نشریه تحقیقات مهندسی سازه های آبیاری و زهکشی
سال بیست و دوم شماره 85 (زمستان 1400)

Control of river bed erosion and consequently river banks is one of the important goals in river training projects. Instream grade-control structures [i.e. cross-vane, J-Hook vane, W-weir, log vane, block ramps, sills, etc.] are commonly used to stabilize the riverbed keeping the river slope in an equilibrium condition. When the steep river is wide, the mentioned instream structures are not the appropriate solutions. Stepped weirs are a type of spillways that creating a nappe flow over the steps, along with a high energy dissipation, lead to a reduction of downstream scour depth. Stepped weirs also can be employed as grade-control structures in the case of wide rivers. Scour depth and energy dissipation downstream of stepped weirs depend on the flow pattern over steps which depends on the weirs slope (i.e. ratio of the height to the length of the step), number of steps, constructing material and downstream hydraulic conditions (Chanson, 2002). Due to the role of scour formed at the downstream of these structures on their safety and stability, in the present study, effect of the installation of apron on variation of scour characteristics at the downstream of stepped weirs with and without labyrinths was investigated experimentally.

Experiments were performed for different flow conditions and weirs slopes of 1: 1 and 1: 2. The experimental measurements were conducted in the physical hydraulics modelling laboratory of the University of Guilan, Iran, in a flume with a rectangular cross-section that was 1.5 m width,1 m depth and 12.5 m length. A centrifugal pump supplied the required flow rate up to 90 L/s. The flow discharge was measured by ultrasonic flowmeter installed on the suction pipe with an accuracy of ± 0.1 l/s. In order to supply sediment particles for the sedimentary bed, sand with a uniform diameter of 2.68 mm was prepared and placed at the recess box with length of 2 m, width of 1.5 m and height of 0.30 m at downstream of weirs.The stepped weirs with slope of 1:1 and 1:2 consisted of five steps made of sheet metal panels. Aprons length are 0.135 (1/3P) and 0.27 (2/3P) meters. The labyrinths geometries was based on the results of research by Kazempor et al., (2019) that had the most suitable performance on reducing scour depth, was chosen. Primarily experiments indicating that the equilibrium bed condition was reached at 6 hours. For each experiment, after installing the weir, labyrinths and aprons and adjusting the sedimentary bed, the flow gradually entered into the laboratory flume and the flow depth gradually was raised. After adjusting the flow discharge, by regulating the downstream butterfly gate, the desired downstream depth was obtained. for all experiments, the temporal development of the scour depth for 6 hours at different time steps was taken by a digital camera and then digitizing using Grapher9 software. Final scour depth at the end of tests was measured using the Laser scanner Leica.

The results showed that by increasing the discharge to maximum value, installation of the apron LA1 at downstream of the stepped-labyrinth weirs SL1K1LA1 with an average 30% reduction of the temporal maximum scour depth had the best performance. The results indicate that by increasing the apron length to LA2, the SL1LA2 weir with an average of 54% reduction of the maximum temporal scour depth had the highest performance.By reduction of stepped weir to 1:2 and installing apron length of LA1 the maximum flow discharge, by the installation of apron length of LA1 stepped-labyrinth weirs SL2K4LA1 with an average reduction of 21% had the best performance on reduction of temporal scour depth. Also by increasing apron length to LA2 length, the stepped-labyrinth weirs of SL2K4LA2 had the most desirable performance with an average reduction of 34% on temporal scour depth.

Comparison of the results of the equilibrium scour depth of the yc/h range from 0.34 to 0.54 for stepped weir with slope of 1:1 showed that by installation of apron length of LA1, the equilibrium scour depth at the downstream of SL1LA2, SL1K1LA2 and SL1K2LA2 weirs reduced 38%, 34% and 45%, respectively, compared to SL1 weir. By increasing the apron length to LA2, the equilibrium scour depth at the downstream of SL1LA2, SL1K1LA2 and SL1K2LA2 decreased by 65, 65 and 63%, respectively in comparison with SL1.At a stepped weir with slope of 1:2, that by installation of apron length of LA1 the equilibrium scour depth of SL2LA1, SL2K3LA1 and SL2K4LA1 weirs was reduced 8, 1 and 10%, respectively, compared to SL2 weir. By increasing the apron length to LA2, the equilibrium scour depth downstream of SL2LA2, SL2K3LA2 and SL2K4LA2 weirs decreased 44, 50 and 48% on compared to SL2 weir, respectively.

Drying almost the whole of Lake Urmia is one of the main environmental crises of Iran nowadays. Despite great efforts to restoration of the lake since 2014, owing to the limitation of inlet flow to the lake, insignificant success has been reached. Actually, in the basin of Lake Urmia, the evaporation rate is very high and based on the reported data it is over 1000 mm annually, while the precipitation is about 330 mm. Hence, the pure evaporation height from the surface of the lake is higher than the lake water level rising during recent years. Therefore, in order to overcome the shortage of inlet flow to Lake Urmia, the evaporation area as well the surface of the water body must be equivalent to the evaporation rate. Samadzadeh et al. (2018), reported that by the construction of new dikes inside the lake, consequently by dividing the lake into some smaller parts and restore each part separately one by one, the lake could be restored with the available inflow of feeder rivers of the lake. However, difficulties of construction of causeway through lake Urmia confirmed that the sedimentary bed materials of the lake are classified as problematic material from a point of geotechnical view (Eslami et al., 2020). Henceforward, dividing the lake into smaller phases is not possible by using ordinary methods like earthen dikes which have been used in the restoration of the Aral Sea. In this regard, we explored the geotechnical properties of bed materials of Lake Urmia to choose a compatible method with the environment of the lake as well as the proper hydraulic structures to divide Lake Urmia into smaller regions proportional to annual discharges of its basin rivers.

Lake Urmia is one of the largest hypersaline lakes located northwest of Iran. The area of the lake and its basin are about 5000 and 52000 km2. During las past two decades the lake has been faced with an intense drawing of water level, and almost the lake has vanished. Based on the published investigation regarding phases restoration of Lake Urmia, two different routes have been suggested by Samadzadeh et al., (2018) based on water balances of the lake. Therefore, we also followed the proposed routes to investigate the geotechnical properties of the bed materials. The first route complies with the constructed causeway. In this route, almost the total of the distance from the west to the east shore has been blocked by road dike, except the bridge with a span of around 1200m. The second route is located in the southern region of the lake and it started from Rashakan on the west coast to the east direction which intersects Espir and kaboodan islands. The length of the current route is about 19 km. For each route, three points with a distance of 200 m from each other (from the west coast) in the form of disturbed and undisturbed specimens have been prepared. Identification tests, shear strength tests include vane shear test, uniaxial shear test, and consolidation test have been carried out. In order to study the effect of salt and fresh water on the mechanical and physical properties of the bed and sedimentary material, some tests such as Aterberg limits have been conducted by using fresh and saltwater separately.

Based on the achieved results of laboratory tests, the bed materials of Lake Urmia in both routes were classified as OH and OL while treated with fresh and saltwater based on the Unified soil classification system, respectively. Also, shear strength tests showed a low strength of about 12 kg/cm2 for the bed materials of route 2 while the half is for the first route in direction of the causeway at the northern part of the lake. The content of organic materials was detected 3.54 and 4.67 for the first and second studied routs respectively. Odometer tests results revealed that the bed materials of the studied routs could be classified as soft or very soft soils. Therefore, construction of any heavy structure such as a levee to divide or isolate the lake is almost impossible with the ordinary techniques, however, light and thin structures like sheet piles could be a good alternative to the aim.

A spillway is a structure used to provide the controlled release of water from a dam or levee downstream, typically into the riverbed of the dammed river itself. One of the types of spillway used in dams is vertical shaft spillway or the same as morning glory spillway. One of the methods to increase the flow rate and reduce the occurrence of vortex currents in the spillway is to modify the shape of the inlet of the spillways. In recent years, spillways with daisy, piano key and zigzag inlets have been proposed known as spiral spillways. A review of the results of previous research shows that the common goal in the study of vertical shaft spillways is to pass the flood flows with the highest possible discharge and the lowest water level and reducing the eff destructive effects of vortex currents. In previous researches, issues such as the effect of the inlet type of vertical shaft spillway and geometric parameters of the structure on the discharge coefficient and the study of vortex occurrence conditions and hydraulic flow of vertical shaft spillway. In this research a new shape of vertical shaft inlet in form of Bow-tied spillway was introduced and discharge coefficient of these spillways was investigated using a series of experiments.

The experiments of this research were performed in a metal cube tank with 1.5 m length, 1 m height and 1 m width with transparent Plexiglas side walls in the hydraulic laboratory of Department of Water Engineering at Zanjan University. Bow-tied spillways were examined with different angles of the bow-tie (60-150 degree) in both cases of with middle arc and without middle arc and the results were compared with a morning glory spillway. In this research, by preparing eight bow-tie spillways and a morning glory spillway with a total length of 60 cm and considering the hydraulic conditions (H/D), 72 experiments were run to investigate the effect of the geometric shape of the spillway on the discharge coefficient.

Results showed that in Bow-tied models without middle arc, increase of the bow-tie angle leads to reduce the flow interference and increase of flow discharge over the spillway. So that B-150 model (with 150 bow-tie angle) had higher discharge coefficient than the other models of bow-tied. This model had better hydraulic performance than morning glory spillway (10 percent). Also, economic advantage of this model was higher than morning glory spillway (31 percent). Results of the tip position of the bow-tie spillway show in tip angle of 120 degree, the tip position of the bow-tie has a significant effect on the discharge coefficient of the spillway, but with increasing the bow tip angle from 120 to 150, the tip position of the bow-tie spillway did not have much effect on the discharge coefficient. In Bow-tied models with middle arc, change of bow-tie angle had no significant effect on discharge coefficient and hydraulic performance of these models was lower than morning glory spillway (5.3-9.7). This could be due to the interference of fall currents and the low internal area of these models.

Comparison of the hydraulic performance of bow-tie models with morning glory spillway shows that the B-150 model has the highest hydraulic performance (10%) compared to other models. On the other hand, this spillway has a better economic advantage (31%) than the morning glory spillway. In the construction of reservoir dams, especially earthen dams, the major part of the executive cost is related to the implementation of concrete structures of emergency spillway. In this situation, by choosing Bow-tied spillway with optimal geometry, a suitable economic savings can be achieved along with improving the hydraulic conditions of the flow.

Restrictions on water resources in the country prevent agricultural development. Pressurized irrigation systems are one of the management strategies to improve productivity and use of water resources. However, by improperly using these systems, these systems themselves cause irrigation losses and water loss. Evaluation of irrigation systems during operation and resolving its defects can prevent such incidents. Therefore, the aim of this study was to evaluate two pressurized irrigation systems (Linier) in a field located in the research station so that the effects of tendency to an efficient irrigation system in increasing water use efficiency index or reducing water losses have been investigated. For this purpose, Kristiansen uniformity coefficient (CU), low quadrant distribution uniformity (DU), low quadrant application potential efficiency (PELQ) and low quadrant real efficiency (AELQ) have been used. The results of field evaluation based on CU and DU showed that the mean of these indices in wheat irrigation system was 89.38% and 83.92% and in rapeseed irrigation system was 76.85% and 70.31%, respectively. Also, from the perspective of potential efficiency (PELQ) and real (AELQ), the average water application of wheat irrigation system was 62.89% and in canola irrigation system was 49.33%, respectively. In a general view, both systems are in an acceptable range based on CU and DU evaluation indicators, while based on the computational values of PELQ and AELQ indices, they are outside the acceptable range, indicating the lack of proper management of the exploiter of the studied systems. The low evaluation indicators of the mentioned pressure irrigation systems indicate that in the absence of attention to the factors affecting during the operation period, it is not possible to expect the improvement of irrigation efficiency to mechanize the perceived irrigation. The operation of pressurized irrigation systems is dependent on several factors, each of which can be effective in the efficiency of an irrigation system. In such a way that cases such as inappropriate design of an irrigation system, disproportionate operation conditions and climatic conditions governing the region, lack of pressure management and other effective parameters during the operation period can affect the efficiency of an irrigation system. On the other hand, an irrigation system is a set of independent components that the proper or inappropriate function of each of these components can affect the efficiency of an irrigation system. In this regard, considering the location of agricultural meteorological station in the vicinity of the fields, some of the factors affecting the efficiency of an irrigation system in two crops were investigated, and the results of hydraulic evaluation of irrigation systems showed that the low evaluation indicators during the operation period were based on factors such as the constant of the average speed of movement of the irrigation system during the whole growth period (which caused deep penetration). The lack of the same height for sprinklers in the irrigation system, the presence of relatively high wind speeds in the region (which causes evaporation and wind blowing of water droplets), not following the proper diameter of sprinkler nozzles during the irrigation system spans (which causes the non-identical distribution of water at the farm level) and the old sprinklers of the irrigation system noted. Evaluation and analysis of field information obtained from the mentioned farms showed that one of the best and most effective factors in improving the performance of the system is recording and analyzing field information during the operation period. In such a way that by monitoring the effective factors such as the function of the system, optimal irrigation management can be applied at the irrigation system level and consequently at the farm level. In addition, inflexibility in irrigation management program and adaptation to operation conditions have also been one of the factors reducing the efficiency of the studied irrigation system. However, in case of more flexibility of irrigation management and compliance with the conditions of the operation period, we can expect improvement in irrigation system performance. However, there are mainly several problems in the field of system management and promotion of technical knowledge of operation. In a general approach, the low evaluation indicators of the irrigation systems under the mentioned pressure indicate that in the absence of attention to the factors affecting during the operation period, it is not possible to expect the improvement of irrigation efficiency to mechanize the perceived irrigation. This means that the efficiency of mechanized irrigation systems such as Linier irrigation system and other irrigation systems (drip and sprinkler) varies in a wide range, which in case of not paying attention to the factors affecting during the operation and design of the system, in some cases, the expected efficiency of these mechanized irrigation systems will not be obtained.

Most rivers are naturally meandering and are constantly eroding on the outer bank and sedimentation on the inner bank. As a result, cognition of the flow pattern in river bends is critical. Today, one of the constructions employed in river bends is the diversion dam. When the position of the bend changes, the diversion dam alters and its position shifts. Moreover, the adjacent agricultural lands' water requirements necessitate the intake construction on both sides. Hence, it is significant to study broad-crested weirs as one of the structures for maintaining uniformity of flow in river bends and during dewatering. In general, the presence of in-stream structures such as sediment control structures or out-of-river structures such as intakes at the bend of rivers require further investigations on sedimentation problems and flow patterns. One way to maintain a uniform flow in river bends is to create a secondary flow by broad crested weirs. Accordingly, the primary purpose of this study is to investigate the flow pattern and evaluate the uniformity of the distribution of unit flow discharge distribution at the intakes located on both sides of the broad crested weir in a 90-degree bend using a laboratory model.

The experiments were carried out in a rectangular flume trough 0.92 width, 0.6 depth, and 90-degrees bend. Indeed, the radius of relative curvature of the bend is 2.05, which falls into the category of sharp bends. The weir model is of the broad crested weir type, and the intakes were placed on both sides of the weir in the direction of flow and with an angle of zero. The weir was installed at an angle of 60 degrees from the bend inlet, and velocity and depth were measured in various transverse and longitudinal sections. All experiments were run at three flow rates of 37, 50, and 60 liters per second.

In general, the results show that bends and secondary flows affected the water level and caused a difference in water depth in the inner and outer banks in the case of without weir. This difference is indeed due to the effects of the bend. In this event, the side slope of the water surface deviates from the horizontal position and falls towards the inner bank of the bend, and rises towards the outer bank of the bend. One of the motives for the problems associated with sedimentation in river bend dewatering is related to this issue and the flow pattern in river bends. With the installation of a horizontal crest weir in the bend, the uniformity of the distribution of unit flow discharge has increased.However, in the case of the inclined sloped weir, the difference in unit flow discharge of the inner and outer bank is the largest compared to the other two cases. Therefore, the performance of the sloped crest weir was not acceptable in the sharp bend and upstream control section. The results of the discharge distribution in the intakes on both sides of the bend confirms the effectiveness of the hypothesis that the slope of the weir crest directs flow to the catchments on both sides of the bend. With the weir installation, more water flows into the intakes than without a weir.

 Regardless of the effect of the weir slope, the distribution of flow in the intakes on either side of the weir is more uniform than without the weir due to weir construction in the bend. The sloped crest weir has contributed to the distribution of intakes discharge. The highest uniformity of dewatering on either side of the weir was at an inlet in maximum flow discharge. The discharge ratio of the outer bank intake to the inner bank in the horizontal crest weir and sloped crest weir was 1.04 and 1.06, respectively. A sloped crest weir crown has the most significant influence on the uniformity water flow on both sides of the weir in all cases of the upstream inlet flows. An average, the discharge ratio of intakes in the outer bank to the inner bank in sloped crest increased by 11%, compared to the case of horizontal crest weir.

The construction of hydraulic structures such as bridge piers in river beds changes the hydrodynamics of the flow and is associated with the scouring phenomenon. This process has been investigated by many researchers with numerical and laboratory methods. The implementation of scouring reduction measures has also been considered in addition to investigating this phenomenon, due to the destructive changes of scouring on the morphology and the river bed shape. In general, these measures are divided into two general categories, direct and indirect, which the use of submerged vanes is one of these reduction measures. Based on less attention to this scour reduction measure; in this study, the effect of a group of two submerged vanes on reducing scour around the cylindrical bridge pier with a numerical approach of the FLOW-3D model is investigated. Dimensional analysis showed that the position angle of the vanes, the location, and the height of the vanes are effective parameters. According to the results, the installation of submerged vanes in all cases reduces scour and the position angle of 30 degrees, in location 0D,1D,2D, and the height of the vanes equal to the sedimentary bed leads to the greatest reduction of scour.

In this research, the flow-3d numerical model has been utilized to analyze the scouring phenomenon around the cylindrical bridge pier. In order to validate the numerical model, first, the sensitivity of the mesh dimensions was performed and the 8.5 mm mesh size was selected. Then the analysis of the geometric model for the bridge pier was conducted with different turbulence models k-ε, k-ε RNG, and LES, and the numerical results were compared with experimental data. It was found that the numerical results of the LES model are the most consistent with the experimental data, so this turbulence model has been used for the conditions of bridge pier with submerged vanes. Different times for scour hole development were investigated to determine the processing time of the numerical model and the computational cost, and finally, it was observed that the scour equilibrium time of 500 seconds is suitable for numerical analysis, and after this time the maximum scour values remain almost constant.

By increasing the position angle of the two submerged vanes up to 30 degrees, the amount of scour depth decreases. But by increasing it by 30 degrees, this trend decreases and does not follow a specific trend. The most suitable position of the group of two submerged vanes is in 0D,1D,2D location, and the location of 2D,3D,4D has the least effect, which reduces the distance between the vanes from the upstream of the channel to the bridge pier, the separation point of boundary layer moves to the bridge pier, thus reducing the thickness of the boundary layer. Therefore, by reducing the distance between the vanes and the bridge pier, the intensity of shear stress to dig bed sediments around the bridge pier is reduced and as a result, the effect of submerged vanes and their protection from erodible bed against scouring phenomenon increases. It was found that the presence of submerged vanes in all cases reduces the maximum scour depth, but this amount of reduction is not the same due to the different positions of the vanes. Observing the flow pattern, it can be concluded that the velocity upstream of the pier is negative and rotational flows are formed in this region, which are the horseshoe vortices that are one of the reasons for the formation of scouring holes.

In all cases of installation of submerged vanes before bridge pier, scour depth was reduced because the presence of vanes caused local scouring around the vane itself and the washed sediment particles were transported by the flow to the scour hole created upstream around the bridge pier. On the other hand, in all locations, by increasing the position angle of the two submerged vanes, the transverse area is more affected by the two vanes, and a stronger drag force is applied to them. In other words, the resistance to current increases, the flow moves away from the bridge pier, and also fewer bed particles are transported around the bridge pier. As the height of the vanes increases, the intensity of the flow colliding with the vanes increases, and as a result, the amount of scouring depth upstream of the vanes increases, and despite the reduction of scouring upstream of the bridge pier, the performance of these vanes decreases.

The stress created in the soil significantly affects its engineering behavior. Changing its value during the construction of earthen dams causes volume change and shear strength, causing rupture, soil compaction and settlement in earthen dams. So measuring soil stresses of dams is essential that it is done by instrumentation installed. Artificial intelligence models such as artificial neural networks for modeling many engineering applications. Also by extending the meta-heuristic algorithms, combined with neural networks have become very popular due to more accurate results.

In this study, the cross-section 19 (cross-section of the middle part of the body and dam foundation) for the modeling of soil stress were used during the construction of the dam Kaboud-val. Also Kaboud-val dam instrumentation data (derived from Golestan Regional Water Co.) was used at the time of construction during the period of 4 years. Type and number of input data is the most important thing in modeling artificial intelligence. By examining data TPC19.1 cells in section 19 in Kaboud-val dam, embankment alignment (F), the water level of the reservoir (R), the construction of the dam (T), speed filling and dewatering speed was selected for input. The soil stress (P) in the body of the dam during construction, intelligent model was selected for output. This process is most effective in a subset of features from the set of input features according to the least error, selected and additional features will be removed. In this research, a meta-algorithm (artificial neural network (NNA) algorithm) is combined with an artificial neural network (ANN) that has the ability to predict complex and nonlinear relationships and extracts effective features for modeling soil stress with appropriate accuracy. In this study, the most effective features in soil stress modeling were determined in a case study (Kaboud-val Dam) using the NNA-ANN hybrid algorithm and a comparison was made between the results of the hybrid model and the numerical model. Five features include reservoir level, fill level, dam construction time, impounding velocity and fill velocity was selected for the input.

Using hybrid algorithm and feature selection method, a combination of three features, including reservoir level, fill level, dam construction time (with RMSE equal to 0.5024) were the most effective features in modeling soil stress in the selected cell. The results showed that the hybrid model in Kaboud-val Dam (with values of R^2, RMSE, MAE and NS equal to 0.9943, 2.5653, 1.9973 and 0.9999, respectively) has better performance in modeling soil stress than the numerical model. (With values of R^2, RMSE, MAE and NS are equal to 0.9625, 26.2567, 16.6725 and 0.9772, respectively). The results showed that the reduction in the input features to reduce the time and cost reduction is more economical and more effective. Because with the increase in the number of features in the hybrid model, the increase in modeling accuracy did not occur. Sensitivity analysis showed that the dam construction time and fill level, of the highest sensitivity factor, the most important feature of the model is the total stress in cells. Modeling with the mentioned features, in another dam with a new construction site and new geotechnical specifications (Masjed Soleiman Dam) showed that the use of artificial intelligence model according to statistical indicators has more accurate answers than the numerical model.

The results showed that the use of artificial intelligence methods in the design and initial estimates of soil stress parameters in earthen dams instead of using numerical methods has high reliability and accuracy. The combination of input data in the hybrid model under study is suitable for Kaboud-val dam and Masjed Soleiman dam and the appropriate combination should be used for each construction site. By completing the number of data in different sections of the dam and the number of construction sites in areas with similar climate and geotechnical conditions, a design software can be obtained to predict the amount of soil stress during construction in the body and foundations of earth dams.