Irrigation and Drainage Structures Engineering Research
Year:2018 | Volume:19 | Issue:71|Papers Count:10

Estimation of flow velocity distribution is considered to be one of the main issues in the open channels, sewers, and rivers. Occurrence of the maximum velocity phenomenon below free surface (Dip phenomenon), is cause of concern and complexity for estimation of the velocity distribution in open channel flows. In this paper, the velocity distribution in the narrow sewer combined channels was estimated using the entropy theory, and the impact of different cumulative distribution functions on the velocity distribution has been investigated. Accuracy evaluation of Marini and Chiu entropy functions in the estimation of the velocity distribution and parameters suggested that a new model with higher accuracy can be proposed in order to optimizethe velocity estimation in these types of channels. Also, the comparison between field data of former studies and the result of proposed model indicated that the proposed model is in accordance with field data in the different levels and depths of channel. The results also showed acceptable accuracy of the proposed model in the velocity distribution estimation (R2=0. 86, relative error = 11%, MAPE = 7. 84% and RMSE = 0. 0758). Further, comparison of proposed model and Chiu velocity distribution model shows that the proposed model has better performance in spite of more simplicities than other existing models.

In present study, the effect of different cross-sections of bridge piers on reducing the bed erosion and the bed shear stress was experimentally and numerically evaluated. In experimental study, the bed erosion and the percentage of its resuction was calculated; also numerically, the flow around pier models was simulated three dimensionally, and the effect of each cross-section on reduction of bed shear stress was investigated. To determine the efficiency of suggested models, the circular model was selected as the reference model and the decreasing of maximum shear stresses in each model was compared with the decreased scour depth. Comparison of the velocity and water free surface profiles was conducted for verification of k   turbulence models and results showed that with () k RNG   model, more accuracy can be obtained. Among the presented models, the A2 model with decreasing scouring depth of 72 percent as copared to the refference model, was found to be best and most effective model. Also the B2 model lead to 8 percent reduction in scouring depth and can be suggested as a model that has the least effect on scouring. The D model causes the scouring depth increase by 7 percent relative to the reference model. Comparison of the numerical and experimental results was another objective of this study due to the complexities of experimental researches. The results showed that there are direct relationship between the bed shear stress and the equilibrium scour depths.

Land consolidation and on-farm improvement project, is considered as one of the infrastructural projects in the agricultural sector. According to national plans traditional paddy fields need to improved and equipped with modern technologies. In this context so far over 76, 000 hectares of paddy fields in the Guilan province have benefited from the plan. Given that farmers are considered the beneficiaries of the project, their feedback and response is of prim importance. In this regard targeted questionnaire can help to improve their status furthermore. In order to analyze and evaluate the views of farmers involved in land improvement and consolidation and on-farm improvement Project, during the year 2011, total number of 455 questionnaire, each with 50 questions, were distributed amongst farmers. The results showed that farmers in terms of age are old, in terms of literacy, are mostly illiterate and lands are in the category of small. The results showed that about 50 percent of farmers have problem in the first and second years after implementation of the project, in the way of supplying water and irrigation management practices. Also construction of roads between farms led to more favorable among farmers. Further, according to results, 62 percent of farmers reported an increase in production after the implementation of the plan upto 300 kilograms per hectare. Generally, the findings showed that more than 75 percent of farmers expressed moderate satisfaction with the implementation of development plan.

Piano key weirs (PKWs), a new type of weirs with a very high discharge capacity, can be used as high performance economic structures. This type of weirs is a good alternative to linear weirs, because they increase the discharge per unit width at the span of non regulated weirs for the same water load and weir width. In this study, the dis charge coefficient of piano key weirs was compared with that of a rectangular labyrinth weir. The results showed 38% increase in the discharge coefficient of the piano key weirs as compared to that of the rectangular labyrinth weir. The difference between the discharge coefficients of the weirs was reduced by increasing hydraulic load when reaching the submergence discharge. The difference was reduced about 24% at high discharges. In addition, the tailwater level was gradually increased from the weir crown level.

Reinforced soil structures are a good choice for coastal walls, dam building, especially at the base of the side walls of the guard bridges, waterways and watercourse side walls, settling basins and irrigation networks and drainage services. In this study, reinforced soil system for increasing the bearing capacity of the soil under the foundation structure was used an experimental model was developed for studying the behavior of geosynthetically reinforced sandy soil. Displacement vectors of the soil and bearing capacity of the strip footing measured in the reinforced mode and unreinforced mode until the impact of variable parameters such as the type of reinforcement, the number of reinforcement layers, the first layer of depth and width of layers also was examined. In addition, numerical models, as well as an experimental model by using Plaxis software was developed and the results were compared with laboratory results. Generally it was observed that the reinforced geogrid as compared to reinforced and unreinforced geotextile soils offers more resistance to load and has more bearing capacity. Further with increasing the number and width of the layers, the above mentioned phenomenon can develop. The evaluation of sandy soil reinforcement and the performance of physical modeling using PIV and numerical Simulation using software Plaxis v8. 2, suggested that the Size, of wedge failure in depth increases, and thus increases the bearing capacity of strip footing in reinforced state as compared to unreinforced state.

Due to considerable economic, environmental and social impacts, scouring around pipelines has been focus of consideration by different researchers and designers of hydraulic structures. Presentresearch was carried out to investigate the flow pattern, scour mechanism, and temporal evolution of scour hole around the submerged pipes at the Hydraulic Laboratory of Department of Water Engineering located in Shahid Bahonar University of Kerman. The experiments were performed for single pipe and two parallel pipes (double pipes) with different spacing and hydraulic conditions. The results showed that, when water flows around the pipe, the scour process started by establishment the piping flow from pipe upstream side to downstream side. Next, the tunneling erosion was occurred and a flow jet passed below the pipeline, which was the main factor for the development of scour hole. In the case of double pipes, depending on the spacing between the two pipes, different profiles were observed at the scour hole. For both cases of single and double pipes, by increasing the flow discharge, the depth of the scour hole increased. In addition, the observations revealed that the scour depth for single pipe was always more than the double pipes. In the case of double pipes, the interactions between flow and pipes weakened the vortices strength. Under this circumstance, the depth of scour hole at single pipe was less than double pipes, so that, for the discharge of 28 L/s, the maximum scour depth of the single pipe was 1. 27 times more than that of the double pipes.

Compound sharp crested weir for measuring the discharge with reasonable sensitivity and accuracy in a wide range of flow, as appropriate solution can be used. Also the transitional water containing sediment and floating will cause problems in how they function. One of the options that can be used to extend weir-gate combined compound sharp crested weir with gate. The purposed of this research, investigation of combined flow in sharp crested weir in the state of compound weir with circular-trapezoidal-rectangular sections by combining gate with opening height of 1. 5, 3 and 4. 5cm. Experiments carried out in an experimental rectangular canal with length of 12 meters and width of 5 meters. Based on experimental data the results show that, discharge coefficient in compound weir is in the range of 0. 58 to 0. 85 and in compound weir-gate is in the range of 0. 38 to 0. 78. The results showed that for a known head over the weir, the discharge coefficient in compound weir-gate is reduced with increasing the height of the gate. The mean values of the coefficient of determination (R2) and the normalized root mean square error (NRMSE) are 0. 96 and 0. 06, respectively. The results showed that the use of a linear combination of flow equations in compound weir with circular-trapezoidal-rectangular sections and compound weir-gate, with acceptable accuracy is able to estimate the discharge coefficient.

In order to evaluate the performance of Yamchi irrigation network located at the downstream of Ardabil reservoir dam, the necessary data with regards to water delivered to irrigated areas during four operating years (2012-2015) and cropping pattern variability of cultivated crops were acquired from Ardabil Regional Water Authority. Next water requirement of crops was estimated using Penman-Montith-FAO method and then performance of the irrigation network was evaluated by different performance indices such as Relative water supply (RWS), Relative irrigation supply (RIS), Water delivery index (WDI) and Ratio of moisture availability. The results showed that the performance indices in last two years were 0. 4 and 0. 5 for RWS and 0. 5 and 0. 6 for RIS respectively. This indicates that water delivered to the crops through irrigation network was up to 50% less than their requirements. Rainfall contribution to crop water requirement in the first two months (May and June) was higher than the last two months (July and August) during the operating period. Delivery and distribution performance evaluation of network with respect to spatial and temporal scale using satellite images showed that the land area due to severe drought increased and that land area depended on irrigation water supply was decreased in the finishing years of project.

In this research, the effect of cement content and AEA on engineering properties of irrigation canal linings were studied. In this context, 9 different concrete mixtures (treatments) were designed and fabricated using 3 levels of AEA; 0, 0. 01, and 0. 03 percent by weight of cement and 3 levels of cement content; 300, 350 and 400 kg/m3. Various experiments included: determination of total air, density and determination of the amount of slump on fresh concrete and density, porosity, compressive strength and electrical resistance tests on hardened concrete samples of all mixtures. The results of experiments on fresh concrete showed that as the AEA increased, the slump of fresh concrete and total air volume also increased whereas concrete density decreased. The results of experiments on hardened concrete indicated that addition of 0. 03 percent by weight of bubble making substance to concrete mixture to any of 3 cement samples, resulted in reduction of density, compressive strength and electrical resistance. According to the existing indicators, the cement content of 300 kg/m3 (with and without AEA) is not a suitable option for irrigation canals lining. In irrigation canals, it is necessary to provide the minimum compressive strength in this regard concrete mixtures of 350 (without weathering) and concrete mixtures of 400 kg/m3 (without AEA) and 0. 01% of AEA cement weight was found to be suitable option. For the concrete lining in cold regions, the best option for ensuring the compressive strength parameter and the durability against frost is concrete mix with a weight of 400 kg/m3 and 0. 01% AEA by cement weight.

There are some intersecting channels which are seen during operation of open channel networks (Irrigation networks, drainage, navigation, and… ). It is possible to produce some bed elevation difference during construction and/or because of some reasons such as inaccuracy in implementation, natural action or human made mistakes. In this paper impact of some factors such as discharge ratio, bed elevation difference ratio, erodible and non-erodible bed and bed material grading is experimentally investigated on scour depth in a 90º confluence. The straight channel is 5m long and 30cm width and the intersecting channel is 2. 5m long and 30cm width. After analyzing the results and comparing the topography when two channels have elevation difference with the case in which two channels have equal bed elevation, one can find that increasing the difference of bed elevation would result in scour depth increment by 78% while the same increment is less by 45% for the case in which the transverse channel is not erodible. This can be because of a jet flow in the case of non-erodible. Also, increment of flow velocity in the produced steep bed in confluence in the case of erodible bed for both channels, can increase the scouring hole depth.