Irrigation
A. Mosaedi; E. Ramezanipour; M. Mesdaghi; M. Tajbakhshian
Abstract
Introduction: Soil erosion and sediment transportation decrease water resources, and cause many social and economic problems. On the other hand, sediment transportation by rivers causes problems such as water quality degradation, reservoirs sedimentation, redirect of rivers, or decrease in their transportability. ...
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Introduction: Soil erosion and sediment transportation decrease water resources, and cause many social and economic problems. On the other hand, sediment transportation by rivers causes problems such as water quality degradation, reservoirs sedimentation, redirect of rivers, or decrease in their transportability. Therefore, finding the proper methods in sediment yield study in watersheds is essential in planning and management of land and water resources. Climatic characteristics, physiography, geology, and hydrology of basins are the most effective factors in producing and transporting sediments according to several sources, but the role and impact of some factors are more pronounced than the others in different areas. As a result, the objective of this study was to investigate and identify the most important climatic, physiographic, geological, and hydrological factors in several watersheds of the northeastern part of Iran, by applying Gamma Test (GT) and principal component analysis (PCA) techniques.Materials and Methods: In this study, the data of discharge flow and suspended sediment concentration, and daily flow discharge recorded in 15 hydrometric stations in Mashhad and Neyshbour restricts and required maps were provided from the Regional Water Company of Khorasan Razavi, Iran. After drawing statistical bar graph period of suspended sediment, daily discharge, annual precipitation, and relatively adequate data, stations with the longest period and with the lowest deficit data were selected to determine the common statistical periods. Therefore, in this study, the time period of 1983-1984 to 2011-2012 was selected, and the run test was applied to control data quality and homogeneity. Then, the most effective factors of sediment yield were determined by principal component analysis (PCA) and Gamma Test (GT).Results and Discussion: The results of the principal component analysis showed that 90 percent of the first five components justify the changes. Among the factors, area and gross gradient of the mainstream from the first component, the average annual flow rate of mainstream, meandering waterways of the mainstream from second component, and drainage density of third component were identified as the most important influencing factors on suspended sediment production. Ninety superior combinations of 1500 proposed combinations were obtained by Gamma Test to evaluate the effects of each parameter on suspended sediment yield. To determine the order of importance of the entered parameters, first, Gamma Test was performed on all 12 parameters. Gamma values of all cases for each proposed combination were compared. The results showed that the impact of these statistics was lowered by eliminating high gamma parameters and the removal of low values. The data analysis revealed that the low levels of gamma and high accuracy of ratio to find the desired outputs from entries. By lowering the gradient, the complexity of the model was lowered and more suitable model was provided. As a result, high levels of gradient represented the complexity of the final model. The results of the percentage values of each of the 12 variables were considered among the superior equations for estimating the suspended sediment composition. In this regard, the mean annual discharge, main channel length, area, average annual rainfall, and percentage of the outcrop of erosion sensitive rocks with a total of 63 percent of the proposed equations were the most important factors affecting the sediment yield in the study area. The average height parameter of area, the average and gross slope of the mainstream had the lowest presence among the optimized compounds.Conclusion: Based on the results of the principal component analysis, the two factors of basin area and gross slope of the mainstream were selected as the most important factors affecting the amount of annual suspended sediment load, respectively. Based on the results of the Gamma Test, 12 main variables affecting suspended sediment load were identified and the effect of each of them on the production and transport of suspended sediment was determined. Based on the comparison of the results of the two methods of PCA and GT, it can be concluded that if the purpose of research or study is to prepare a model with the highest accuracy in estimating suspended sediment load, the 12-variable model of GT includes factors related to physiographical, geological, climatic and hydrological factors are suggested. However, if the preparation of a model with appropriate accuracy and a limited number of input variables is considered, a 5-variable model derived from the PCA method is proposed. At the same time, if the purpose is to prepare a model with the least input variables and their easy access and calculation and initial estimation of suspended sediments, a bivariate model (based on basin area and gross slope of the mainstream factors) resulting from PCA is proposed. According to the results of the present study, it can be concluded that the study of more parameters has provided grounds for evaluating their importance in sediment yield. Finally, due to the correlation of many parameters with each other, a limited number of parameters that have a more important role in suspended sediment estimation, were selected. Another finding of this study is the increase in the accuracy of the sediment model’s preparation due to achieving more important and effective parameters in sediment yield and identifying them in order to investigate the best sediment management measures in watersheds. It is suggested that similar research should be done in other watersheds with different conditions in terms of climatic conditions, topography, geology, and so on.
maryam tajbakhshian; Mohamad Hosien Mahmudy Gharaie; Asadollah Mahboubi; Reza Moussavi Harami; Iraj Ejlali
Abstract
Introduction: Elemental sulfur is byproduct of natural gas refining which during this process, H2S is removed from sour gas and after changes to solid sulfur, it is stored in large block forms. Continuous precipitation of sulfur and its oxidation causes soil acidification and as a result, nutrient cations ...
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Introduction: Elemental sulfur is byproduct of natural gas refining which during this process, H2S is removed from sour gas and after changes to solid sulfur, it is stored in large block forms. Continuous precipitation of sulfur and its oxidation causes soil acidification and as a result, nutrient cations such as Ca2+, Mg2+, Na+ and K+ will leach from the soil profile. Also, sulfate accumulation led to soil acidification and accelerates the silicates weathering in upper layer of the soil profile. Accumulation of water soluble sulfate in the soil and increase the nutrient cations leaching from the soil depend on sulfate resistance rate. Also, addition of sulfur to the soil for a long time can cause calcium sulfate formation that will cause problems such as increase in soil salinity. Shahid Hashemi Nezhad gas refinery is located about 35 km south of Sarakhs city and about165 km east north of Mashhad. In addition to exploiting, refining and producing 50 × 106 m3.day-1 natural gas, recovered sulfur with %99/9 purity and 2000 tons per day production capacity is one of the byproducts of this gas complex.
Materials and Methods: 22 soil samples were collected from surface soil in Shahid Hashemi Nezhad gas refinery (3 samples) and nearby areas (19 samples) (Fig.1). Soil extracts pH was measured in equilibrium with pure water and with KCl 1M solution in 1:2.5 soil solution ratio. EC of the soil samples was measured in different soil water ratios to obtain the EC 1:1 (Fig.2). Total sulfate content was measured by gravimetry method at geochemistry laboratory of Faculty of Sciences at Ferdowsi University of Mashhad. To get the digestion extract, a mixture of 2 ml concentrated HF, 5 ml HCl and 8 ml HNO3was added to 0.5 gr soil in a teflon vessel, then heated for 60 min at 170° C. After cooling, the solution was evaporated at 130 °C to dry it. Then, the dried salt was dissolved in a mixture of 2 ml HNO3 and 2 ml HCl and diluted with deionized water up to 25 ml. Ca2+ and Mg2+contentswere measured through titration of the soil extract with EDTA 0.01 N and in EBT reagent at the first stage, and titration of the soil extract by EDTA 0.01 N and in Moroxide reagent at the second stage. Na+ and K+ contents were determined using AAS method at geochemistry laboratory at Ferdowsi university of Mashhad after extraction with CaCl2 0.01 M.
Results and Discussion: Based on EC values, 77% of the soil samples were non-saline (EC < 2 dS m-1), 18% were slightly saline (EC= 2-4 dS m-1) and 5% were highly saline (EC=8-16 dS m-1) (Fig.3). In addition, low ΔpH values in the soil samples showed high salinity and similar results to EC. SAR index had the highest value in TS5 sample, and the cations content in this index can be attributed to evaporative sediments with carbonate and sulfate salts in the area (Shurijeh and Chehel-Kaman formations). Moreover, the halite bearing formations in the study area can be regarded as a source for Na+. Based on SAR and EC, majority of the samples (except TS5 in saline and non-sodic) were non-saline and non-sodic that were suitable for agriculture. ESP index of less than 15% in all samples indicated that Na+ concentration has no danger to crops. Relation between the total sulfate content to pH and EC was inverse and direct, respectively. This indicates that recovered sulfur affect in the soil acidification within the refinery site and increase the soluble salts content. These effects are very considerable in the soils inside the refinery site.
Conclusions: Salinity is the major factor affecting decrease of the samples quality for agriculture. Exposed formations in the area with highly soluble rocks causes to increase the soluble salts in the soil. The second factor is high temperature and low precipitation that led to increase the evaporation from the soil surface and accumulation of salts on the soil. Recovered sulfur from natural gas processing can reduce the soil pH and increases the soluble salts to some extent, especially in the inside refinery samples, and then decreases the soil quality for agricultural purposes. Except for one, all studied samples were classified as non-saline and non-sodic soils. Furthermore, the samples were classified in two classes of flocculated soils and potentially dispersive soils based on SAR and EC. ESP index indicates that there is no serious problem regarding sodium concentration in the soils. The pH values indicate that the samples were almost alkaline soils except for the samples inside the site, which are slightly acidic. Acidity of those few samples are attributed to the sulfur released from gas refinery process and its effect on the soil pH.