Nowadays the design and implementation of concrete, rocky and earthy structures constitutes one of the most suitable ways of control, diversion and exploitation of rivers. Spillways and chutes are designed to discharge enormous water rates while minimizing the risk to both the structure and its surroundings. Moreover, spillways are intended to harness the massive kinetic energy of water. Stepped spillways are regarded as cost-effective structures capable of protecting embankment dams and chutes against flood-induced erosion. The stepped shape increases the hydraulic resistance, thus improving the dissipative efficiency of these specific spillways. A smart approach to increasing energy depreciation is the use of intersecting flows. The present study was aimed at increasing energy depreciation through installation of holes on the bottom or the walls of the spillway. As the second objective, increased discharge coefficient was sought by decreasing the reservoir level and changing the stage-discharge curve. The purpose of this study is to investigate the angle of colliding flow as well as the shape and arrangement of the holes. In doing so, a physical model of stepped spillway with a constant slope of 1:2.5 was constructed and the following scenarios were considered.
by defining two different positions for the discharge path of the inward passage (the floor and wall of the stairs) as well as two different layouts for placing the aperture in height (Continuous and one among) and taking into account two different shapes for the aperture (rectangular slot and circular pores) and then performing 8 experiments with a different discharge rate of 25 to 60 liters per second for each model, and in total Performing 80 experiments, the amount of energy dissipation of the structure and its effect on the hydraulic jump characteristics, including hydraulic jump length, jump conjugate depths and length of the rollers in this type of overflow Fall. A simple chute and a regular spillway were also used for the comparative purposes and verification of the results. The results indicate that stepped spillways passing flows through the steps bottom can increase the amount of energy dissipation between 6.5 to 8.1 percent on average compared with regular spillways. In addition, the upstream water level would decrease by 14% to 17.7% on average. Installing holes on the spillway walls does not alter the energy dissipation; even it might have an opposite effect. However, such an arrangement of the holes leads to a 12.9% ~ 15.7% decline in the upstream water level on average. In other words, although the wall-perforated models increase the discharge coefficients, they have no major effect on either the amount of energy dissipated or the characteristics of the downstream hydraulic jump. On the other hand, models passing flows through the steps bottom decrease the Froude number at the downstream of the spillway, thereby reducing the length of jump and the length of rollers as well as the conjugate depth ratio. Based on the results of these models, the average reduction in the hydraulic jump characteristics ranges between 16%~21%, 23%~31% and 22%~28% for the hydraulic jump length, length of the rollers and the conjugate depth ratio respectively.

 
Sedimentation is the most important factor in reducing of dam reservoir useful capacity. Density current is the most important factor of sediment transport in the dam reservoirs. So recognition of this phenomenon and presenting methods for its control is very important. In this study 4 modes of installation of Three height proportions of obstacles were determined according to the average body height of density current of the control samples, namely h_r=0.5,0.75,1 (h_r=h_m/h where h_m is the obstacle height and h is the average body height of density current of the control sample) were considered. The heights were considered equal in the 3 modes of installation, and in the fourth mode, the three obstacles were installed in ascending order of the values mentioned earlier. The experiments were carried out using 3 bed slopes of 0%, 1.5 % and 2.5 % with density values of 10 and 20 gr⁄lit and density current discharge was considered constant and equal to 1 l⁄s. The results showed that installation of consecutive obstacles has significant effect on the density current of front and body control. Velocity and density current of front and body were decreased after obstacles due to the bed slope and height of the obstacles. This is because, the partly sediment of density current through interaction with obstacles.
The maximum and minimum amount of density current front control for 10 and 20 gr⁄lit occurred in the mode of hr=1 with bed slope of 0% and in the mode of hr = 0.5 with bed slope of 2.5% profile by the rate of 84, 87 percent and 25, 31percent, respectively. The highest possible percentage of density current body control for 10 and 20 gr⁄lit observed in the mode of hr= 1 with bed slope of 0% by 49 and 63%, respectively while the lowest percentage recorded in the mode of hr =0.5 with bed slope of 2.5% by 16 and 22%. In general, the percentage of density current body and front control decreased by increasing the height of obstacles and wise versa they decreased by increasing the bed slope

 Sediment deposited in dam reservoirs, in addition to destroying the intended purpose of building a dam, can affect the downstream river system from many aspects. Pressure deposition is one of the economical methods for deposition of sediments. In this research, using the physical model at Shahid Chamran University of Ahvaz, the effect of sediment deposited and reservoir water heights and sediment height from the flume floor on the scour cone dimensions were investigated. The experiments were carried out for 3 different granulation of sediments with average diameter of 0/25, 0/5 and 0/75. Mm for a circular aperture with a cross section of 18 cm2 and under 4 different blue diameters of 15, 30, 45, 56 cm in comparison to the center of the stomach, which resulted in the production of 4 doses of 2, 2/8, 3/38 and It was 3/78 liters per second. A total of 36 experiments were conducted. The results showed that by increasing the average diameter of the sediments, the average size of the scour cone is reduced by about 50%. Also, with the increase in the height of the water above the dispenser stomp, the scour cone volume increases. The highest efficiency is observed in sediment experiments with a mean diameter of 0/25 mm in the case where the height of sediment is deposited from the bottom of the reservoir to the center of the discharge opening.

Stilling basin with continuous across sill is a basin in which one or more continuous walls are used instead pool blocks to dissipate more excess energy. The purpose of this study is to investigate the efficiency of perforated continuous sill in stilling basin on the relative head loss, and the specifications of hydraulic jump such as length and conjugate depth and also the length of roller of jump. Also in this research study the optimum height for one and two perforated sills in terms of energy dissipation and hydraulic jump specifications is determined. A number of experiments without sill and with one and two continuous perforated sills were designed and conducted in a rectangular flume with 1000cm length, 80cm wide and 65cm depth in physical modeling laboratory of Shahid Chamran University. 8 Froude numbers were considered ranging from 3.6 to 11.2 (corresponding discharges of 47.3 to 145.5 lit/s) for experiments, with the supper critical flow being generated using a sluice gate with controllable head installed at the upstream. The tail water was controlled by a sluice gate installed at the end of flume. The perforated sills were built using plexi glass with constant opening of 50%. 24 experiments with one perforated wall (3*8, wall height * number of Froude numbers), and 72 experiments with a couple perforated walls (9*8, 9 combination of wall heights * number of Froude numbers), in total 104 experiments were carried out (8 experiments without any wall). The distances of walls from the toe of hydraulic jump were kept constant (LS1=60cm, LS2=90cm). The variable wall height was ranging from 5 to 15cm. In this research study, the specifications of the forced hydraulic jump with one or two continuous walls were compared with the corresponding measurements obtained for the free hydraulic jump. According to these specifications which include requirement tail water conditions, head loss, length of hydraulic jump and rollers, the optimum height of one or two perforated walls were determined. The results showed that constructing wall against super critical flow causes for better control and fixing of hydraulic jump, with the two continuous perforated walls being more efficient in terms of higher energy loss, smaller sequent depth and length of hydraulic jump. Furthermore, the results showed that the higher height of wall has not necessarily the best performance in control of hydraulic jump. For one perforated wall the ratio of hydraulic jump length to sequent depth decreased up to 2.3 (L_j/〖y_2〗^* =2.3), the corresponding value for two perforated walls was obtained 2.1. Sequent depth for one perforated wall was obtained up to 21.5% less than the corresponding value for free hydraulic jump. This value was about 30% for experiments with two perforated walls. The length of rollers in hydraulic jump for one and two perforated walls were obtained up to 65% and 72%, respectively, less than the corresponding values for the free hydraulic jump.

 Development of computers in the last three decades has led the scientists toward a tendency in use of this technology in solving equations concerning themselves with fluid science. Since experimental methods in study and design of hydraulic structures and expensive and takes a lot of time, numerical analysis is becoming more popular in this field of study. One of the common studies in this field is the analysis of flow regime close to spur dikes. These structures play a major role in protecting the rivers bank by leading the flow through the axis of river and accordingly changing the flow and sedimentation regime. This becomes more important when the flow passes through a bend; since in accordance to the influences of secondary flows in these bend, erosion increases and expands. In this study FLOW-3D model, is applied in order to analyze the flow regime near series of spur dikes in a 90 degree bend. And the results of mean depth velocity profile and shearing stress are investigated and verified.9 experiments by shaker(1392)with R/B ratio of 4, width of 70 cm,flow rate of 30 lit/s and fluid level of14cm is performed. Series of spur dikes used are10.5,14 and17.5 cm in length which cover respectively 15,20 and25 percent of channel width, each is set to have three angles of 60, 90 and120 with the flow.An experiment as well as control experiment the spurdikein the same condition performed. First with calibration model of turbulence models LES, RNG and K-ε, turbulence model LES with the most care were selected . For verifying of the model FLOW-3D, without the spurdike and the spurdike with the length of 17/5cm which is equivalent to 25% of the channel width and angle of 90 degrees with the flow were simulated. Then to define the scenario by keeping all conditions instead of the directly spurdike, T-shaped spurdike and L-shaped spurdike was placed. The results indicate acceptable performance model FLOW-3D simulationof flow and suitable mesh in90 degree bend with series of spurdikes. This software modeling as well the composed vortices around the spurdikes .Flow vectors indicates that spyrdikes cause flow diversion to inner walls and middle of channel . The pattern of shear stress indicate that maximum shear stress and also erosion get away from outer wall. The L-shaped spurdike has the most velocity and shear stress than T-shaped and direct spurdikes.

 There are different types of stilling basins, including Standard stilling basin USBR, Stilling basin SAF, Stilling basin with continuous sill and stilling basin with perforated sill noted. The purpose of this study is evaluation of one and two perforated sill(s) in stilling basin and its impact on characteristics of hydraulic jump such as length of hydraulic jump, length of roller, decrease secondary depth of hydraulic jump, dissipation of energy and required tailwater depth. Also determine the optimal distance of one and two perforated sill(s) from the beginning of the stilling basin with a fixed height for perforated sill and ratios of opening of holes equal 50%. Experiments were carried out in the form of 72 tests for different discharges in range of 47 to 145 lit/s and Froude number in ranges of 3.6 to 11.2 Based on the results of experiments, an analytical expression was developed for the prediction of the length of hydraulic jump in the case of two perforated sills. Results of experiments on two perforated sills showed that they can only reduce the length of hydraulic jump to an acceptable level that the distance between them provide the conditions for creating a stable jump and the length of jump does not decrease by reducing the distance between the sills. Also they decrease the relative length of hydraulic jump until 1.89 times of secondary depth of free hydraulic jump, secondary depth of forced hydraulic jump up to 27.75 percent less than secondary depth of free hydraulic jump, length of roller up to 76.9 percent less than length of roller of free hydraulic jump and the amount of energy loss is reduced up to 87.1 percent for Froude number of 11.2.

 When the water from the top of any spillway from the high to the low flow, A lot of potential energy to kinetic energy that turns the screw. Whatever the spillway height is more and tailwater depth is lower, This intense energy conversion and the result will be higher flow velocity. Such a flow has considerable destructive power that which may be of total hydraulic structures and downstream structures to cause serious harm. So in a way the flow of energy must be dissipated. Stilling basins are one of the most common structures in the energy dissipation That costs too much, it can be spent on the construction of dams, Obviously, the greater the energy loss of water during the spillway the water entering the stilling basin with less energy and therefore reduced the length of hydraulic jump which in turn can be used in the design of the stilling basin it is also considered less.
In this study, with the aim of further economic stilling basin the model with blade in ogee spillway flow path before and after lower bypass output under different angles of the lower bypass outlet (30, 45 and 60 degree) over the horizon, to combination flow with overflow and underflow to increase turbulence and increased energy dissipation of flow is used. A total of 60 run in 9 different models with three angles bottom outlet listed with the presence or absence of blades, as well as a standard ogee spillway model and each test was conducted on six different discharges. In model bladed, blades installed in two places, once before and once after the lower outlet slot is located. Energy dissipation caused by interference flows at the toe of the spillway for the model with lower outlet at 30 degrees with upstream blades is more than other models used in this research that amount of this dissipation energy on average until the design discharge is equal to 45.50 percent and decrease percent of length and sequent depth jump at toe of spillway on average, respectively equal to 36.11 and 21.23 percent.

 Nowadays design and construction of concrete, rocky and earth structures is one of the proper ways to control and divert water from rivers. Stepped weir consists of steps which start from near the crest and continue to the toe of the weir. Recent developments in technology like gabion wire with a polymeric cover and the use of RCC, has begun a renovation in design of stepped weirs. One kind of stepped weirs with proper performance is gabion stepped weirs which are made of soft steel galvanized mesh and stone. Gabion stepped spillways are used on the path of water flow to dissipate the water energy and reduce the erosion power, and traps some of suspended sediments in the upstream while reducing the flow energy. The flow energy dissipation is much, due to the interflow through inside of the porous body, so the stilling basin dimensions and its construction costs is reduced. Also, the gabion stepped spillway can prevent the cavitation phenomenon to a high degree due to the passing flow aeration and the speed reduction on the spillway, which is one of the hydraulic structures design problems, such as spillways. These types of weirs have more flexibility in comparison with the impervious type, and are resistant and stable against loads caused by water pressure. In this study the range of variables are specified, considering the existing facilities and the laboratory limitations to investigate the effect of porosity and end sill in impervious stepped spillway and gabion stepped weir on the amount of energy dissipation of flow and downsteram hydraulic jump characteristics. Hence, by setting up physical models including a simple chute, gabion stepped weirs in three different porosity (30, 40 and 45 percent) and an impervious stepped spillway and putting six different types of end sill with different height and slope of upstream on the outer edge of the steps, a total number of 203 experiments were carried out (for control and stepped models) in seven different discharges ranging from 20 to 50 lit/sec, and the amount of energy dissipation of structure and downstream hydraulic jump characteristics were investigated. The slope and height of all models were considered to be constant and equal to 1:2 (vertical:horizontal) and 60cm, respectively. The results showed that the increasing ratio of energy dissipation in impervious stepped models (with simple step and with end sill) and gabion stepped spillway with porosity of 35, 40, 45 percent (with simple step and with end sill), in comparison to the simple chute model is 2.97, 3.26, 3.39, 3.54 on average, respectively. Thus, the gabion stepped spillway with porosity of 45 percent and the impervious stepped spillway, produced the most and the least increasing ratio of energy loss in comparison with the simple chutes. Totally, the variation of height and slope of upstream end sill does not have a significant effect on structure energy loss and downstream hydraulic jump characteristics.

In recent years due to the simplicity construction, easy availability, durability and being economic, gabion structures have been widely used for excess energy dissipation in special for erodible channels. Gabion stepped weirs are mostly constructed to protect river beds and erodible waterways. These weirs due to proper capability in energy dissipation by the mixture of through and over flow, have been noticed by the designers. The main purpose of this study is to investigate the effect of slope and number of stairs of spillway on the hydraulic characteristics of flow and downstream hydraulic jump. In order to achieve the goals of this study, a simple chute and rigid stepped spillway has been used as a control and also built three models from each of the variables, with the results being compared with the corresponding values obtained from the control model. Physical model of gabion stepped spillway was constructed in three different slopes (21.8, 26.6 and 35 degree or z=1:2.5(horizontal:vertical), z=1:2 and z=1:1.5, respectively) and three different number of steps including, 8, 6 and 4 (with height of each step equal to 7.5, 10 and 15 cm). In total a number of 105 experiments with 5 discharges between 30 to 50 l/s were carried out.
In these experiments, the energy dissipation of structure and its effect on the downstream hydraulic jump characteristics including, length of hydraulic jump, conjugate depths and length of roller are examined in this kind of overflow.
The results showed that in all slopes and number of stairs, energy loss in gabion stepped spillway is more than the control models (stepped spillway and simple chute). Also the measured energy dissipation values illustrated that the maximum and minimum values were for the slope with 21.8 degree and 4 steps, and 38 degree with 8 steps, respectively. Energy dissipation in gabion stepped spillway was obtained about 81.5 percent, when the residual energy in downstream of structure compared with the corresponding value in upstream of weir. Also in this spillway, energy dissipation values increased from 9 to 20 percent and 55 to 74.3 percent in comparison with the corresponding values for the regid stepped spillway and the simple chute, respectivly. The conjugated depths ratios in gabion stepped spillway were calculated from 26.2 to 35.8 percent less than the corresponding values in simple chute, wheres these values were obtaied 20.1 to 23.3 percent for the regid stepped spilways. The percentage of reduction in average length of hydraulic jump in all gabion models was 44.1 and in stepped model was 28.8. Also the percentage of reduction in average roller length in all gabion models was 45.5 and in stepped model was 30.
 

Analyze and prediction the amount of sediment load in rivers is one of the most important and studies in hydraulic sediment and river engineering. The importance of river engineering projects and utilization of the hydraulic structures in water flow direction exacerbates sediment control plan in rivers and reservoirs. Nowadays, the numerical models are used as the suitable tools for simulation the flow, water quality and sediment transport in riverine zones. In this research study the flow was dynamically modelled and simulations were carried out for the suspended sediment transport processes by the numerical FASTER model in a reach from regulating dam to Pole Kaleh along Zayande Rood river. The hydrodynamic part of the FASTER model was first calibrated using Manning roughness coefficient in order to have precise estimate of water elevation and discharge at any time and space during simulation progress. Two periods during the year 2010-2011 were specified for model calibration and verification. Different existing experimental fall velocity equations and the suspended sediment load equations for equilibrium conditions in the literature were added to the FASTER model enabling it to have different simulations for suspended sediment load. Also the different experimental equations for estimating longitudinal dispersion coefficient in the current literature were used as a main part of suspended sediment simulation in FASTER model. Therefore, the user was able to choose any fall velocity equations, equilibrium suspended sediment load equations and equations for estimating longitudinal dispersion coefficient. It was found that the variable Manning roughness coefficient based river discharge give the best calibration and verification for water elevations and discharges estimation. Also a combination of Kashefipour Model for suspended sediment load for equilibrium conditions, fall velocity based on Cheng model, and with zero longitudinal dispersion coefficient, was found to have the best suspended sediment concentration simulation in Zayandeh Rood river.

Density current is one of the effective procedures of sedimentation in dam reservoirs. In simple, density ‎current phenomenon called to a fluid by density (‎ ‎) that moves in other fluid by difference ‎density (‎ ‎). Density current causes sediment transport close to dam and damage to lateral installations. So ‎investigation about control of density current in dam reservoirs is very important. In this study the effect of ‎slope, discharge and roughness on salty density current characteristics including velocity and concentration ‎profiles, water entrainment and velocity of head, has been investigate. Experiments were carried out in ‎physical and hydraulic models laboratory of Shahid Chamran University of Ahvaz. Experiments ‎performed by three discharges (0.6lit/s to 1.2lit/s), three slopes (0% to 3.4%), four roughness (0mm to ‎‎15mm) and one concentration (20gr/lit) in 7.8m length, 35cm width and 70cm height of flume by using ‎salinity water that totally caused 36 tests. Roughness arrangement waz‏ ‏zigzag and from 1.5m to 4.5m of ‎bed, has been covered. Concentration of body, velocity and height of head and velocity profiles in the ‎body were measured. Acoustic velocity meter (DOP 2000) used to measure the velocity profiles in the ‎body of current, digital camera and ruler to measure velocity and height of head, EC meter to measure EC ‎of density current and Flow meter to measure discharge. By examining concentration profiles, were ‎observed that by increasing of roughness height, density current body thickness increased and density ‎current concentration in depth decreased, also by increasing of slope, density current body thickness and ‎concentration decreased. By examining velocity of head was observed that by increasing of slope and ‎discharge and by deccreasing of roughness height, velocity of head increased. Sensitivity analyses of ‎velocity of head was observed that by increasing of discharge and roughness height, Sensitivity of velocity ‎of head to slope decreased and by increasing of slope and deccreasing of roughness height, Sensitivity of ‎velocity of head to discharge decreased. Also by moving of current during bed, velocity of head ‎decreased. By examining velocity of body profiles, were observed that by increasing of slope, maximum ‎velocity increased and height of zero point and maximum velocity decreased and velocity profile is ‎stretched whereas by increasing of discharge, maximum velocity and height of zero point and maximum ‎velocity increased. However by increasing of roughness height, velocity profile thickness and height of ‎zero point increased and velocity of density current decreased, for example velocity in smooth bed than ‎bed with 15 mm roughness, on average 35.3% increased. Also by moving of current during bed, maximum ‎velocity decreased and its distance from bed increased. However Keulgan coefficient for this study on ‎average about 0.34 was obtained. By examining water entrainment was observed that by increasing of ‎slope, discharge and roughness height, water entrainment coefficient (Ew) increased. On average Ew by ‎increasing of slope from 0% to 3.4%, increased about 36%, by increasing of discharge from 0.6lit/s to ‎‎1.2lit/s, increased about 51% and by increasing of roughness height from 0mm to 15mm, increased about ‎‎42%.‎

 Rivers has been changed under phenomenon of erosion and sedimentation. Some of these kinds of changes are change of direction, transversal and longitudinal transposition, shortcuts, river bed level change and geometric properties change. Section changes especially in intrados are very important and it has specified a lot of research in recent years. According to special condition of flow in river bend, erosion of outer banks of bend and sedimentation in inner banks cause gradual changes in form of the river which makes many different and significant social and economic problems. So many researchers have begun studies for erosion control in outer bend that lead to the creation of different methods to stabilize the river bank at the bends. The use of spur-dike is one of indirect procedures to protect the banks. Spur-dikes are hydraulic structures which are made in the bank of river as transverse walls and they absolutely help to the protection of walls by removing flow from the banks and focusing and keeping it in the middle. Spur-dikes are made into two ways: permeable and impermeable. Because the spur-dikes are as obstacle against flow, the will be exposed to scouring. Knowing about amount of scouring around spur-dikes can strongly help to designing them precisely and actually prevent destruction and overturning under effect of erosion. The aim of the present study is to investigate the effect of permeability and the placement distance of spur dykes on the changes in scour-hole dimensions and bed topography in 90° mild bend in submerged condition. a total of 36 experiments have been conducted around vertical spur dike by considering 3 different permeability (0.0%, 33%, and 64%), 3 placement distance (3Le, 4Le and 5Le) and 4 flow Froude number (0.21, 0.23, 0.26, and 0.28), and in each experiment, changes in scour-hole dimension around it was investigated. All of the experiments were conducted in a laboratory flume with 90° mild bend, R/B ratio of 4, and constant width of 70 cm. Results indicated that increased permeability, reduced scour rate significantly, such that, the maximum amount of depth, width and length of scour-hole was related to spur dyke with permeability of 0.0% and the minimum amount belonged to the spur dyke with 64% permeability. Investigating the effect of the placement distance of spur dykes indicated that the maximum scour-hole depth in all three permeability occurred in 5Le distance and the minimum amount was related to 3Le distance. For example, in permeability 0%, maximum depth of scouring in Fraud number 28% at situation distance 3Le and 4Le had decreased 20% and 5.14% respectively rather than situation distance 5Le. Also the results showed that the maximum and minimum length and width of scouring trench in aforesaid permeability are related to situation distance 5Le and 3Le respectively.

 River mechanism is such that its cross-section is subject to substantial changes with time. These changes, specifically in rivers bend, are more evident due to secondary flows and leads to erosion of river banks in outboard bends, which in turn causes economic and social problems. Spur dykes are among indirect methods in protecting river banks, which through diverting flow streamlines from outboard bank toward the river centerline and reducing the power of secondary flow, yield a reduction in erosion of river bends. In addition, inducing a laminar flow within the area between spur dykes, provides the required condition for sedimentation, and gradually stabilizes new river direction. Since spur dykes are obstacles to the flow, they themselves are subject to scour. Understanding the rate of scour on the sides of spur dykes helps to improve their design and prevents destruction of the spur dykes by erosion. The aim of the present study is to investigate the effect of permeability and the placement angle of spur dykes on the changes in scour-hole dimensions and bed topography in 90° mild bend in submerged condition. A total of 36 experiments have been conducted by considering 3 different permeability (0.0%, 33%, and 64%), 3 placement angle (60, 90, and 120 degrees with respect to upstream side of the flume) and 4 flow Froude number (0.21, 0.23, 0.26, and 0.28), and in each experiment after choosing critical spur dyke, changes in scour-hole dimension around it was investigated. All of the experiments were conducted in a laboratory flume with 90° mild bend, R/B ratio of 4, and constant width of 70 cm. Results indicated that increased permeability, reduced scour rate significantly, such that, the maximum amount of depth, width and length of scour-hole was related to spur dyke with permeability of 0.0% and the minimum amount belonged to the spur dyke with 64% permeability. Investigating the effect of the placement angle of spur dykes indicated that the maximum scour-hole depth in closed spur dyke occurred in 60° angle (repulsive condition) and the minimum amount was related to 120° angle (absorbent condition). Where, in spur dykes with permeability of 33% and 64% maximum depth of scour-hole occurred in 120° angle (absorbent condition), and minimum amount occurred in 60° angle (repulsive condition). Moreover, results indicated that the maximum length and width of scour-hole dimension occurred in every permeability related to 60° angle (repulsive condition), and the minimum amount of them in closed spur dyke was in 90° angle and in permeable spur dykes occurred in 120° angle (absorbent condition)

 

 

According to the flow pattern specific conditions in river bend, outer shores bend erosion and sedimentation in the inner bend causes the gradual shift form the river. Accounting rivers in the bend with goals such as preventing a change in the curvature of the bend, avoid changing bed morphology and bed level, protection the outer wall of against erosion, sedimentation control is done in the adjacent inner wall. One of the common methods of organizing and erosion control in the bend of river is use of the spur dike. Spur dike to divert the flow of the river to prevent erosion of the river bank is and on the other hand the new model is the cause scour around spur dike. The main objective of this study was to evaluate the effect of permeability and effective length the spur dike of the scour hole dimensions non-submerged on the 90 degree mild bend. Therefore, experiments with three effective lengths of (10.5, 14 and 17.5) equivalent to (15, 20 and 25 percent of the width of the flume), three permeability of (0%, 33% and 64%) and four flow rates of (25, 27, 30 and 33 liters per second) respectively corresponding to the Froude numbers (0.21, 0.23, 0.26 and 0.28) under the clear water conditions. Angle position of the spur dikes of 90 degree bend to the outer wall and the distance between them (a/L_e=4) and depth of 14 cm was fixed. Experiments in a laboratory flume 90 degree mild bend with R/B ratio of 4 and width of 0.7 m rectangular carried out was. The results show that by increasing the permeability of the in all three effective length of the spur dike in dimensions of the scour hole will reduce the Froude number of fixed landing. As with, the increasing permeability rate of 64% as compared to the impermeability, at Froude number 0.28 and effective length spur dike 10.5 cm, depth, length and width of the relative scour, respectively 86.35, 73.33 and 48.88 percent reduction. Also effective length spur dike 14 cm, depth, length and width of the relative scour, respectively 82.88, 65.95 and 47.52 percent reduction. Similarly, in the effective length spur dike 17.5 cm, the aforesaid ratio of, respectively 78.125, 63.94 and 40.01 percent reduction. By increasing the effective length the spur dike of the permeable and impermeable in the amount of the dimensions of the scour hole around the spur dike at the same Froude number increases. As with, increasing the effective length of the spur dike with 33% permeability, the Froude number 0.28, from 10.5 to 17.5 cm, depth, length and width of the relative scour, respectively 42.37, 46.66 and 38.83 percent has increase. Similarly, by increasing the effective length of 14 to 17.5 cm, the aforesaid ratio of, respectively 6.69, 18.34 and 27.07 percent increase. Also, by increasing the Froude number in all three of the effective length and permeability of the spur dike scour hole size increases. According to the topography of the substrate can be concluded that the maximum amount of scour generally occurred along the one-third of the last part of bend.

 

Amongst natural disasters, flood and storm damage to human communities have been the most significant worldwide. This is also true in the case of Iran, with a large percentage of the annual budget to reduce damages from natural disasters, being spent to compensate flood damage. Floodplain management is one of the most important topics in river engineering due to reducing the fatality and damages caused by flood. The purpose of flood predicting is to estimate data regarding flood volume, intensity, duration, location and inundated area expanse. In addition it can significantly help in determining the capacity of a river channel and the behavior of surrounding floodplains which enables the engineer to predict possible changes in storage capacity and determine the location and time of flood situations. All flood management methods require a suitable hydraulic model to determine flood maps which are fundamental for floodplain management and damage mitigation. Several hydrodynamic models including 1D, 2D, 3D and coupled hydraulic models have been developed in the world. The 1-D models have the advantages of simple domain equations, low computational nodes, limited computational time and the possibility of a more straightforward analysis of the results when compared to 2D and 3D models. 1D models determine the average of hydraulic parameters such as velocity, depth, top width, etc and provide no details about flow current in the floodplain. On the other hand, 2D, 3D and coupled models provide details about flow on floodplains without defining the flow paths but, because of the heavy computational grid, they need more time to run. Dez river in Khuzestan province is surrounded by wide low elevation plains. Since the elevation of floodplains is lower than the main channel, when overbank flow occurs, two flows with different velocities and depths must be considered in the main channel and floodplains. Moreover, because of the low gradient of the floodplains, there is no possibility for a quick flow return to main river channel. In the present study four scenarios including: 1) 1D hydrodynamic simulation using existing cross sections, 2) 1D Hydrodynamic simulation using extended cross sections, 3) Quasi 2D Hydrodynamic simulation using LINK CHANNELS and 4) 1D-2D (couple) modeling with MIKE FLOOD, were investigated. Data were recorded from February 2005 (1384) has been used to calibrate the mathematical model with the roughness index value of each reach calibrated. The results indicate the quasi 2D model, despite of the limited computational time than 1D-2D model, has an acceptable accuracy in predicting discharge, water level, inflow and overbank flow simulation and reduction in inundation volume, which is compatible with the fact of inundation volume stored in the floodplains can separately be computed from the hydraulic parameters of main river and floodplains. But, due to lack of overbank flow modeling, there is no possibility for models with main cross sections and extended sections to represent correct results about flood propagation. Setup, run time, and time need to fix errors for coupled model is significantly high. Set up time for the quasi 2D model is also high, but its run time is low such as other 1D models. Although modeling with extended sections partly fixes problems concerning modeling with main cross sections, extending cross sections necessitate time and accuracy and dominate the GIS software. Short run time of the first three scenarios, in comparison to the long run time of the coupled model is one of the achieved results, and provides the possibility to appropriate responses by using a quasi 2D model in a shorter run time. Moreover, the appropriate accuracy of topographic maps for accurate calibration, as well as modeling accuracy of results that can be trusted, is required. Ultimately, according to the results of current study, it is recommended to apply the quasi 2D LINK CHANNELS model or 1D-2D MIKE FLOOD model to incorporate inflow and overbank flow and flood volume changes for plain area.

The intraction between spur dike and flow makes vertical and horizontal vortices which are the main reason for producing a local scour hole around the structure and finally damaging it. This experimental study is about the effect of a spur dike's angle and its permeability on scour hole dimentions in non-submerged conditions. According to the results, when permeability increased up to 50%, scouring decreased significantly. For Fr= 0.24, and the vertical position of spur dike (90 degrees), relative depth, length, and width of the scour hole decreased 67% , 75.3%, and 45.5% respectively in comparison with impermeable spur dike. Also, for the repelling spur dike (120 degrees), relative depth, length and width of the scour hole declined 64.1%, 72.1 % and 35.4% respectively. The similar results was obtained for the arracting spur dike( 60 degrees) with the reduction of relative depth, length and width of the scour hole being measured 60.2%, 68.74% and 38.8 % respectively. In addition, for 50% permeability, the highest level of scouring was for the arracting spur dike, whose average relative depth, length, and width were 0.19, 0.7, 1.2 respectively. According to the maximum scour depth, and the behavior of the flow, for both permeable and impermeable arracting spur dike, the maximum scour depth generally occur around the sructure nose, while for the two types of vertical and repelling spur dikes, the depth can occur along the structure. Finally, for predicting the scour hole dimentions , an emprical equation was developted with the use of frude number, angle of spur dike installation, and its permeability percent

Sedimentation in reservoirs and the corresponding loss of storage capacity is one of the most serious problems in dam engineering. One of the most effective techniques for removing the deposited sediments from reservoirs is pressure flushing which has only much local effects. It is often applied as a clearing process to remove sediments around the entrance of intakes. In flushing methods, the previously deposited sediment would be flushed from the reservoir by opening the bottom outlets. . In order to make rational design of bottom outlets and other sediment flushing structures, the understanding of the characteristics of a scour funnel in under pressure flushing is significant. The physical model was constructed in the Hydraulic Laboratory at the water and science collage of the University of Shahid Chamran Ahwaz and by performing various experiments on the effect of bottom outlet shape on the volume and dimensions of flushing cone was investigated experimentally.For this purposes, the experiments on 4 bottom outlet with a circular, semicircular, rectangular and square cross-sectional area equal to 18 cm2, five water level of 30, 45, 55, 65, 78 cm, resulting in five different discharges on the bottom outlet, was performed. The results of this shape bottom outlets is an important parameter is the pressure flushing. Results also showed that for a constant water level in the reservoir at a specified time, the scouring dimensions for square and semicircle valves is more than rectangular and circle valves and this difference is more noticeable at lower heights. Scour the length and volume of flushing cone the head rises. In addition, a non-dimensional relationship was identified by dimensional and statistical analysis on experimental data, which can eventually be used to estimate the development of flushing cone dimensions

In planning of construction projects, estimating of manning roughness coefficient is necessary
for computation of accurate and exact value of discharge, flow velocity and depth, capacity of conveyance and maintenance of floodplains. Velocity distribution is a key parameter and is generally used for specifying the flow characteristics such as discharge, shear stress distribution, flow pattern, sedimentation, erosion, energy loss, and energy and momentum coefficients. This research focuses on the effect of density and height of artificial cubic roughness elements on flow resistance and velocity profiles' shapes and characteristics.
To reach the goals of this study, in total 48 experiments were conducted with three values of roughness height (5,10,15 mm), two percentages of roughness density (25% and 50%), two kind of roughness layout arrangement (regular, staggered) and four discharge values, on a length of 3.7m from bed of the flume and four experiments with soft and smooth bed. For each experiments, bed material was glued on the test section then pomp was turn on and the flow allowed entering the flume at a desired discharge then water surfaces profile , flow depth and velocity profile into three segment (at the begin, middle and end of roughed length ) was measured. The results showed that the velocity profile form is very sensitive to the height, density and arrangement of artificial roughness elements. The value of maximum velocity profile decreased and shear velocity of flow increased with increasing height and density and changing the roughness pattern from regular to staggered. Non- dimensional results of velocity profiles indicate that relatively velocity of flow decreases with significantly difference with decreasing height, density and changing into roughness pattern from regular to staggered. the effective of roughness arrangement is much more of two another variables. In addition relatively flow submergence decreases from start to the end of roughed length with increasing roughness height in constant density percentage in both regular and staggered patterns. by use of dimensional analysis and assessing effects of effective non-dimensional parameters, some equations was proposed according to logarithmic velocity distribution. in averaged, Manning roughness coefficient in regular and staggered pattern was estimated respectively 46.63 and 94.67 percentage more than this value for smooth bed. According to presented equation for manning coefficient according to relatively roughness , density percentage, Froud number and a factor related to roughness pattern.