the effect of land use change on water balance components was evaluated, focusing on the relationships and change of the main indicators of water yield and sediment yield. Based on this, the Markov chain model was used to predict land use in 2040. Also, the American soil and water assessment tool was developed as a base model for evaluating and estimating hydrological indicators in the Taleghan Watershed as a mountainous watershed with structural heterogeneity. The results of model showed that the increase of settlements and urban development in Taleghan watershed will result in increased runoff, increased water yield and sediment yield indicators, and more sedimentation. Land use change leads to an increase of sediment yield by 11 times until 2040. The conversion of pastures to barren lands is the most important land use change that can increase sediment yield. Also, the increase of barren lands will be the reason for the reduction of evapotranspiration in some sub-basins of this watershed. Increasing rainfall and decreasing soil permeability will increase surface runoff, and as a result, soil erosion and sediment yield will increase. In this study, exactly the sub-basins that had the highest quantitative amount of predicted water yield index also had the highest quantitative amount of sediment yield index and increased sedimentation. In this research, it was determined that land use change as a type of structural change in the land will have visible effects on the functions and hydrological responses of the watershed.

The study of erosion and sedimentation is a crucial aspect and an integral part of watershed studies in a basin. The methods employed to prevent erosion and sedimentation play a significant role in basin management planning. However, due to the lack of accurate statistics on erosion and sediment amounts, it becomes necessary to utilize estimation models for assessing erosion and sedimentation. These models are often region-specific and may have a wide range of uncertainty in different areas. One notable benefit of modeling, regardless of its type, is its ability to analyze natural processes within the basin. On the other hand, understanding erosion and sedimentation processes in a region can be an effective step in managing, planning, and prioritizing available resources. In this research, the aim was to determine the sensitivity of the MPSIAC model to the relationships among its parameters. Additionally, the goal was to assess the model's sensitivity to changes in these parameters and their impact on sedimentation. By identifying the influential ground and atmospheric parameters, it becomes possible to prioritize their effect on water sedimentation in the region.

Through the sensitivity analysis of the model, it is possible to identify the flexibility of the model to the changes of its various parameters. It is also possible to determine the relationships between model variables and prioritize the parameters affecting the model output. Sensitivity analysis can be used in the calibration stage, in such a way that results are accurate, and time and cost are saved. In this study, to analyze the sensitivity of the MPSIAC model, first, the nine parameters of the model were examined. Then, according to the arrangement of different parameters in the structure of this model, the parameters were numbered from X1 to X9. Then, the score range of each parameter was entered in its calculation table according to the modified model of PSIAC. In this step, the average of each parameter was calculated according to its upper and lower limits. To achieve this, the nine parameters of the model were standardized, and the sedimentation rate was estimated by varying each parameter within its lower and upper limits while keeping the other parameter(s) fixed at their averages. With each change, the sediment discharge was calculated.

In the analysis of the results, the slope of the curves of the standardized parameters relative to the dependent variable (specific sediment) is considered. So that, any part of the curve that has more slope changes means that the model is more sensitive to minor changes in that parameter in that interval. In this study, the results of this sensitivity analysis reveal that the slope factor and runoff volume have a considerable influence on sediment yield. For slopes up to approximately 15%, the slope parameter has a relatively smaller impact compared to other parameters. However, as the slope value increases, its effect becomes more pronounced, indicating that high slopes (greater than 15%) have the greatest impact on sedimentation. The runoff factor exhibits a sudden increase in sensitivity at higher flow rates.

In examining the effect of different parameters on the model performance, the parameters that had the largest slope of changes can be considered as the most effective parameters in sedimentation of the basin. In other words, the model demonstrates high sensitivity to slight changes in specific peak discharge values above 20 m³/s/km2. Therefore, implementing integrated (biomechanical) management measures to control slope steepness and reduce runoff volume can be an effective strategy for mitigating sedimentation. Therefore, based on the results, the role of land factors is very important, such as slope and then runoff, in the erodibility and sediment production in basins. Of course, it should be noted that climatic parameters directly and indirectly affect the amount of peak flood discharge and should not be neglected for their importance and influence in flooding and subsequently the erodibility of the watershed.

Introduction and Objective:

Soil is a part of every ecosystem and one of the most valuable and important sources of food production in every country, which plays a significant role in the continuation of human life. Today, soil erosion is one of the most important threats to water and soil resources and has become one of the most important human environmental problems. Soil supports food security and environmental quality, both of which are essential for human life. The purpose of this research was to evaluate the performance of watershed management measures in the treated sub-watershed of Khamsan representative watershed. The lake of Gavshan Reservoir has receded at the maximum level to the outlet of the Khamsan watershed. This has caused soil erosion from this watershed to enter the Gavshan dam lake directly and with the shortest distance. Therefore, it is very important to evaluate the performance of the measures taken in this watershed, especially based on the distribution map of erosion and sedimentation.

Materials and Methods:

The first step of measuring soil erosion using cesium-137 is to select a control or reference area. Slope and land use maps were used to determine the final sampling points in this research. After measuring the activity of cesium-137 (becquerels per kilogram of soil), the presence of cesium-137 per square meter of soil sample is needed to calculate soil erosion. The activity of cesium-137 in reference points was compared with the activity of cesium-137 remaining in the research points. If the cesium-137 activity of the soil samples was lower than the activity in the reference profile, soil loss and erosion occurred. The increase in the activity of cesium-137 in the soil samples compared to the reference profile was indicative of soil transfer to the sampling point and considered as a sedimentation site.

Results  and Discussion:

The results of the comparison of the same points in the rangelands in both treated and control sub-watersheds showed that sedimentation conditions prevail over erosion. The amount of sedimentation in the rangelands with watershed management measures (contour trenching, seeding and exclosure) in the treated sub-watershed with a slope of 20-30% was more than the rangeland with the same characteristics in the control sub-watershed. In rangeland with watershed management measures, erosion conditions prevailed in the slope of more than 30-60%, but erosion in protected conditions was less compared to the same point in the control sub-watershed.

Conclusion and Suggestions:

The results of the amount of erosion and sedimentation in both treated and control sub-watersheds in rangeland with a slope of 20-30% showed that sedimentation conditions prevail. However, the amount of sediment deposition in the rangeland with watershed management measures in the treated sub-watershed showed an increase of 1445.65% compared to the rangeland without protective measures in the control sub-watershed, which indicates the positive effect of watershed management measures in the treated sub-watershed rangelands with a slope of 20-30%. This finding shows the special effect of contour trenching on increasing sediment trapping, reducing the volume and speed of runoff, and thus reducing the power of sediment transfer. Also, in the slope of 30-60%, although erosion conditions prevailed in both treated and control sub-watersheds, watershed management measures in rangeland in the treated sub-watershed showed a 28.57% reduction in soil erosion compared to the same point in the control sub-watershed. Considering the positive performance of watershed management measures, especially contour trenching, it is suggested to use these measures in other watersheds similar to Khamsan representative watershed.

The cycle of soil erosion (including removal, transport and deposition) that controls the sedimentation of watersheds, includes a set of complex and highly nonlinear processes. On the other hand, the factors influencing sedimentation in watersheds are very diverse, and according to the specific conditions of climate, soil, vegetation, geology, topography, etc., in each basin, the weight and role of each of the mentioned factors in sediment production is very different. Accurately determining and measuring these factors and making mathematical relationships between them are often difficult, expensive, time-consuming and error-prone, and this is the case with the use of models based on computational intelligence and the use of a limited number of basin dynamic variables, it is possible to simulate the behavior of the watershed in sediment production. Regardless of the type of intelligent models, in most of the conducted research (especially in internal research), the simulation of suspended sediment is mainly based on the discharge variable and the role of variables such as precipitation (especially precipitation obtained from satellite images), which are effective in the sedimentation of basins, have received less attention. In addition to precipitation, the skewness of sediment measurement data is also one of the issues that lack of recognition and attention will reduce the efficiency of estimator models. In the present study, the role of variable daily rainfall (taken from CHIRPS satellite) in the simulation of suspended sediment of Qarachai River has been investigated.

Multi-layer perceptron artificial neural network was used in order to simulate the daily suspended sediment concentration of Qarachai River (at the Ramian hydrometer station in Golestan province). In this regard, the variables of discharge and previous discarge (in instantaneous and daily scales) as well as the average daily and previous rainfall of the basin (taken from CHIRPS satellite) for a statistical period of 37 years (1980-2017) as variables model input was used. In order to increase the generalization power of the models, self-organized mapping neural network (for data clustering) and gamma test was used to find the best combination of input variables. In order to improve the efficiency of network training, a variety of activation and loss functions as well as the overfitting prevention algorithm were used. In order to investigate the effect of using activation and loss functions in suspended sediment estimation, different scenarios were considered, which led to the construction of 9 models. After that, using validation indicators, the effectiveness of the models in simulating suspended sediment was investigated and compared, and then the best model was selected.

The results obtained from the present research showed that among the different models, the neural network model with Huber's activation function and ReLU loss function, having the average absolute value of the error equal to 368 mg/l, the root mean square error equal to 597 mg per liter, the Nash-Sutcliffe coefficient of 0.87 and the percent bias -2.2% were selected as the best model. The results also showed that the use of the rainfall variable (as one of the important factors in causing erosion and sediment transfer in the basin) has improved the efficiency of the models, therefore, considering the ease of using CHIRPS satellite rainfall data, it is suggested in order to simulate the suspended sediment of rivers, this data is also used along with other predictive variables.

In the simulation of suspended sediment, discharge variable is often used as the only predicting variable of suspended sediment, while in basins with rainy, or rainy-snow regimes, the role of precipitation in the production of surface runoff and soil erosion is very important and plays an important role in the production and transport of sediment in the basin. In this regard, although the use of rainfall data obtained from ground rain gauge stations has played an effective role in increasing the efficiency of data-based models in estimating suspended sediment, however, the preparation of hundreds of spatial distribution layers of daily rainfall from the data point data of ground stations, the use of this variable in the simulation of the suspended sediment of the basin has been faced with many problems (such as the lack or inappropriateness of the spatial distribution of rain gauge stations, statistical deficiencies, the use of inappropriate interpolation methods and time-consuming calculations). Therefore, in practice, the variable of river flow is often used as a predictor of sediment, and precipitation is used less often. One of the solutions to the problem mentioned in the present study is the use of CHIRPS satellite data, which was investigated for the first time in this study. These data, available since 1981, can easily be used to simulate suspended sediment or other applications related to watersheds. Another important point that needs to be taken into account in the simulation of suspended sediment is the presence of high skewness in sediment measurement data (both suspended sediment and flow rate), which lack of attention in the process of training (or recalibration) and testing the models leads to It will lead to the construction of weak models in terms of efficiency and the existence of uncertainty in the accuracy of their results. In this regard, it is necessary to use logarithmic transformations or suitable functions of activation and loss in the training process, which in this research, two functions, ReLU and Huber, were proposed respectively. Another important point is to pay attention to the generalization power of data-based models, which is largely dependent on the data used in their calibration or training process. These data should be selected in such a way that while they are representative of the data in the entire statistical period, they are similar and have the same distribution with other data sets (such as cross-validation or test sets). According to the results obtained from the present research and in order to increase the efficiency of artificial neural network models in estimating the suspended sediment of watershed hydrometric stations, it is suggested to use the experiences obtained in this research in other sediment measuring stations of the country.

Gully erosion affected by many factors causes the destruction and loss of large volumes of soil along with great economic and social damage. The variability of diversity, the number and size of the influence of different factors from one point to another and the difference of their participation in the formation and expansion of gullies is based on the conditions of the land. Such conditions have caused more researches to be carried out to identify as many factors as possible in the phenomenon of gully erosion and the extent of their participation in the formation and expansion of this phenomenon. In this regard, the present study has been planned with the aim of monitoring and evaluating the effective factors in the development of gullies in the Haddam and Sharif watersheds of Khuzestan province. Modares Shushtar watershed, having Sharif and Hadam subwatersheds, as one of the important and typical basins of the province, every year a large area of its agricultural land is threatened by gully erosion.

In order to carry out this research, first, the parts with gullies in the study area were identified on the topography map with a scale of 1:250,000 during the 20-year period (1993-2012). Then, 15 gullies have been identified and investigated from each climate class of hot-dry desert and hot-semi-arid. Features such as the slope of the initial point of creating a gully and the slope of the front of the gully were calculated by the field method and using a tape measure, level and inclinometer measuring device and the mirage area of the gully front in the Google Earth softwave. Also, the physical and chemical characteristics of the soil of each gully were tested.

The results showed that the average percentage of bare soil above the head cut of selected gullies in Haddam and Sharif watersheds is 99.8% and 97.26%, respectively. Based on soil characteristics, the main cause of soil instability and erosion in gullies in both watersheds is EC. The morphometric characteristics of the gullies showed that in the Haddam watershed, all gullies are V-shaped in terms of cross section, and in the Sharif watershed, only gullies are B12, V-shaped and the rest are U-shaped. The Haddam watershed has the highest depth, width, and top of the gully compared to the Sharif watershed. The total volume of soil loss in Sharif and Haddam watersheds is 23000 and 51579 m3, respectively. Gullies A18 and B1 in Haddam watershed have the highest and lowest soil loss volume, at 11599 and 1612 m3, respectively. In the Sharif watershed, the maximum and minimum soil loss volume of gullies related to gullies A2 and B4 are 5282 and 369 m2, respectively.

Conclusion and Suggestions  :

The most important factors in the volume of soil loss and expansion of gulies are the characteristics of the watershed located upstream of the gully front (such as the extent and slope of the watershed) as well as the fineness of the geological formation (silt) and high soil salinity. Due to the excessive bareness of the soil, increasing the roughness of the soil surface with the establishment of vegetation is one of the compatible and low-cost methods in protecting soil resources. In order to control the spread of gully erosion, it is necessary to increase soil organic matter, modify saline and sodium soils with the use of modifiers, and also divert the runoff from the gully front.

Water storage dams are considered as strategic constructions of every country. The issue of soil erosion in the watershed of the mentioned dams and the transfer of produced sediment to the reservoir of the dams is one of the issues that is always raised regarding these types of dams. Cheshme Ashegh dam in Fars province is one of the mentioned dams. In the present study, erosion and sediment studies and estimation has been carried out for the first time in this watershed by RUSLE and MPSIAC models as well as the regional analysis method for the aim of design and implementation of suitable conservation measures as well as making policy and plan for soil conservation in the watershed of the dam and preventing the production and transfer of sediment to its reservoir. The results of this research showed that, based on the MPSIAC and RUSLE models, the amount of special sediment is estimated by 1.58 and 3.17 ton/ha/y, respectively. Considering that the result obtained from the regional analysis method based on Gozoon station, the amount of special sediment is estimated by 3.5 ton/ha/y, it can be said that the result of the estimation obtained from the RUSLE model is closer to the amount calculated from the regional analysis method. Therefore, it can be said that the results obtained from the RUSLE model are more efficient than the MPSIAC model for estimating the amount of sediment and future soil conservation measures in the Cheshme Ashagh Dam watershed.

Accelerated soil erosion and high sediment production are important issues in many parts of Iran. The identification of high erosion risk regions is necessary for the planning of soil and water conservation measures in order to reduce erosion damages. Empirical models are required for estimating soil erosion and sediment yield in the absence of gauged small watersheds. The Erosion Potential Method (EPM), originally developed in Croatia, is a popular erosion estimating model in Iran; however, its efficiency across the country has not been thoroughly assessed. Therefore, a calibration study was carried out by comparison between the model the estimated and measured sediment yields through sediment survey for 63 reservoirs at the outlet of small catchments in the Semnan, Markazi, Isfahan, Chaharmahal va Bakhtiari, West Azarbaijan, Lorestan, Fars, Golestan, and the Khorasan Razavi Provinces. All required maps and information of the study basins for estimating the EPM sediment yield were produced via field survey as well as data analysis. Comparison of the results showed that in most cases, the model estimates (0.19 to 9.71 tons per square kilometer per year) are lower than the measured sediment yields ​​at the reservoir inlets (0.44 to 459.64 tons per square kilometer per year). Thus, we calibrated the EPM by modifying its original tables and evaluated the results using the Nash‐Sutcliffe efficiency coefficient in two scenarios, a, all basins, and b, after dividing into three geographical zones, which significantly improved the estimates. The Nash ‐ Sutcliffe efficiency coefficient for scenario a was 0.66, and 0.68, 0.50 and 0.89 for the Central, Zagros, and Northeast zones, for scenario b respectively. Based on the results, it is strongly recommended to use the modified EPM instead of the original model.

Changes in plot size can be determine its effects on parameters changes of runoff and soil loss. On the other hand, the generated runoff in eroded soils is one of the most important obstacles and challenges of human in conservation of water and soil resources and it is also a threat to well-being and life. One of the most important of controlled factors of surface runoff and increasing soil infiltration is the application of conditioners or amendment materials on soil. But it should be noted that the size change can also control the runoff and soil loss variations. Therefore, the present study was carried for the effect investigating of size change in laboratory plots in two sizes of 0.5 × 0.25 and 1 × 0.5 m2 using application of organic manure with rates of zero (control treatment) and 62.5 and 125 g m-2 (conservation treatment) on changing time to runoff, runoff coefficient, soil loss and sediment concentration. The obtained results showed that the plots with size of 0.5 × 0.25 m2 and the application of organic manure with rate of 62.5 g m-2 had the little effect on the increasing time to runoff compared to control treatment. But, time to runoff increased with increasing plot size and also rate of organic manure. The effect of plot size on parameters of runoff coefficient, soil loss and sediment concentration, organic manure on parameters of time to runoff, runoff coefficient and soil loss and interaction effect of size change and organic manure on parameter of soil loss was significant at level of 99 percent. Also, in plot with area of 1.0 × 0.5 m2, the changes of time to runoff and runoff coefficient, soil loss and sediment concentration for organic manure with rate of 125 g m-2 toward 62.5 g m-2 were 72.83, 53.52, -212.27 and -142.92 2.12 percent, respectively. While, the changes of studied parameters for plot of 0.5 × 0.25 m2 were 594.24, -212.63, 4.06 and 13.70 percent, respectively.

Sediment accumulation is one of the major factors that reduce the beneficial life span of artificial reservoirs. Conservation and improving vegetative cover conditions may reduce sediment accumulation. A framework for implementing the PES was proposed assuming that the cost of soil and vegetation cover conservation may be considered as an investment in water supply through economic incentives, consisting of vegetative cover change projection, erosion and sediment transport modeling, reservoir sedimentation estimation, and the PES scheme design. Based on the results of increasing the amount of total sediment production from 486637.6 m3/yr in the current situation to 564217.5 and 658925.4 m3/yr, respectively over the next 20 years, and reduction of the useful lifespan of the Shirin Darreh reservoir (17.3%), the minimum payment for ecosystem services was considered 104 million Rials/yr. Furthermore, the volume and the total value of sediment control services provided by the vegetative cover was also determined by considering a complete degradation of the vegetative cover scenario and opportunity cost of 740535.5 m3/yr and 3.7 billion Riyals. Furthermore, the maximum payment was also estimated by considering the total value of the sediment control services and the estimated net present value of range conservation to be about 3.9 billion Rials/yr.

Soil, as one of the components of any ecosystem and an important source of food production, has a very serious role in the continuation of human life. Therefore, the need to support and protect the soil and prevent its erosion is essential. Regarding the amount of soil erosion and sediment yield in the country, different figures have been mentioned and in some studies, the difference is with several times. These figures vary from less than one to more than five billion tons per year. Therefore, calculating and plotting erosion and sedimet yield maps provides important information that is used in the design of dams, reservoirs, canals, soil protection operations, onsite and offsite erosion damage assessment, and land use planning and land capability assessment projects. Soil erosion map is one of the basic, scientific and applied maps in various executive, research and educational sectors. Due to the need of determining the amount of soil erosion and sediment yield for the entire country and determining the executive priorities in areas with high soil erosion potential, this project was defined and carried out by the Soil Conservation and Watershed Management Research Institute. Accordingly, the watersheds of the seventh category were divided into seven regions or districts, including 1) Eastern Alborz 2) Middle Alborz 3) Western Alborz 4) Central Iran 5) North Zagros 6) Middle Zagros and 7) South Zagros. Long-term sedimen data of 118 hydrometric stations in these areas were analyzed and the amount of sediment in each station was determined by the logged mean load within discharge classes method. According to the amount of river bedload rates and using EPM model, the amount of sediment yield and cosidering sediment delivery ratio of watersheds, the amount of soil erosion were etermined and the soil erosion map of watersheds overlooking hydrometric stations was prepared. Results showed that the average sediment yield and soil erosion in the watersheds overlooking hydrometric stations are 3.3 and 16 tons per hectare per year, respectively. The lowest and highest soil erosion rates of 9 and 32.4 tons per hectare, belong to the Middle Zagros and South Zagros regions, respectively.

Soil erosion is one of the most important environmental problems in the world, which has created many problems for human societies. Therefore, accurate evaluation of soil erosion in erosion and sedimentation studies is necessary to design and implement appropriate, targeted, and cost-effective conservation measures due to the severity of the problem and socio-economic effects. Therefore, it is necessary to select a suitable and appropriate model for estimating erosion and sedimentation according to the available data, different topographic and climatic conditions of the country and considering the information needs and complexity of the models. Accordingly, in the present study, the strengths and weaknesses of four experimental models including EPM, MPSIAC, RUSLE and IntErO were analyzed qualitatively. The results showed the acceptable results of MPSIAC model in arid regions, the RUSLE model in Mediterranean mountainous areas, high slope forest areas and agricultural areas and EPM and IntErO models in mountainous area and also for watershed management and water resources management. Therefore, it is recommended to select erosion and sediment estimation models in accordance with management goals, available data, topographic and climatic conditions. As a result, it is expected that having suitable selection of a soil erosion and sediment yield model will lead to save time, designing and implementing appropriate, selective and cost-effective conservation measures.

Erosion and sediment resulting from it, is one of the most important factors in watershed management. The estimation of sediment yield and prioritization of watersheds in terms of water erosion is the main objectives of watershed management. One of the ways to estimate soil erosion and sediment yield is to use empirical models. The aim of this research is to evaluate the efficiency of the EPM Model in Fars Province. To examine this, five small watersheds were selected in Fars Province. Five basins in which the earth dams and check dams were built were selected. There is no overflow from these dams in rainfall events and the most of them was made near to 10 years. The amount of sediment deposited in upstream of the reservoirs was calculated by means of precision mapping. Deposit bulk density was determined in the field to convert the volume into the weight. In parallel, the sediment yield of the basins was determined by EPM Model. Results showed that the minimum and maximum sediment yield measurements varied from 0.89 to 2.62 tonh-1y-1, but the estimated sediment was between 3.3 to 6 tonh-1y-1. The results of the relative error of estimation of EPM Model in each of the studied basins showed an over estimation in all basins (minimum 121.5 and maximum 447.2 percent). The Relative Root Mean Square Error (RRMSE) of the model was calculated as 2.39, which indicates a too much error of the model. Statistical analysis results comparison of actual sediment yields of watersheds with estimated values by model, using paired t-test, shows that there is a significant difference between these values (t=8.728 and sig.=0.001). According to the presented findings, the results of this model estimation for the investigated areas are not accepted.

Rangeland exclusion is one of the watershed management methods that is applied for range rehabilitation. However, most rangeland hydrology studies have been focused on exclusion effects on soil loss at plot scale, whereas their effects on sediment yield at micro-watershed in seasonal and annual scales have rarely been considered. The present study was conducted in two sub-watersheds under exclosure and open grazing treatments, with area of 1.0 and 1.1 ha, respectively, in Sanganeh Watershed, Khorasan Razavi Province, Iran. Runoff and sediment associated with 56 storm events occurred during 2006 to 2016 were estimated at the main outlet of the watershed. The results showed the significant decreasing effect of exclosure treatment on sediment yield at micro-watershed scale (p≤0.05). So that, 582% decrease in sediment yield was obtained in exclosure treatment compared to open grazing. Results also showed seasonal and annual variations of exclosure on hydrological processes so that, maximum and minimum differences in sediment yield among study treatments were founded. The results of this study suggest that livestock grazing management during sensitive seasons as well as rangeland exclosure, if its social problems are resolved, is a practical solution to reduce watershed sedimentation.

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.

The erosion rate ranking of geological formations can be a useful way for identifying and prioritizing the watershed sub-basins and it is important in view of decision making and management of the watersheds. Therefore, the present research was conducted with the aim of prioritizing the implementation of soil conservation operations in the Hablehrood sub-basins in northern Garmsar based on the degree of sensitivity of rock units to erosion. The method is based on the expert opinions and rainfall simulator experiment and comparison of the obtained results with erosion and sediment estimations of empirical models such as PSIAC, EPM and SWAT. Results showed that erosion rate ranking of the sub-basins based on the results of rainfall simulator conformed to the output of the three mentioned models in 12 sub-basins of 21 sub-basins and in other six sub-basins with two models, and in the remaining three sub-basins, it only conformed to one model output. Rainfall simulation results showed the highest correlation with the PSIAC model with a specific sediment yield of 9.2 t km-2 and based on the results of the observation data of the Bonkouh sediment-debit station, a special sediment of 8.02 t km-2 without considering the bedload, it became clear that the PSIAC model provided the most reliable estimate of sediment yield. Thus, matching the results of rainfall simulator in the erosion rate ranking of sub-basins with the PSIAC model shows that the rainfall simulator study on lithology units quite reliable with a 90% confidence level for erosion ranking classification of sub-basins and it can be used in similar basins.

Land use changes can significantly affect the hydrology of a forest watershed. Ground cover is important to protect the soil against erosion. Timber harvesting has been changed the canopy cover and forest soil was exposed to the wind and water. Soil compaction and removing the forest floor in the skid trails was reduced the capacity of water absorption in mineral soils and thus reduced water infiltration, increased runoff, which caused to soil erosion. In order to measure the rate of sediments in two slopes and to study the effect of skid trails on the amount of sediments, the plot-level study was carried out in the Gorazbon district in Kheyrud forest in the control area and skid trail after skidding operations in the sample plot. The results showed that the most sediment value was 1.938 g. liter-1 in the skid trail with a 20-40 percent slope in the autumn and the lowest deposition was 0.103 g. liter-1 in the control area with a slope of 20-40 percent in the autumn. Type of Coverage (skid trail and control area), the season and the interactions between the cover and the season statistically have significant effect on the sediment yield, but the slope and the interactions between the slope and cover, as well as the interactions between the slope and season have no statistically significant effect on the sediment yield. Duncan’s test showed that there was a yield statistically significant difference between sediment yeild in different seasons and the autumn had the highest sediment

Marl formations have problems in watersheds due to high sediment yield. The purpose of this research is the marls classification of Isfahan province according to erodibility indices and their physical and chemical properties. In this regard, region marl units were identified and their sediment yield was measured using rainfall simulator. Then, based on erosion type, they were sampled and soil physical and chemical properties were analyzed. Cluster analysis statistical method was used to classify marl units. Statistical analysis was performed by three sets of data including chemical, physical and both chemical and physical accompanied by slope and measured sediment from six mmh-1 rainfall in each step of the analysis. Results showed that the most important similarity factors in marls are chemical properties and the effect of climate. According to information obtained from investigations, climate is the most effective factor of differences among marl units in this province. In addition to its direct impact on creation and evolution of marls, it affects on other parameters directly and indirectly and choosing either of these parameters is related to climate.

Landslides are the major causes of erosion and sediment yield in the sloping and mountainous basins. However, evidence suggests that the amount of sediment to the river of the mountainous regions in Ardabil province due to landslides is significant, but in quantitative terms it has not been provided the certain value based on scientific research for it. In this study, the subject was evaluated in the Balekhlou-Chay catchment of Ardabil province using data extracted from the aerial photographs, field investigations and the sediment discharge measured data at Pole-Almas hydrometric station. Sediment volume in the sediment measurement stations associated with the catchment was estimated by determining the relationship between flow rate and it′s corresponding sediment discharge. It was attempted to compare the estimated amount of sediment at different time periods with its amount in the periods of activity of landslides and to determine the possible effects of the landslides in increasing erosion and sediment yield in the catchment. The noted large landslides have caused a significant increase in the sediment load of the available rivers. The effects of these slides can be observed in the suspended load passing through Pol-e-Almas station. The mean of the suspended sediment concentration of Balekhlou-Chay catchment has been estimated about 46566.30 tons per year based on sediment discharge values from field data during 40 years (from 1972 to 2001), however the mean of the suspended sediment concentration is 30831 tons per year based on sediment discharge values from field data during 36 years, which means with the elimination of the data related to landslide years (from 1980 to 1983). In conclusion, according to the calculated sediment carried by the Balekhlou-Chay river after the occurrence of the Sarighaye and Ilanjigh landslides during the period of 4 years (from 1980 to 1983) has been increased rapidly.

Correct and consistent uses of natural resources preserve this valuable wealth. Using optimization knowledge can assist us to achieve this object. Thus, this study aims to compare linear programming as a classical method of optimization with genetic evolutionary algorithm for land use optimization of the Bayg watershed. Results showed that linear programming reduced dry farming acreage and increased the acreage of irrigated agriculture. After minimization, surface runoff and sediment yield declined by 1.16, 12.91 percent, respectively. Genetic algorithm led to an increase in rangeland, irrigated agriculture and horticulture acreages, while almond orchard and dry farming acreages were reduced. Furthermore, surface runoff and sediment yield declined by 13.95 and 31.99 percent, respectively. Linear programming acted stronger in satisfying the constraints, as compared with genetic algorithm. The constraint “total acreage” was satisfied by linear programming, while genetic algorithm could not meet this constraint. Sensitivity analysis of linear programming showed that the most critical factor in minimizing runoff and sediment yield function was the coefficient of dry farming with a reduced cost of 67.52. Results also established that the constraints “total acreage and minimum acreage of rangeland” with the shadow prices of 397.40 and 233.28, respectively had the highest negative impact on the optimal solution. Meanwhile, the constraints “maximum acreages of irrigated horticulture and almonds garden” with the shadow prices of -134.97 and -118.44, respectively had the highest positive impact on the optimal solution. As a general conclusion it can be stated that in land use optimization problems with a large number of constraints, genetic algorithm show poorer performance in satisfying constraints, as compared with linear programming.