sediment yield

The continuation and stability of the river catchments depends on the passage of water and the transfer of sediment. Just as river flow information is vital for many practical applications such as water allocation, long-term planning, catchment management operations, flood forecasting, design of hydraulic structures, etc., amount of sediment yield in rivers is important from a variety of aspects such as river morphology, engineering designs to river water resource, reservoir dams, river organization to Inhibition of erosion and floods, irrigation networks, etc. are important. Proper and sustainable use of water and soil resources within the river catchments requires awareness of the spatial variations of hydrogeomorphic elements (water discharge, sediment discharge) and the determinants of these variations. Various studies refer to the key role of forests in the water cycle, soil protection and habitat protection, and show that increasing or decreasing forest cover has had an effective role in the hydrogeomorphic regime of the rivers. Due to the importance of interdisciplinary studies and understanding of interactions between different biological and non-biological components of river catchments in regards to sustainability and continuity of natural and human environment, the present study intends to be aware of the quality and quantity of relationships between forest cover and discharge/sediment yield in the Talesh catchments, NW. Iran.

This study was based on correlation and regression analysis of the ecohydrological relationships. The research statistical population included the Talesh region and the research sample population included 12 important catchments in this region. The data used included monthly water discharge and sediment yield data of hydrometric stations on the one hand and the digital satellite images included the Aster digital elevation model (DEM) and Landsat 8 image on the other hand. Data analysis tools include geographical information system (GIS), Google Earth, SPSS and Excel. The steps of conducting the research were such that: firstly, the hydrogeomorphic variables including the mean, maximum and minimum rates of water discharge and sediment yield (S.Y), were calculated for 2020yr. Then, the 12 watersheds were extracted based on the position of the hydrometric stations from the DEM with a spatial resolution of 30 meters. The next step was to extract the forest cover from the Landsat 8 image, which was obtained on June 3, 2022. In this regard, the satellite image classification in the form of two class of forest and non- forest was through the maximum likelihood algorithm. Satellite images were classified using 300 training points. Finally, the correlation test between the forest cover and water discharge and sediment yield was performed in the SPSS software. The significant level of correlation relationships was ≤0.05.

The results of the correlation test showed that there was a significant relationship between the percentage of forest cover and the water discharge in the catchments. The correlation coefficients (R) were -0.58, 0.58, -0.46, respectively for mean, maximum and minimum discharges, indicating that definite and positive role of the forest in preventing rapid and erosive runoff. In contrast, the relationship between the percentage of forest cover and S.Y in the studied catchments was not significant and the correlation coefficients for mean, maximum and minimum S.Y are at -0.07, -0.05, -0.06 respectively, which is indicative of the weak correlational relationship between the two variables. However, the separation of catchments as large catchments and small led to improvement of correlation relationship between forest cover and S.Y, despite being insignificant, so that correlation coefficients in small basins for mean, maximum and minimal S.Y, respectively of -0.656, -0.60, 0.339, respectively. Given the significant relationships, it was possible to provide regression prediction equations for monthly mean and maximum discharge based on the percentage forest cover in the catchments. The insignificant relationships between forest cover and the sediment load can be explained by complex nature of the sediment load transfer, especially storage and re-movement of sediment load, making it difficult to establish significant relationships between the sediment yield (S.Y) and the environmental variables affecting it. On the other hand, the relationship between vegetation and the S.Y in catchments is usually complex and nonlinear, and therefore the use of nonlinear relationships may make the relationship more complete and obvious. Finally, the multiplication of the factors involved in the production and transferring of sediment load makes it difficult to model and predict the spatial variations of sediment load.

The present study attempted to provide a quantitative analysis of the spatial relationship between the forest cover and the rates of water discharge and sediment yield (S.Y) in the Talesh catchments by adopting an interdisciplinary approach. The results of correlation analysis show that the presence of significant and inverse relationships between the percentage of forest cover and water discharge of the catchments reflects the distinct role of the forest in reducing runoff and the incidence of dangerous floods in the Talesh catchments. In contrast, the relationships between forest cover and S.Y in the studied catchments are not significant. This conclusion shows that we are not able to provide a prediction model of S.Y variations based on the percentage of forest cover in the catchments, but the reverse relationship between the percentage of forest cover and the S.Y of the catchments implies the protective role of the forest in adjusting the process of precipitation, runoff- erosion and enhancing of the environmental quality in catchment systems. First of all, it should be noted that the forest cover variable is considered as a modulator variable or interface between the inlets and outputs of the catchments system, so it is likely that the direct role of the forest on runoff and sedimentation couldn’t be easily grasped by statistics analysis. In this context, there are various natural and human factors that may play a more effective role in the S.Y variation of the catchments than the factor of forest cover. Increasing of correlation coefficients (R) between the percentage of forest cover and S.Y in small catchments indicate that these catchments are an ideal scale for identifying controlling factors of sediment yield.

The phenomenon of soil erosion in Iran is one of the serious problems in the fields of agriculture and natural resources, the effects of which appear in various forms and the result of which is the creation of direct and indirect costs for the country. Most of the soil erosion researches in Iran have dealt with the technical investigation of this phenomenon, and the lack of scientific information on the economic consequences of soil erosion is quite noticeable. In this study, the direct economic cost of soil erosion using the Nutrient Replacement Cost Method (NRCM) and the analysis of nitrogen, phosphorus and potassium (NPK) losses in sediments deposited behind check-dams in the Nehzatabad watershed with an area of 5570 hectares in Kohgiluyeh County was estimated. The results showed that in the studied time period (2018-2019), a total of 378.42 tons of sediment was deposited behind the 11 study Check-dams in the Nehzatabad watershed, and these sediments contain 0.03, 0.53 and 5 tons of nitrogen, phosphorus, and potassium, respectively. Taking into account the price of a 50 kg bag of triple superphosphate, urea and potassium sulfate 5500, 1500 and 6250 thousand rials respectively (government rate, year 1402), the cost of buying the chemical fertilizer necessary to maintain and restore soil productivity in the area the of Nehzatabad watershed is equivalent to 1620417.5 thousand rials. By calculating the amount of soil erosion through the volume of sediments deposited behind the Check-dams, it was also determined that the total direct cost of soil erosion losses in average, maximum and minimum NPK losses is 5328413.39, 26693396.77 and 52463.83 thousand rials, respectively. Of course, this amount of cost is based on soil erosion calculated from 0.001 to 1.08 tons per hectare per year in the upstream basins of the Check-dams built in the Nehzatabad watershed, which is compared to the average soil erosion rate in Iran, which in most the mentioned scientific documents of about 16 tons per hectare per year is a very small number.

Water soil erosion is one of the most common types of soil degradation, which has very destructive effects on the environment and human life. This phenomenon reduces the quality of the soil in the site and may cause sedimentation problems in the downstream or reservoirs. The severity of soil erosion is usually estimated using different models. The Revised Universal Soil Loss Equation (RUSLE) is the most common soil erosion model due to its simplicity, less need for data, and adaptability to different environmental conditions. Studies around the world show that this experimental model is very efficient for estimating annual soil losses at the watershed scale. Sediment Delivery Ratio (SDR) is used to estimate the rate of sediment yield based on the soil erosion rate obtained from RUSLE. Dizgaran watershed, located on the border of Kurdistan and Kermanshah provinces, western Iran, is one of the mountainous areas of the country and has rough topography, vegetation cover, and weather conditions that make it prone to severe soil erosion. This research aims to estimate the annual average rate of soil erosion and sediment yield in the Dizgaran watershed and also to investigate the correlation between different RUSLE factors and the erosion rate to better understand the effect of each factor on the erosion rate. In this research, the rainfall-runoff erosivity (R) factor was created using the WTLS linear regression method based on the Digital Elevation Model (DEM). According to the results of the RUSLE/SDR model, the average rate of soil erosion was 45.09 tons per hectare per year and the average rate of sediment production was 19.42 tons per hectare per year in the watershed. 1.3% and 4.66% of the area of the area were placed in very low and low erosion classes, respectively. 16.18% of the area was in the moderate erosion class, and 36.18% and 41.68% of the area were in the severe and very severe erosion classes, respectively. Also, the results indicate that the two factors of topography (with a correlation coefficient of 79%) and cover and management (with a correlation coefficient of 47%) have the highest correlation with the soil erosion rate, respectively, and therefore play the most important role in changing the erosion rate in the watershed. The results of this research show that this watershed is involved in severe erosion, as can be seen from the presence of different forms of soil erosion in the field investigation. The results of this research can be used to carry out management measures to reduce the rate of soil erosion in the points with a high rate of erosion and to protect and manage the Dizgaran watershed.

Soil erosion is one of the environmental problems that pose a threat to natural resources, agriculture and the environment. Quantitative assessment of erosion and sediment using erosion and sediment estimation models is one of the solutions through which erosion and sediment can be controlled to some extent and its amount minimized. In the present study, the aim is to predict the annual soil loss potential and sediment load. To predict these cases, the Revised Universal Soil Loss Equation (RUSLE) has been used in the context of the GIS. The amount of annual rainfall erosivity factor was calculated using 22-year monthly rainfall data at 18 stations around the basin. Its spatial variations were then estimated using conventional kriging. Soil erodibility index was obtained from soil map, which was prepared using field survey and remote sensing data. The topographic factor was extracted from the digital elevation model with a spatial resolution of 30 m. The annual vegetation factor was also estimated from remote sensing data. Since soil protection operations are insignificant in the study basin, the amount of soil protection factor was considered 1 throughout Basin. In this study, the mean values ​​of R, K, LS, C and P factors were equal to 264 MJ mm ha-1h-1y-1, 0.35 Mg ha h ha-1MJ-1mm-1, 2.00, 0.51 and 1. The average annual sediment yield in the study basin was estimated to be 16.137 th-1y-1, which was close to the value obtained from the sediment measuring station of the basin outlet (16.58 tons per hectare per year). The results of the erosion map in this model show that most erosion is located in the western and middle part of the basin. Because this region is composed of unstable formations and prone to erosion. The steep slope of the region, in addition to rainfall and land use change in this area, has faced many areas with soil erosion crisis. According to the results, the largest area of ​​the basin is related to the very low, low and medium erosion class, which is generally distributed throughout the basin, and the lowest basin area is in the high to very high erosion class (20%). Due to the fact that 20% of the study basin is in the high to very high erosion class, the need for protection measures in these areas is mandatory. The results of this study also showed that LS factor with a correlation coefficient of 0.81 had the greatest effect on estimating annual soil erosion by RUSLE model. This study proved the effectiveness of RS and GIS for quantitative estimation of soil erosion amounts, sediment yield and also erosion management.

Today, soil erosion is one of the major problems of watersheds and agricultural areas and natural resources, which causes land degradation and decreases soil fertility. Therefore, the purpose of this study is to investigate the relationship between vegetation and geomorphic indices with the values of erosion and sediment in the watershed of Koot-e-Tootraghi basin, which was done by using the capabilities of GIS to extract the geomorphic characteristics of the basin. For this purpose, erosion and sedimentation rates were calculated using the modified Psiac model (MPSIAC). Also, in order to extract physiographic and geomorphic features including: TWI topographic moisture layers, SPI current strength, SLOPE slope, domain curvature, profile curvature and sub-basin plan curvature, from the height digital model with a spatial accuracy of 30 meters, as well as other layers used in the MPSIAC model including1:25000 topographic maps, 1:100000 geological maps were used. According to the box diagram, the indices related to curvature have little changes in the studied area. Also, the indices related to curvature have little changes in the studied area. Based on the results, there is a positive and significant correlation of 0.47 (p-value less than 0.01) between the standard index of vegetation cover and topographic humidity index. In addition, there is a significant correlation (0.63) between waterway power index and slope. It was also found that the relationship between the slope and the normalized index of vegetation has an inverse and significant relationship (0.48) (p-value less than 0.01.).

Today, the increasing population and, consequently, the demand for agricultural products have caused the natural cover of land, especially forests and pastures to be destroyed by humans at an alarming rate to become agricultural land; even in many areas due to lack of water and nutrients, vegetation growth is limited. Declining vegetation worldwide due to human activities such as overgrazing and deforestation reduces permeability and consequently increases runoff and can reduce soil particle adhesion and predisposes fertile soil particles to erosion. Soil erosion in managed ecosystems such as crops, pastures, or forests, as well as in natural ecosystems leads to extensive damage. It also reduces the infiltration capacity due to runoff and reduces soil organic matter and thus valuable soil nutrients. At the same time, it significantly reduces the diversity of plant and animal species. To this end, controlling soil erosion is one of the most important goals in water conservation and management programs. Vegetation can be a very important tool to control water erosion and regenerate the ecosystem. Vegetation reduces the shear stress by increasing the roughness and decreasing the water flow velocity, and the hydraulic resistance created by the vegetation causes the absorption and deposition of suspended sediments. Vegetation and its associated factors on a long-term scale also play an important role in modifying the hydrological properties and soil erodibility and sediment load. The role of vegetation in reducing runoff and soil erosion in different studies has been proven. However, the effects of different vegetation compositions have not been studied extensively in runoff and soil erosion control. Accordingly, the present study was planned to investigate the effect of different compositions of graminea and bushes with different coverage percentages on runoff and sediment components.  

The study area is part of the natural rangelands located in the surroundings of the University of Mohaghegh Ardabili, Ardabil, NW of Iran. A total of nine treatments from different vegetation compositions including low-height graminea predominance (T1), the composition of dense bushes with graminea (T2), bushes with low-height and medium-distribution (T3), sparse bushes mostly with low and medium height (T4), the composition of sparse bushes with graminea (T5), dense bushes in upper parts (T6), low-height bushes with very low distribution (T7), dense bushes with almost uniform distribution (T8), and no vegetation cover (control) (T9) were selected. In addition, the effect of different percentages (zero, <40, and 40-60) of vegetation on changes in runoff and sediment components was investigated. It should be noted that the vegetation in the control plots was removed at the soil surface in the desired plots as much as possible. Considering that, 27 field plots surrounded by galvanized sheets with an area of 2 m2 with a slope of 12-15% were installed. Study treatments with three replications were designed in a completely randomized block with help of field plots with dimensions of 2*1 m and an approximate slope of 12-15%. This study was performed using a rainfall simulator with an intensity of 32 mm h-1 and a duration of 18 min. The plots were placed in a rectangular in the direction of the slope, using 15 cm high metal sheets, five cm of which were sunk into the soil so that the generated runoff did not seep out of the plots. Totally, five components including time to runoff, runoff volume, runoff coefficient, soil loss, and sediment concentration were measured for each plot.

 

The results showed that the effect of different vegetation compositions on runoff and sediment components was significant (p-value <0.0001). The maximum time to runoff (1388.33 seconds) in treatment T4 and the minimum runoff (0.41 L) and runoff coefficient (2.14%) in treatment T2, respectively with +98, -82, and -82 % change compared to the control treatment has been obtained. In addition, the minimum soil loss was equal to 1.30 g in treatment T2 and the minimum sediment concentration was equal to 6 g l-1 in treatment T8 with -86 and -69% change compared to the control treatment, respectively. Statistical analysis of the effect of different vegetation percent also showed that there was a significant difference between the mean time to runoff and sediment concentration (p-value<0.001) and a non-significant difference between the mean runoff amount and coefficient (p- value<0.73), and soil loss (p-value<0.15). In general, treatments with less than 40% vegetation were more effective in controlling runoff components and treatments with vegetation between 40 to 60% were more effective in controlling sediment components.

The runoff threshold in different compositions and percentages of vegetation has a significant difference compared to the control treatment. Vegetation in both groups of <40 and 40-60% by delaying the formation of runoff has increased water permeability in the soil. Low-height graminea predominance (T1) treatment, the composition of dense bushes with graminea (T2), bushes with low-height and medium-distribution (T3), and sparse bushes mostly with low and medium height (T4) had the maximum effects (more than 80%) in increasing time to runoff. Although the treatment of the composition of sparse bushes with graminea (T5) was not effective in increasing the runoff threshold and reducing the amount and coefficient of runoff, it reduced the soil loss and sediment concentration by 21 and 57%, respectively, compared to the control treatment. Therefore, it can be concluded that if this type of erosion management strategy is adopted, this type of composition can also be considered. While it is not a suitable management option for runoff and flood control, treatments T4, T3, T2, and T1 should be used effectively. In addition, treatments with <40% vegetation cover had better performance compared to treatments with 40-60% vegetation in improving runoff components; nevertheless, 40-60% of vegetation with a slight difference has played a better role in improving erosion and sediment components. Previous research has confirmed that soil loss processes due to water erosion are closely related to the runoff process. Compared to runoff reduction, vegetation treatments have provided better benefits in reducing erosion and sedimentation. For future studies, the morphological effects of vegetation types on the hydrological and hydraulic properties of degraded soils could be investigated.

Ecological indicators have become important tools for evaluating and monitoring natural resources. Understanding the relationship between biological activities and ecological interactions is essential to their structure. On the other hand, human activities have significant effects on landscape evolution through changes in sediment production, transport, and storage. Therefore, this issue should be considered in the comprehensive management of different watersheds and ecosystems. Accordingly, the present study was conducted to evaluate the spatial heterogeneity of the hydro-sedimentologic disturbance index (HSDI) in the watershed located in the central part of Ardabil province. For this purpose, sediment transport (ST), hydrological stress (HS), recharge potential of groundwater (Rec), and soil erosion potential (SEP) were first calculated for 27 different sub-watersheds. Then, these factors were weighted using the Shannon entropy method. The hydro-sedimentologic disturbance index (HSDI) was calculated and zoned using the weighted average. The results showed that the mean, maximum and minimum values of the HSDI index in the Samian watershed were 10.17, 45.67, and 0.20, respectively. In addition, 87.67, 5.33, 5.32, and 1.68% of the watershed area were classified into very low, low, medium, and high levels of disturbances, respectively. Sub-watershed 19 located in the northern part, and sub-watersheds 20 and 21 located in the central part of the Samian watershed have the most disturbances, so they are prioritized for management actions. The present research framework can be used as a potential tool to support decisions that should focus on improving natural resource management.

The knowledge about spatial relationships of vegetation with sediment yield (S.Y) in watersheds is essential for optimal controlling and managing of water and soil resources. The purpose of this study was to recognize and determine the relationship between vegetation cover and annual S.Y of Sabalan catchments, N.W Iran. In this regard, the possibility of presentation of regional S.Y estimation models based on correlation and regression analysis were considered. Independent variables include average, minimum and maximum NDVI (Normalized Differential Vegetation Index), extracted through the processing of Landsa.t 8 satellite imagery in the ENVI environment. The dependent variable, which was the annual S.Y, was obtained through calculations on sediment load data of 10 sample hydrometric stations. Results of correlation test showed that there was a strong and significant relationship between the average NDVI and the annual S.Y in the catchments (r = -0/758). This inverse relationship emphasizes the importance and apparent role of vegetation in reducing sediment production and transporting in the region. Moreover, the results of regression tests showed that is possible to present the regional estimation models regards to annual S.Y by fitting linear, quadratic and power functions. In this regard, the quadratic model has the highest performance and explain 75% of the annual S.Y variance. The linear relationship was also able to explain 57% of the annual sedimentary variance.

Erosion and sedimentation in watersheds has caused many problems in healthy and sustainable use of water and soil resources, and is considered as one of the major threats to global economic and environmental sustainability. The increase of sediment yield in watersheds has consequences such as dam filling, river diversion, conductivity capacity reduction of waterways and water facilities, and changes water quality for drinking and agriculture. So, spatial modeling and prediction of sediment yield in watersheds is very important, especially in arid and semiarid environments. In this regard, we should consider the whole process of erosion (destruction, transport and deposition), so that the relationship between inputs and outputs of the system are understood well. The Systematic view of geomorphology on the issue of erosion and sediment yield can be very effective and useful, considering the relationship between forms, materials and processes in the context of landform components. Recognizing the different processes of erosion and sediment production in the range of landform components can provide a more comprehensive and practical view of these processes in watersheds. Given the importance of the issue and the need to use digital elevation models in order to model the sediment yield variations, which have been recently considered, this study intends to analyze the relationship between the Landform components distribution and sediment yield in the Qarasu watershed, N.W. Iran. 

We use extensive and integrated statistical analysis of non-parametric (χ2) and parametric (regression) methods to understand the relationships between sediment yield (S.Y) variation (dependent variable) and distribution of components or classes of landforms (independent variable). 19 sub-watersheds, which have sufficient and reliable data of sediment yield (ton/y), were selected for analysis. As catchment area acts as a misleading variable in the  relationships between sediment yield and physiographic variables, a specific sediment yield (S.S.Y) ​​ (ton/km2/y) was used as a dependent variable. Also, an independent variable (landform components) was extracted of digital elevation model (DEM) with a resolution of 30 m. 6 landform classes, including 1- ridge 2- upperslope 3- midslope 4- toeslope 5- flat 6- valley, were delineated in the geographic information system (GIS) environment. Then, the percentage area of the landform classes was calulated as an independent variable. In order to perform the nonparametric test, it was necessary to convert the variables from quantitative to categorical and qualitative form. Classification of S.S.Y was done in 2 categories (low, high) and 3 categories (low, medium, high). Also, the classification (categorization) was done for the independent variable. These transformations and statistical tests were performed in the SPSS environment. The significance level of qualitative and quantitative tests were ≤ 0.05. It should be noted that the classes can be assumed to be both nominal and ordinal, ie low (1), medium (2) and high (3). Therefore, statistics related to the crosstabs can be obtained for both nominal and ordinal scales, indicating the quality and quantity of the relationships. On the other hand, the correlation test can be done in two ways, Pearson and Spearman.

In the first step, results of the non-parametric analysis showed that there are significant relationships between the distribution of S.S.Y classes and the Landform components classes expect 2 landforms: valley and ridge. meanwhile, the importance and certainty of the relationship between midslope and S.S.Y was determined in respect to repetition of significant relations during three χ2 tests. In the next step, the results of Pearson correlation analysis showed the positive correlation between ridge, midslope, valley landforms and S.S.Y. On one hand, and the negative correlation between upperslope, lowerslope and flat ladforms and S.S.Y on the other hand. The highest and lowest correlation coefficients were observed in midslope (R = 0.4) and upperslope (R = -0.03) components, respectively. The Results of the latest test, the Spearman correlation test, were indicative of similarities with the χ2 test, showing the significant relationships between flat, toeslope, midslope landforms and S.S.Y. Although more contribution of the midslope in sub-watersheds area and higher difference among sub-watersheds in terms of midslope contribution influence its relations with S.S.Y,("but" not needed) close and direct relationship between the midslope area and S.S.Y is attributed to high sediment supply and the occurence of dynamic sediment transport within this landform component.

Erosion and sediment yield (S.Y) within watersheds due to their extensive environmental dimensions as well as the complexity of the erosion process (destruction, transpotation and sedimentation) are the focus of systematic approach of geomorphology to provide useful and comprehensive knowledge of the inputs and outputs of the watershed system. Dividing the catchments into landform components and establishing a relationship between their distribution and S.Y of the catchments can be a key solution in this regard. In this research, applying the approach through both parametric (Regression) and non-parametric (Croostabs) statistical analyzes showed that important information about the relationships between landforms and S.Y can be acquireed at synthetic statistical method. Although the relationship between the independent and dependent variables in the qualitative test had superiority to the quantitative test in terms of the significance of the relationship, the type and strength of the relationship was determined by regression analysis. Meanwhile, the existence of a close and definite relationship between miidslope distribution and S.S.Y refred the necsessity for geomorphic prioritization of watershed management and soil protection measures in this landform class. In general, it seems that the classification of variables nominally and ordinally reduces the effects of residuals and makes the relationships of variables more meaningful. Furthermore, the distribution of landform components among the catchments and the existence of homogeneity/heterogeneity in this regard affect the quality and quantity of relationships, which is necessary to pay attention to in regional analysis of S.Y variations.

The comparison of different geological formations in term of sediment yield is one of the most important issues in many soil and water conservation studies. Moreover, the measurement of runoff production rate and sediment production is the prerequisite of watershed management. The potential of a watershed toward erosion is the result of erosivity, erodibility of geological formations, slope gradient and land use types in the watershed. Accordingly, runoff is one of the important factors in the water erosion issues. Different geological formations depending on the rock composition, erosion and slope gradient, have a potential to produce sediment and play an important role in the amount of soil losses. The behavior of rocks and quaternary deposits against weathering and erosion depend on the nature of the rock and environmental affecting factors. Therefore, the main aim of the present study was investigating and comparing the geological formations regarding the runoff and sediment yield along with runoff threshold in Gharehshiran watershed of Ardabil province using a rainfall simulator measurement.

Based on the geologic map of the studied area, the boundaries of different geological formations were defined and then according to the objectives of the present study, a field rainfall simulator (100 × 100 cm) with a height of one meter was used for field experiments. Theoretically, the use of rainfall simulator systems saves time and cost, which can be used for monitoring the amount of runoff and sediment along with all processes involved in erosion and sediment production. However, it should be noted that the use of rainfall simulators is also subject to limitations that can never fully create natural conditions. The plot scale measurements have been conducted through 45 samples in predefined geological formations of the studied area. The runoff threshold initiation time and the amount of runoff and sediment were recorded through field experiments. The runoff and sediment samples were collected in individually stored containers and were then, transferred to the laboratory. The values of runoff were measured and the samples were oven-dried for 24 hours at 105 °C and then the deposited amount of sediments were obtained. The amount of sediment in each sample was determined using a producer of precise weighting. Then, the normality of the data was analyzed using Kolmogorov-Smirnov test. The comparison of the geological formations was examined with respect to sediment amount, runoff, and initiation time threshold using One-way ANOVA method through SPSS software. Furthermore, the significant different in mean values of studied variables between geological formations were compared with Duncan's test. Then, the correlation between the studied variables in various geological formations was evaluated using Pearson correlation analysis in SPSS software.

The results of one-way ANOVA test showed that there was no significant differences between different geological formations considering runoff and sediment yield (p<0.05). While, there was a significant difference between geological formations with respect to the runoff threshold initiation time (p<0.05). Comparison of the mean values ​​of runoff threshold time using Duncan test indicated that the highest and lowest thresholds time of runoff production were observed in Qt2 (alluvial terraces) and Qb (basaltic lava) formations with the values of 8.28 and 2.28 minute, respectively. According to the results, there was an inverse relationship between runoff and sediment variables in different formations. Also, the correlation between the runoff threshold time and the amount of runoff was negative with -0.318 correlation coefficient (p<0.05), while, correlation between the runoff threshold time and sediment yield values was positive (r=0.327) at 5% confidence level.

Many of the geological formations in this area were related to Quaternary and Tertiary periods. Young alluvial terraces and upland terraces, along with marl, sand, conglomerate, and clay formations were related to the Quaternary period, which were the results of erosion from rock units of past periods. It is suggested that the effects of other effective factors on erosion and sediment production processes should be considered in future researches to make a better and comprehensive conclusion. In conclusion, it can be said that studied geological formations were assigned to the Quaternary era and had a similar behavior in term of runoff and sediment production, while the difference in composition and mineralogy of different formations led to differences in runoff threshold.

1- Soil erosion by water is a dominant geomorphic process which threatens food security in most parts of the world .The geomorphic characteristics of a watershed play an important role in watershed hydrology, soil erosion processes and sediment yield. Geomorphic characteristics can be an indicator of soil erosion and sedimentation of a watershed. Geomorphic characteristics of watersheds are classified into linear, relief, and areal categories. Linear characteristics include stream number, bifurcation ratio, stream length and streams order. Relief characteristics include three-dimensional features of the watershed such as hypsometric integral, ruggedness number, and relative relief. Areal characteristics encompass morphological characteristics such as drainage density, stream frequency and watershed shape parameters. Accessibility to Digital Elevation Models and remote sensing data as sediment yield predictors simplify the calculation of the watershed geomorphic characteristics. The purpose of this study was to use the latest capabilities of geographic information system to extract the watershed geomorphic characteristics and determine their relationship with sedimentation in the subwatersheds of Khorasan Razavi province.
2- This study was conducted in 22 subwatersheds in Mashhad, Neyshabour and Fariman watersheds in Khorasan Razavi province. In order to select appropriate subwatersheds, the hydrometric and rainfall data for hydrometric and meteorological stations were obtained from Khorasan Razavi Regional Water authority for the selected watersheds. Annual sediment load was calculated using sediment rating curve method. Physiographic and geomorphic characteristics including 30 geomorphic parameters were calculated for each subwatershed using Digital Elevation Model with spatial resolution of 30 m. In order to determine the relationship between geomorphic characteristics and sediment yield of the subwatersheds, a multivariate regression stepwise analysis was used. In the multivariate regression, the important geomorphic characteristics which affected watershed sedimentation were identified and based on those parameters, the best annual sediment yield and geomorphic characteristics equation were presented.
3- The subwatershed areas under study vary from 40 square kilometers for the Chakaneh Olya to 9339 square kilometers for the Hossein Abad subwatershed. The average annual sediment yield for the studied subwatersheds during the period of 30 years varied from 1026 tons per year in the Jang subwatershed to 274572 tons per year at Hossein Abad watershed. The subwatersheds of Kalateh Rahman and Jang had the highest and lowest sediment yield, respectively, with 317 and 5 tons per square kilometers. The relationship between geomorphic characteristics and sediment yield of subwatersheds showed that the annual sediment yield had a positive correlation at the 5% confidence level with form factor and annual rainfall. The results of this study showed that the watershed shape parameters including form factor, elongation ratio and shape index had high correlations with sediment yield with the pertaining coefficients of 76.8, 76.5 and 72 percent, respectively. Also, the correlation coefficient of annual rainfall with annual sediment yield was 73.9 percent. After rainfall and form factor, elongation ratio was the third parameter that had a high correlation coefficient (76%) with sediment yield. In addition, watershed shape index which was a function of form factor was correlated with sediment yield at 72%. Among these characteristics, the annual rainfall and watershed form factor were used in the stepwise regression in the final model and were selected as predictor variables for sediment yield. Study results showed that the annual rainfall and watershed form factor variables could predict 64% of the annual sediment yield of the studied watersheds.
4- Discussion & The results of this study indicated that there was a significant relationship between the geomorphic characteristics of the studied watersheds and annual sediment yield. Watershed form factor was a dimensionless index for flood flow and movement, erosion severity and sediment transport capacity of watersheds. This factor was a function of watershed area and length. The runoff and the amount of flood peak in bigger watersheds will increase the sediment yield. Many researches have reported a high correlation between rainfall and sediment yield. Arid climate and poor vegetation coverage in the selected watersheds were the main reasons for the high correlation of rainfall and sediment yield. Soil erosion and sediment yield would increase due to the high intensity and low duration of rainfall along with the scarcity of vegetation coverage and erodible soils in this region. Overall, the study results indicated that with the development of new technologies and the possibility of extracting different physiographic and geomorphic parameters of watersheds from a Digital Elevation Model, it is possible to present regional equations for the prediction of sediment yield using geomorphic characteristics that can be used in sediment control and Watershed Management Programs.

Soil is considered as one of the most important elements of the environment. Soil erosion is an unavoidable phenomenon that increasingly destroys soil and pollutes water. Accurate estimation of water erosion and deposition of sediments is very important to evaluate potential soil loss and storage capacity of dams. Water Erosion Prediction Project (WEPP) is a computer model that can estimate erosion and sediment of Hill slope and catchment area , based on each individual precipitation event or in successive years. The data required for WEPP model are entered in four files, namely soil file, management file, climate file and slope file. In this study, water erosion and sediment amount was estimated by three methods of Hill slope, catchment area and flow path. In these methods sediments estimation were 0.623, 0.325 and 0.824 ton/ha/year, respectively. The results were compared with the observed value (0.665 ton/ ha/ year) of Aladyzgeh. on this basis, the Hill slope method was closer to the observed value (0.665 ton/ ha/ year) of hydrometric station and is suitable for estimating the erosion and sediment amount in Aladyzgeh catchment area.

This study was done for evaluating and providing an suitable model to estimate sediment load in the Almas Bridge water gage established on Balikhly river regarding harmful economic and environmental effects caused by river sediment load. In this context, we evaluate and compare synthetic methods into regression analyses based on classification of discharge and corresponding sediment load data over 31 years in order to increase accuracy and efficiency of sediment rating curve. Various models were tested based on significance level of 0/05 and standard error of estimate (SEE) in SPSS software to select the suitable sediment load estimation model. Results indicated good performance of the exponential model among regression models and the monthly model among temporal models. Thus, the monthly power regression model with the lowest SEE (0/81) was selected as the proper model for estimating suspended sediment load. In contrary, the temporal model used for fitting regression functions to discharge and sediment load data based on all data without classification, was recognized as the most non-efficient model. Finally, it is concluded that the monthly model can be useful to know of sediment yield regime and complexity of sediment load transport in the watershed.

This study seeks to identify and determine the spatial-temporal variations of sediment yield in Qarahsu watershed situated in Ardabil province. To do so, the relations between sediment yield and precipitation were examined in term of temporal-spatial variations in order to provide the estimate model of sediment load in the subwatersheds. Data gathered from six water and rain gauges of the same name over a 22-years period was used. The method followed regression analysis between precipitation and sediment yield by SPSS software and analysis of temporal variations of precipitation and sediment yield by Excel software. Analysis of temporal relations between sediment load and precipitation indicated a higher correlation in intra-annual than in inter-annual scale. In terms of intra-annual variations, except for Hir water gauge, that underwent an increasing trend, other stations had decreasing trends in sediment load. Nonetheless, the increasing trend in annual precipitation of 4 rain gauges was considerable. Results of regression analysis, on one hand, indicated weak correlation between precipitation and sediment load in intra-annual scale, but on the other hand, indicated high correlation in inter-annual scale. Meanwhile, the Fournier index, as seasonal precipitation index, can explain 65% variance of specific sediment yield in the studied watershed. Hence, the index, as indicator of precipitation erosive power, can be effectively used to estimate specific sediment yield in the watershed.

In this study، to investigate situation of soil erosion and sediment yield in the Sorkh Abad watershed of Mazandaran province، first measured the specific sediment observed by aspects of sediment accumulated behind two of stone and mortar dam in the output of the mentioned watershed was considered then using models FSM، PSIAC and EPM performance of each of these models to estimate the amount of erosion and sediment yield was evaluated. According obtained results of the observed and measured sediment rate behind dams in the study area was 390. 997 ton per square kilometer per year، which were obtained for FSM (equation 10)، PSIAC and EPM models 611. 411، 239. 157 and 280. 436 ton per square kilometer per year respectively. Also، the relative error percentage calculated for the above models، respectively 22، 36 and 50 percent. According to the results، the EPM model with relative error percentage less than other models used was better performance to estimate of erosion and sediment yield in the Sorkh Abad watershed.

In this research, PSIAC, MPSIAC, EPM, Fournier, Douglas, Musgrave, Stehlik, Kirkby, Geomorphology and Hydrophysical models in Babolroud watershed were investigated to determine appropriate model to erosion and sediment estimation. Sediment observation data (43 years data of Ghoran talar station) was utilized, to evaluation of used models and determine of appropriate model. In order to evaluation of results, statistical methods such as paired t-test, correlation coefficient, relative difference, BIAS, RE, RMSE were used. Results showed that in 95% confidence level, haven’t significant difference between observation data and results of MPSIAC model and also mentioned model with values of relative difference, BIAS, RE and RMSE 7.93, 0.013, 7.35 and 8.63 relatively, and by correlation coefficient equal 0.86 was the best model identified for estimation of sediment yield in Babolroud watershed. Afterward MPSIAC model, Geomorphology model with values of relative difference, correlation coefficient, BIAS, RE and RMSE equal 10.98, 0.78, 0.02, 12.34 and 11.95 relatively and haven’t significant difference in 95% confidence level was the second appropriate model to sediment yield estimation.

The growing population led to greater human need to use natural resources such as sand and gravel mines. Direct removal of sands from the bed river leads to increase suspended sediment concentrations in downstream of harvested area and creates other problems viz. filling reservoirs، change in hydraulic characteristics of the channel and environmental damages. However، the range of temporal and spatial effectibility of such human interferes has been rarely considered. The present study، therefore، aimed to investigate the spatial and temporal variation of suspended sediment concentration in the Kojour River in Educational and Research Forest Watershed of Tarbiat Modares University in Mazandaran Province، Iran. Towards this attempt، the effect of a conventional sand and gravel mining on suspended sediment concentrations was studied in a range of 0 to some 4 h and 0 to some 200m from the beginning and location of mining، respectively. The results showed that the exploitation from a local small sand and gravel mines had remarkable impact on suspended sediment concentration at a distance of approximately 100m and 2 h after mine exploitation. The statistical results by General Linear Model in Repeated Measure factor verified the increasing trend in suspended sediment in range of 50m after about 30 min of mining (P=0. 05)، while the effect of mining on increasing suspended sediment concentration could be recognized up to 200 m from the location of study up to about 10 min (P=0. 01) of time of sand mining.

In this research, it is tried to investigate the soil erosion by the indices of rainfall erosive, evaluation of the basin potential for trench erosion, morphometric of trenches and statistical analysis to suggest some required recommendations for erosion control. Also we used hydro climatic indices for studying the above said factors. Also in relation with the high development of trenches in the study basin, we did morphometric work in the 20 trenches.With respect to steep slope of the skirts, great interfere of human (existence of 19 villages in the study basin), stormy rainfall, water way systems has caused the destruction and movement of non-resistant materials from the areas (fertilized agricultural soils)The average annual soil erosion in Kalgan Chayi basin is 235.79 ton/ha/y(table No.1) and the total erosion in whole of the area is 5552845 ton/per year. The index of wet soil (WS) in February and March were negative and indicates the potential of the under study area for trench erosion in these months. Hydrothermal coefficient (HTK) 1.715 in the limit of 1.25 up to 2.5 shows the potential of the area soil for creating trenches.Comparison of the results of statistical analysis by linear power regression showed that linear regression is better than power one in trenches study.Some suggestions:Therefore, applying watershed management methods appropriate with the climatic and topographic conditions of the area are presented as the following:- Creating terrace at the mild slopes and making banquette(U,V gradients) at the pendants by using Sakardent formula which is adapted with semi-arid areas(by calculating distances, gradient and amount of earth filling and earth moving)- Applying watershed management methods of change in the slopes by dry laid masonry and establishment of weirs in the waterways and active trenches (check dam and log) which their material exist in the environment.- Avoiding plow in the slopes (perpendicular to the contour lines) and preventing excessive and over grazing, burning bushes and trees.