مجله هیدرولیک
سال ششم شماره 3 (پاییز 1390)

Using effective methods to provide optimal performance of irrigation networks is inevitable becauseof limited water resources and poor performance of irrigation networks. Different algorithms are usedfor automatic control of water level in irrigation canals with their own limitations. Fuzzy logic iscapable of resolving some of these limitations. Although fuzzy logic is successfully used in manyengineering applications, it has not been used for water level control in irrigation canals. In this studyfuzzy algorithm with two rule base is used for automatic water level control on pivot weir. Automaticcontrol system was constructed on laboratory scale, and its performance for the situation of high flowvariation was evaluated. One of the main components of the fuzzy controller is rule-base decisionmaking. In the experiments conducted in this study two types of rule-base decision making are appliedand the results are compared. The results show that in high flow variations (400%), maximum absoluteerror (MAE) and cumulative absolute error (IAE) indices values are in the range of 6.9 to 9.2 and 0.79to 1.17percentages respectively and variations are stabilized within less than 2 minutes. Using thesecond type of rule-base, system, stability is improved and water level variations and number ofstructure adjustment is decreased. The fuzzy automatic control system is suitable in controlling waterlevels and its application for irrigation canal control is recommended.

In this study, the variation of velocity profile at different sections of hydraulic jump were evaluated inrelation to changes in the length of roughness on a rough bed performing the tests in a flume withlength of 12m, width and the height of 0.40m. Nine profile variation tests were carried out for 3Froude numbers and 3 lengths of roughness. In each test, four sections of hydraulic jump wereselected in which the velocity was measured at 1 cm intervals. The impact of changes of roughnesslength on velocity profile was surveyed at short, medium and long reaches of effective length. Theresults indicated that although the dimensionless velocity profiles on the rough bed are similar, theirshapes are different from that of on a smooth bed. The boundary layer was another subject studied inthis research. The results showed that the boundary layer thickness increased with an increase in thelength of roughness and finally dimensionless boundary layer thickness reaches the values of 0.26 forshort and 0.37 for medium and long roughness lengths.

Several studies using Computational Fluid Dynamics (CFD) techniques for modeling the process ofsedimentation in settling tanks have been carried out to predict the fluid flow patterns and particledeposition during advection and dispersion process in tanks. To simulate the movement of thesediments in the settling tank, a Lagrangian approach is implemented. For this purpose, the finitevolume method is used. After modeling sediment flow pattern, analysis of particles move ment andtrap efficiency in sediment tank are presented.

In this study, a probability- based methodology is formulated to evaluate quantitatively andsystematically the overtopping risk of earth dams. This study considers the overtopping phenomenainduced by the occurrence of flood and wind effects. The risk analysis based models for overtoppingconsist of random modeling of the flood generation, wind dynamic aspects, reservoir routing, reservoirgeometry, inflow discharge, outflow discharge, dam height, initial water surface and correction factorfor increasing water induced by wind. For calibrating the results of simulation and modeling, Vanakdam in Charmahal Bakhtiari is used as a case study. The case study was employed to demonstrate howthe total risk of overtopping over a practical case could be estimated based on the proposedmethodology. Annual maximum series of peak flow discharge and wind velocity of Vanak dam areused to analyze extreme flood and wind with different frequencies by using hydrological frequencyanalysis software (HYFA). Risk analysis results show that considering uncertainties of randomparameters affects significantly the dam reliability. Also overtopping risk of Vanak dam is notsensitive to increasing initial water surface. By increasing uncertainty of inflow flood, overtoppingrisk is increased.Risk overtopping increases, while the uncertainty of reservoir geometry increased.Also dam reliability is decreased by malfunction of spillway’s gates. Based on this analysis both theeffect of wind and flood together influence the overtopping risk of earth dam.

Obtaining an analytical solution for bed variation equations, is a hard task and often impossible.However, if a quasi–steady state is considered for flow condition, analytical solution may not beunreachable provided that necessary simplifications are made. The main purpose of this paper is todevelop an analytical model to predict bed variations in flood conditions with upstream sedimentsupply. In this study, non–uniformity of bed material size has been considered by hiding function. Inaddition, governing equations have also been applied and solved to compute values for unknownparameters such as hydraulic parameters, bed material size, water surface slope and elevation and bedload at various times from the beginning of flooding. Model validation with observed experimentaldata have been made and followed by sensitivity analysis. Finally the effect of flood hydrographshapes has also been investigated on bed variations in gravel bed rivers. Results have shown thathiding function has modeled non–uniformity of the bed materials appropriately while a reasonableagreement has been found with observed experimental data for flow Froude number of less than 0.8.

In areas with sediment laden floodwater, sediments are carried into the intakes and decrease thechannel conveyance capacity. These sediments are settled at different locations, including theseparation zone at the upstream section of the lateral channel. Therefore, it is important to determinethe length and width of separation zone. In this study, hydraulics of the flow in an intake from arectangular channel using SSIIM2 is investigated. The ratio of intake width to main channel width,diversion angle, Froude number and ratio of diverted discharge on separation zone dimensions areamong the effective parameters in the hydraulics of intakes. These parameters were investigated andnumerical results were compared with those of experimental ones. There was a good agreementbetween the numerical and experimental results. For estimation of the above parameters severalequations were developed. k-3 turbulence model was also found to be suitable for intakes hydraulics.

Urmia lake is one of the largest and most saline Lakes of Iran. This lake plays a key role in anenvironment of the northwest of Iran. In the last decade, construction of several dams on the riversdischarging to the lake has caused water level decrease of the lake and as a result adverse effects onthe lake environment. In this research, by using Mike 3D model, water level and salinity pattern of theUrmia lake have been predicted. Inflow decrease to the lake was considered to be both gradual andinstantaneous. Salinity and water level of the lake during coming years were also simulated.According to the results obtained, reduction of inflow to the lake has caused decrease of water level inthe lake. This decrease will cause atrophy of major part of the lake. Water level reduction of the lakevaried from 1.5 to 2.5 meter depending on the amount of inflow diverted and used upstream.Furthermore, several scenarios have been investigated to improve the lake condition. These resultshave also shown that creating an extra opening in the west of causeway, does not have any significanteffects on the salinity pattern of the lake.