Agricultural Meteorology
S. Pourentezari; K. Esmaili; A.R. Faridhosseini; E. Ghafari
Abstract
Introduction Precipitation is one of the most important input parameters of the hydrological models for rainfall-runoff simulation, which due to the lack of proper dispersion of rain gauge stations and the newly established some of these stations in most basins of the country, the use of these precipitation ...
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Introduction Precipitation is one of the most important input parameters of the hydrological models for rainfall-runoff simulation, which due to the lack of proper dispersion of rain gauge stations and the newly established some of these stations in most basins of the country, the use of these precipitation data faces serious challenges. Therefore, the use of remote-sensing methods is one of the ways that can be used for the streamflow simulation using hydrological models. Runoff is also one of the most important hydrological variables and rainfall-runoff modeling is one of the key items in hydrological sciences to estimate runoff characteristics such as volume, peak flow and arrival time to peak flow. In the present study, we used reanalyzed precipitation data and then evaluated the simulated streamflow using this precipitation data in the Zoshk subbasin. The precipitation data was validated with in situ data, of Kashafrood basin.Materials and Methods The reanalysis precipitation data was selected from the ERA5 precipitation data, and the HEC-HMS was used for the rainfall-runoff simulation. The basin parameters were calculated by the GIS menu. This menu is the newest option in the HEC-HMS software that needs only the DEM basin for calculating the basin parameters. In the present study, we should validate the ERA5 reanalysis precipitation data with in situ data, so we did that in the Kashafrood basin. The number of the rain gauge stations were 34, but some of the stations didn't have complete data and omitted them from the list of the rain gauge stations. For the validation ERA5 reanalysis precipitation data was used from the R, NSE, RMSE, Bias, FAR, POD and TS statistical indicators. These indicators were calculated by programming in EXCEL Visual Basic. The ERA5 precipitation data was evaluated for the Kashfarood basin at daily and monthly time steps. The DEM Zoshk was downloaded with the spatial resolution of 12.5 meters from ALOS-PALSAR satellite and then the basin parameters were calculated by the GIS menu. The SCS curve number was selected as a loss method. In this method, the calculations related to the percentage of impermeability and the average curve number of each sub-basin were obtained through land use and curve number layers, respectively. The SCS unit hydrograph was selected as a transform method. The recession method was selected as a base flow method. NSE and PBias were used for the calibration and validation events in HEC-HMS. In this way, at first the HEC-HMS model was calibrated by tow in situ rainfall-runoff events (91/1/11 and 91/2/6), and then validated by one in situ rainfall-runoff event (99/1/23). For validation streamflow of the ERA5 reanalysis precipitation data, the event on 99/1/23 was used and their streamflow hydrographs were evaluated with each other in Zoshk station.Results and Discussion The results showed that the reanalysis precipitation data of ERA5 had underestimation in daily and monthly time steps. Also in monthly time step, the accuracy of these precipitation dataset in detecting precipitation events (in terms of FAR, TS, and POD indices) was higher than a daily one. In addition, in monthly time steps it had worse accuracy in summer months than the rest of the year in detecting precipitation events (in terms of FAR, TS, and POD indices). For streamflow evaluation, in the calibration phase both NSE was in very good and good ranges, and PBias was in very good, good and acceptable ranges. In addition, the model underestimated the observational one. Finally the ERA5 reanalysis precipitation data was compared by 99/1/23 hydrograph event. The streamflow hydrograph from the ERA5 reanalysis precipitation data was underestimated due to ERA5 underestimation of the precipitation at the Zoshk rain gauge on the days corresponding to the 23/6/99 incident. The ERA5 reanalyzed precipitation data with NSE and Bias percentage coefficients in unacceptable range (NSE≤0.5 and PBias≤±25), compared to flow hydrograph obtained from Zoshk station precipitation data, the efficiency of this precipitation dataset is low. The range of the streamflow hydrograph from the ERA5 precipitation data was unsatisfactory in compared to the observational hydrograph (NSE = -0.47 and PBias = -55.16).Conclusion In general, the accuracy of the flow hydrograph of this product compared to the flow hydrograph of the precipitation data of Zoshk station (NSE = 0.64 and PBias = -15.82), cannot be a relatively reliable source instead of in situ rainfall data in hydrological simulation. The suggestion for future studies is to evaluate other rainfall data based on remote sensing methods in hydrological modeling.
S. Khalife; S.A. Esmaili; K. Esmaili; S.R. Khodashenas
Abstract
Introduction: Flood is a natural phenomenon that can cause numerous financial and life casualties in civil, industrial, and agricultural areas. Therefore, knowing its characteristics such as its peak during a period and in different places of the river is of the utmost importance. In general, forecasting ...
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Introduction: Flood is a natural phenomenon that can cause numerous financial and life casualties in civil, industrial, and agricultural areas. Therefore, knowing its characteristics such as its peak during a period and in different places of the river is of the utmost importance. In general, forecasting these characteristics and changes in depth and flow in the river could be done using the flood routing methods. Flood routing is one of the most important issues in water engineering projects. Hydrologic routing is common particularly in braided rivers and rivers with the lack of mid-basin data. To do that, there is a need to perform cross-sections and determine the river slope in every region. The Muskingum method is frequently used to route floods in the hydrology literature. The implementation of metaheuristic algorithm methods has shown satisfactory results in this regard. Therefore, in this study, we evaluated the efficiency of the Symbiotic Organisms Search (SOS) in estimating the optimal parameter estimation of the Non-linear Muskingum model.
Materials and Methods: This study evaluated the performance of Symbiotic Organisms Search (SOS) algorithm in estimating the optimum parameters of the Muskingum Non-linear model. To investigate the research’s findings desirability, the results of the Symbiotic Organisms Search (SOS) were compared to the results of otherMeta-Heuristic methods including the Genetic Algorithm (GA), the Particle Swarm Optimization (PSO), and the Imperialist Competitive Algorithm (ICA). Meta-heuristics sample is a set of solutions which are too large to be completely sampled. Meta-heuristics may make few assumptions about the optimization problem being solved, and they may, therefore, be usable for a variety of problems. SOS algorithm simulates the interactions between two species in a way that one species seeks to find the most suitable. SOS algorithm starts with an initial population called ecosystem. In the early stages of ecosystem, a group of organisms (decision variable) are randomly generated in the search space. Each organism is a candidate for a solution that corresponds to a certain degree of fit, representing the degree of conformity with the intended purpose (amount of objective function). This algorithm uses a new solution by mimicking the biological interaction between the two species in the ecosystem. Three distinct phases (cross-use), commensalism, and parasitic, similar to the biological interaction model in the real world, are introduced. Each interaction is defined based on the type of interaction. In this way, the two-way profit represents the cooperation phase, the one-way profit represents the commensalism phase, and the one-way profit and the other side losses represent the parasitic phase. In all phases, each is being interacted randomly with the other. This process continues until the process is completed (reaching the maximum number of iterations). In this research, the Kardeh River in Khorasan Razavi province was chosen as a real instance and Wilson River as a previous instance (1974), to investigate the performance of algorithms used in the non-linear Muskingum equation in the flood routing model. In this study, minimizing the sum of squares (SSQ) between the volume of real and routed outputs was considered as an objective function to evaluate the optimum parameters of K, X, and m in the non-linear Muskingum equation. The obtained optimum parameters from algorithms for both rivers showed that the SOS, PSO, and ICA algorithms could approximate the SSQ to optimal value and all meta-heuristic algorithms could route the output flood as well.
Results and Discussion: The SSQ algorithm results for the rivers showed the minimization of the sum of squares (SSQ) which MSE was equal to 5.85 and SSQ was equal to 128.78 for the Wilson River, and MSE was equal to 0.505 and SSQ was equal to 4.55 and had better functionality than the GA algorithms same as the PSO and ICA algorithms. The meta-Heuristic methods were from solutions which succeeded to estimate these parameters. In this study, the novel Symbiotic Organisms Search (SOS) was used to estimate the non-linear Muskingum model parameters. The observational data of two river studies of Kardeh and Wilson Rivers were employed. The results of SOS implementation were compared to other meta-heuristic algorithms such as GA, PSO, and ICA to investigate the SOS functionality. In this research, firstly, the experimental example used by the researchers was investigated to survey the optimum Non-linear Muskingum flood routing model parameters. The results showed the SOS precise estimation was comparable to the previous methods. According to the results, the SSQ was improved by using the objective functions as compared to the other reported algorithms at a rate of 7% in GA, and 0.004% in ICA. In the second experimental river, which is a real flood routing, estimated statistical parameters for the Kardeh River were 0.5059 for MSE and 4.5528 for SSQ in the SOS algorithm. This shows that the appropriate functionality of the Symbiotic Organisms Search algorithm in estimating the optimum Non-linear Muskingum flood routing model parameters. Finally, this research work highlights the SOS ability to optimize the Muskingum model parameters.
Conclusion: In the SSQ flood stream, SOS showed good performance, such as the PSO and ICA algorithms. In this regard, SOS was 13% better than the GA in the objective function SSQ and MSE, and improved the objective function SSQ and MSE by 0.002 and 4%, respectively, in respect to the PSO and ICA. This denotes the appropriate functionality of the Symbiotic Organisms Search algorithm in estimating the optimum non-linear Muskingum flood routing model parameters. The findings indicate the SOS ability to optimize the Muskingum model parameters. Therefore, using the SOS in flood routing with the Muskingum model is recommendable.
Saeed Salehi; Kazem Esmaili
Abstract
Introduction: Today, always some occurrences threat the earth. One of the most important of this event is seepage from earth dam. It can wash interior body of earth dam that finally might ruins whole the earth dam. For investigating these events in this research some experiments for expressing some alternatives ...
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Introduction: Today, always some occurrences threat the earth. One of the most important of this event is seepage from earth dam. It can wash interior body of earth dam that finally might ruins whole the earth dam. For investigating these events in this research some experiments for expressing some alternatives to solve this problem in earth dam with clay core were investigated. In first step has been introduced new design in earth dam that it includes earth dam with clay core.
Materials and Methods: In order to determine the height of the filter after the vertical clay core in non-homogeneous earth dam,3 experimental model with length 2/4 meter and a height of one meter and Body slope 1H: 2V was prepared. This model made in Shahrekord University. In flume that has 0.6 meter with, 6-meter length and 1-meter height. This flume has a drain in downstream which determine the discharge through earth dam. Front of flume made glass for visual inspection and behind flume made by steal sheet that was welded. Also, for embankment model, two types of fine-grained and coarse-grained soils were used that determine the range of hydraulic conductivity of soils was performed with Using aggregation experiments model and Soil Mechanics hydrometer. For embankment model use layer have 0.1meter height and this layer was impacted after an after. Finally, dam was built. The slope of models was elected in reference that had normal range and had economical cases. In the first downstream the dam crest was used fine-grained soil and upstream of the dam crest was used coarse-grained soil finally experiment done. In models 2 and 3 with cutting fine grained soil from the toe of the dam to the dam crest vertical clay core was created. The parameter a /L was introduced. A is thickness of clay core and L is the Length base of the dam although in the second model and the third model was selected. Level of water in pound was performed in 3 water height 80 and 55 and 30 and in 3 level of water determinate pressure with 30 embedded piezometers and this data was used in method model .as well as phreatic line was determinate by using of wells and 30 embedded piezometers in the model. Seven holes were instated in body of earth dam in 3 models for visual inspection of phreatic line. In 3 model of earth dam decline clay core in laboratory for show this effect in discharge and phreatic line use Method model. Then the rates of decline in clay core in the laboratory with modeling in software PLAXIS V8.5 were compared. The rate of high filter after the clay core with safety factor 1.2 (Encounter Line Leak with 20% of the bottom filter) was introduced. Finally use SAS software to compare the result of data in filth and software after that comparing show can use software for continue the experiment with Method Model. With change the permeability in PLXIS V8.5 modeling another state. Permeability, this modeling showed that tackiness and permeability of vertical core soil effect in height of vertical filter in downstream. So, can decline this case with choose non-permeability in core. That show in result of this paper. With the class of soil and permeability and change the tackiness of core can estimate height of filter in downstream.
Results and Discussion: Finally, Analysis and comparison between water Failure in interface of fine-grained and coarse-grained soils, both of Software model and laboratory model have a relatively well fit. To obtain the height of Suggested filter, the software model was used to simulate the experiments and Subtracting the thickness of the fine-grained. By applying safety factor of 1.2, Height was designed to filter and after that the clay core was introduced. Software model results show that by increasing clay core thickness the angle of broken-seepage line is increased. Also, the experimental model can emphasize this matter. Finally, by using vertical clay core against the clay core with slop can improve the application of earth dam and by using his plan can improve and diminish the seepage from the earth dam body that this design process was expressed in this research.
D. Houshmand; K. Esmaili; A. Keshavarzi; A. Faridhosseini
Abstract
The existence of bridge pier in streamflow causes a complex 3D flow formation, which also causes the scouring around bridge pier. Since rivers are usually curved, it is necessary to investigate the impact of change in flow patterns caused by passage of flow through the curve on the scouring around bridge ...
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The existence of bridge pier in streamflow causes a complex 3D flow formation, which also causes the scouring around bridge pier. Since rivers are usually curved, it is necessary to investigate the impact of change in flow patterns caused by passage of flow through the curve on the scouring around bridge pier. By developing Computational Fluid Dynamics (CFD), there is a possibility to simulate the flow pattern around the bridge piers. Therefore, the purpose of this research is modeled a 3D flow stream near the bridge piers in a curved channel. For this purpose a fluent model software was employed, and solved by stream equations using finite volume method of centralism. For discretization of Navier Stocks equation, three turbulence models of K-ε, K-ω, and RSM were used. In order to consider free surface, Fluid Volume Method was applied. The numerical model was validated with measured experimental data around the bridge piers in the meandering flume with 5 sequential curve paths. The results showed that the RSM turbulence model performed well compared to the other two models. When comparing the flow of upstream to downstream of bridge piers it can be observed that the placement of bridge piers in the middle of curved shape channel may lead secondary flow towards the inner curve of a channel. Also, the resulted vortex continues with a 150 degree curve.
Ashkan Alebouyeh; Saeed Reza Khodshenas
Abstract
Flash flood is due to rapid precipitation in arid and semi-arid areas. This flood is example of unsteady flow which has hydrograph with little time duration and high discharge. Investigation behavior of these floods is very important on sediment transport and characteristics streams. In this research ...
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Flash flood is due to rapid precipitation in arid and semi-arid areas. This flood is example of unsteady flow which has hydrograph with little time duration and high discharge. Investigation behavior of these floods is very important on sediment transport and characteristics streams. In this research evaluated the effect of flash floods on bed load transported to downstream. The input hydrographs are symmetric and Asymmetric triangles. Time duration of hydrograph was selected 90 second and constant and the maximum discharge were changed 6.58 to 16.18 l/s. The median size of particles is 2.5 mm; three bed slopes 0.005, 0.01 and 0.02 were select in these experiments. The results show that a temporal lag was found between the flow hydrographs peak and the sediment hydrograph peak. The temporal lag was found to be about equal to 5 - 11% of flow hydrograph duration. Also bed slope and maximum discharge of hydrograph are effect on upstream erosion and transportation of sediment to downstream. Since increases the bed slope from 0.005 to 0.01 increased 50% bed load transported and with two times the slope it show increase 400% in bed load transported. Bed load transported to downstream with symmetric triangle hydrographs more than symmetric triangle hydrograph.
R. Mansouri; K. Esmaili; A.N. Ziaei; Hossein Ansari; S. R. Khodashenas
Abstract
In arid and semi-arid regions, collection of surface and subsurface waters in small seasonal rivers is very crucial, particularly in dry seasons. The cost of construction and maintenance of classical water intakes makes them inappropriate for these rivers. In this study a rather new method to divert ...
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In arid and semi-arid regions, collection of surface and subsurface waters in small seasonal rivers is very crucial, particularly in dry seasons. The cost of construction and maintenance of classical water intakes makes them inappropriate for these rivers. In this study a rather new method to divert surface and subsurface water is experimentally evaluated. In this kind of intakes, a couple of trenches are excavated and the drain pipes are installed in them and then filled with very porous materials. Indeed the system acts as a river drainage network. This method not only reduces the construction and maintenance costs but also minimize the disturbance of river topology and morphology. Therefore this intake is also suitable for rivers with high sedimentary loads. In a few small rivers in Khorasan Razavi province, Islamic republic of Iran, such systems have been installed but their design and applicability have not been evaluated. In this research, experimental model of the intake to collect flow was built for flow diversion and flow rate deviation examined. Results showed a direct relationship between flow diversion with water level and with increasing distance between the drainages, the drainage flow increases. Drainage flow in the porous medium is initially decreased and then increased and drainage flow is the lowest in the middle drainage. In the review drainage arrange, the drainage of two deep with shorter porous medium is more suitable. Finally, regression mathematical model for the structural design of the intake subsurface with porous medium and drainage system were presented.
R. Badizadegan; K. Esmaili; M. Faghfour Maghrebi; M. Saneie
Abstract
Abstract
One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. It occurs when a supercritical open channel flow changes into sub critical flow. In the present research, the experimental study of the hydraulic jump on seven sinusoidal corrugated beds with different ...
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Abstract
One of the most frequently encountered cases of rapid varied flow is the hydraulic jump. It occurs when a supercritical open channel flow changes into sub critical flow. In the present research, the experimental study of the hydraulic jump on seven sinusoidal corrugated beds with different wave steepness. The wave steepness of sinusoidal corrugated beds is in the range of 0.1667 to 0.75 and Froude number was in the range of 4.5 to 12.26. The results showed that the tail water depth of a jump on a corrugated bed is about 20% smaller than that on smooth bed in Froude number 12 and the length of jump on corrugated beds is about 35% less than that for smooth bed.
Keywords: Hydraulic jump, Corrugated bed, Wave steepness
F. Koorosh Vahid; K. Esmaili; M. Faghfur Maghrebi; A. Alizadeh; B. Naghavi
Abstract
Abstract
Bottom intake is one of the most appropriate systems for diverting discharge in steep rivers. Bottom intake with porous media is a new system of diverting discharge which can be replaced by bottom rack intakes. To investigate the hydraulic flow characteristics on diverted discharge of this ...
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Abstract
Bottom intake is one of the most appropriate systems for diverting discharge in steep rivers. Bottom intake with porous media is a new system of diverting discharge which can be replaced by bottom rack intakes. To investigate the hydraulic flow characteristics on diverted discharge of this intake, an experimental model was designed in which the inflow, diverted discharge and remained flow of porous media intake can be measured. In the present research, measurements of the diverted discharge were performed for different rates of flow, grain size distributions as well as surface slopes of intake with clear water. According to the obtained results, by increasing the inflow discharge, the rate of diverted discharge increases gradually and then reaches to a constant value. Any increment of the surface slope above the intake also decrease the relation diverted flow. It is found that the grain size of the porous media has a great influence on the diverted flow. By increasing the grain size diverted flow increases, too. Dimensional analysis and experimental results were used to estimate the discharge coefficient of porous media. Analytical analysis on experimental data shows that the discharge coefficient of porous media intake is about 0.1. Also an empirical-theoretical relation is proposed to evaluate the diverted discharge of this kind of bottom intakes.
Keywords: Bottom intake, Porous media, Discharge coefficient, Free surface flow
B. Abasi; K. Esmaili; J. Abrishami
Abstract
Abstract
Although many studies have been carried out about dam break, this phenomenon still is one of the most important issues in the field of hydraulic engineering due to its hazards to human societies. Predicting the critical conditions including coincidence of flooding and dam break indicates more ...
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Abstract
Although many studies have been carried out about dam break, this phenomenon still is one of the most important issues in the field of hydraulic engineering due to its hazards to human societies. Predicting the critical conditions including coincidence of flooding and dam break indicates more field studies requirement. In this research the mutual effects of coincidence of negative surge due to dam break and flash flood has been studied using under different stored water levels. In addition, the effects of bed slope, existence of reservoir sediment and different initial reservoir depth have also been studied. Due to unsteady condition of flow, the stereoscopy method was employed to measure the hydraulic parameters such as depth. Using two digital cameras, results showed that by increasing the initial depth in dam's reservoir and channel slope, the reservoir would evacuate faster. Furthermore, sediments in which act like step in the flow direction can cause an increase in speed of the positive surge toward downstream. In addition by increasing the maximum of flow rate and base time of hydrographs, water rise in downstream was monitored as well.
Keywords: Usteady flow, Dam break, Flash flood, Experimental simulation
K. Esmaili; B. Naghavi; F. Koorosh Vahid; J. Yazdi
Abstract
Abstract
Weirs are the most common structures for discharge measurement in engineering research. Streamline curvature, non hydrostatic pressure distribution on weir and nappe adherence to the weir lead to differences between calculated and measured discharges. Thus discharge coefficient, which is the ...
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Abstract
Weirs are the most common structures for discharge measurement in engineering research. Streamline curvature, non hydrostatic pressure distribution on weir and nappe adherence to the weir lead to differences between calculated and measured discharges. Thus discharge coefficient, which is the ratio of real and theoretic discharges, is usually less than unity. In circular weirs the pressure distribution and velocity differs from sharp crested weirs which affect on flow discharge and extend the discharge coefficient more than unity. In this study, pressure distribution and velocity of different circular weir measured in laboratory models and compared with Fluent simulation as a numerical code. The results showed significant relation between measured and simulated data. Also it is found that the critical flow depth and separated flow are located respectively before and after the crest of weir. Nappe separation depends on overflow discharge and will shift to the downstream face of the cylinder in high discharges. To recognize the location of critical flow conditions and nappe separations, theoretical formulations has is proposed. The equations are found to be dependent on weir size and inflow conditions. The theoretical predictions showed good agreement in comparison with experimental results.
Keywords: Circular weir, Velocity and pressure distribution, Nappe separation, Critical depth, Fluent
B. Naghavi; M. Faghfour Maghrebi; K. Esmaili; S.R. Khodshenas; F. Koorosh Vahid
Abstract
Abstract
Bottom rack intake is one of the most appropriate structures for diverting water in steep rivers. The problems of corrosion, deformity and clogging of the bottom racks in long term, inspires a new system of bottom intake in which a filled trench of porous media is replaced by the bottom racks. ...
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Abstract
Bottom rack intake is one of the most appropriate structures for diverting water in steep rivers. The problems of corrosion, deformity and clogging of the bottom racks in long term, inspires a new system of bottom intake in which a filled trench of porous media is replaced by the bottom racks. Diversion of a specified amount of discharge through the porous media when void space in the granular material are filled with fine sediment in comparison to the bottom racks, requires much larger structure. However, for the new system of water intake, lower cost of construction and maintenance and higher compatibility with the river morphology in long term are considered as major advantages. The present research deals with an experimental model with two-storey channel, the lower one is used to divert water through the porous media and the upper one is used to convey the remained flow. Measurements of the diverted discharge were performed for different rates of flow, grain size distributions as well as surface slopes of intake with clear water and sediment flow. The influence of clogging phenomena on diverted discharge is also examined. The experimental results show that the effect of clogging in sediment flow in comparison to the clear water is decreased as the surface slope of the porous media is increased. It is revealed that the discharge coefficient of bottom intake when clear water is passed through the channel is varied in the range of 0.06 to 0.13. When sediment flow is passed over the bottom intake, due to clogging phenomena discharge coefficient is reduced up to 5 to 35% in comparison to the clear water. Experimental equations prepared for the discharge coefficients show that the significant factors affecting the efficiency of the water intakes are grain size distribution and surface slope of the bottom intake. The results show that the discharge coefficients for the water intake with the clear water and sediment flow when the above mentioned factors are selected appropriately are close to each other.
Key words: Bottom intake, Porous media, Discharge coefficient, Clear water flow, Sediment flow, Clogging
K. Esmaili; S.M. Kashefipoor; M. Shafai Bejestan
Abstract
Abstract
For investigating the effect of bed form in alluvial channels on the amount of bed load transport, a set of experiments was carried out in a tilting flume under unsteady flow conditions (hydrograph). The produced hydrographs were in triangular form with a maximum discharge of 30 to 45 lit/s/m. ...
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Abstract
For investigating the effect of bed form in alluvial channels on the amount of bed load transport, a set of experiments was carried out in a tilting flume under unsteady flow conditions (hydrograph). The produced hydrographs were in triangular form with a maximum discharge of 30 to 45 lit/s/m. Three size of sediment particles were used with equal to 1.5, 2.1 and 3.0mm, clear water without any feeding was supplied from upstream. To analyze the time varying of bed resistance, a numerical model with initial and boundary conditions was used and its outputs were depth, velocity and discharge. The results showed that the inflow made considerable erosion at the starting time of flowing near the channel inlet, and this is a cause of producing bed form, increasing roughness and bed resistance. However, by the time the erosion trend was declined with increasing discharge. Despite of increasing flow turbulence, Froude number and bed erosion decreased gradually when the discharge approaching to its maximum value increasing flow depth. In this process, because of bed elevation changing along the flume, Froude number at any point is different from the other points and bed particles move toward downstream as a progressive wave. The bed resistance coefficient, n, was increased at the start of inflow time and after a proper time it was again increased, and this matter has very important role in sediment transport for non cohesive beds.
Key words: Movable bed, Bed form, Coefficient roughness, Unsteady flow
B. Naghavi; S.R. Khodshenas; M. Faghfour Maghrebi; K. Esmaili; F. Koorosh Vahid
Abstract
Abstract
Bottom rack intake is one of the most popular structures used for diverting water in mountain region. Corrosion and rotten problems of bottom racks inspire the introduction of a new system of bottom intake in which a porous media is replaced by the bottom rack. Obviously, clogging and reduction ...
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Abstract
Bottom rack intake is one of the most popular structures used for diverting water in mountain region. Corrosion and rotten problems of bottom racks inspire the introduction of a new system of bottom intake in which a porous media is replaced by the bottom rack. Obviously, clogging and reduction of diverted discharge are the most important problems in this new system, too. In this paper, the effects of different media grain size, longitudinal slope, sediment grain size and flow discharge are investigated. Results show that despite of clogging role of suspended sediments in porous media, using appropriate grain size and slope for the porous media, would attenuate the side effects of the problem. Compare with clear water flow, the discharge reduction induced by clogging is not significant and efficiency of system in long time and no operation effort are confirmed. To recognize the effective parameters on infiltration resistance in porous medium intake an empirical theoretical formulation has been diverted from the Darcy’s law in surface infiltration. The equation is found to be dependent on size ratio, Reynolds number and hydraulic gradient. The theoretical predictions have been compared with experimental results, with good agreement.
Key words: Bottom intake, Porous media, clogging, Discharge reduction, Infiltration resistance
K. Esmaili; M. Shafai Bejestan; M. Kashefipoor
Abstract
Abstract
To investigate the effective parameters and simulate the conditions under which sediments are transported in ephemeral rivers and compare it to perennial rivers a series of experiments were performed in a laboratory flume. The hydrodynamic equations were solved for initial and boundary conditions ...
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Abstract
To investigate the effective parameters and simulate the conditions under which sediments are transported in ephemeral rivers and compare it to perennial rivers a series of experiments were performed in a laboratory flume. The hydrodynamic equations were solved for initial and boundary conditions using numerical method. Triangle hydrographs with time duration of 40, 60 and 80 seconds and five different flow rates for each situation were considered. Three slopes of 0.006, 0.014 and 0.018 were selected. A fine and uniform sand with d50 of 1.5, 2.1 and 3 mm from river materials was used as the mobile bed. Clean water (with no sediment) was used. The results of 85 experiments showed that the bed slope was the most important parameter in sediment transportation and it could be used for predicting the sediment transport. The base time of hydrograph was also found to have an effective role in sediment transport, and the results showed that by increasing the base time the transported sediment was decreased. The bed form had a big role on the flow resistance and also affected the sediment transport. The sediment ratio of unsteady to steady flow found in this research was found to be similar with those of Tun Lee.
Key words: Ephemeral rivers, Perennial rivers, Bed load, Sediment
