Hossein Afzalimehr

Hossein Afzalimehr
Isfahan University of Technology | IUT · Department of Irrigation

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96
Publications
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1,104
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Publications

Publications (96)
Article
Abstract This research is analyzed the flood hazard using two ensemble models in Mazandaran Province, Iran and assess how the experience contributed to community flood preparedness by household surveys. For this purpose, two approaches of Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Attributive Border Approximation...
Article
Full-text available
Golestan Province is one of the most vulnerable areas to catastrophic flood events in Iran. The flood severity in this region has grown dramatically during the last decades, demanding a major investigation. Accordingly, an authentic map providing detailed information on floods is required to reduce future flood disasters. Three ensemble models prod...
Article
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To implement soil conservation approaches, it is necessary to estimate the amount of annual sediment production from a watershed. The purpose of this study was to determine the erosion intensity and sedimentation rate from a watershed by employing empirical models, including the modified Pacific Southwest Inter-Agency Committee (MPSIAC), the erosio...
Article
A large proportion of flow resistance can be due to vegetation in open-channel flows. Classic methods are unable to estimate flow resistance in the presence of vegetation. In this study, drag coefficient was estimated as a parameter to represent the flow resistance in emergent and submerged vegetation patches with different densities. Emergent vege...
Article
Full-text available
Determination of skin friction factor has been a controversial topic, particularly in gravelbed rivers where total flow resistance is influenced by the existence of small-scale skin roughness and large-scale topographic forms. The accuracy of existing models predicting skin friction factors in conditions where small-scale skin roughness and large-s...
Article
Full-text available
This paper investigates the incipient motion of sediment particles under non-uniform flow in river and laboratory. In rivers, the non-uniform flow is often observed due to the presence of various bed forms. Threshold condition has been examined by using the Shields diagram based on the uniform flow assumption, however, this approach can be led to f...
Article
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Vegetation patches and strips either along riverbanks or in channel beds are essential for the protection of erosion and sedimentation processes. In the present study, the drag coefficient of submerged flexible vegetation patches in gravel bed rivers was investigated. A total of 13 vegetation patches with different densities were studied in dispara...
Conference Paper
Full-text available
پیش بینی هندسه هیدرولیکی کانال های پایدار و رودخانه های آبرفتی از اهمیت بالایی در طراحی و مدیریت در مهندسی رودخانه برخوردار است. تاکنون روابط زیادی توسط محققین متعددی برای پیش بینی هندسه هیدرولیکی کانال های پایدار ارائ هشده اند. در این تحقیق تلاش شده است که با استفاده از یک بانک اطلاعاتی شامل 111 داده میدانی از میان داده های جولین و وارگادالام (199...
Article
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...
Article
Full-text available
Citation: Kazem, M.; Afzalimehr, H.; Sui, J. Characteristics of Turbulence in the Downstream Region of a Vegetation Patch. Water 2021, 13, 3468.
Article
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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)...
Article
Full-text available
Comprehensive preview of flow characteristics and bedforms in rivers is one of the imperative purposes of river restoration projects. This study aimed to assess the application of double averaged technique for estimating the flow velocity and shear velocity in gravel bedforms by field research throughout the Babolroud River in north of Iran. Also,...
Article
Full-text available
In the present experimental study, the effect of vegetation on flow structure and scour profile around a bridge abutment has been investigated. The vegetation in the channel bed significantly impacted the turbulent statistics and turbulence anisotropy. Interestingly, compared to the channel without vegetation, the presence of vegetation in the chan...
Article
Full-text available
Determination of the flow velocity and shear stress is fundamental for river restoration projects. There are few studies in estimation of these parameters in the presence of 3D pool and riffle which are dominant bed forms in coarse-bed Rivers. Considering the interaction of 3D bed forms and the flow characteristics in the presence of wall vegetatio...
Article
Full-text available
By using model vegetation (e.g., synthetic bars), vortex structures in a channel with vegetation patches have been studied. It has been reported that vortex structures, including both the vertical and horizontal vortexes, may be produced in the wake in the channel bed with a finite width vegetation patch. In the present experimental study, both vel...
Article
The purpose of this study is to develop a reliable model for identification of flood susceptible areas. Three multi-criteria decision-making techniques, namely Analytical Hierarchy Process (AHP), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), and Attributive Border Approximation Area Comparison (MABAC) methods combined...
Article
Understanding the interaction between the flow structure and the dune bed form which is covered by the vegetation patches is crucial for the river engineering due to its impact on the transport of the sediment and the bed stabilities. Therefore, at this study, an attempt was done to investigate experimentally the effects of the flat crest dune and...
Article
Full-text available
In this study, the incipient motion of four groups of sand, ranging from medium to very coarse particles, was experimentally examined using an acoustic Doppler velocimeter (ADV) in different water depths under the hydraulically transitional flow condition. The transport criterion of the Kramer visual observation method was used to determine thresho...
Article
Vegetation in open channels alters turbulent and other hydraulic characteristics of flow. Hence, conventional methods for computing bed shear stress in bare channels are not applicable in such channels. The present study, therefore, experimentally investigates the distributions of velocity in 3D in gravel bed channels with vegetation and investigat...
Article
Full-text available
This paper reports a laboratory study of turbulent flow characteristics over a pool bed-form at different cross-sections in a flume. Experiments were conducted for two cases, with and without the presence of vegetative over gravel bed-form, to investigate interactions between pool bed-form, vegetation, and flow non-uniformity. Artificial grass was...
Preprint
Full-text available
Floods are one of the most damaging natural disasters throughout the world. The purpose of this study is to develop a reliable model for identification of flood susceptible areas. Three Multi-criteria decision-making techniques, namely Analytical Hierarchy Process (AHP), Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), an...
Article
The submerged vegetation patch affects the flow structure significantly. Quantifying this structure, which is crucial for river engineers, depends on estimating the drag coefficient accurately. However, most of the available empirical and semi-empirical relations have some uncertainties. So, the present work attempts to estimate and evaluate the dr...
Article
Full-text available
In rivers, irrigation canals, and drainage channels vegetation patches often appear over the bed. Flow over vegetation patches is in non-developed region which significantly influences the flow structures, thus affecting the estimation of friction factor. In the present study, the experiments were conducted in a laboratory flume to investigate the...
Article
Pool–riffle sequences are common bed forms in mountain rivers that have a significant effect on hydraulic and hydro-environment characteristics. Relatively few studies exist on the comparison of two and three dimensional modeling for bed forms in gravel channels. In this paper, flow structure and habitat modeling are performed in an urban river, by...
Article
Full-text available
In present study, among six gravel-bed river reaches, two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found, one river reach with vegetation on bedforms and the other without vegetation on bedforms. Based on field measurements, the impacts of vegetation over bedforms on flow characteristics hav...
Article
Full-text available
Investigation of the interactions between submerged vegetation patch and flow structure is of crucial importance for river engineering. Most of hydraulic models have been presented for fully developed flows over uniform vegetation in the laboratory conditions; however, the mentioned interactions are complex in river flows where the flow is not deve...
Article
Full-text available
Many species of flexible submerged vegetation are observed in natural streams in which the flow is rarely uniform. For better understanding the effect of flexible submerged vegetation density on the flow, experiments were conducted in the Hydraulics Laboratory of Isfahan University of Technology, Iran. Two runs with grassy artificial weeds with hig...
Article
Full-text available
The effect of fully submerged boulders on the flow structure in channels has been studied by some researchers. However, many natural streams have bed material with boulders that are not fully submerged under water. In many natural streams, boulders cover between 1% and 10% of the area of the stream reach. The effect of non-submerged boulders on the...
Article
In this experimental study, the effect of a submerged vegetation patch with individual plants on the incipient motion of sediment has been examined. Results showed that a vegetation patch in the channel bed affected the incipient motion process of sediment and resulted in significant impacts on flow velocity, turbulence intensities, turbulent kinet...
Article
Full-text available
Pools and riffles in gravel-bed rivers have a major effect on the variables of the flow equations. Obtaining measurements of these variables requires comprehensive research conducted in rivers. Detailed measurements were taken from one reach of the Kaj River, Iran. The subsequent results showed a phase shift for: X-component of velocity, near bed v...
Article
Full-text available
Planning and design of river engineering works depend on the changes in bed forms and their interaction with flow. This paper investigated the application of Coles law in the outer region of the boundary layer and compared it with the parabolic law on riffles; developed a relationship between Coles parameter and dimensionless pressure gradient β; d...
Article
Full-text available
To better understand the influence of non-uniform flow in coarse-bed streams with a submerged vegetation strip on flow characteristics, data were collected from experiments in a laboratory flume and field investigations in a cobble-bed river reach in central Iran. The results of the experiments and field observations showed that the velocity profil...
Article
Full-text available
Experiments have been carried out in a flume with one 2D pool-riffle sequence and one 3D pool-riffle sequence, respectively. Objectives of this study are to determine whether or not the convergence of lateral flow exists. Variations of the near-bed shear stress have been studied. The characteristics of the secondary currents along a pool-riffle seq...
Article
Full-text available
On the basis of experiments carried out in flume with a wavy bed with vegetation cover, flow velocity, turbulence intensities and Reynolds stress distributions are investigated. The wavy bed was similar to dune in this study. The fixed artificial dunes were constructed over the bed and artificial vegetation put over them in a laboratory flume. An A...
Article
Full-text available
Estimation of hydraulic and geometric parameters of a gravel-bed river such as dimensions of bedforms is very difficult task, although they play a fundamental role in river engineering projects. One of the methods to get essential information regarding the bedform characteristics is to find the relations between the flow parameters and bedform dime...
Article
Full-text available
امروزه بررسی و مطالعه خصوصیات هیدرولیکی جریان در رودخانه های شنی مورد توجه بسیاری از محققان قرار گرفته است که پیش از آن درک خصوصیات مورفولوژی رودخانه به منظور شبیه سازی در کانال های آزمایشگاهی بسیار حائز اهمیت است. مطالعات رودخانه دشواری و خطرات جانبی زیادی دارد از این رو کمتر به بررسی‌های رودخانه‌ای ازجمله توزیع و دانه بندی ذرات بستر پرداخته شده ا...
Article
Full-text available
The present study deals with the turbulence structure in order to better understand the interaction of bedform and flow characteristics in a gravel-bed river. Data measured above a bedform is used to analyze the importance of coherent structures in turbulent transfer. The Reynolds stress and turbulence intensity in stream-wise direction illustrate...
Article
Full-text available
This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95,...
Research
Vegetation in channels, rivers, reservoirs, and wetlands alters the flow turbulence characteristics. Vegetation has both positive and negative effects, depending on the objective of the hydraulic conduit.
Article
Full-text available
Bed forms and vegetation significantly influence flow characteristics. Macro-scale bed forms, such as pools, result in non-uniformity in flow; vegetation alters turbulence intensity, shear stress, and velocity distributions. To date, limited work on impacts of pools and vegetated banks on flow characteristics has been reported. Based on experiments...
Article
Full-text available
Experiments were carried out over a 2-dimentional pool with a constant length of 1.5 m and four different slopes. The distributions of velocity, Reynolds stress and turbulence intensities have been studied in this paper. Results show that as flow continues up the exit slope, the flow velocity increases near the channel bed and decreases near the wa...
Article
Full-text available
Field observations showed that in many gravel-bed rivers, rice stems and gravel interact with each other and affect the flow structure. This calls to conduct research in more details in laboratory to better understand impacts of interaction between rice stems and gravel bed rivers on the flow structure. The outcome of such investigations can improv...
Article
This study examines velocity components in 3D and shear stress distributions in flows with adverse pressure gradient over a gravel-bed channel using three types of vegetation on banks, rice, straw and Typha stems. Results of this experimental study are compared with those for flows in the bare bank channel. Results show that the flows with adverse...
Article
Bed load transport is needed for river training works, reservoir management, watershed management, and ecosystem maintenance. A number of equations have been developed for determining bed load transport, primarily for alluvial rivers. This study applies the boundary-layer characteristics to evaluate bed shear stress and the rate of bed load. Also,...
Article
Failure of bridges due to local scour in the vicinity of bridge abutments is a common occurrence. In this study, experiments under two different channel conditions were conducted to assess the impacts of vegetation on channel banks on local scour around a wing-wall abutment with circular edges. Some experiments were conducted in channel with vegeta...
Article
Using hydraulic data collected in thirteen cross-sections in a 250 m long reach of Babolroud River, Iran, this study investigated the relation between flow resistance and vegetation in a gravel-bed river with vegetated banks. It was found that the maximum flow velocity occurred on the water surface for bare bank cross-sections, but near the vegetat...
Article
This study investigates the contribution of form friction to the total friction factor, using observed data from Babolroud River located in north of Iran and south of the Caspian Sea. Results show that form friction (f") contributes up to 65% of the total friction factor (f) of a gravel-bed river. Most of the equations in the hydraulics literature...
Article
Bed load transport is of fundamental importance in river engineering. Although there are many bed load transport equations, there is still no consensus on which equation is the best and how to select a particular equation for a particular river. Often there are large discrepancies in the bed load transport values yielded by different equations and...
Article
Using laboratory experiments and a numerical model, this study examined the influence of dune dimensions on the separation of flow. Different conditions, depending on the dune height, material, and angle and flow depth and velocity, were considered. Experiments were conducted in a horizontal flume with one side wall being transparent for applicatio...
Article
This research presents recent advances on morphodynamic modeling over gravel dunes. Boundary-layer separation over gravel fixed dunes is investigated by Acoustic Doppler Velocimetry (ADV). Using the measurements of flow over dunes at laboratory scale, examined the influence of dune lee sides on the separation of flow. Experiments were conducted in...
Article
Weirs are used for flow measurement, flood control in reservoirs and water level control in irrigation systems. In this study, a new weir entitled of quarter-circular crested weir is investigated. This weir is geometrically consisted of a quarter-circular crest of radius R, upstream slope α and vertical downstream face. The downstream face of the w...
Article
The effect of cobble concentration and vegetated banks on the mean flow and turbulence of streams has not yet been investigated. Cobble concentrations ranging from 10 to 30 cobbles/m2 were tested by this study. In total, 27 velocity profiles were measured using an acoustic Doppler velocimeter (ADV) at a sampling frequency of 200 Hz. The results sho...
Article
It is common for engineers to use countermeasures to protect hydraulic structures against scour. This study aims to explore the effect of jet injection through the pier body as a pier-scour countermeasure. Laboratory experiments were conducted in two different flow depths (10.5 and 28 cm) using 1-jet and 3-jet injections, different jet locations, a...
Article
This paper primarily presents velocities, Reynolds stresses and turbulence intensities of flow over a series of two-dimensional asymmetric sharp-crested, gravel bedforms. The bedforms have a mean wavelength of 0.96 m, a mean height of 0.08 m, and a width of 0.4 m (equal to the flume width) and a lee slope of 28°. The results show that extrapolati...
Article
Full-text available
Experiments were conducted in an 8 m long, 40 cm wide, and 60 cm deep re-circulating flume with vegetated banks and gravel bed to study the effects of accelerating and decelerating flows on the flow structure. Significant dip phenomenon was observed in velocity profiles under decelerating flow and the velocity defect law was not suitable due to the...
Article
Acoustic Doppler Velocimeters (ADV) experiments have been conducted over a fixed-dune to examine the effects of interacting dunes on the flow structure. The shape, dimensions and side angle of selected dunes were based upon previous empirical and field studies of dune morphology. Experiments were carried out on flow over a train of fixed 2D rough w...
Article
In this experimental study, the turbulent flow in a channel with vegetation by using sprouts of wheat on channel bed was investigated. Two different aspect ratios of channel were used. An Acoustic Doppler Velocimetry was used to measure parameters of turbulent flow over submerged sprouts of wheat, such as velocity profiles. The log law and the Reyn...
Article
This paper presents results of the friction factor of cobble-bed and boulder-bed rivers based on 23 field measurements in three mountainous rivers in Iran. Results reveal that features of our measured velocity profiles in boulder-bed rivers in mountainous region do not present a specific shape but illustrate specific pattern in cobble-bed rivers. T...
Article
On the basis of laboratory experiments, this paper investigates the effect of different bed forms and vegetated banks on flow velocity, Reynolds stresses, and turbulence intensities. Experimental measurements were made over fifth and sixth dunes in a series of seven of two-dimensional (2D) asymmetric gravel dunes that had lee-slope angles of 28° an...
Article
The behaviour of the bed shear stress in the presence of a decelerating flow over a gravel bed has been examined. The collected observations revealed that the velocity distribution in the outer region of the boundary layer may be described by a parabolic law. The results obtained by parabolic law are comparable to the bed shear stress estimated via...
Article
Full-text available
In this paper reduction of scour around group of two and three piers using circular collar has been carried out for the case of clear-water flow over uniform sediment. The efficiency of collars, with different sizes and spaces between piers is studied through experiments in group of two and three piers. The result reveals that collar has more influ...
Article
This study investigated the sediment entrainment and critical shear stress in gravel-bed rivers. Measured rates of bed load transport were used to estimate the Shields stress parameter. The computed parameters were compared to those derived from the Meyer-Peter-Muller method. The agreement between these methods was good and the values of tau(*c) ob...