فصلنامه پژوهش های فرسایش محیطی
سال هفتم شماره 3 (پیاپی 27، پاییز 1396)

Introduction Soil erosion and sediment production include fundamental limitations in the use of soil and water resources. The sediment yields watersheds in addition to the loss of soil fertility, causing water quality reduction. Therefore, evaluation processes that govern their behavior to better understand and assess the systems of watershed management practices are important. The role of soil erosion and sediment productuion in soil fertility decline and waste as well as in filling reservoirs dams is a global problem. This is due to the destruction of the environment and human factor on landuse cover. WEPP erosion model is a physical model that estimates the amount of erosion and loss of soil using the approach of local development assessment. WEPP model can assess the amount of runoff and erosion process in a watershed. Nearly 2 billion tons of resource soil is destroyed, and much damage equivalent to 18.5 × 1012 Rails enters the country of Iran. Therefore, to prevent this destruction of natural resources, suitable management for preventing erosion and sediment movement is needed. While erosion is a natural process, human activity is the cause of erosion. Also, erosion caused a devastating impact on the landscape and natural resource. These effects included decrease in the agricultural productivity resulting in ecological collapse. Water and wind erosion are the two primary causes of land degradation; both of them together are responsible for about 84% of the global extent of degraded land.
Methodology In order to achieve the purpose of the research, a case was studied and identified based on the WEPP and Hydro physical Models. In this study, to estimate soil erosion and sediment production, the WEPP and Hydro physical models were used. In the research, to prepare database for estimating soil erosion and sediment production, suitable map, topography map, slop, and land use were produced. In the second step, in the environment of GIS software, all the layers were corrected and analyzed. Many data were collected through field work. In this study, WEPP and Hydro physical models were utilized for estimating soil erosion and sediment production in the watershed of Chardavol in the northern Ilam province. In the WEPP model, for data collection, geomorphology methods were used to determine the work units. In WEPP Model, the type of data collection run in six classes was classification, which contained the files of soil, climate, management, slope, drainage, and tank. In the soil class, information such as texture, action exchange capacity, organic matter, some pebbles, and effective hydraulic flow was used. In file management, information such as the type of landuse cover, vegetation, soil and plant phonological characteristics were dominant. Klyghen sowftware was used to build the climate file. Information required in this file included daily rainfall and temperature. For the stream slope and the scope of slope, the software of geo-WEPP was used.
Results According to the results of weighting maps and the data about the potential of sedimentary basins, the basin A8, with a potential production of 13.76 tons of sediment per square hectar, was the highest rate of sedimentary and erosion. Also, the lowest sedimentary was located in the sub-basin A3 with a potential production of 2.64 tons of sediment per hectar. The highest erosion rates in the three sub-basins in the southeastern part of the basin Chardavol were located in this part of the basin due to slopes and high rainfall, low vegetation and poor pastures. The rate of erosion was very high due to natural and human destructive factors. These areas have the highest amount of sediment in the study area. In this study, the lowest rate of erosion in western and northern study areas is located in the areas covered with dense forest and semi-dense and high vegetation with protective programs.
Discussion and Conclusions The results of the study based on the WEPP model showed that the amounts of sediment in the three methods of domain, watershed and flow direction were 7.64, 6.01, and 11.87 ton/ha/year, respectively. According to the estimated results, the domain and flow direction methods with 7.64 and 11.87 ton/ha/year were in good agreement with the actual amount (10.5), and were suitable for the erosion and sediment estimation in Chardavol watershed. Also, the results obtained in the Hydro physical method indicated that the amount of sediment was 8.066 ton/ha/year (Table 1).

Introduction Soil erosion is one of the most important problems in the arid and semi-arid areas in Iran and the knowledge about its content has an important role on the management practices of soil conservation. Topography as one of the soil-making factors affects the physical properties of the soil through the aspect and the degree of the slope. The aspect of the slope changes the soil moisture, temperature, and the activity of the soil micro-organisms, causing changes in the soil organic matter at different slope degrees, and as a result, creating different soil qualities. Different slope degrees through transportation, the clay particles, and even the organic matter down to the low lands as well as the change in the soil bulk density may change the quality of the soil. In order to maximize the utilization of agricultural lands, to minimize the environmental degradation, and to prevent soil erosion, investigating the soil quality is essential. The aim of this study was to evaluate the amount of soil erosion and quality in different degrees of the southern and northern slopes in the catchment of Torogh dam located in the southwestern Mashhad.
Methodology To evaluate the soil erodibility index and quality, 40 soil samples were collected from 0-30 cm depth at the southern and northern slopes including less than 10%, 10-20%, 20-30% and more than 30% slope degrees in the catchment of Torogh dam located in the southwestern Mashhad. 5 samples were taken from each position and some soil properties, including the particle size distribution, the percentage of the soil organic matter, the mean weight diameter of aggregates, the water dispersible clay and silt contents, and the soil structural stability index (SI), were measured. The soil erodibility index was calculated based on five characteristics including sand, silt with fine sand, organic matter, soil structure class, and the infiltration rate class of the soil profile. In addition, the soil quality index, i.e. Integral Quality Index (IQI), was calculated according to the data set. To calculate the soil quality, the score of each property were determined based on the scoring functions and their weights calculated by dividing the communality value of each property to the total communality of all the properties in the JMP4 software. Then, the soil quality index (i.e. IQI) was calculated through multiplying the score and weight of the studied properties and their sum.
Results The results showed that the mean of the organic matter in the North aspect was significantly more than the South slop due to the coarse soil texture and the scarce cover crop in the South aspect. The weight diameter of the aggregates (MWD) in the northern aspect was significantly lower than the southern one because of the higher contents of the silt, fine sand, and the water dispersible clay and silt. Therefore, the low instability of the soil structure in the northern aspect was compared to the southern slope. Also, the MWD had a significant difference between the diverse degrees of the southern slope. In addition, the soil erodibility index in the northern aspect of the slope was significantly greater than that of the southern aspect due to more contents of the water dispersible clay and silt in the northern aspect compared to the southern one. The lowest value of the soil erodibility index was obtained at less than 10% of the North aspect that had a significant difference in relation to the other slope degrees. The difference of the soil erodibility index was not significant in different slope degrees of the South aspect. In addition, the quantitative value of the soil quality index in the northern slope was significantly more than that of the southern slope. Because of the optimal values of most soil properties in the North aspect, therefore, the soil quality in this aspect was higher than that of the South. There was no significant difference between the slope degrees in the South slope, but in the North aspect, the difference between various slope degrees of 20-30% was significant (P Discussion & Conclusions In the studied area, the annual precipitation is low, so that the plant residue and the organic matter are low, and as a result of this, the impact of the organic matter on soil erodibility was low. Therefore, other soil properties, i.e. the contents of silt, sand, clay, water dispersible clay and silt have important roles in controlling the soil erosion. In this research, the effect of the slope aspect on the soil quality was more than the respective degree, so that the soil erosion value in the North aspect was greater than that of the South one, and diverse slope degrees had no significant effects on the soil quality. With regard to the low content of the organic matter in this area, it is suggested that the soil management practices be performed to increase the soil organic matter, to decrease the soil erodibility, and to improve the soil quality.

Introduction The phenomena of erosion, sediment transport, and sedimentations have tremendously destructive effects on the environment and hydraulics structures. In general, the sediment transportation depends on river discharges, but the proposed equations inherited serious errors. The estimation of suspended sediment load (SSL) is one of the most important factors in river hydraulics, morphology and sediment hydraulic studies. An accurate estimation of suspended sediment loads (SSL) is crucial for the management and construction of the water resources projects. This factor also is the fundamental basis for the proper management planning of the soil and water resource in the watershed. The estimation of the total suspended load of the river with measured data in the hydrometric stations using the relation sediment rating curves are possible through the conventional methods. Accurate and reliable suspended sediment estimates are required in a variety of experimental and operational hydrological situations for scientific and/or river management purposes. Sediment ratings may, for example, be used to estimate the long-term rates of landscape denudation, to reflect the river morphological changes, to gauge the sensitivity of catchments for varying land-use practices, or to accomplish specific project applications, such as the estimation of the reservoir lifetimes, or the identification of the tolerable effluent discharge, and/or the water quality inputs, around the hydroelectric turbines. Suspended sediment loads (SSL) are often estimated through an empirical relation between suspended sediment load (L) and streamflow (S). This relation is usually defined as a power function, L = aSb, and is referred to as a suspended sediment rating curve. This function can be formulated as either a linear or non-linear model to find the solution of the rating curve parameters (a and b). Formulation of the power function as a linear model requires a logarithmic transformation to linearize the function and a subsequent correction for the transformation bias. Rating-curve parameter estimates for both the bias-corrected, transformed-linear or non-linear models can be obtained through the method of least squares.
Methodology In this paper, the rate of the sediment load in Zaremrood river was estimated using USBR, Polyline USBR, moderate categories curve, seasonal rating curve and FAO models. In addition, during 30 days (60 samples), the suspended load sampling was conducted, then, the selected model was evaluated using a direct sampling of the suspended load. To evaluate the suspended sediment loads and an optimized model on them, in this research, the data were collected from the Iranian water resources management company and Mazandaran regional water authority. The data analysis first included the control and adequacy testing, detection of outliers and normality test. Also, to ensure the homogeneity of the data, the homogeneity test was performed using Kolmogorov-Smirnov test in the SPSS software. Finally, the five models were derived using the corresponding data of flow (Qw) and sediment discharge (Qs).
Results The results of this study showed that the moderate categories curve model had the lowest RME rate (173/65) and the highest coefficients of determination (96%) (table 1), and as a result, this model was selected as the best model to estimate the suspended load of Zaremrood river (Figure 1).
Also, with regard to the linear rating curve model having a maximum deviation from the observational data, it was recommended to apply this model to estimate the total suspended load, through the methods with the latest error to estimate the river sediment load in this case study. Finally, the results showed that the highest amount of suspended sediment load (SSL) in the spring season is due to the land use type in this season and also the high intensity of rainfall in this watershed.
Discussion & Conclusions Correct estimation of sediment discharge and consequently, sediment load is an essential component in river management. The key objective of this study was to determine the best model to estimate the suspended sediment load (SSL) in Zaremrood river, Mazandaran province. Flow and sediment discharge data were collected and used to establish a sediment rating curve models. Then, five rating curve models including Single Linear Rating Curve Model, Multiline Rating Curve Model, Moderate Categories Curve Model, Seasonal Rating Curve Model and FAO Model were conducted. Suspended sediment was sampled using a direct method and analysis in the laboratory to be evaluated through statistical evaluation indices. As a result, the moderate categories curve model was selected as the most suitable and best model for estimating the suspended sediment load in Zaremrood river. Zaremrood watershed was the most important in sediment production located at the upper Sari plain where agricultural land and rice fields were present. So, by considering the results of this research and the management of the sediment produced in this watershed, it is possible to prevent the damages caused by the sedimentation of the Zaremrood watershed. To conserve the water and soil in the watershed, a similar research is necessary. The selected model can estimate the total sediment load used in the water and soil resources management plan, including the identification of sources of sediment production, the determination of the areas with high potential sedimentation in order to reduce erosion in the studied area.

Introduction The study of the behavior of rivers in the arid and dry areas is one of the most important tasks in the country. Because the area has increased the effects of drought due to the sensitivity of the area and rainfall shortage, it causes changes in the flow and sediment regime, water resources, agriculture, and so on. Since plants react more precisely to the specific climate changes of the environmental water changes, historically, they have been regarded as important indicators to identify the type of climate and its changes. In the recent years, as the satellite images are regularly and accurately separated from the surface, the growing role of vegetation cover associated with drought conditions is more assumed. The NDVI index was first introduced in 1973 and is the most comprehensive indicator ever used in many studies. This index can well reflect changes in the areas with more rangeland coverage. Also, given that the water has a lower NDVI than other surface coatings, therefore, the areas that are covered with the water can be detected by the changes in their NDVI values before and after the flood.
Methodology First, in order to identify the trends and droughts in the region, the hydrometric and climatic data (1955-2011) were analyzed. Based on the annual flow diagram of the Qasr-e-Shirin station, the diagrams of rainfall and precipitation were identified using the 45-year moving average index in the river to identify the maximum points of the land as well as the wet points, and subsequently, the data from the satellite imagery of 1987 (first year of landing), the maximum drought of 2005, the maximum wetland of 2003, and those of 2015 were used to collect the satellite images from the hydrometric chart. Subsequently, multispectral images were taken to produce a green index. Using the controlled classification method and the statistical parameter, the least space was used to classify the images. Finally, using the observations, measurements and field observations, with the accuracy of 90 meters at 5 points around the river, the findings of the extracted images were corrected and controlled.
Results An investigation of the hydrologic regime of the basin in the drought and wet periods indicates changes in the river flow and the impact of the climate and environmental factors on it. Despite the continuity of the river flow and the same rainfall (264 mm) during the two periods, the average of the mean and the basin water levels decreased sharply and the flow of the river at the location of the river divisions has changed from a volatile to a seasonal, which has led to the blockage of the river by the sediment yields from them. Using the NDVI index, land use has been classified into cropping water, rain, and pastures. A comparison of the classified images shows that 70% of the vegetation degradation is related to the rangelands and marginal lands of the river and river basins, which are natural in the region. The remaining 30 percent of the vegetation degradation is related to aquaculture and dry-land farming. The research findings from the discovery of changes through the illustrations reveal the role of the climate change in the Alvand river basin. 10188 ha of the damaged land is due to the drought. In other areas, and especially around the river, the changes in the coverage elucidate a negative trend. In the rivers of Khosravi plain, 8001 ha of the pastures around the river is destroyed.
Discussion & Conclusions The results of this study showed that the vegetation level in the region has changed during the research period throughout the studied years. The NDVI index showed a desirable correlation with the moving average drought index Therefore, it is suggested that the method described, that is, the combination of the climatic and hydrological elements and the vegetation indices derived from the satellite images, which have been investigated and proved by various researchers, have been repeatedly correlated with the drought to investigate it by the vegetation index in the rangeland and semi-arid areas of the country. The results of this study showed that the NDVI index could be a favorable alternative to moving average, and in the hydrological drought studies, the semi-arid and rangeland areas can be trusted.

Introduction Forest roads are among the largest sediment transport sources to drainage network. So, estimating the sediments of the road network is an important factor in the evaluation of the impact of the road construction. One of the biggest problems caused by the road construction in the forest is the increase in various forms of erosion, such as Gully erosion and masses movements around the roads. The main cause of this process is the destruction of vegetation, soil destruction, increasing runoff rate and unstable slopes. Therefore, in designing forest roads, not only the costs, but also the proper management of the water and soil should be considered. Research results have shown that the forest roads produce a high volume of forest land sediments. An optimal management of forest areas requires having a forest road network with a proper distribution on the forest. Hence, it is one of the most important cost factors for the forest management. Forest roads differ from rural roads and highways. They have low traffic and heavy vehicles. In the areas where these roads are built, there are usually different types of erosion. Therefore, the ability to predict erosion correctly can reduce their negative sedimentation effects. Accordingly, the purpose of this study is to estimate the sediment and erosion of different parts of Shabankar forest road in Zagros region, and to determine the final rate of the road sediment yield, as well as to identify the high potential deposits of the sediments by SEDMODEL.
Methodology In this study, Road Sediment Delivery Model (SEDMODL) was used to estimate the erosion of a paved forest road in 24 km northwest of the Rawansar in Kermanshah province. The road was divided into 5 parts and the factors such as geology, elevation and the cover of cut slope, road traffic, the distance from the streams and rainfall were estimated that were the effective parameters of the model. To estimate the amount of the sediment production, after an evaluation of the factors of the model, the erosion and sediment delivery amount to the streams were estimated in 5 sections of the road. In order to implement the model, the geological maps, topography, slope, road and waterway networks with a scale of 1: 50,000 were produced in the ARC GIS environment.
Results The results showed that the fifth part of the road has more sediments delivery to the waterways among the other sectors. According to results, the total sediment production is 11.92 tons and the sediment delivery to the waterways is 2.06 tons while the area of this road makes about 0.03 percent of the total watershed. In addition, according to the Pearson correlation results, the height of the cut slope and the longitudinal slope of the road were recognized as the main factors affecting the erosion of the road. In this area, the factors such as the length of the road, longitudinal slope, cut slopes and vegetation, and sediment delivery factor were different in various parts of the road leading to differences in erosion and sediment production. The third part of the road, due to having the highest amount of road length and wall height and the minimum coverage, has the highest amount of erosion. After that, the highest erosion belongs to the fourth part, while the length of this sector of the road is less than the first and second parts, due to the high height of the excavation walls in the fourth part, as well as the absence of the wall coverings relevant to the parts one and two. According to Table 10, only the second and fifth parts, due to the intervals of less than 60 meters from the closest waterway, were involved in the delivery of the sediment to the currents of the basin. The high erosion rate in the fifth part is greater than the third and fourth parts due to the minimum level of road surface covered by the fifth part compared to that of the second.
Discussion & Conclusions The construction of roads in the forest areas is one of the factors affecting erosion and sediment production. As the results of this study showed, one of the capabilities of the SEDMODL model is identifying the erosion-sensitive points. According to the results of this research and other similar studies, it is necessary for the erosion control activites to be done in the upstream of the roads having high erosion potential due to the steeper slope to the lower parts, as well as in downstream units due to being close to the waterways and having sediment transfer factor to reduce erosion per unit area of the road.

The land use change of watersheds has entailed many impacts on the processes of erosion and sediment yield over the time, and has caused the loss of soil quality and fertility. On the other hand, an increase in the sediment generation and its accumulation would reduce the capacity of the reservoirs. In this respect, the purpose of this study was to evaluate the effects of the implementation of land-use change scenarios on runoff and suspended sediment from the outlet of the watershed. The simulation of runoff and sediment was investigated according to the defined scenario for the Dinevar watershed with a focus on SWAT model based on the statistical indicators. The results of NS and R2 indicators above 50 and 60 percent for both calibration and validation steps, respectively, imply the model efficiency regarding the hydrological data simulating in the watershed. The results of the coefficient of determination and Nash-Sutcliffe were 0.55 and 0.6, respectively, in the calibration, and were 0.58 and 0.62, respectively in the validation, implying the model efficiency in the watershed. The suggested scenario was applied to improve the lands. This means that the bare land, which increased during this period, was planted by the evergreens and deciduous. The results of this scenario showed that the implementation of this land use change in the scenario reduced the suspended sediment and runoff into 52 and 32 percent, respectively.
INTRODUCTIONLand use with inappropriate vegetation patterns can cause severe water, soil and food losses and land degradation. Land use change is a large and fast process and assessing such changes and their impacts on the development, and management of the water resources in the future is very important. In order to better understand the process and the fate of the pollution and also the hydrologic regime, the SWAT model was used to simulate the runoff and suspended sediment under the influence of land use change over time during a given period based on the hypothetical scenarios in Dinewar watershed.
METHODOLOGYDinewar watershed with 214577 hectares is located in the northeast of Kermanshah. The average of the annual precipitation of this area during a 25-year period is 549.1 mm. The types of visible erosion in this watershed include surface erosion, rill erosion, water way erosion, gully and bank river erosion. The existing land use in the watershed included 34% agriculture, 1% garden, 10% free, 52% rangeland, 1% stone, 2.5% roads and residential areas. One of the models used to investigate the effects of land use change and climate change on runoff and sediment in the watershed scale was SWAT model. In the SWAT model, there is a possibility to assess the effects of different natural or managerial changes on runoff, sediment, nutrients and chemical balance in the watershed. With regard to runoff and sediment simulation, the data pertained to the synoptic station of Kermanshah and the meteorology stations of Sahne, Bisotun, Sonqor and Hasan Abad Sofla were utilized. Also, with regard to calibration, the validation and uncertainty analysis of results, i.e. the SUFI-2, was applied. To evaluate the simulated results, the performance criteria of the model including "P factor" and "R factor" as well as the two parameters of determination coefficient (R2) and Nash-Sutcliff were used.The new scenario was defined based on the previous and current proceeding land uses and the results of the simulation were compared to the current situation related to 2010.
RESULTS Flood and suspended sediment data of 1998 to 2006 were used for calibration, and 2007-2010 were used for validation. The results for flow data showed that determination coefficients of both the calibration and validation steps were higher than 0.77, and the Nash-Sutcliff coefficient was about 0.6 and higher. The results of the calibration step for sedimentation data were also equal to 0.55 in the determination coefficient and 0.66 in the Nash-Sutcliff coefficient, and the results of the statistical indices during the validation period increased 0.1 percent. The P factor is closer to the one that implied a higher percentage of observation data in the uncertainty band and the R factor is closer to zero that implied better simulation at this step. In the new scenario, degraded and no vegetation areas were replaced by the evergreen and shrubbery trees with moderate density, and the simulations were carried out based on a new scenario. The land use map for 2010 was taken as a control map. The results of the simulation based on the new land use scenario showed that the daily average runoff is 4.86 m3 / s (32.72%), and the maximum discharge rate during the studied period decreased to 74.13 m3/s (36/69 %). The proposed scenario can also reduce the daily average suspended sediment in the study period by 252.98 mg / s (52.83%) and decrease the maximum suspended sediment rate by 9050 mg / sec (71.54%).
DISCUSSION and CONLLUSIONS In the defined scenario in this study, a change was made whose implementation is possible in reality. Many changes, such as reducing the area under the cultivation, residential and industrial areas, are not applicable in most of the watersheds. The new scenario, which aims at improving the vegetation cover and soil conservation, reduces sediment yield from the watershed, and this effect is especially noticeable at the peak of the simulation curves, and little effect is observed in places where the amount of sediment is lower. In addition, the results of the statistical indicators implied the high performance of the SWAT model in simulating hydrological processes which demonstrates the impact of various management measures and land use on these processes in the studied watershed.