R. Ghobadian; H. Shekari
Abstract
Introduction: The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a ...
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Introduction: The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a river reach. Although most of flow in nature are unsteady, the quasi-steady flow condition was considered to be simple in this study and the water surface profile along the river reach with irregular cross sections was calculated by standard step-by-step method. In order to calculate suspended sediment load under non-equilibrium condition, the advection-diffusion equation with source term was numerically solved. In the present sediment model, ten discretization methods, five relations for calculating capacity of suspended sediment load, eight relations for diffusion coefficients and eight relations to calculate particle fall velocity were used and their effects on suspended sediment distribution along 18480 m of Gharasoo river were investigated.
Results and Discussion: The HEC-RAS model output was used to calibrate the present hydraulic model. The models were run with the conditions as same as Manning roughness coefficient and river geometry conditions. The results showed that the calculated water surface profile along the river reach by two models are completely overlapped each other. In other words, the present model has a very good accuracy to predict the water surface profile in the river reach. As most commercial 1-D models (same as HEC-RAS) only consider the equilibrium condition for sediment transport and the bed or total load sediment, comparing the results of present sediment model with them seems not to be reasonable. Therefore, to validate the present suspended sediment model and finding the best method of discretization, an especial shape concentration hydrograph was introduced to the present model as input hydrograph and the model was run when the source term has been deleted deliberately. The volume below the input concentration hydrograph and calculated hydrographs in different cross sections was compared to each other. Comparing the hydrographs showed that the maximum error in calculating the volume of concentration hydrograph with the input hydrograph was 0.029% implying that the model satisfies the conservation laws as well as reliable programing. Among ten discretization methods, the best method for discretization of the advection-diffusion equation was Van Leer's method with the least error compared to other methods. After validating the model, effect of five relations for calculating capacity of suspended sediment load was investigated. The results showed that using the Wife equation estimated the amount of suspended sediment higher than other equations. The Toffaletti equation also estimated suspended sediment load lower than other equation. Among eight particle fall velocity formulas, Stokes relationship estimated the fall velocity larger than other equations. Hence, the Stokes equation application decreases the possibility of suspending the sediment particles. However, employing Van Rijn and Zanke relationships resulted in a greater suspended sediment load distribution along the river reach. Among eight relationships for diffusion coefficients, Elder and the Kashifipour - Falconer equations exhibited the lowest and the highest amount of diffusion in the concentration hydrograph, respectively. Furthermore, the calculated suspended sediment concentration under non-equilibrium conditions was 11.7 % higher than that under equilibrium conditions along the river reach.
Conclusion: Most 1-D numerical models only simulate the bed and total loads sediment transport under equilibrium condition while sediments are transported under non-equilibrium conditions in nature. Sediment transport under non- equilibrium conditions may be greater or lower than the equilibrium condition known as the capacity of sediment transport. In this research, a numerical model was developed to simulate the suspended sediment transport in a river reach under non-equilibrium conditions. The amount of suspended sediment concentration was calculated for each sediment grain size. The results showed that the distribution of suspended load along the river reach is not significantly sensitive to the fall velocity relations while the type of sediment transport equation affected the suspended sediment transport concentration. The concentration of suspended sediments for non-equilibrium conditions was also 11.7% higher than the concentration of sediments in equilibrium condition.
sabah mohamadi; Rasool Ghobadian; mahmood kashefipoor
Abstract
Introduction: It is so important for engineers to be able to predict the places in which deposition and scouring occurs. In recent two decades using the numerical models arecommon for simulating flow and sediment transport. Numerical models are valuable tools for estimating flow conditions and sediment ...
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Introduction: It is so important for engineers to be able to predict the places in which deposition and scouring occurs. In recent two decades using the numerical models arecommon for simulating flow and sediment transport. Numerical models are valuable tools for estimating flow conditions and sediment transport, and are widely applied in water resources management. For this reason, many researches focus on modeling and simulation of flow on a mobile bed in natural and alluvial rivers. Analyzer of sediment transport is one of the most complicated topics in sediment and river hydraulic.
Material and Methods: In this research a one dimensional, unsteady, hydrodynamic model is developed which can be used for simulating flow and sediment transport as semi-coupled model in river systems. In this research, the Saint- Venant’s first order partial differential hyperbolic equations are numerically solved using the Visual Basic program for river systems. In this research study a semi implicit finite difference scheme is developed to solve the Saint- Venant equations for unsteady flow. The linear equations are produced based on the partial differential equations and the staggered technique, so it is possible to employ the tri-angular matrix algorithm (TDMA) to solve them, with this algorithm the time of running model being minimum due to the least mathematical computations. The matrix form of the linearized momentum and continuity equations for a channel with upstream and downstream boundary conditions is provided. Another technique used to solve the matrix of the linear equations is Influence Line Technique (ILT). Base flow discharge and depth in each branch are introduced into the model as the initial conditions. To avoid divergence in numerical calculations, the downstream end discharge of each branch is calculated using initial flow depth and stage-discharge or Manning’s relationship. At the junctions, the upstream discharge is calculated using the algebraic sum of the discharges of the downstream branches and vice-versa; this process is continued up to the last branches at the upstream of the river system. After solving the above equations, the computed hydraulic parameters in this part are sent to the sediment transport segment. In the sediment subroutine the bed and suspended dynamic equations are discretized by finite volume method, and solved with flow equations as semi-coupled scheme. In this study the bed and suspended load rates are individually solved. The dynamic advection- dispersion equation and the bed load differential equation were applied to calculate the suspended sediment concentration and bed load transport, respectively. The Exner equation is then used to predict the changes in the river bed elevations innon-equilibrium conditions. Because ofthe nature, the sediment transport is often in non-equilibrium form, in this study, the non-equilibrium Exner equation is used to compute the bed elevations, unlike many of the known models. The use of non-equilibrium method due to the complexity of the solution and the presence of non-equilibrium parameters such as coefficients of the adaptation length and recovery is very difficult.
Results and Discussion: In non-equilibrium conditions, the numerical models have high sensitivity to two parameters including, the adaptation length coefficient for bed load and recovery coefficient for suspended load, with the sensitivity analysis for these coefficients being carried out in this research. In this study, a sensitivity analysis was performed on these parameters using developed numerical model. The developed model has this ability to simulate flow and sediment transport in complex and loop river systems. Finally, the model was simulated for the Chaudhry loop river systems. Thisriver system has 9 branches that form the loop. All channels have rectangular sections and their flows are sub-critical. The upstream boundary condition is an unsteady hydrograph with peak discharge of 250 cubic meters per seconds and base time of 8 hours. The calculated stage and discharge by the model (using Manning’s equation) was supplied to the model as a downstream boundary condition at last node. The model outputs are discharged hydrographs on different sections of each channel. The developed model has good ability to simulate the flow and sediment transport in river systems. The result showed that by selecting the adaptation length coefficient, equivalent to a multiple of 1 to 3 times the distance between cross sections, the results of the numerical model can be more realistic. Also it was concluded that empirical equation of Lin(1984) used for the recovery factor of the suspended load.
R. Ghobadian; M. Basiri
Abstract
Introduction: Flow and sediment transport has an important role in entrance deformation of open channel junctions. As water moved through a drainage network, it forced to converge at confluence. Due to increasing of water discharge and collision of converging flows, a complex three-dimensional and most ...
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Introduction: Flow and sediment transport has an important role in entrance deformation of open channel junctions. As water moved through a drainage network, it forced to converge at confluence. Due to increasing of water discharge and collision of converging flows, a complex three-dimensional and most highly turbulent location were occurred in the vicinity of the junction. Therefore a deep scour hole and point bar has developed in this area that caused the change in rivers morphology. Despite the large amount of research carried out on flow patterns in river confluences, only a few researches have focused on sediment transport.
Materials and methods: In this research three dimensional model (SSIIM1) was used to study of flow pattern and sediment and erosion pattern at 60 degree Junction .the Navier-Stockes equation of turbulent flow in a general three-dimensional geometry are solved to obtain the water velocity:
, (1)
Where U is average velocity, ρ is density of water, is pressure, the Kronecker delta, which is 1 if i is equal to j and 0 otherwise and general space dimension. The last term is Reynolds stress, often modeled with the following equation:
(2)
Where and k are eddy viscosity and turbulent kinetic energy respectively. Van Rijn's relations were used to calculate sediment suspended and bed load transport.
Dirichlet and zero gradients boundary conditions were used at inflow and outflow boundary respectively. fixed-lid approach was used to computed free surface by using zero gradient for all variables. The wall law for rough boundaries was also used as a boundary condition for bed and wall.
In equilibrium situation, The sediment concentration for the cell closet to the bed was specified as the bed boundary condition. Specified value was used for sediment concentration of other boundary conditions at upstream boundary and zero gradients for the water surface, outlet, and the sides. the only simulation of local scouring and sedimentation at confluence area was also considered.
The SSIIM1 model used structured grid and computer program to provide the required meshand the experimental data was applied to validated model.
The experimental setup consisted of a main flume 9 m long with 75 cm depth for the first 2 m and 45 cm for remaining section and 35 cm wide, and a lateral flume 3m long, 45cm depth and 25 wide. Both flumes had a horizontal slope. An 11cm layer of uniform sediment (D50 = 1.95 mm) was also laid on both channel beds.
Results and discussion:The results showed that the ability of model is relatively good to predict the position of the erosion and sedimentation pattern. The values of maximum scour depth for experimental test and simulation were 0.052 and 0.047 m respectively. However the maximum error to predict scouring depth value was about 10%. This difference could be due to the weakness of Van Rijn's equation to sediment transport and probably measured error. It must be noted that SSIIM1 only used the Van Rijn's equation for bed load transport.
The result Also showed that simulation and experimental test were similar and no sediment transport occurred in the tributary and main channel before the confluence. To investigate the effect of angle 60, 90 and 135 degrees and also discharge ratios of 0.5 and 0.66, the model was applied. A direct relationship was observed between discharge ratio and scouring depth . There was a difference between scouring of discharge ratio 0.5 and 0.66 on a specified angle andthis difference was more obvious with increasing confluence angle. Figure 1 showed the effect of discharge and confluence angle on scouring depth.
Figure 1- The effect of discharge ratio and confluence angle on scouring depth
rasool ghobadian
Abstract
To drainage design and management it is necessary water flow toward drain, water table variation between drains and drainage discharge have been simulated. With recent development in numerical method, it is possible the none-linear differential equation governing saturated-unsaturated flow in soil ...
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To drainage design and management it is necessary water flow toward drain, water table variation between drains and drainage discharge have been simulated. With recent development in numerical method, it is possible the none-linear differential equation governing saturated-unsaturated flow in soil is numerically solved. In this study a computer model has been developed in which two dimensional equation of saturated-unsaturated flow in soil is solved using finite volume method and Crank-Nicolson scheme. The soil hydrodynamic properties function and soil moisture characteristic curve proposed by Van Genuchten were employed. After model calibration and evaluation, water table variation between two drains with 20 m distance and installation depth of 1.2 m was simulated. The result showed during discharge phase water table falls very fast at the first and then falling speed reduces until reach a constant value. During recharge phase water table raises very low at the first and then rising speed increase. Drainage discharge has similar behavior same as water table. Drainage discharge has a lag time related to time that recharge begins. In this study the lag time was 3.125 day.
Ensyeh merati
Abstract
Since measuring the flow discharge is difficult during a flood event in a hydrometry station, the estimated Stage–discharge relationship of non-flood conditions is extrapolated for flood conditions. Hence the results might show underestimated values. Indeed during the flood bed form is developed and ...
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Since measuring the flow discharge is difficult during a flood event in a hydrometry station, the estimated Stage–discharge relationship of non-flood conditions is extrapolated for flood conditions. Hence the results might show underestimated values. Indeed during the flood bed form is developed and flow resistance changes. In order to establish a more accurate stage–discharge relation, it is important to apply a method which considers (or takes into account) the bed form resistance. This research tries to determine the best method for developing such relationship in hydrometry stations located on the Qarasu river basin such as: Ghorbaghestan, Doabmereg, Khersabad, Hosseinabad and Sarasiab. To reach this aim, the required data (e.g. river cross section, bed material gradation) were measured for these hydrometry stations and methods of Einstein–Barbarossa, Shen, White, Engelund, Brownlie and VanRijn are used to obtain the stage–discharge relationship. A computer program was developed to estimate stage-discharge relation based on afore mentioned methods. Different statistical tests were accomplished to compare estimated and observed discharges. The results in Ghorbaghestan and Hosseinabad stations showed that the regression slope between the measures and calculated values by the Einstein–Barbarossa’s method respectively 1.029 and 1.182. by using Shen’s method in Doabmereg, Khersabad and Sarasiab stations respectively 1.08, 1.054 and 0.926 While regression slope in other methods is greater than 1, also AME and RMSE is much less than other methods on the appropriate methods. In hydrometry stations with coarse bed material Einstein–Barbarossa’s method is more convenient to estimate stage-discharge relation in comparison with other methods. Also for hydrometry stations with fine-grained bed material Shen’s method was found a reasonable method to estimate stage-discharge relation.
R. Ghobadian
Abstract
Abstract
Due to transmission losses and lack of initial flow, flood routing in ephemeral streams is not possible with common methods and it is necessary the flood routing models have been developed for these streams. Therefore in this study a computer model for natural river cross section has been ...
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Abstract
Due to transmission losses and lack of initial flow, flood routing in ephemeral streams is not possible with common methods and it is necessary the flood routing models have been developed for these streams. Therefore in this study a computer model for natural river cross section has been developed in that after linearization of partial differential equations of unsteady none uniform flow, they are solved by stagger method. This model can consider tributary flow and infiltration into river bed simultaneity. For estimation of transmission losses Muscat, Davis-Wilson, and Ingham methods have used and liked with unsteady flow equations in prepared model. Evaluation of model accuracy viewpoint programming, ability to simulate uniform flow and satisfying the continuity equation performed using 60 Garasoo River cross sections in a reach with about 18 km length. Lane’s hydrograph and Hughes Wash river properties were used to investigation model accuracy to estimate flow behavior and transmission losses. The result showed that prepared model can simulate uniform flow and satisfies continuity equation with height accuracy. Additionally when Muscat relation is used developed model can predict start and peak flood times correctly. Also transmission losses and volume of output hydrograph have predicted with maximum error less than 20 percent. While application of Davis – Wilson and Ingham relations showed unsatisfied result compare in situ measurement data.
Keywords: Transmission losses, Ephemeral stream, Flood Routing, Saint-Venant equations
M. Daryaee; M. Kashefipoor; J. Ahadiyan; R. Ghobadiyan
Abstract
چکیده
احداث ساختمان ها و سازه های مختلف، باعث به هم فشرده شدن ذرات خاک و در نتیجه نشست خاک می گردد. نشست خاک تابع عوامل مختلفی مانند تغییر شکل فشاری، خارج شدن هوا و آب ...
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چکیده
احداث ساختمان ها و سازه های مختلف، باعث به هم فشرده شدن ذرات خاک و در نتیجه نشست خاک می گردد. نشست خاک تابع عوامل مختلفی مانند تغییر شکل فشاری، خارج شدن هوا و آب از خلل و فرج و ... می باشد. یکی از روش های محاسبه نشست، استفاده از شاخص فشردگی است که از طریق آزمایش تحکیم بدست می آید. تعیین این ضریب از طریق آزمایش تحکیم بسیار وقت گیر است. لذا از گذشته سعی بر این بوده که شاخص فشردگی را به پارامترهای فیزیکی خاک از قبیل حد خمیری، حد روانی، نسبت پوکی، چگالی نسبی که همگی به سادگی قابل اندازه گیری هستند، ارتباط دهند. به همین جهت روابط تجربی زیادی در این خصوص ارائه شده است. در این مقاله با استفاده از شبکهی عصبی مصنوعی5 (ANN) ، همبستگی آماری بین خصوصیات فیزیکی خاکهای ریزدانه و شاخص فشردگی مورد بررسی قرار گرفت. همچنین یک واسنجی بین روش های تجربی مختلف موجود برای تعیین شاخص فشردگی با شاخص فشردگی اندازه گیری شده در آزمایشگاه صورت پذیرفت. نتایج نشان داده است که رابطه رندون و هررو از میان روابط تجربی با بالاترین ضریب همبستگی و کمترین درصد خطا، بالاترین دقت را در برآورد شاخص فشردگی دارد. در مقابل شبکه های عصبی مصنوعی شاخص فشردگی را با دقتی بالاتر و درصد خطای کمتر از رابطه رندون و هررو برآورد می کند. همچنین کالیبره کردن ضرایب رابطه رندون و هررو با استفاده از مجموعه اطلاعات موجود، تاثیر چندانی در دقت این رابطه برای تخمین شاخص فشردگی خاکهای منطقه مورد نظر ندارد.
واژههای کلیدی: خاکهای ریزدانه، شاخص فشردگی، شبکه های عصبی مصنوعی، خصوصیات فیزیکی خاک
R. Ghobadian; K. Mohammadi
Abstract
Abstract
Information on spatial and temporal variations of soil hydraulic conductivity (k) is essential to improve soil and water management. However several techniques have been proposed for measuring of soil hydraulic conductivity above water surface table, but reliability and easy use of these ...
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Abstract
Information on spatial and temporal variations of soil hydraulic conductivity (k) is essential to improve soil and water management. However several techniques have been proposed for measuring of soil hydraulic conductivity above water surface table, but reliability and easy use of these methods in various conditions were always concern for engineers. The purposes of this study are measuring of the soli hydraulic conductivity by Guelph permeameter as a reliable method and determination of the best single-depth analysis method equivalent to two- depth method. To achieve this goal, 40 boreholes with depth of 60 cm were drilled in a grid of m in the research farm of agricultural faculty, Razi University, Kermanshah. Soil texture of the study area is silty-loam. After identification tests such as soil gradation, determination of the soil liquid and plasticity limits and determination of the specific gravity, soil saturated hydraulic conductivity and matric potential were measured by Guelph permeameter for three fixed ponding depths 5, 15 and 25 cm. Because of heterogeneous of equations in three-depth method only 17 success well obtained while in two-depth method for two ponding depths 5 and 15 cm, 26 successful well obtained. Data of these 26 boreholes were used for statistical analysis. The results of statistical analysis showed that: 1) Mean of soil hydraulic conductivity in the study area is , 2) Among the single depth methods, Richards regression basic analysis with values of 0.205 and 0.994 for and respectively is the nearest method to tow-depth method, 3) There is a significant difference at 5% level between the results from two-depths analysis of Guelph permeameter with Richards and Laplace single-depth methods, 4) Average values of and in the study area were calculated and respectively, and 5) Values of have less variation coefficients and standard deviation than values of sorptive number ( ).
Keywords: Hydraulic conductivity, Guelph permeameter
R. Ghobadian; K. Khodaei
Abstract
Abstract
Among activities that can be used to prevent piping phenomena and reduce seepage and exit gradient are installation of cutoff wall and drain under hydraulic structures. Hence in this study, to investigating the influence of each mentioned parameter on uplift force and exit gradient a computer ...
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Abstract
Among activities that can be used to prevent piping phenomena and reduce seepage and exit gradient are installation of cutoff wall and drain under hydraulic structures. Hence in this study, to investigating the influence of each mentioned parameter on uplift force and exit gradient a computer model has developed in which general equation of fluid flow into the isotropic and anisotropic soil was solved numerically by Gauss-Seidel method. Verify model, experimental result and result of WinMseep model that is an acceptable model was used. One of the relative advantages of this model is consideration of permeability value for cutoff curtain. The result of this study showed, bye construction of one cutoff curtain in any location values of exit gradient relative to basic exit gradient (without cutoff) reduces. Also, maximum uplift force and minimum exit gradient is observed when cutoff curtain is located in toe. For situation with two cutoff walls in toe and heel of dam and one drain in between it is observed that when drain is located at far distance whit respect to heel influence of it on uplift force and exit gradient increases. Additionally with increasing upstream cutoff depth in comparison to downstream cutoff, values of exit gradient decreases and intensity of this decrease for shallow downstream cutoff is more sensible. Distribution of uplift pressure and calculated exit gradient for isotropic and anisotropic condition are very consistences to those are computed by WinMseep model.
Key words: Hydraulic structure, Cutoff wall, Uplift pressure, Exit gradient, Finite volume
