A comprehensive overview of flow characteristics in natural channels with bedforms is a vital iss... more A comprehensive overview of flow characteristics in natural channels with bedforms is a vital issue in river management projects. Pool-riffle sequences as common bedforms in the gravel-bed rivers significantly impact flow characteristics and turbulence intensity. The present study was taken by field investigation in the Babolroud River, Iran. A 95 m reach with variable width was chosen in this river and velocity components and shear stress were obtained in different sections. Quadrant analysis was also applied to determine the dominant bursting event in the pool section. The results revealed a phase shift for stream-wise velocity, near-bed velocities, and bed shear stress versus bed profile. In the pool, vertical velocity components were oriented downward near the bed and upward near the water surface, while in the riffle section vectors were oriented towards the bed. The findings of quadrant analysis demonstrated the ejections and sweeps as a dominant event close to the bed and water surface, respectively.
Stochastic Environmental Research and Risk Assessment, Mar 18, 2021
Flood is one of the most destructive natural disasters globally and is a concern due to its high ... more Flood is one of the most destructive natural disasters globally and is a concern due to its high vulnerability. In this study for identification of flood susceptible areas, artificial neural network (ANN) and Multi-Attributive Border Approximation Area Comparison (MABAC) combined with Weights of Evidence (WoE) and Analytical Hierarchy Process (AHP) Models were used in Mazandaran province, Iran. MABAC method was used for the first time to evaluate the flood-prone areas in this study, and Attempts have been made for evaluate the performance of this new method by comparing with ANN model. The output of the neural network was discharge values in hydrometric stations. Using Geographic Information System (GIS) with eight effective factors including rainfall, distance from rivers, slope, soil, geology, elevation, drainage density, and land use, a flood model developed. Three precision parameters containing R2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${R}^{2}$$\end{document}, RMSE and MAE were applied to show the performance of the ANN model which yielded the values of 0.89, 0.0024 m3/s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${m}^{3}/s$$\end{document}, and 0.0018 m3/s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${m}^{3}/s$$\end{document}, respectively for testing data. The verification results indicated satisfactory agreement between the predicted and the real hydrological records. Also, based on flood inventory map and using the area under receiver operating curve, predictive power of the MABAC-WoE-AHP model was evaluated. The AUC value for prediction rate of this model was 86.1% which indicates the very good accuracy in predicting flood-prone areas. Comparison of flood susceptibility maps for ANN and MABAC-WoE-AHP models showed the good agreement between two models, that clarifies the efficiency of the new proposed method for future preventive measures.
The world's large lakes and their life‐supporting services are rapidly threatened by eutrophi... more The world's large lakes and their life‐supporting services are rapidly threatened by eutrophication in the warming climate during the Anthropocene. Here, MODIS‐Aqua level 3 chlorophyll‐a data (2018–2021) were used to monitor trophic state in our planet's largest lake, that is, the Caspian Sea that accounts for approximately 40% of the total lacustrine waters on Earth. We also used the in situ measurements of chlorophyll‐a data (2009–2019) to further verify the accuracy of the data derived from the MODIS‐Aqua and to explore the deep chlorophyll‐a maxima (DCMs) in the south Caspian Sea. Our findings show an acceptable agreement between the chlorophyll‐a data derived from the MODIS‐Aqua and those measured in situ in the coast of Iran (coefficient of determination = 0.71). The oligotrophic, mesotrophic, and eutrophic states cover 66%, 20%, and 13% of the sea surface area, respectively. The DCMs are dominantly regulated by water transparency and they generally observe at depths of less than 20 and 30 m during the cold (autumn and winter) and warm (spring and summer) seasons, respectively. Our results suggest an ever‐increasing chlorophyll‐a in the shallow zones (i.e., coasts) and even in deep regions of the sea, mainly due to nutrient inputs from the Volga river delta. Alarming increase of chlorophyll‐a in this transboundary lake can amplify eutrophication under the lens of global warming and further threaten the lake ecosystem's health, where almost all legal agreements have not yet been implemented to protect the lake environment and its rich resources.
ABSTRACT Vegetation on banks of natural channels exercises a significant influence on the flow st... more ABSTRACT Vegetation on banks of natural channels exercises a significant influence on the flow structure and in turn on the velocity distribution as well as the distribution of Reynolds stress (the random turbulent fluctuations in fluid momentum). This study experimentally investigated the effect of vegetation on banks on accelerating flow in a gravel-bed flume. The results showed that in the presence of vegetation the Reynolds stress distribution became nonlinear and the velocity distribution took on a deformed S shape near the vegetated banks. In addition, vegetation on banks had more influence on the location of maximum velocity than had the aspect ratio. The log law fitted the data near the bed up to y/h=0.2 (h=flow depth and y=distance from the bed), however, very near the bed the scatter in data was significant. Finally, the Coles law cannot be applied for accelerating flow when the vegetation was present on banks.
AbstractHydraulic structures in rivers employ abutments of different shapes. An abutment causes a... more AbstractHydraulic structures in rivers employ abutments of different shapes. An abutment causes a scour hole around the bottom of the structure in the river. The scour hole grows no further when th...
Using a large set of field and laboratory data, this study investigated the effect of slope and t... more Using a large set of field and laboratory data, this study investigated the effect of slope and the Shields parameter on the friction factor. It identified the ranges of critical shear stress and bed slope for which Froude number would or would not play an important role in the evaluation of friction. It was found that the prediction of friction factor for slopes less than 0.000 81 was not satisfactory. For the Shields parameter range of ( 0.01< τ∗c <0.1 ) and the range of slope of 0.000 82–0.01, the prediction of friction factor was satisfactory even without considering the effect of Froude number. On the other hand, the inclusion of Froude number improved the estimation of friction factor for the range of ( 0.01< τ∗c <0.05 ) and steeper slopes (0.01–0.02). Finally, in gravel/sand rivers in Iran, friction factor can be estimated whether or not the flow velocity is known.
Vegetation in rivers and streams plays an important role in preventing erosion and improving bank... more Vegetation in rivers and streams plays an important role in preventing erosion and improving bank stability. Comparison between emergent vegetation (bank vegetation) and submerged vegetation, in terms of velocity and Reynolds stress distributions, for the same aspect ratio and flow discharge, has received limited attention in the literature. This study investigates the velocity and Reynolds stress, as well as the log law for submerged and emergent vegetation in a laboratory flume and compares the results for a different set up with different sediment size and aspect ratio but the same discharge. The results indicate that the influence of submerged vegetation on the secondary currents generation is less than emergent vegetation. In addition, the log law application is valid for both submerged and emergent vegetation cases, however, it is valid up to y/h = 0.75 for emergent vegetation (in which the vegetation cover in banks is partly out of the water) but up to y/h = 0.25 for vegetati...
Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameter... more Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameters in hydraulic engineering, mechanical engineering, fluvial morphology, and environmental studies. Based on this necessity, in this study, the values of bed shear stress in four reaches of rivers in Iran were estimated and compared using the methods of boundary layer characteristics, logarithmic law, and Darcy–Weisbach. Data collection in this study started in February 2021 and ended in April 2021. Estimation of flow resistance is a key factor in many numerical and physical models. In order to obtain a reasonable evaluation of this factor, it is necessary to measure and calculate the key variables of resistance to flow. Accordingly, the experimental design in this study includes surveying operations, velocity measurement, and sampling of bed sediments. The results show that due to bed forms, vegetation patches, and variations of flow depth and grain size in the river, the universal veloc...
A comprehensive overview of flow characteristics in natural channels with bedforms is a vital iss... more A comprehensive overview of flow characteristics in natural channels with bedforms is a vital issue in river management projects. Pool-riffle sequences as common bedforms in the gravel-bed rivers significantly impact flow characteristics and turbulence intensity. The present study was taken by field investigation in the Babolroud River, Iran. A 95 m reach with variable width was chosen in this river and velocity components and shear stress were obtained in different sections. Quadrant analysis was also applied to determine the dominant bursting event in the pool section. The results revealed a phase shift for stream-wise velocity, near-bed velocities, and bed shear stress versus bed profile. In the pool, vertical velocity components were oriented downward near the bed and upward near the water surface, while in the riffle section vectors were oriented towards the bed. The findings of quadrant analysis demonstrated the ejections and sweeps as a dominant event close to the bed and water surface, respectively.
Stochastic Environmental Research and Risk Assessment, Mar 18, 2021
Flood is one of the most destructive natural disasters globally and is a concern due to its high ... more Flood is one of the most destructive natural disasters globally and is a concern due to its high vulnerability. In this study for identification of flood susceptible areas, artificial neural network (ANN) and Multi-Attributive Border Approximation Area Comparison (MABAC) combined with Weights of Evidence (WoE) and Analytical Hierarchy Process (AHP) Models were used in Mazandaran province, Iran. MABAC method was used for the first time to evaluate the flood-prone areas in this study, and Attempts have been made for evaluate the performance of this new method by comparing with ANN model. The output of the neural network was discharge values in hydrometric stations. Using Geographic Information System (GIS) with eight effective factors including rainfall, distance from rivers, slope, soil, geology, elevation, drainage density, and land use, a flood model developed. Three precision parameters containing R2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${R}^{2}$$\end{document}, RMSE and MAE were applied to show the performance of the ANN model which yielded the values of 0.89, 0.0024 m3/s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${m}^{3}/s$$\end{document}, and 0.0018 m3/s\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${m}^{3}/s$$\end{document}, respectively for testing data. The verification results indicated satisfactory agreement between the predicted and the real hydrological records. Also, based on flood inventory map and using the area under receiver operating curve, predictive power of the MABAC-WoE-AHP model was evaluated. The AUC value for prediction rate of this model was 86.1% which indicates the very good accuracy in predicting flood-prone areas. Comparison of flood susceptibility maps for ANN and MABAC-WoE-AHP models showed the good agreement between two models, that clarifies the efficiency of the new proposed method for future preventive measures.
The world's large lakes and their life‐supporting services are rapidly threatened by eutrophi... more The world's large lakes and their life‐supporting services are rapidly threatened by eutrophication in the warming climate during the Anthropocene. Here, MODIS‐Aqua level 3 chlorophyll‐a data (2018–2021) were used to monitor trophic state in our planet's largest lake, that is, the Caspian Sea that accounts for approximately 40% of the total lacustrine waters on Earth. We also used the in situ measurements of chlorophyll‐a data (2009–2019) to further verify the accuracy of the data derived from the MODIS‐Aqua and to explore the deep chlorophyll‐a maxima (DCMs) in the south Caspian Sea. Our findings show an acceptable agreement between the chlorophyll‐a data derived from the MODIS‐Aqua and those measured in situ in the coast of Iran (coefficient of determination = 0.71). The oligotrophic, mesotrophic, and eutrophic states cover 66%, 20%, and 13% of the sea surface area, respectively. The DCMs are dominantly regulated by water transparency and they generally observe at depths of less than 20 and 30 m during the cold (autumn and winter) and warm (spring and summer) seasons, respectively. Our results suggest an ever‐increasing chlorophyll‐a in the shallow zones (i.e., coasts) and even in deep regions of the sea, mainly due to nutrient inputs from the Volga river delta. Alarming increase of chlorophyll‐a in this transboundary lake can amplify eutrophication under the lens of global warming and further threaten the lake ecosystem's health, where almost all legal agreements have not yet been implemented to protect the lake environment and its rich resources.
ABSTRACT Vegetation on banks of natural channels exercises a significant influence on the flow st... more ABSTRACT Vegetation on banks of natural channels exercises a significant influence on the flow structure and in turn on the velocity distribution as well as the distribution of Reynolds stress (the random turbulent fluctuations in fluid momentum). This study experimentally investigated the effect of vegetation on banks on accelerating flow in a gravel-bed flume. The results showed that in the presence of vegetation the Reynolds stress distribution became nonlinear and the velocity distribution took on a deformed S shape near the vegetated banks. In addition, vegetation on banks had more influence on the location of maximum velocity than had the aspect ratio. The log law fitted the data near the bed up to y/h=0.2 (h=flow depth and y=distance from the bed), however, very near the bed the scatter in data was significant. Finally, the Coles law cannot be applied for accelerating flow when the vegetation was present on banks.
AbstractHydraulic structures in rivers employ abutments of different shapes. An abutment causes a... more AbstractHydraulic structures in rivers employ abutments of different shapes. An abutment causes a scour hole around the bottom of the structure in the river. The scour hole grows no further when th...
Using a large set of field and laboratory data, this study investigated the effect of slope and t... more Using a large set of field and laboratory data, this study investigated the effect of slope and the Shields parameter on the friction factor. It identified the ranges of critical shear stress and bed slope for which Froude number would or would not play an important role in the evaluation of friction. It was found that the prediction of friction factor for slopes less than 0.000 81 was not satisfactory. For the Shields parameter range of ( 0.01< τ∗c <0.1 ) and the range of slope of 0.000 82–0.01, the prediction of friction factor was satisfactory even without considering the effect of Froude number. On the other hand, the inclusion of Froude number improved the estimation of friction factor for the range of ( 0.01< τ∗c <0.05 ) and steeper slopes (0.01–0.02). Finally, in gravel/sand rivers in Iran, friction factor can be estimated whether or not the flow velocity is known.
Vegetation in rivers and streams plays an important role in preventing erosion and improving bank... more Vegetation in rivers and streams plays an important role in preventing erosion and improving bank stability. Comparison between emergent vegetation (bank vegetation) and submerged vegetation, in terms of velocity and Reynolds stress distributions, for the same aspect ratio and flow discharge, has received limited attention in the literature. This study investigates the velocity and Reynolds stress, as well as the log law for submerged and emergent vegetation in a laboratory flume and compares the results for a different set up with different sediment size and aspect ratio but the same discharge. The results indicate that the influence of submerged vegetation on the secondary currents generation is less than emergent vegetation. In addition, the log law application is valid for both submerged and emergent vegetation cases, however, it is valid up to y/h = 0.75 for emergent vegetation (in which the vegetation cover in banks is partly out of the water) but up to y/h = 0.25 for vegetati...
Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameter... more Bed shear stress in coarse–bed rivers with vegetation patches is one of the challenging parameters in hydraulic engineering, mechanical engineering, fluvial morphology, and environmental studies. Based on this necessity, in this study, the values of bed shear stress in four reaches of rivers in Iran were estimated and compared using the methods of boundary layer characteristics, logarithmic law, and Darcy–Weisbach. Data collection in this study started in February 2021 and ended in April 2021. Estimation of flow resistance is a key factor in many numerical and physical models. In order to obtain a reasonable evaluation of this factor, it is necessary to measure and calculate the key variables of resistance to flow. Accordingly, the experimental design in this study includes surveying operations, velocity measurement, and sampling of bed sediments. The results show that due to bed forms, vegetation patches, and variations of flow depth and grain size in the river, the universal veloc...
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