A. Sharifi; H. Shirani; A.A. Besalatpour; E. Esfandiarpour
Abstract
Introduction: Interrill erosion is one of the major types of erosion playing key role in the transport of fine particles of the soil, particularly in arid and semi-arid regions, which leads to the decrement of soil fertility and surface water pollution. Land-use change is one of the main ways which reflect ...
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Introduction: Interrill erosion is one of the major types of erosion playing key role in the transport of fine particles of the soil, particularly in arid and semi-arid regions, which leads to the decrement of soil fertility and surface water pollution. Land-use change is one of the main ways which reflect the interaction of human activities and the natural environment and can impact soil aggregation, aggregate stability, and erodibility. Hence, this research aimed to evaluate the susceptibility of soils under different land-use types (four types) to interrill erosion using both rainfall simulation test and soil aggregate stability indexes. The location of study area was around Jiroft city.
Materials and Methods: This study was conducted in four types of land use around Jiroft city in southern Iran, including disturbed pasture, undisturbed pasture, protected forests, and artificial forest. For each land use, 25 points were selected (A total of 100 points for all land uses). To measure soil physical and chemical properties, disturbed and undisturbed soil samples were collected from each point at a depth of 0–20 cm. The samples were transported to the laboratory where these samples were then air-dried. Some soil properties such as texture, organic carbon, electrical conductivity, soil acidity, calcium carbonate equivalent, and bulk density were measured, and available nitrogen, phosphorus, and potassium in the soil and sediment samples were also determined. Furthermore, some characteristics of soil particles, including the geometric mean diameter, geometric standard deviation, particulate organic matter, water-dispersible clay, tensile strength of soil aggregate, mean weight diameter and fractal dimension of aggregates were determined. To assess how susceptible are soils to interrill erosion, rainfall simulator was used to generate rainfall with an average intensity of 60 mm/h.
Results and Discussion: According to the results, the undisturbed pasture revealed the highest content of organic matter, particulate organic matter, clay, and tensile strength, while the minimum values of bulk density, sand percentage, and fractal dimension have been observed in this land use. For this reason, it is assumed that the aggregates of undisturbed pasture (intact rangeland) show more stability than other three land uses. The maximum and minimum values of bulk densities were observed in the protected forest (1.58 g cm-3) and undisturbed pasture (1.43 g cm-3), respectively. On the other hand, the highest value of aggregates fractal dimension, as well as minimum values for mean weight diameter and dispersible clay in the protected forest demonstrated that this land use had either no aggregate or its aggregates were very fine. As a matter of fact, lack of organic matter and insufficient clay content can be considered to be the reasons for poor aggregate stability in this land use. The highest and lowest values for tensile strength of soil aggregate were found in the undisturbed rangeland (64.82 kPa) and protected forest (34.38 kPa), respectively. The variations in the tensile strength of soil aggregate can be attributed to the changes in the contents of clay and organic matter in different land uses. Moreover, despite the maximum amount of total organic matter in the undisturbed pasture (or intact rangeland), the amount of sediment organic matter in this land use was lower than the other three land uses. It is because of the fact that most of the OM in this area was of a stable organic matter type, which was under the soil surface and was accordingly protected from surface erosion. The particle size distribution of sediment was smaller in the undisturbed pasture, whereas it was found to be larger in the protected forest. The reason can be attributed to the coarse-textured soil in the forest compared to the finer-textured soil in the undisturbed pasture (or intact rangeland). In addition, the highest sediment concentration and the highest rate of erosion were observed in the disturbed pasture. The artificial forest accounted for the minimum sediment concentration, while the artificial forest, as well as the protected forest, revealed the lowest erosion rate.
Conclusion: The results of the current research demonstrated the high rate of interrill erosion in all land uses so that the disturbed pasture and artificial forest accounted for the highest and the lowest rate of erosion (7 and 2 ton/ha) respectively. According the results, intrinsic soil characteristics such as soil texture played major role in some land uses, while for the others, the slope impact was more crucial. On the other hand, both erosion rate and sediment concentration revealed the same trend under four different land uses of the study area. Therefore, because of the fact that the highest and the lowest rate of erosion, as well as sediment concentration, were found to be in the disturbed pasture, and the artificial forest, respectively, therefore the sediment concentration can be considered to be an important index for soil erosion. Due to high rates of erosion occurring in the study areas, some measures have to be undertaken to prevent and control soil erosion in this area. To achieve this aim, preventing people from entering the vulnerable area, avoiding livestock grazing, protecting existing plants and restoration of native plants can be mentioned as efficient measures to improve conditions.
Amin zoratipour; mohammad moazami; mohammadreza ansari
Abstract
Introduction: During the last decades, important research efforts were conducted to identify and quantify the contribution of different sources delivering suspended sediment to the rivers. This knowledge also proved to be essential to provide estimations of catchment sediment budgets. The type of sources ...
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Introduction: During the last decades, important research efforts were conducted to identify and quantify the contribution of different sources delivering suspended sediment to the rivers. This knowledge also proved to be essential to provide estimations of catchment sediment budgets. The type of sources (i.e. soil types, rock types, and land uses) to discriminate depends on the local catchment context. Generally, the targeting of sediment management strategies is a key requirement in developing countries because of the limited resources available. Proper implementation of the soil conservation plans and sediment control programs should be done to inform of the relative importance of contribution the sediment resources as well as identification of crisis centers in the watersheds. During the last decades, this approach has been increasingly applied to identify and ‘trace’ several distinctive characteristics of the source material that can be compared to the same characteristics measured on river suspended sediment samples. Todays, fingerprinting techniques, provide an appropriate method for rapid and low cost information on main sources of sediment.
Materials and Methods: in this study, the mentioned technique in the contribution of sediment resources, identify the critical units using the seven geochemical tracers' properties in the Dare Anar basin of Baghmalek in the Khuzestan province. The focus of this paper is upon quantifying the sources of suspended sediment transported on the Bakhmalek River in order to help guide future surface water sediment reduction efforts for turbidity-impaired streams. The statistical methods were used by the comparison of means and discriminant analysis, to select the optimal combination of tracers and contribution sediment sources. The geochemical tracers tested for their ability to distinguish between sediment sources with the Kruskal–Wallis one-way analysis of variance H test, which is able to test for the independence of more than two variables without presuming either normal or non-normal distributions. Tracers proving significance (p<0.05) between sources were retained. Tracers passing the Kruskal–Wallis H test that were non-conservative (suspended sediment tracer values that were not bracketed by sediment source tracer values) and removed before the performance of the mixing analysis. Tracers passing the first stage of statistical analysis were entered into a stepwise Discriminant Function Analysis (DFA) intended to optimize the number used in the mixing model. This analysis results in the smallest combination of tracers that are capable of correctly distinguishing 100% of the sources through the minimization of Wilks’ Lambda (Collins et al.1998). The analysis was run separately for each drainage basin using IBM SPSS Statistics v. 20.0. From the seven measurement fingerprinting properties, three of them were selected for geology formations and land use by statistics method such as discriminate analysis and compare means tests. Then, a portion of each source determinate by mixed models.
Results: Outputs from the discriminant function analysis show the discriminatory power of the final composite of tracers to be 100% successful in the sources classification for Catchment. Finally, among the seven selected tracer included the Lead, Zinc, Copper, Iron, Manganese, Nickel, and Chromium, have identified sediment sources by three elements included the Copper, Manganese, and Iron the amount 54.7, 31 and 14.3 percent respectively. Quaternary and Gachsaran formations, having the highest share in the sedimentary; the aspect ratio was 1.4 and 1.38 respectively. The poor pasture and forest land uses were responsible the highest and the lowest values of the basin sediment with 71.5 and 0.3 percent, respectively.
Conclusion: The mitigation of nonpoint-source pollutants, such as sediment, in larger basins is rarely a straightforward procedure due to the number of sources and erosional processes contributing to their concentration in waterways. Therefore, the fingerprinting techniques with the relative efficiency 98.2 percent, having the high accuracy and precision in determinate appropriate method to sediment sources basin and separated of the sediment active units. Low relative error and high model efficiency coefficient confirm the results. Also the field observation is the same as model results. The results were indicating the environmental management strategies must be comprehensive for the study area, that need to reduce surface erosion and hill-slope/channel connectivity and the control gullies development by the commercial cultivation and the range reclamation. Sediment fingerprinting revealed that stream bank erosion in general, and of legacy sediments in particular, from Quaternary and Gachsaran formations to Baghmalek River is at the root of the regional sediment loading problem.
Davood Davoodi Moghadam; Seyed Hamidreza Sadeghi; Mahmood Azami Rad
Abstract
Introduction: It is vital to control land degradation, for conserving precious natural treasures. Quantification of runoff production and soil and nutrient loss from wild lands under different managerial systems is one of the scientific and optimal management in agriculture and natural resources, as ...
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Introduction: It is vital to control land degradation, for conserving precious natural treasures. Quantification of runoff production and soil and nutrient loss from wild lands under different managerial systems is one of the scientific and optimal management in agriculture and natural resources, as a major component of sustainable development. Many researches have been conducted to assess the effects of different land uses on soil erosion and runoff generation throughout the globe. Most of which, mainly verified the detrimental effects of human intervention on land degradation. However, limited comprehensive and comparative studies have been conducted to consider the amount of surface runoff generation, and soil and nutrient loss from watersheds with different management patterns viz. untreated and treated small watersheds.
Materials and Methods: The present study aimed to compare surface runoff generation,soil and nutrient loss in Kakhk treated and untreated watersheds with an area ca. 222 ha and precipitation of some 243 mm per annum. Other physical and geological characteristics of the paired watersheds were also similar to allow assessing the effects of study measures on soil, water and nutrient losses. The area under consideration has been located in Khorasan Razavi Province in northeastern Iran. The present study was performed in plots with standard size of 22.1 × 1.8 m in treating and representative areas, with three replicates and on the storm basis occurred during early 2011 and mid-2014. The treated plots were covered by biological measures viz. seeding, bunching and exclusre. The study plots have been situated on eastern,western and northern aspects with respective slope of 55, 40 and 40 %. The entire runoff from study plots were collected in a container in 0.5×1×1 m. The sediment concentration was also measured in 2-liter samples taken from the container after a complete mixing of the entire collected runoff. The sample was treated by decantation technique, oven dried and weighted by high precision scale. The transported elements, i.e. potassium, phosphorous and nitrogen were also measured in solute and particulate forms. Ultimately, the data bank was developed in Excel 2010 and got ready to be processed in SPSS 19.0 software package and statistically compared with the help of analysis of variance (ANOVA) test.
Results and Discussion: The results showed that the soil loss, nitrogen concentration, potassium concentration and sediment concentration had significant difference (p
B. Mohammadnezhad; J. Behmanesh
Abstract
Bridges are the most important structures in river engineering. One of the most causes in bridges destruction is local scouring around the bridge piers. Many bridges failed in the world because of the extreme scour around piers, which have caused to disappear a lot of investments. Then, it is essential ...
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Bridges are the most important structures in river engineering. One of the most causes in bridges destruction is local scouring around the bridge piers. Many bridges failed in the world because of the extreme scour around piers, which have caused to disappear a lot of investments. Then, it is essential to predict the scour depth around bridge piers. In this research, the Fluent three-dimensional numerical model was used to investigate the scouring around the group cylindrical pier in clear water and uniform sand bed conditions. In this model, sedimentary flow was considered as two-phase flow (water - sand) and Eulerian two-phase model was used. To estimate the parameters of flow turbulence in the water phase, the RNG K-ε model was used. To evaluate and verify the numerical model, the computational results were compared with experimental data. The maximum scour depth in front of the first pier on a numerical model equal to 12.5 cm and in experimental model equal to 12 cm have been measured. Also scour depth at the second pier less than that at the first pier and scour depth at the third pier has been less than the values of the first and second pier .The results showed that the two phase model can simulate the scour phenomena around the pier.
