فهرست مطالب

  • Volume:5 Issue:2, 2014
  • تاریخ انتشار: 1392/10/12
  • تعداد عناوین: 7
|
  • Uncertainties in Evaluation of the Sediment Transport Rates in Typical Coarse-Bed Rivers in Iran
    Mehdi Yasi, Rahim Hamzepouri, Alireza Yasi Page 1

    Flow and sediment transport processes are different and more complex in coarse-bed rivers than in sand-bed rivers. The main goal of the present study is to evaluate different modes of sediment transport using different hydrometric and hydraulic methods, and to address the major uncertainties. Four river reaches were selected as representatives of coarse-bed rivers in the Northwest of Iran. A sediment transport model (STM) has been developed to calculate the sediment loads from 5 hydrometric and about 60 hydraulic methods. The extent of the data and flow domain and also the effects of bed material characteristics were examined. The order of prediction intervals of 50%, 75% and 90% were determined. Results indicated that the order of 40% to 70% error is expected despite using the standard sediment measuring system and fitting the measured data to the best predictors. Predictions from the best-fitted hydraulic relationships indicated an order of error between 77% and 200%. This paper presents the prediction results and the order of errors for different modes of sediment loads applicable to similar coarse-bed river reaches.

    Keywords: Coarse, Bed rivers, Sediment transport, STM model, Uncertainties
  • Investigating the Influence of Filter Uniformity Coefficient and Effective Pore Size on Critical Hydraulic Gradient and Maximum Erosion of Dispersive and Non-dispersive Samples
    Jalal Bazargan, Hamed Reza Eskandari Page 2

    Filter is one of the main components of embankment dams. By a simple but effective performance, filter protects the dam against erosion and soil scouring in impervious core caused by leakage (piping) and makes it safe. Interaction between filter and erodible base soil is a complex phenomenon which is dependent upon several factors, and has challenged researchers for better understanding the filtration system behavior. Therefore, more investigations in this field are needed. Identification of dispersive soil filtration is of great importance because of high erodibility potential of these soils. In this study, in order to evaluate dispersive soil filtration a device is designed and made by the authors for filter testing. This device can measure the hydraulic gradient in flow path by using a controlled flow head. By performing filter tests on dispersive and non-dispersive soil samples, the effect of uniformity coefficient and effective pore size of the filter on critical hydraulic gradient has been studied. The critical hydraulic gradient varies with the change in filter uniformity coefficient, and by increasing the effective pore size of the filter, critical hydraulic gradient is decreased.

    Keywords: Dispersive soil, Critical hydraulic gradient, Uniformity coefficient, Effective pore
  • Characteristics of S-jump on Roughened Bed Stilling Basin
    Kobra Neisi, Mahmood Shafai Bejestan Page 3

    Formation of hydraulic jump is necessary for dissipation of the excess kinetic energy downstream of spillways and gates. Hydraulic jump stilling basins of sudden expansion are one of the energy dissipater structures which are used where the available tail water depth is less than the required sequent depths. In the present study to further reduce the hydraulic jump sequent depths ratio, a roughened bed type of stilling basins of sudden expansion is experi-mentally investigated. Four different expansion ratios of 0.33, 0.5, 0.67 and 1 were studied under wide range of flow conditions, Froude numbers between 2 and 10. Results of the present study show that sequent depths ratio is 16-20 percent lower and the jump efficiency can increase 20 percent in comparison to the classical jump.

    Keywords: Hydraulic jump, Abrupt expansion, Stilling basins, Roughened bed
  • Introducing a Relationship for Estimation of the Sediment Transport Rate through Rockfill Structures
    Ebrahim Amiri Tokaldany, Jafar Chapokpour Page 4

    Rockfill dams are accounted as useful measures in watershed management projects. How-ever, the sediment transport through the rockfill materials, could impact their lifetime duration. Previously, researches have been conducted to describe the various hydraulically issues of the flow passing through these structures However; there is no general relationship to estimate the sediment transport rate passing through the of rockfill structures. In this research, by using several sets of data provided from three various sources, we introduced a more general rela-tionship to estimate the sediment transport passing through the rock materials. We compared the predicted results from the new equation with those estimated from the other equations. We found that the accuracy of the new relationships is much more than previously introduced equ-ations. Using more measured data, we found that the mean relative error of the predicted re-sults is %21 showing the reasonable accuracy of the present relationship.

    Keywords: None Darcy flow, Reynolds number, Rockfill structures, Sediment transport rate
  • Discharge Estimation by using Tsallis Entropy Concept
    Hossein Bonakdari, Marjan Moazamnia Page 5

    Flow-rate measurement in rivers under different conditions is required for river management purposes including water resources planning, pollution prevention, and flood control. This study proposed a new discharge estimation method by using a mean velocity derived from a 2D velocity distribution formula based on Tsallis entropy concept. This procedure is done based on several factors which reflect the basic hydraulic characteristics such as river bed slope, wetted perimeter, width, and water level that are easily obtained from rivers. This method avoids putting the environment at risk and significantly reduces time and costs. Validation of the method was carried out by comparing the results with measured values in the experimental sites. Predicted results are in good agreement with the measured data in a cross section of the Tiber River, Italy. Extended usage of this method will make it possible to measure discharge and better estimate the flow rate conveyed from rivers under different hydraulic conditions.

    Keywords: Mean velocity, hydraulic characteristics, rivers, probability
  • Investigating the Hydraulic Properties and Design Criteria for the River Subsurface Intake with a porous media without cut off
    Ramin Mansouri, Alinaghi Ziaei, Kazem Esmaili, Hosein Ansari, Saeedreza Khodashenas Page 6

    Surface and subsurface water collection in small seasonal rivers is very crucial, particularly in dry seasons. In this study a type of intake is introduced which acts as a river drainage network. An experimental model of the subsurface intake was constructed and the effective parameters such as upstream discharge, installation depth, and drain intervals were evaluated. The results showed that the water diversion was mostly influenced by the upstream flow rate. The very small drain interval reduced the discharge of each drain. It was also revealed that the total drained discharge in the very transmitting media was mostly controlled with the number of drains and drain interval did have a marginal effect, the total discharge of drains in length of 100 cm has increased 63% in comparison to the total discharge of drains in length of 50 cm, whereas this increase was about 90% in length of 150 cm comparing to the length of 50 cm. Finally the regression equations were developed to estimate the discharge of each drain based on dimensional analysis, which facilitate the design of this structure.

    Keywords: Subsurface intake, Porous media, Drainage system, Design criteria
  • Sources of contamination in rainwater by major and heavy elements in Arak, Iran
    Feridon Ghadimi, Mohammad Ghomi, Mohsen Ranjbar, Abdolmotaleb Hajati Page 7

    Measurements of Pb, Cu, Zn, As, Ni, Hg, and Fe heavy metals and major elements and components such as Ca, HCO3, SO4, Na, K, Mg and Cl in soluble rain fractions were performed on rainwater collected at Arak plain during the rainy seasons of 2012. Concentrations of the heavy metals in the soluble fractions decreased for Fe, Pb, Zn, Ni, Cu, As and Hg, respectively and the major elements and components of HCO3, SO4, Ca, Na, Mg, Cl and K, respectively. Enrichment factors related to the relative abundance of the elements in crustal material were calculated using Fe as the reference. High enrichment factors (EFcrustal and EFplayawater) suggested that, in general, heavy metals had an anthropogenic origin and major ions had a natural origin. Factor analysis with varimax normalized rotation grouped the analyzed elements into four factors. Factor 1 indicated a high loading for positive nps-K, nps-Mg, nps-Ca, nps-Cl, nps-HCO3 and negative Cu, Ni, nps-SO4 components and represented the crust and anthropogenic origin. Factor 2 indicated a high loading of As and Zn. These metals are characteristics of anthropogenic origin. Factor 3 indicated an anthropogenic origin for Pb and Fe. Factor 4 indicated crustal source for Hg. Calcareous soils and alkalin soils in Arak plain are the sources of major elements and industrial activity and traffic are the sources of heavy metals in the rainwater samples in Arak city.

    Keywords: Contamination, Heavy metals, Major elements, Natural, anthropogenic sources, Enrichment factor, Factor analysis, Arak