s. m. kashefipour

Local scour around bridge piers is one of the most significant factors for the bridges’ destruction. Therefore, it is necessary to investigate the scour depth around the bridge piers. The effect of the skew angle of the single-column pier group related to the flow direction in two different arrangements including 1×2 and 1×3 piers on the maximum scour depth around the pile group was investigated in this study. The experiments were carried out under steady flow conditions. The pier group was placed in the 1×2 arrangement at the skew angles of 0 to 90 degrees and in the 1×3 arrangement at the skew angles of 0 to 45 degrees. The results showed that increasing the skew angle of the pier group is almost ineffective on the maximum scour depth around the first pier. However, it has a great effect on the maximum scour depth, its temporal development, and the expansion of the scour hole around the second and third piers in different arrangements of the pier groups. The maximum scour depth of the pier group in both different arrangements occurred at a skew angle of 30 degrees, in the arrangement of 1×2 around the second pier and by 13.33% more than the first pier and in the arrangement of 1×3 around the third pier and by 21.57% more than the first pier.

Oak (Quercus spp.) forest cover is one of the most important living ecosystems in the western region of Iran and the Kermanshah Province. One of the important managerial needs of this cover is the water requirement of the oak plant. Currently, determining the amount of water required by the oak plant is one of the main priorities of the country's natural resources sector. Among the practical methods for estimating the evapotranspiration of vegetation (water requirement) at different levels are remote sensing techniques. In this study, in order to determine the rate of evapotranspiration of forest cover in the Robat Mahidasht region in the Kermanshah Province, the SEBAL algorithm and four images of Landsat 5 in the period of June, July, and august of 2010 were used. Then, using Sentinel satellite images, the forest areas of the Robat-Mahidasht region were extracted and matched with the calculated evapotranspiration map. Based on the obtained results, the average rate of 24-hour evapotranspiration of forest cover in the desired time period has varied between 3.4 to 5.09 mm. The correlation coefficient between the estimation of evapotranspiration by SEBAL and lysimetric measurement in Mahidasht region was about 0.9967 and the absolute difference between them was about 0.53 mm per day, which indicates an error of less than 10%. The estimation of SEBAL algorithm is acceptable. Remote sensing technique and the SEBAL algorithm can be used in the compression classification and even the health of forests if there is a suitable sequence of images and with the help of satellite data of other sensors such as Sentinelimages.

In recent two decades using the numerical models is common 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. The main goal of this study is to develop one dimensional, unsteady, hydrodynamic model in which flow and sediment transport can be simulated as semi-coupled in river systems. In this research, the Saint- Venant’s equations are numerically solved for river systems and 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. After solving the above equations, the computed hydraulic parameters in this part are sent to the sediment transport segment. The dynamic advection- dispersion equation and the sediment continuity partial differential equation are applied to calculate the suspended sediment and bed load transport rates, respectively. The Exner equation is then used to predict the changes in the river bed elevations. Finally, the model is compared to the Hec-Ras Model and the results show that the developed model has a good accuracy. There are differences in the predicted depth for scour and deposition, which are not unexpected due to differences in the bases of numerical models and between the equilibrium and non-equilibrium conditions of the Exner equation.

Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph’s parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion’s ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph’s peak led to increasing depth erosion from 7% to 22%.

The construction of bridges within the river beds often makes changes to the shape and direction of the rivers. These changes take the natural actions of the river, that one of them is the local scouring around the bridges' piers and can cause annually damage. Therefore, many researches have been carried out to control and reduce the scouring. One of the methods presented by researchers is using slot at piers.  In present study, the effect of Pier Opening Area on local scouring around the pier with rectangular section is experimentally investigated. For this purpose, piers with square shape slots and different dimensions were used. The piers were tested at three levels (near the water level, on the bed and under the bed) and four Froude numbers.  The result showed that the maximum scouring depth and the volume of hole scour had a direct relationship with slot level relative to bed and Froude number and an inverse relationship with Pier Opening Area. The best performance belonged to the slot with greater dimensions which was located under the bed level in the minimum Froude number condition that reduced the depth of scouring about 55.4 percent.

Turbidity current phenomenon is one of the most important factors in reservoir sedimentation and sediment distribution, which causes management and operational problems and decreases dam’s useful life. Study and investigation of progressive section (head of turbidity current), as the most significant and considerable section is essential for sustainable management of dam reservoirs. So far, most of the studies have been conducted under experimental conditions on rigid beds. But In this study, in order to achieve more realistic results regarding natural conditions in rivers and reservoirs, the experiments were carried out on an erodible and mobile bed. So dynamic of turbidity current head was analyzed on rigid and erodible beds for different effective hydraulic conditions. It was shown that erodible bed increased the head velocity of turbidity current and Keulegan coefficient up to about 20% and also, increased the relative forehead height up to about 40% with increasing flume bed slope. In addition, in order to estimate the averaged head velocity, an equation with correlation coefficient of 0.86, was developed using multivariate linear regression and effective dimensionless parameters. Finally sensitivity analysis of the equation’s dimensionless parameters showed that the most effective parameter in estimation of the head velocity average is Richardson number.

Bandal-like structure is a kind of a spur dike which is a combination of a permeable and an impermeable spur dikes that are usually used in Indian Sub-Continents for riverbank protection and improvement of navigation conditions in alluvial rivers. It is considered as a suitable alternative for these spur dikes. In this research effect of the submergence and angle of the bandal-like structure on the maximum scour depth in a 90 degrees’ mild bend flume was investigated. Therefore, a series of bandal-like structures were placed in the flume with three different angles (60, 90, 120) and three different submergence ratios (1.16, 1.65, 2.15) and were examined under four different Froude numbers (0.21, 0.23, 0.26, 0.29). The results showed that the maximum and minimum scour depths belonged to the bandal-like structures with 90 and 60 degrees angles respectively. Also by increase of the submergence ratio the maximum scour depth was increased.

One of the common ways for bank protection against erosion along rivers’ bends is spur dike application. Spur dike changes the flow pattern and diverts it towards the river centerline and as aresult protect the river bank from erosion. However, a new flow pattern is formed with higher velocities and this phenomenon causes the local scour around the structure nose to be increased. The length of spur dike is one of the important parameters affecting the local scour around the structure. In order to investigate the effect of the permeable spur length (permeability was 33%) on local scour, experiments were conducted in a rectangular laboratory flume with a mild 90 degree bend (R/B=4; where R=radius and B=flume width). In this research a series of spur dikes with three different spur length including 10.5, 14.0 and 17.5 cm, corresponding to 0.15, 0.2 and 0.25 of flume width, respectively, was installed along the bend for each experiment. Four Froude number values including 0.21, 0.23, 0.26 and 0.28 with a constant flow depth of 14cm under clear water condition were applied for each spur length. The results show that the maximum scour depth increased with increasing the spur length for a constant Froude number; so that the maximum scour depth was happened for the length of 17.5cm with a Froude number of 0.28, which was 10.71% and 42.86% more than the spurs with 14.0m and 10.5cm length, respectively. The maximum local scour was observed to happen at the end part of the outer bank of the bend. It was generally found that with increasing Froude number and the spur length the scour hole dimensions increased.

Determination of flow resistance is an essential parameter for studying and hydraulic analysis of the open channels. Manning roughness coefficient is often be used for description flow resistance or relative roughness of a channel or floodplain. This research was focused on the effect of the height, density and arrangement of the artificial cubic roughness elements on Manning roughness coefficient. In total 48 experiments were conducted with three values of roughness height (5,10 and 15 mm), two percentages of roughness density (25% and 50%), two types of roughness arrangement (regular and staggered patterns), four flow discharge values on rough bed and four experiments with smooth bed in a laboratory flume. A length of 3.7 meter of the flum bed was designed as the rough bed according to the experiments plan. The results showed that the influence of the roughness arrangement on changing the value of Manning roughness coefficient (n) is more than the influence of the height and density of roughness. Also the mean value of Manning coefficient increased from 0.009 in smooth bed to 0.0132 in regular pattern and 0.0175 in staggered pattern. At last in order to compare with the results of previous works, some relationships have been offered in order to estimate the Darcy-weisbach coefficient (f) on the basis of the roughness density percentage at the bottom (C), relative submergence ( y ks ), Froude number of flow ( Fr ) and a factor related to roughness arrangement(€).

In an experimental investigation of the density current inflow into reservoir, the influence of bed slope (0.000 to 0.003), type of suspended particles (salt and two sizes of sediment particles) and advance distance (at three sations) on density and velocity profiles were investigated. Experiments were carried out in a tilting flume. Observations and measurements showed that the velocity and density profiles nondimensionalized with integral scales, in the same current but at different stations were the same. Furthermore, there was a fairly good similarity between the velocity profiles measured for types of currents flowing on different slopes. The dimensionless density profiles measured in different current types were not similar. Turbidity currents with coarse sediment had an almost linear density profile near the bed, whereas the saline density currents showed an almost constant relative density near the bed.

Using permeable spur dikes is one of the controlling methods of rivers’ bank erosion. In this study، the influence of Bandal- like spur dike on the longitudinal velocity profile is investigated in non-submerged situation. Bandal-like is a new type of spur dike that is made of combination of permeable and impermeable spur dike. Due to its combinatorial construction، this structure has important effect on the velocity controlling and decreasing. In this study، longitudinal velocity profiles around series of Bandal-like spur dikes in 3 permeability rates of 30%، 45% and 64%، were investigated. The results indicated that this structure played an important role in controlling and decreasing the velocity in the banks due to the permeable zone. Also by increasing permeability percentage from 30% to 64%، the value of increased about 6% in velocity profiles.

Spur dikes are the most common structures for river bank protection. Spur dikes are used in the submerged and non-submerged forms. The submerged type is used when navigation is dominant in a river and in other cases the non-submerged ones are usual. Since construction of this structure causes higher flow velocities around it, this structure is exposed to erosion. Riprap around the dike structure nose is one of the most common and economic ways to protect spur dike. In this study the riprap stability and different modes of riprap failure in a mild 90-degree bend have been investigated. Experiments were conducted in a laboratory flume with a 90-degree bend. After specifying the critical spur dike along the bend, this one and the other two spurs setted before and after the critical one were protected by riprap. The variables were the length of the structure, spur spacing and height, riprap size and different Froude numbers, with a total of 200 experiments being carried out in this flume. Three modes of riprap failure including rolling, sliding and undermining as had been detected for straight channels and other hydraulic structures in the literature, were verified and finally an equation was developed to determine the mode of failure, which would be probably useful for designing riprap in real river engineering projects.

In this study the controlling of density current by obstacle and roughness has been investigated. Experiments were carried out in a flume with length of 780 cm with 3 variable lengths of insertion roughness (0. 5، 1 and 1. 5 m) in upstream، downstream، and two sides of obstacle، and 3 heights of roughness (0. 5، 1 and 1. 5 cm) for each setting. The height of obstacle was considered equal to the height of density current body. Also two concentrations of density current، 10 g/L () and 20 g/L () and two bed slopes، 0% and 2. 5% were considered. A series of experiments was performed without using roughness. The results indicated that using roughness with obstacle had significant impact on the controlling of density current. So that without using roughness and just by using an obstacle with the height equal to density current body in the same concentrations and bed slopes، about 31% of density current was blocked. Whereas by using roughness with obstacle in some conditions 100% blocking of density current was obtained. Insertion of roughness in upstream of obstacle had relatively more impact (about 11%) on the controlling of density current as compared with the condition of roughness insertion in downstream of obstacle.

Spur dike use is one of the most common structural methods for improvement and bank protection in river engineering. This structure is generally built across the river from the bank towards centerline in order to protect the banks from erosion and to increase sedimentation along the protected banks. However، the scour hole around the nose of the structure is formed due to reducing flow width and increasing velocity and shear stress. In order to investigate the effect of permeability of spur dikes on scour hole dimensions، experiments were carried out in a laboratory flume with 7. 3m length، 0. 56m width and 0. 6m depth. Four quantities of permeability including 0% (impermeable)، 30%، 40% and 50% with four Froude numbers at constant flow depth (0. 15m) were conducted and all experiments were carried out with clear water. of the bed sediments was equal to 0. 7mm. Dimensional analysis was applied to produce the related non-dimensional parameters and by using the measured data and regression analysis a few equations for estimating scour hole dimensions were developed. The results showed that with increasing Froude number the scour hole dimensions increased up to 1. 5 times (in non permeable condition). The maximum scour hole depth increased up to 4 times، whereas the spur dike permeability decreased from 50% to 0%. The scour hole dimensions for the first and second spur dikes were also decreased by increasing the spur dike permeability.

Groynes are effective and economical structures for river bank protection along bends. The flow analysis around the constructed groynes along the outer bank is complicated. This is mainly due to the effects of groynes on the flow pattern and secondary currents and also interaction effects between the groynes. In the present paper، the effects of series of groynes along a 90-degree mild bend on the flow variables such as mean flow distribution، secondary currents and shear stresses have been investigated. The experiments were carried out in a bend flume with 0. 7 m width and 0. 8 m height. The R/B ratio for the channel bend was 4 and depth of flow was 0. 14 m. The non-submerged Groynes were used in 3 lengths: 15%، 20% and 25% of the channel width. Also the groyne spacing was 3 times greater than its length. The analysis of data showed that the presence of groynes caused uniformity in the velocity distribution at upstream and the high velocity zone moved toward the center of the channel and inner wall. Groynes also reduced strength of the secondary currents. Due to existance of groynes relative shear stress was increased and by increasing of groynes lengths it was increased but lengths of groynes didn’t have significant effect on the location of relative maximum shear stresses and it happend at sections of 70 to 80 degrees of bend in all conditions.

Spur dike is a structure made of stone, sand, rock, soil or concrete, which is usually built with an angle relative to the bank to divert the flow from the banks and concentrate it towards the centerline of the river in order to prevent bank scouring. One of the main problems regarding this structure is its stability due to possibility of the scouring around the nose of structure. Therefore modeling the amount of the scouring around the structure according to the flow conditions is important and essential. In this research the laboratory data of scouring around a spur dike for different flow conditions in a 180° bend were applied for modeling this phenomenon using Fuzzy Logic model (FLM) and Artificial Neural Network (ANN). The scour was modeled as a function of the length and the installation angle of spur dike in bend, and the upstream Froude number. The results showed that the ANN and FLM models were able to predict the amount of scouring, accurately. A regression equation was also developed for describing the amount of scouring around the spur dike using the corresponding measured values empolyed for producing and calibrating the pattern of the ANN and FLM models. The results obtained from ANN, FLM and regresion models were then compared together using another series of existing data, which had not been applied for developing those models.

One of the most important ways for dissipation of excess energy in downstream of overflow dams is the occurrence of hydraulic jump. In this research the hydraulic jump phenomenon was simulated using the Flow-3D software with two different turbulence models including the standard and RNG models. For this type of phenomenon and most accurate predictions of hydraulic jump characteristics، these two turbulence models were first verified using the data measured in a laboratory flume by Chanson and Chacherau. It was found that the RNG turbulence model performed much better than the standard turbulence model. The model was then applied for simulation of hydraulic jump in the physical model of Nemrood dam stilling basin. The computed pressure، velocity distributions and water surface profiles were compared with the corresponding experimental measured data that matched together successfully.

Stilling basins are the most important energy dissipating structures placed at the end of spillways and any source of supercritical flow to control the hydraulic jump. Due to its importance and high construction costs، modeling of stilling basins are necessary prior to construction. Physical modeling of stilling basins are time consuming and costly، therefore attempts have been made so far to relate the hydraulic jump characteristics such as the jump length، energy loss، etc.، to some hydraulic parameters like Froude number، divergence and the bed slope. In this study hydraulic jump characteristics such as the jump length and energy loss in divergent rectangular sections on inverse slopes were modeled as functions of Froude number، angle of divergence and inverse bed slope، using Artificial Neural Network. The accuracy of the model for estimating different hydraulic parameters was also verified. The results indicated that the model was capable of predicting hydraulic parameters with high accuracy. Furthermore، the weight of each parameter for estimating hydraulic characteristics was determined. Data Fit software was used to produce relationships between the parameters. The relationships found to be accurate enough to predict the hydraulic jump characteristics.

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.