Irrigation
H. Saeediyan; Hamid Reza Moradi
Abstract
Introduction: Erosion and sediment production studies along with other natural resources studies in decision making and success and efficiency of watershed plans are of great importance. In order to plan and be aware of the destructive situation of the watershed, it is necessary to have erosion and sediment ...
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Introduction: Erosion and sediment production studies along with other natural resources studies in decision making and success and efficiency of watershed plans are of great importance. In order to plan and be aware of the destructive situation of the watershed, it is necessary to have erosion and sediment production from each watershed. The information about sediment load of basins can show the prospect of erosion. Sediment scatter from the soil surface by the impact of raindrops and shear force of runoff and is transported to downstream by spraying from raindrops and mainly by runoff. Also, the stress characteristics of soil particles are important in the process of effective transport. In recent decades, soil erosion has been intensified due to the human interference, inappropriate land management and land use. This is much more important in developing countries, because soil erosion is a serious risk to sustainable development in these countries. Soil erosion on farmland occurs due to the interaction between nature and human activities that have been being intensified in recent years. Estimation of sedimentation in watersheds, dealing with sediment accumulation risks in water structures and reservoirs of dams are the main objectives in water resources management that leads to sustainable development. One of the most erodibility of Iran is the Gachsaran formation. Gachsaran formation is about 1600 meters thick. A viewpoint of lithology is consisting of salt, anhydrite, colorful lime, and some shale. Gachsaran formation age is lower Miocene. Materials and Methods: In this study, in order to determine sediment estimation by using different erosion components in different land uses of Gachsaran formation deposits, a part of Kuhe Gypsum watershed of Izeh city with an area of 1202 hectares was selected. In this study, the relationship between produced sediment and different erosion components such as runoff,soil permeability,runoff, and erosion threshold in different land uses of Gachsaran formation was determined by multivariate regression. Then, sampling of erosion different components was done at 6 points with 3 replicates and at rainfall different intensities of 0.75, 1 and 1.25 mm/min in three land uses of rangeland, residential area and agricultural using rain simulator. SPSS and EXCEL softwares were used for statistical analysis. Results and Discussion: The results showed that sediment estimation using different erosion components presents acceptable results and can be used for other watersheds. The results also showed that in sediment estimation by erosion different components, runoff and erosion threshold had the most positive and negative effect and in eight cases played a role in modeling. Then, soil permeability has the average effect of positive and negative and has played a role in modeling in seven cases. In addition, runoff has not played a role in modeling in any of the three different land uses and intensities of precipitation. Conclusion: Sediment estimation by erosion different components, the runoff and erosion threshold had the highest effect. Soil permeability had a moderate influence and runoff rate has not played a role in modeling in any of different land uses and precipitation intensities, it indicated the much more important role of runoff and erosion threshold and soil permeability in this modeling method in estimating sediment production. Finally, sediment estimation method by using erosion different components showed that it could be more applicable in sediment estimation in hard-to-reach watersheds in the future and be more effective in soil conservation and erosion reduction with appropriate and rational estimates in more appropriate implementation of watershed projects.
Y. Ostovari; S.A.A. Mousavi; H. Mozaffari
Abstract
Introduction: Soil erosion is one of the most important and serious threats to food security and as a consequence of human life. In order to perform soil protection activities against soil erosion, knowledge about the amount of soil loss tolerable is very important. In fact, the soil loss tolerable is ...
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Introduction: Soil erosion is one of the most important and serious threats to food security and as a consequence of human life. In order to perform soil protection activities against soil erosion, knowledge about the amount of soil loss tolerable is very important. In fact, the soil loss tolerable is the potential for soil erosion, loss of productivity and lost production, and the final criterion for controlling soil erosion and degradation of land. Soil thickness methods, particularly Skidmore equation, based on their ability to estimate the tolerable amount of soil loss have been widely used. In the mathematical function developed by Skidmore based on soil thickness, the soil loss tolerable is calculated based on the soil's current depth, the lowest and maximum soil depth for sustained growth of crops, and the upper limit of tolerable erosion in accordance with the environment. Since the determination of soil loss tolerance by soil thickness method and the Skidmore equation requires time, cost and energy, the researchers have tried to estimate the soil tolerance is supported by regression methods using pedotransfer functions and easily available soil properties. Therefore, the present study was carried out with the aims of determining the tolerable tolerance of soil loss by thickness method and the development of regression pedotransfer functions for estimating this property in the upstream of the dam.
Materials and Methods: The study is place on Kamfiruz Watershed with an area of 422 km2, an average annual precipitation of 443 mm and an average annual temperature of 14 °C. It is closed to the Dorudzan Dam sub-basins and is considered as one of the five parts of Marvdasht plain in Fars province. For this work, 60 soil profiles were excavated by excavating machine. In addition to measuring the depth of soil, some physico-chemical soil properties were measured from the surface layer (0-30 cm) including; soil texture, organic matter, salinity, percentage calcium carbonate, mean weight diameter in the laboratory and filed. In order to develop regression models for estimating the tolerable soil loss, information from 60 soil profiles was divided into two data-sets. One set of the data with 42 samples (70% of whole samples) was used for developing the models and another set of the data with 18 soil samples (30% of whole samples) was used for validation. Multiple linear regression was used to develop the linear models. The same soil properties used in the multiple regression method were considered as inputs in the tree regression method to estimate the tolerable amount of loss.
Results and Discussion: The results showed that the minimum and maximum Z1 parameters (the lowest soil depth for stable growth of crops in the study area) were considered as 0.25 and 0.51 m based on the current depth of soil. Organic matter of the soils with the highest standardized coefficient (Beta = 0.44) and the highest correlation (-0.77) with soil loss tolerance was the most important soil properties for estimating the soil loss tolerance. In the regression model, only the coefficients of four characteristics of permeability, soil aggregate stability, pH and organic matter appeared among the soil grazing characteristics and entered into the model. Based on the evaluation statistic, tree regression method with the highest determination coefficient in both calibration data sets (R2 = 0.96) and validation (R2 = 0.78) and the lowest error value in the validation data (RMSE= 0.29 ton ha-1 year-1) and validation (RMSE = 0.125 ton ha-1 year-1) were more efficient than the multiple regression method in estimating the tolerable soil loss.
Conclusion: Soil loss tolerance was estimated using regression methods (multiple linear regression and regression tree) in Doroudzan Watershed, Fars province. The soil loss tolerable determined using Skidmore method, was 1.04 tons per hectare per year ranging from 0.29 to 2.25 ton ha-1 year-1. The soils of this area are slightly deep and their depth varies from 0.4 m in the marginal areas in the upstream parts of the catchment area of the dam and the slope of mountain up to 2 meters in the center of the plain with agricultural lands uses. In general, the tree regression method had a better performance than linear regression method for estimating the soil loss tolerance based on the statistical indices.
Malihe Ebrahimi; Hossein Asadi; Arezoo Sharifi; Eisa Ebrahimi
Abstract
Introduction: The study of physical properties of suspended sediments is one of the main topics in river studies. Sediment size distribution is one of the sediment physical properties which indicate the relation between the sediment source and its sedimentation process in watersheds. It is also important ...
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Introduction: The study of physical properties of suspended sediments is one of the main topics in river studies. Sediment size distribution is one of the sediment physical properties which indicate the relation between the sediment source and its sedimentation process in watersheds. It is also important for prediction of the load of non-point source pollution, and for planning sediment trap structures. The Anzali Wetland, located on the southern coast of the Caspian Sea in northern Iran, is a large complex of freshwater lagoons with extensive reed-beds, shallow impoundments and seasonal flooded meadows. Environmental conditions in the Anzali Wetland have been degraded due to the increased inflow of sewerage, wastewater and solid waste from the industry, agriculture and urban area, and sediment from the upper stream mountainous area. The lagoon has decreased in size since the 1930s to less than a quarter of its former extent. The aim of the present study was to assess the changes in size distribution of suspended sediment in Pasikhan River as the most important river interring to Anzali Wetland.
Material and Methods: Pasikhan River originates from the South Mountains, has two branches namely Siahmezgi and Imamzadeh Ebrahim. The sampling carried out during a seven month time period (October 2013 to April 2014) at two hydrometric stations; Mobarakabad (upstream) and Nokhaleh (downstream). The samples were collected in 15 days intervals by depth-integration technique at normal condition. Particle size distribution was measured by Pipette method based on Stocks law. The mean weight diameter (MWD) of sediment particles was calculated, the sediment size distribution curve was drawn and the median grain size (d50) was calculated. According to the European classification, the particles size distribution was divided into four groups of fine sand (0.2 mm), coarse silts (0.06 mm), medium silt (0.02 mm), and fine silt and clay (equal to and less than 0.006 mm). The data were compared for each sampling time for both Stations. Flow discharge and suspended sediment load were also determined at each sampling date.
Results and Discussion: At the Nokhaleh station, the maximum observed flow discharge and sediment concentration were 51.4 m3/s and 4.162 g/L, occurred in February 4, 2014 and November 3, 2013, respectively. The highest flow discharge and sediment concentration of the Mobarakabad were 9.8 m3/s and 2.633 g/L which were observed on February 19, 2014 and April 4, 2014, respectively. These changes and differences were partly due to topography and land use differences between upland and lowland and partly due to rainfall pattern. Results showed that the MWD and d50 were 0.062 and 0.052 mm on average, respectively at Mobarakabad station, and 0.055 and 0.051 mm, respectively at Nowkhaleh station. The maximum values of MWD and d50 were observed to be 0.07 and 0.061 mm, respectively at normal condition at Mobarakabad station. The study of sediment size distribution indicated that the particles smaller than 2 mm comprised 83-94 percent of the suspended sediment at Mobarakabad station, and 87-99 percent at Nokhaleh station. The percentage of particles smaller than 0.02 mm were observed to be 12-33 and 10-64 at Mobarakabad and Noukhaleh stations, respectively. Also the amount of fine silt and clay in suspended sediment were 3-16 and 5-24 percent at these stations. There was not any correlation between flow discharge and sediment concentration or sediment size distribution characteristics.
Conclusion: In most of the samples, there was not any relationship between the flow discharge and particle size distribution of suspended sediment which emphasize on the non-hydraulic nature of sediment transport and the effects of different factors including sediment sources, the season, transport energy, rainfall erosivity, soil erodibility and deposition process. Generally, the size of sediment particles at Mobarakabad station was coarser than Nokhaleh station. This could be due to the type of soil erosion which is different at upstream and downstream. In upstream regions, mainly because of severity of topography and vegetation cover including forest and rangeland, the occurrence of gully erosion and landslide is higher in comparison with surface soil erosion. But in downstream especially in paddy fields, the soil erosion type is mainly splash and sheet erosion. Also the cultivation practices including plowing and paddling of the field usually provides fine particles entering to the river. In addition, the river profile is very gentle at the plain before the Nokhaleh station which resulted in deposition of coarser particles.
Vida Atashi; Mahmood Shafai-Bajestan; Ideh Golrokh
Abstract
Introduction: Flow patterns within the river bend is three dimensional. Occurrence of secondary flow due to centrifugal force and formation of helicoidally vortex in river bend usually causes the outer bank of river erodes whilst the sediment are deposited in inner bend which appears in the form of point ...
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Introduction: Flow patterns within the river bend is three dimensional. Occurrence of secondary flow due to centrifugal force and formation of helicoidally vortex in river bend usually causes the outer bank of river erodes whilst the sediment are deposited in inner bend which appears in the form of point bars. To reduce the river bank scour, many techniques have been developed which may be classified as covering technique and modified flow patterns methods. The W-weir is among such structures. In the present paper, by measuring three components of flow velocity with and without presence of W-weir, variation of flow patterns and shear stress distribution in a 90-degree sharp bend have been investigated. The main purpose of this study is to see the installation of different locations of W-weir in the bend on reduction of outer bank scour. In the present paper, by measuring three components of flow velocity with and without presence of W-weir, variation of flow patterns and shear stress distribution in a 90-degree sharp bend have been investigated. The analyses of data showed more uniform flow upstream of the weir and also revealed that the effect of transverse and centrifugal forces are modified in such a way that the secondary flow is diminished. The results showed that for 30, 60 and 90-degree bends maximum erosion depth in the vicinity of the outer bank with Froude number of 0.206 in comparison with 0.137 has increased up to 84, 90 and 118 % respectively. In both Froude numbers, installation of W-Weir in 30 degree has the most reduction in bed in comparison with 60 and 90 degree.
Materials and Methods: To reach the goal of this study a physical model of 90 degree sharp bend was constructed in the hydraulic lab of Shahid Chamran university of Ahvaz. The ratio of R(radius)/b(flume width) was less than 2 which shows a sharp bend. The W-weir was built with 1mm galvanized steel. Flume bed was covered with sediment of D50=1.5mm. The W-weir was installed at three different locations of 30, 60 and 90 degrees from the bend entrance. Two sets of tests were carried out with and without weir. For each location two different flow discharges (Fr= 0.137 and Fr=0.206) were studied. The flow depth for all tests were kept constant equal to 15cm. At the end of each test the flume was drained and bed topography was recorded using laser meter. Measured bed topographic data were used in SURFER and TECPLOT software to compare the results of the W-weir location
Results and Discussion:
a)W-weir in 60 degree location
b)W-weir in 30 degree location
a)W-weir in 90 degree location
Fig.1 Bed topography after W-weir installed(Q=10l/s)
The results showed that W-weir concentrated the flow toward the flume center thus the bed only will scour at the downstream of W-weir whilst the bed at upstream is neither of weir nor eroded. This is because the flow patterns within the bend has been modified in such a way that diminishes the strength of helicoidally vortex upstream of the weir thus the scour or deposition will not occur. The results of tests with Q=15 l/s also was similar with the exception that in these tests the Froude number is higher and the scour depth downstream of weir is much larger. The results also showed that the scour depth is much higher when the weir is installed at 60 degrees. The scour depth for weir at 90 degree location showed reduction of about 33% and 39% compare to the weir in 30 and 60 degree location respectively.
Conclusion: In this research, by assessing the cross velocities and the scour depth downstream of weir in 90 degree sharp bends and studying the impacts of w-shape weir on those parameters, following results were obtained: The W-weir can modify the flow patterns within the flume bend in which no scour and deposition is observed upstream of the weir. The scour downstream of weir with higher depth closed to the outer bank is observed in all tests. The scour depth is much higher when the weir is installed at 30 degree location whilst is minimum when the weir is installed at 90 degree location.
Hanifeh khormai1; farshad kiani; Farhad khormali
Abstract
Introduction: Globally, Soil erosion is a principal degradation process resulting in negative impacts on different soil functions (food and other biomass production, water storing, filtering and transformation, habitat and gene pool, physical and cultural environment for mankind, and source of raw materials) ...
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Introduction: Globally, Soil erosion is a principal degradation process resulting in negative impacts on different soil functions (food and other biomass production, water storing, filtering and transformation, habitat and gene pool, physical and cultural environment for mankind, and source of raw materials) which ultimately causes irreversible effect on the poorly renewable soil resource. Determination of the soil erodibility factor (K-factor) is a cumbersome and expensive undertaking in the effort to predict the soil loss rates. Soil erodibility (K-value) is a key parameter in erosion prediction and is important for conservation planning in the face of a rising need for protecting the limited land resources. The technique proposed by Wischmeier& Smith for estimating the soil erodibility factor is among the most important methods in this regard.
Materials and Methods: Given the high amounts of silt and lime content in loess soils of eastern parts of Golestan province, the purpose of this study was to evaluate the ability of Wischmeier& Smith index to estimate the soil erodibility of this region. In this study, soil erodibility was obtained by Wischmeier’s nomograph and then was compared with the actual values obtained by selecting three plots and then performing physical and chemical tests on these samples. The Universal Soil Loss Equation (USLE) developed by Wischmeier and Smith (1978) is the most frequently used empirical soil erosion model worldwide. Soil erodibility is one of six factors affecting soil erosion in the USLE that reflects the ease with which soil is detached by splash during rainfall, surface flow or both. To check soil erosion,three plots of 15 meters long and three meters wide with a slope of 16 percentwere selected in the next sites of the station. The plots were separated by metal fences to a height of 30 cm,.To measure the soil profile parameters, the sampling was performedin one stage from depth of0-30 cm in the middle of July 2010 and the samples were transported to the laboratory. The erosion Wischmeier& Smith Index (A), as well as those obtained by SWAT model and two obvious erosion indices of (R) and Fournier was Carefully evaluate based on the half-hour rainfall intensity.
Results and Discussion: The analysis of soil profile parameters showed that the soilsweremostly silty loamwith 20.29%sand, 66.54% silt and 13.66% clay, with 2% organic matter and 16.6% CaCO3. The soil aggregate stability expressed as MWDwas about 0.8 mm. Overal, 74 rainfallsoccurredin 2010-2011. The minimum and maximum intensities of deposit-producing rainfalls were 2.98 and 73.589 mm h-1, respectively. Using the nomograph, Wischmeier index was calculated to 0.05-0.092 Mg h MJ−1 mm−1. The results showed that Wischmeier index was 182 times the actual value of erosion obtained from plots and half-hour rainfall intensity and 4.11 times that value while considering Fournier index (R); this parameter was also 6 times the value obtained by SWAT model and half-hour rainfall intensity and 0.35 times that value while considering Fournier index. According to the results,there was a negative correlation between clay and soil erodibility factor in USLE, so the rates of erosion in loess soils increases with the decrease in the clay content. Aggregate stability was affected by organic matter content and there was a negative correlation between aggregate stability and the K-factor. The results showed that the soil mostly contained silt and had a medium texture. This is due to the presence of loess parent materials in the soils of the study area. Based on the laboratory results, the actual soil erodibility was0.35 to 182 times smaller than the value estimated by USLE nomograph. The results showed that the parameters used in determining soil erodibility index have shortcomings for use in the soils of the study area. Therefore, corrections must be done according to soil characteristics or other indicators should be used. The particle size and the amount of lime in the soil are two factors that affect the index.
Conclusions: The obtained results showed that the erodibility estimated by Wischmeier& Smith index was higher than the actual measured value. Also,Wischmeier &Smith’snomographhas been proposed by assessing the erodibility of almost non- calcareous soils with limited amount of silt. While in arid and semiarid loess soils of Golestan province, limestone and siltstone have key roles in erodibilityand aggregate stability. On the other hand, the nomograph is based on rainfalls of semi-humid areas of Central America that are different from rain characteristics (intensity and duration) of the study area. Poor performance of this index in loess soils indicates the need for further research in this field.
F. Asadzadeh; manoochehr gorji; A. Vaezi; S. Mirzaee
Abstract
Introduction: Field plots are widely used in studies related to the measurements of soil loss and modeling of erosion processes. Research efforts are needed to investigate factors affecting the data quality of plots. Spatial scale or size of plots is one of these factors which directly affects measuring ...
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Introduction: Field plots are widely used in studies related to the measurements of soil loss and modeling of erosion processes. Research efforts are needed to investigate factors affecting the data quality of plots. Spatial scale or size of plots is one of these factors which directly affects measuring runoff and soil loss by means of field plots. The effect of plot size on measured runoff or soil loss from natural plots is known as plot scale effect. On the other hand, variability of runoff and sediment yield from replicated filed plots is a main source of uncertainty in measurement of erosion from plots which should be considered in plot data interpretation processes. Therefore, there is a demand for knowledge of soil erosion processes occurring in plots of different sizes and of factors that determine natural variability, as a basis for obtaining soil loss data of good quality. This study was carried out to investigate the combined effects of these two factors by measurement of runoff and soil loss from replicated plots with different sizes.
Materials and Methods: In order to evaluate the variability of runoff and soil loss data seven plots, differing in width and length, were constructed in a uniform slope of 9% at three replicates at Koohin Research Station in Qazvin province. The plots were ploughed up to down slope in September 2011. Each plot was isolated using soil beds with a height of 30 cm, to direct generated surface runoff to the lower part of the plots. Runoff collecting systems composed of gutters, pipes and tankswere installed at the end of each plot. During the two-year study period of 2011-2012, plots were maintained in bare conditions and runoff and soil loss were measured for each single event. Precipitation amounts and characteristics were directly measured by an automatic recording tipping-bucket rain gauge located about 200 m from the experimental plots. The entire runoff volume including eroded sediment was measured on storm basis using the collection tanks. The collected runoff from each plot was then mixed thoroughly and a sample was taken for determining sediment concentration by weight. The per-storm soil loss was then obtained.
Results and Discussion: A wide range of rainfall characteristics were observed during the study period.The results indicated that the maximum amount of coefficients of variation (CVs) for runoff and soil loss from replicated plots were 60 and 80 percent, respectively, which were considerably higher than the variability of soil characteristics from these plots. CV of runoff and soil loss data among the replicates decreased as a power function of mean runoff (R2= 0.661, P
