نشریه تحقیقات مهندسی سازه های آبیاری و زهکشی
سال بیست و یکم شماره 80 (پاییز 1399)

Weir structure is widely used as a flow measurement, grade control structure and water surface control in sewer systems, open channels and stilling basins. Having a simple stage-discharge relationship is the most important reason for using these structures as measuring instruments. Curved weir is part of a circle with the non-linear crest axis. To increase the discharge coefficient, one can used curved weir.

 In this study, hydraulic performance of curved weir and system of compound curved weir with central angles of 90, 120 and 150 degree and with 18 centimeter height were used to investigate and obtain equations for discharge coefficient and flow discharge of this structures.

The experiments were conducted in a rectangular channel with length of 9 meter, height and width of 40 centimeter. The results showed that the increase of parameters h/p < /em> (water head of the weir to the height of the weir), H/L (water depth upstream of the weir to the length of the weir), h/B (water head of the weir to the width of the channel) and Froude number led to increase discharge coefficient in simple curved weir and compound curves weir. Comparing the weir discharge coefficient showed that the curvature and compounding of weir has a great influence on the discharge coefficient of this structures. So that in simple curved weir, angle of 90 degree has a greater discharge coefficient, but in compound curved weir, angle of 150 degree has a greater discharge coefficient. Also checking of results showed that compound simple compound weir, led to increase value of discharge coefficient around 17 percent.

Checking of discharge coefficient on compound curved weir showed that, increasing dimension of second step in compound curved weir, led to increasing discharge coefficient. So that in discharge equals 12 (lit/sec) discharge coefficient of compound curved weir that height of second step to the width of second step (b2/b1) in that equals 0.26) towards compound curved weir that height of second step to the width of second step (h2/b1) in that equals 0.4 in vertex angles of 90, 120 and 150 respectively increasing 6, 1.5 and 7 percent .

Seepage losses are a significant portion of losses along the main earthen canals in irrigation networks. The correct estimation of these losses will greatly help improve water productivity in the irrigation network. Due to the high capability of numerical models such as SEEP/W to estimate seepage rates in the canals, this method has been used as one of the most widely used in various researches (Barkhordari et al., 2019; Mohammad Rezapour Tabari & Mazak Mari, 2016). Despite various investigations in this regard, the seepage rate was not evaluated for the presence of heterogeneous and non-isotropic conditions in the canal bed. Therefore, in the first step of this study, the Seepage rate in the earthen canal of Moghan irrigation network was evaluated using the SEEP/W model. In the second step, in order to further investigate and predict the possibility of changing the hydraulic properties of the soil in the long-term, a comprehensive assessment was carried out on the permeability coefficient.

After collecting field data and measurements based on the existing and governing conditions (hydraulic, geometrical data, and soil geotechnical) along the Moghan canal, and also based on changes in some of these parameters, the problem is defined in the SEEP/W model based on 7 reaches. In order to calibrate the model, evaluation of simulated values with measured values of seepage using the CRM statistical coefficient was considered. Then, in order to further investigate and predict the possibility of heterogeneous and non-isotropic conditions in the soil system, a separate seepage analysis was conducted in the Moghan canal by changing the values of kx and ky kx-1. To achieve this objective, a reasonable range of 5×10-8 to 8×10-7 m/s was determined for kx based on the canal bottom and side walls materials. The range of 0.1 to unity was selected for ky kx-1.

The results of the main simulated showed that the deviation of the simulated values by model seepage from the measured values (CRM) is less than 0.1. Considering the distribution of other parameters such as the hydraulic gradient and pore-water pressure, concluded that due to the higher hydraulic gradient in the canal bottom than its side walls (equal to 1.6 and 1.2 at reaches 1, 2 and 3, and also 1.4 and 1 at reaches 4, 5, 6 and 7, on the bottom and its junction with the side walls in the canal, respectively), the water outlet potential is greater in this area. Therefore, the uniform lining of the bottom and side walls in water canal reaches can be considered as a successful solution that is based only on modelling results. Also, the maximum amount of pore-water pressure is at a distance of 3-4 times of the water depth in the canal, relative to the bottom of the canal and along the vertical profile of the soil. Further, the results of seepage analysis indicate that considering the severity of each of the long-term sedimentation and erosion conditions, it is possible to estimate a maximum seepage rate to 20838.6×103 L/day and a minimum to 245.4×103 L/day as an initial estimate, without the need for modelling in this canal, is predictable.

In this study, seepage rate in the earthen canal of Moghan irrigation network was evaluated using the SEEP/W model. The modelling results showed that the deviation of the simulated values by model seepage from the measured values (CRM) is less than 0.1. Then, in order to further investigate and predict the possibility of changing the hydraulic properties of the soil in the long-term, due to the possibility of heterogeneous and non-isotropic conditions in the soil system, a comprehensive assessment was carried out on the permeability coefficient. The results of this analysis indicate that considering the severity of each of the long-term sedimentation and erosion conditions, it is possible to estimate a maximum seepage rate to 20838.6×103 L/day and a minimum to 245.4×103 L/day as an initial estimate, without the need for modelling in this canal, is predictable. Also, the results of this model regarding the distribution of other parameters such as hydraulic gradient and pore-water pressure, showed that the maximum amount of hydraulic gradient was 1.4 to 1.6 in the bottom and also at the junction with the side walls of the canal. Also, the maximum amount of pore-water pressure is at a distance of 3-4 times of the water depth in the canal, relative to the bottom of the canal and along with the vertical profile of the soil.

Bridges are one of the main components of the transportation. One of the main causes of bridges failure, especially during flood times, is the development of scour depth near and below the pier and its foundation. Therefore, protecting the pier from scouring is an important issue in the safety of bridges at design stage . In general, scouring can be divided into three types: general scour, scouring due to the contraction of the river section and local scouring such as around bridges and abutments . The flow pattern around the bridge pier include downflow, horseshoe vortices, and wake vortices. By increasing the local shear stress in the vicinity of the bridge piers, these vortices cause erosion in front of the piers and gradually extend to the sides of those. The separation of the flow at the sides of the pier creates so-called wake vortices, which is unstable and shed alternatively from each side of the pier. These vortices act as little tornadoes lifting the sediment particles from the bed. As a result of these processes, a scour hole is formed around the pier and gradually developed. Regarding to the importance of scour around the bridge piers, many studies have been conducted on understanding of governing process and estimation of the scour depth around bridge pier. Although many literature have been documented for single pier but due to geotechnical and economical reasons, multiple-pile bridge piers and complex piers have become popular in bridge design and have attracted interest of researchers. Due to the importance of reduction of scour around the bridges, different countermeasures have been introduced and evaluated in the literature. In general, the countermeasures against pier scour are broadly classified into two categories: (1) flow-altering countermeasures, and (2) bed-armoring countermeasures.One of the devices to reduce scour depth around the bridges piers is an installation of bed sill in vicinity of the foundation. In this research, the effect of the upstream sill on time development and maximum scour depth around inclined bridge pier group was investigated for different pile cap thicknesses, top level installation of pile caps, array and diameter of piles. The bridge pier consist of two rectangular piers with 2.5 and 3.5 cm dimensions which mounted at an angle of 28 degrees on a pile cap with 10 cm width, 16 cm length, 3 and 5cm thickness which placed on an array of 2×2 and 2×3 piles with different diameters. The experiments were performed for relative flow depth (y/D) 6.42, relative pile cap levels (Z/D) 0, 1, 2, 3, 4, relative pile diameter levels (dp/D) 0.57 and 0.85 in clear water conditions. A total of 72 runs was performed for hydraulic and geometric conditions. Comparison of the results indicated that at the level of Z/D =0, by installation of sill at upstream of pile cap, the maximum scour depth decreases 24.5 percent. At the top installation of pile cap of Z/D =1, the maximum scour depth decreases 29 percent of sill installation location at upstream of pile cap. At the level of Z/D =2, by installation of sill at upstream of pile cap, the maximum scour depth decreases 32.5 percent. At the top installation of pile cap of Z/D =3, the maximum scour depth decreases 35 percent of sill installation location at upstream of pile cap. At the level of Z/D=4, by installation of sill at upstream of pile cap, the maximum scour depth decreases 36.8 percent. Comparison of results indicated that installation of upstream sill length of scour hole decreased 26 percent approximately. However, width of scour hole increased 2-3 times of corresponding scour width of non-sill conditions.

Water, food and energy are the main resources needed for the development of societies. Recently, comprehensive management from Nexus' point of view has been examined and evaluated by focusing on these three sources at the macro, regional and basin levels. However Nexus approach has received less attention in irrigation networks, which consumes energy, and the most water, and produce the most food. (Mabhaudhi et al., 2018). International Commission of Irrigation and Drainage (ICID) announced the Nexus as one of the main topics for 2017 and 2018 congress. Some papers were presented with the focus on food security, energy consumption for ground water extraction, and climate change. As conclusion of both congress it is stated that even though the nexus approach is fast growing, however its application is very limited. Therefore Nexus knowledge and capacity building among stakeholders should be developed, and its application in development planning of irrigation networks should be considered (Hassan, et al. 2017 & Pandya, et al. 2018). Relationships of water, food, and energy at irrigation networks, due to the problems of each component, and their interactions are quite complex. In this study systems dynamics approach used to investigate existing structures between these sources, and causal relationship between different components is determined as a conceptual model. Subsequently, by development of quantified model, the Nexus model of Qazvin Irrigation Network from productivity, adequacy and sustainability of water delivery has been produced. Three scenarios regarding water, food and energy, including, reducing surface water resources, increasing cultivated area, and increasing energy consumption, were evaluated. System Dynamic approach enables us to consider the complex interactions between water, food and energy components in long term in irrigation networks, and examined the impact of different scenarios, to decide on more sustainable policies. In this approach by problem definition, and determination of the boundaries of the system, the dynamics of the system in form of casual loops are defined. Four archetypes are identified which are Limits to Growth, Shifting the Burden, Fixes that Fail, and Eroding Goals. Considering casual loops in water, food, and energy systems, the conceptual model of the Nexus in irrigation networks is developed. By collecting the required data from Ghazvin irrigation network the quantitative model is developed and verified using VENSIM model. The quantitative model is developed by defining mathematical relations between different components. The equations are defined in four subsystems including water demand and supply, food production, productivity, and water utility. In these relations, different information such as ground water extraction, surface water supply, required agricultural inputs, etc. are defined based on collected data in form of 10 year time series. Model verification is done by behavior investigation and boundary value test. The model estimated crop production, show good consistency with actual data with average error of 0.1%, and boundary value test show expected results. Therefore the verification results show appropriate performance of the model. Three scenarios for each resources (water, Food, and Energy) were examined which include, increasing energy consumption for ground water extraction, increasing cultivated area, and decreasing surface water.Testing three scenarios provide the following

Continuation of the present condition, will led to increase of crop production up to 60% in early 10 years. However due to activation of controlling mechanisms it sharply decreases by 50% in 5 years. Water utility shows similar manner, initially 20% increase, and 10% decrease afterward. Increasing energy consumption and ground water extraction causes crop production increase in almost all the simulation period with lower variations. Four years delay in impact of controlling mechanism is visible. Water utility has been increased as well, and it is 7% more at the end of simulation period. Due to limited potentials of increasing cropped area, this scenario performs similar to continuation of present condition, with marginal improvement in crop production and water utility. Decreasing surface water has the greatest impact in decreasing crop production and water utility, with respect to continuation of present condition. The maximum decrease in crop production and water utility are 23%, and 32% respectively. Even though due to activation of balancing mechanisms crop production shows 60% increase, however it happens with 5 year delay and decreases sharply afterward. Considering limited water resources, and its greatest impact on crop production and water utility, it could be suggested that water management policies, take higher priority in Nexus approach. As a general conclusion it could be stated that, system dynamic is a suitable method to implement Nexus approach in irrigation networks, and to investigate the long term impact of different scenarios, to select more sustainable policies for irrigation development.

The durability of concrete is defined as its ability to resist weathering action, chemical attack, abrasion, or any other deterioration process to retain its original form, quality, and serviceability when exposed to harsh environment. To a large extent, it is commonly accepted that concrete durability is governed by concrete’s resistance to penetration of aggressive media. This media may be present in a liquid or gaseous state and that may be transported by various mechanisms such as permeation, diffusion, absorption, capillary suction, and combinations of the items just mentioned (Azarsa and Gupta, 2017).Over the last few decades, a great deal of attention has been paid to research and development of electrical resistivity measurement techniques as a nondestructive technique (NDT) to evaluate the durability of concrete structures. Irrigation canals are water structures that transport water supplied from supply sources, such as diversion dams, to the point of consumption for drinking or agricultural purposes. To prevent water seepage losses, the canals beds are lined with various materials such as concrete, stone and sandstone mortar, asphalt, etc. The use of concrete lining in irrigation canals has been more common in Iran and other countries than other materials. Concrete used in irrigation canals is non-reinforced with a thickness of 5 to 10 cm. The basic requirements for good concrete-lined in hardened state are satisfactory compressive strength and sufficient durability. After the implementation of any construction structure, in order to know the desired performance and quality of implementation, it is necessary to evaluate that project. To prevent water seepage in irrigation canals, most of them are lined with concrete materials. Destructive method of core sampling is often used to evaluate the quality of concrete lining in irrigation canals. This is a very costly and time consuming process and requires a great deal of specialized manpower and equipment, while the effects of core damage are not easily remedied. To evaluate executed concrete projects, they are often used using destructive methods and various laboratories are run on them in the laboratory. Although this method achieves relatively real and direct results from the desired parameters, it also has side effects that are sometimes difficult to compensate for. These include project damage, high costs, the need for extensive equipment and equipment, and time consuming, which can sometimes lead to downtime. To prevent these complications, non-destructive testing methods, which are much simpler, faster, and less expensive, can be used if there is evidence of correlation. These include electrical resistance testing, ultrasonic and Schmidt hammers. Today, non-destructive concrete experiments have a good and practical effect on the repair of concrete structures. Non-destructive concrete experiments, by providing various data on existing structures, allow experts and specialists to judge and decide on the performance, needs and methods of repair and reconstruction of concrete structures.

The criterion for evaluating the quality of concrete cover of irrigation canals in different environmental conditions, in practice, is the same as in non-water structures and concrete cover of irrigation canals in the country, the basis of which is the amount of compressive strength and technical criteria, respectively. It is published in 108 (Anon., 2014). In this publication, durable concrete is introduced as concrete that has a relatively high compressive strength and is executed correctly. In this study, in order to establish a relationship between non-destructive electrical resistance tests on site with the parameters of water absorption and compressive strength, which requires destructive testing for their achievement, 13 section from 7 main canals in different study basins were selected in Hamedan province. The electrical resistivity of concrete lining these sections was carried out by using of 4-point Wenner method. The Wenner probe technique was first introduced for the geologist’s field in order to determine soil strata by Wenner at the National Bureau of Standards in the 1910s and then modified through time for concrete application. In this technique, four equally spaced linear electrodes are used to measure the surface electrical resistivity of concrete (Figures 1 and 2). The two exterior electrodes apply an AC current to the concrete surface while the electrical potential is measured from the interior probes. It should be noted that DC current is not desirable as it may result in inaccurate readings because of polarization effect. About 12 cores from each canal and totally 156 cores were prepared. In the laboratory, the compressive strength, initial, boiling and capillary water absorption was measured and the relationships between the non-destructive electrical resistivity tests with each of the parameters of laboratory experiments on the cores were investigated.

Based on the results, it was found that only 3 of the concrete-lined canals were durable in the cold region and the remainder lacked durability. According to the results of the electrical resistivity values with the compressive strength, the correlation direct correlation of 87% is established, so that due to the non-destructive nature of the electrical resistivity test, it can be used to determine other durability and resistance parameters. The results also indicate that the other parameters of durability of the concrete lining in the studied irrigation canals include initial, boiled and capillary water absorption with a correlation coefficient of 87%, 89% and 85%, respectively, and an indirect exponential relationship with electrical resistance values.

Based on results of this paper, without destructive testing, all of these parameters can be estimated accurately by non-destructive 4-point electrical resistance testing and projects can be evaluated.

Forests as Green Belt reduce the height and energy of waves passing through them, reducing their ability to erode sediments and to cause damage to structures such as dikes and sea walls, (Mclvor and et all.,2012). It is well-accepted that wave attenuation by emergent and submerged vegetation is a function of plant characteristics as well as hydrodynamic conditions, (Augustin et al., 2009). (Hirashi and Harada, 2003) showed that the pressure difference on the sides of the green belt is mainly due to drag resistance. this study a new and unique method based on the principle of momentum and direct force measurement has been used to measure wave energy decay simulated by the Green Belt.Most previous studies have been conducted to analyze the wave forces on emergent structures and obstacles. Relative submergence is considered to be the relative roughness of trees and is a factor influencing the resistance of the forest to the passage of waves, (Davoudi et al., 2016). So the resistance of the canopies in the submerged state is one of the important factors in wave damping. Also, in previous studies, variable still water depth has been considered to create different ratios of submergence, which will change the characteristics of the wave. Therefore, in the present study, decided that the resistance of the canopy against broken waves in the submerged state would be determined by changing the height of the obstacles, which will be examined in this study (Figure 1).Figure 1-- Schematic view of the Rigid vegetation with different relative depth of submergence

Experiments were conducted in the Hydraulic Modeling Laboratory of the Faculty of Water Engineering, Shahid Chamran University of Ahvaz, in a 8.3×0.8×0.55 rectangular flume called Knife Edge Flume. Flume has Plexiglas sidewalls and bed and designed to measure the force exerted by the wave force on the barriers at its shore by means of a dynamic load cell installed between the movable and fixed parts of the flume. At the beginning of the experiments, wooden circular cylinders with 1 cm in diameter, fixed parallel arrangement were placed in the moving part of the flume with constant slope of zero. By changing the height of obstacles and generating breaking waves with constant height the absorption force by the canopies was monitored via an electrical display connected to the dynamic load cell.

The submerged ratio of tree canopies is equal to height of inundation depth to height of trees. Therefore, in the submerged state, the ratio is greater than one, and in the emergent state it is less than one. What is important in this study is that different ratios of immersion with different heights of barriers have been created.

Flow over spillways has a great amount of potential energy, which is converted into kinetic energy downstream control structures. This energy should be dissipated to prevent the possibility of excessive scouring of the downstream waterway bed, minimize erosion and undermining of structures, which endanger the structure safety. Local scour downstream is usually one of the most important issues in designing process of hydraulic structures, which is mainly some applications have been proposed to reduce this occurrence. Present study has been carried out on the effects of V-shaped baffle piers in order to reduce the local scour downstream of the ogee spillway.

Experiments were carried out in a flume which is 6 m long, 0.5 m wide and 0.6 m deep with horizontal bed slope. A pump with a maximum discharge capacity of 14 lit/s circulated water from sump. A movable weir located at downstream of flume controlled water level. The hydraulic and geometric characteristics of these baffle piers were investigated with three different discharges (20, 24 and 28 Lit/s.m). The positions and height of these blokes were presented to decrease the amount of scour downstream. The position and height parameters were defined based on the length of stilling basins as follows respectively, Lb/Lf=(0.22, 0.44, 0.66, 0.88) and Hb/D=(0.66, 1, 1.33, 2). The test area in the channel was 2 m long and 12 cm in height, 2.5 m from the beginning of the channel. The experiments were carried out using non cohesive sediments with median diameter of 0.72 mm, specified gravity of 2.65 and geometric standard deviation of 1.12.

The presence of the block decreases the final depth of scour and the length of the scour which shows the role of the blocks and their role in this case. According to laboratory observations, the existence of the block distinguishes three types of flow around it. The first is a flow that jumps above the block. The second is the convergence flow between the blocks and the third the eddy flow that forms in front and inside the blocks. The presence of the block and the three types of flows resulted in greater turbulence and reduced jump energy, resulting in a shorter jump length and an earlier secondary depth. Taken together, these factors reduce the flow strength at the bottom of the plate and also cause less sediment transport downstream. The more the Froude number increases, the more stable the jump is due to the category of jump types. (Depending on the group of jumps created in this study) The amount of scour depth decreases due to the presence of blocks. Also, the result indicates that by decreasing the distance of baffle from weir toe, the length and the depth of scour have been remarkably diminished. Meanwhile the raise of baffle height decreases the scour depth across a longitudinal section. In addition, in different block positioning, as the height of the blocks increases, the length of the scour decreases. So that block with height (Hb/D=2) has a significant decrease during scouring compared to block with height (Hb/D=0.66).

Overall, the suitable geometrical condition proposed in order to reduce this sediment deposition which is propose based on length of stilling basins and Froude number as, Hb/D=2, Lb/Lf=0.22 It assumes that the scour depth is decreased between 30 to 76 percent and the scour length is decreased between 57 to 71 percent. The present study demonstrates the importance of positioning the blocks and their height at different Froude numbers. Therefore, pre-execution modeling is suggested for better conclusions to achieve the best position and height of the block.

Grapes is one of the most important horticultural products in terms of cultivation area, economic and high nutritional values. Iran with an annual production of 2.8 million tons, is among the top countries in the production of grape product in the world. However, there are not accurate information on the volume of irrigation applied water and water productivity of this product in Iran. Therefore, this study was conducted with the aim of measurement of applied water at field scale and evaluation of water productivity of grape in vineyards farms at different hubs of this crop production in Iran.

The volume of irrigation water provided by gardeners in 164 vineyards were measured in the provinces of Qazvin, Fars, Khorasan-Razavi, Zanjan, West Azarbaijan, East Azarbaijan, Hamedan, Markazi, Northern Khorasan, and Semnan as hubs of this product. These hubs covered about 80 percent of the irrigated vineyard cultivated areas. In each hub, 1-4 cities with the highest area under vineyard cultivation were selected for evaluation. The measurements were carried out in different irrigation and planting methods, various soils, different salinity of irrigation water and soil and different grape varieties during the growing season of 2018-2019 without interfering with the farmer's irrigation program. The measured values were compared with the net irrigation water requirement estimated by the Penman-Monteith method using the last 10 years meteorological data and also with the national water document values. Crop yield was recorded at the end of the growing season and water productivity was calucated as the ratio of yield to total water (irrigation applied water and effective rainfall). Analysis of variance was used to investigate the possible difference between applied water and water efficiency among the hubs. Data adequacy was assessed by using the method prposed by Sarmad et al. (2001).

The results showed that the average of applied water and water productivity among the hubs were significant at 1% probability level. The applied irrigation water used in the vineyards and water productivity were 6669 m3/ha and 2.63 kg/m3, respectively. Drip irrigation was about 20% effective compared with surface irrigation in reducing the applied irrigation water in the studied vineyards. Water productivity in drip irrigation orchards was essentially the same as surface irrigation and was not statistically significant. The reason was the lack of proper use and utilization of modern irrigation methods.The average net irrigation water requirement in the study areas estimated by the Penman-Monteith method using meteorological data for the last 10 years as well as the national water document were 6645 and 6456 m3/ha, respectively. The range of irrigation application efficiency in the studied vineyards was from 68 to 100 and its average was 89%. Comparison of applied water and net irrigation requirement indicated deficit irrigation due to water shortage in vineyards of most hubs. In total, 31% deficit irrigation occurred in the studied vineyards, which is a threat to soil salinity and destruction of soil structure in long-term. Grape planting method had a significant effect on reducing the applied water, increasing grape yield and consequently water productivity. Scaffolding method had a positive and significant effect on all studied indices in comparison with the crawling/reptile planting method. It caused a decrease of about 15% in applied water, an increase of 41% in yield and 37% in crop water productivity.

Due to the fact that vineyards are faced with deficit irrigation and water stress, training the farmers about the accurate and scientific methods of deficit irrigation in the vineyards can be effective to reduce the destructive side effects of water stress. Due to the widespread use of surface irrigation in the vineyards, training and application of methods to improve surface irrigation performance (evaporation reduction methods, using low pressure methods such as gated pipes, mulching, etc.), to increase irrigation efficiency and to reduce irrigation water applied is recommended. Changing traditional planting methods from crawling/reptile to scaffolding and surface irrigation (qana) to furrow, in addition to reducing evaporation, are the effective ways to increase the yield of vineyards and water productivity.