فصلنامه علوم و مهندسی آبیاری
سال سی و چهارم شماره 2 (پاییز 1390)

Gates are used in different applications and shapes as water regulation structures. The radial gate is one of the most common water control structure in irrigation and drainage networks. Ease of construction, installation, and power saving nature, can be considered as the main advantages of radial gates. These benefits leaded to increase of their application for controlling the flow in dams and water conveyance structures. Many methods and empirical equations have been presented to estimate the discharge and discharge coefficient from radial gates. However, submerged flow condition has been less considered. Discharge calculation from the gate opening, could be carried out with the integrated solution of energy and momentum equations. In this research, 16 measured discharges were used in two intakes of diversion dams of Gotvand and Shohada in Khuzestan State of Iran. The results indicated that the momentum equation always underestimates the submerged depth due to disregarding of flow turbulence and non-uniformity of the velocity distribution. Thus, calculated discharge is always greater than measurement ones. Therefore, through direct measurement of submerged depth instead of tail water (the omission of momentum equation) and using energy equation, the results would be closer to the true values. Finally, Toch contraction coefficient has been calibrated using integrated solution of energy and momentum equations in Lingo software (non-linear optimization tool).

Having knowledge of groundwater quality in arid and semi-arid areas can result sustainability of this valuable resource. For this reason, it is necessary to estimate Sodium Adsorption Ratio (SAR) and Chlorine in the groundwater quality accurately. Nowadays, many attentions have been arisen on geostatistical methods to detect spatial variability using same data (Kriging) or using auxiliary variables (Co-kiriging) in groundwater science. The quality of groundwater for agriculture is very important, however its measurement is time consuming and expensive. Therefore, finding solution to estimate SAR and Cl from easily measuring parameters is essential. This study is done in Boukan region using Co-kriging estimator in which water salinity (EC) is considered as an auxiliary variable. The results of Co-kriging and Kriging, were compared and evaluated using RMSE criterion. The results showed that Co-kriging method with high correlation coefficients is more precise than Kriging models in estimating SAR and Cl. RMSE values were 3.07 and 3.82 in estimating SAR and Cl respectively.

Drought is a phenomenon that occurs frequently in all over the world. It is clear that cannot basically campaign with drought. However, one is able to adapt with planning and preventing actions. Southern Alborz area selected for drought studies. This area is limited to Alborz chain in northern way and central salt desert of Iran in southern way. Researching stations are located in different elevations from 900 to 2500 meters above sea surface elevation. By using of different indices of drought, calculated and analyzed different precipitation states. In all of stations, often years and in most of drought indices, all precipitation categories existed. By two ways, it proved that precipitation states, especially droughts, become independence from elevation. These two ways are, 1. Amount of drought indices regress and analyze with elevation, 2. Amount of drought indices classified and these classes regress and analyze with elevations.

Fall velocity of sediment grains affect sediment transport phenomenon significantly. In the present study some experiments were conducted in a circular flume of the Hydraulic laboratory of Shahrekord University, Iran, with 1.9 m of outer diameter. Cohesive sediment samples were taken from the North Karun watershed. Modified Krons's equation has been applied for calculating of the cohesive sediments fall velocity. In order to determine the equation's parameters, the velocity and the shear stress profile and sediment concentration were measured at various times for each experiment. The results showed that increasing in concentration causes the fall velocity of the sediments to be decreased. It denotes inverse correlation between sediment concentration and fall velocity. Finally, based on the obtained results of this study an equation was obtained to calculate the cohesive sediments fall velocity.

Sustainable management of groundwater resources in underdeveloped regions is one of the essential objectives for the future, especially when the rising demand for clean drinking water by these fast growing communities is considered. Uncontrolled expansion of industries, agriculture and settlements as well as insufficient management imposed on groundwater resources are main reason for proper management methods. Based on capability of good match advanced models in groundwater simulation with hydraulic system of aquifer and prediction of future situations created suitable conditions for management and exploitation these resources. Objects of present research is evaluating of precision of MODFLOW mathematical model in order to representative of proper management in groundwater resources in Garbaygan plain as a region with strategic importance in farming. To start doing this study, input layers of model was created by using geographic information system (GIS). Afterwards boundary condition and discertization of aquifer have determined. Also calibration in steady and transient state was done by using available information. In order to confidence of simulation results, verification test did on data rest. Therefore representative hydrograph and water table contour in 10, 30 and 50 future years (1397, 1417 and 1437) was forecasted. Result showed that drawdown trend of representative hydrograph will be 0.331, 0.298 and 0.27 meters per year in 10, 30 and 50 future years respectively. So it understands that drawdown trend will decrease with increase of forecasted period.

Application of Flip Bucket in dams, in comparison with other structures needs more research due to fact that the forces that Jet stream inflicts in their collision place to downstream bed lead to scour or fracture of floor slab. Characteristics of dynamic pressure on collision place in various conditions will enable us to determine probability of scouring and exact amount of it, in case of such circumstances in administrative structures, and also it is possible cracking of the downstream slab floor or to determine the stage of particles separation from bed which is important in design of plunge pool. In this study, with providing conditions to measure the dynamic pressure created on the floor due to the collision of flip bucket jet trying to extract data in different conditions from discharge jet output and depth. The results suggest that the plunge pool downstream of Flip Bucket jets will be effective when ratio of water depth on the thickness of the jet is greater than 3.

This paper numerically investigates the 3D flow pattern at the 900 equal-width rectangular open channel junction. The Reynolds-Stress Model (RSM) is applied to simulate the turbulent flow. The flow is analyzed under steady-state conditions. Shumate's experimental findings are used to test the validity of the numerical modeling. Comparison of the modeling data with the experimental ones indicated a close proximity between the flow patterns of two sets. The average prediction error of velocity showed a range between 3.5%-10%. Effects of the discharge ratio on separation zone dimensions, created in the main-channel, downstream of the junction, indicated an inverse relation, where increase in discharge ratio, will entail a decrease in the length and width of the separation zone. In this research, the shape index of separation zone was found to be an average value of 0.18. Comparison of the results further showed that the increment in discharge ratio will lead to decreased in the maximum value of bed shear stress. The study also found the Fluent as a powerful numerical tool for the analysis of flow pattern in the feasibility stage of the hydraulic engineering projects.

Nitrate leaching from the agricultural fields to the surface water via subsurface drainage systems is one of the disadvantages of these systems. As these nitrogen losses often lead to the pollution of both surface and groundwater, they are likely to result in environmental degradation that will be detrimental to aquatic life, plants, animals, and humans. There are some traditional methods for nitrogen removal such as biological processes, chemical processes and physical operation. Recently, the biological processes have proven to be the most economical, feasible and efficient method for nitrogen removal. Furthermore, this method is the most promising method available for removing nitrate from water in the saturation conditions. Since subsurface soils are generally limited in the amount of available organic carbon, most microbial denitrification processes require additional carbon sources to sustain these activities. In this study, barley straw was used as a carbon source to enhance the denitrification processes and the effect of that on effluent nitrate and ammonium were evaluated. Two forms of position of this biofilter near the drainage pipe to remove the nitrate form the drainage water were investigated in the laboratory study. The results showed 60% of influent nitrate was removed by these two forms of position over the study period. These biofilters also could remove more than 85% of influent nitrate after 8 weeks. Also, the results showed that this treatment had reduced the effluent nitrate concentrations below the USEPA maximum contaminant level for drinking water of 45 mg L-1 nitrate at the end of the study.

The Instantaneous Unit Hydrograph (IUH) concept is widely applied for runoff estimation in watersheds with scanty data. In this paper, the method of geomorphological unit hydrograph of reservoir (GUHR) was applied to Liqvan watershed located in East Azarbaijan, Iran. This method is based on the cascade of linear reservoirs which are assumed to contain the stream flow of related sub-watershed area. Hence sub-basins are replaced with consecutive reservoirs according to watershed geomorphology. Indeed the model is the routing of flood through these reservoirs and to determine the unit hydrograph in the basin outlet. The results showed GUHR has efficiency enough in simulating the rainfall-runoff by the use of watershed geomorphologic characteristics of a basin. The sensitivity analysis of model was carried out by changing the parameter values. Results showed that to decrease in K values caused to increase in the peak of hydrograph (qp) with less time of peak (tp) and vice versa.

Proper irrigation system selection is an important step in optimum utilization of soil and water resources. Different impressive factors in proper pressurized irrigation system selection have made it as a complicated issue. In this research, providing water, Soil and climatic parameters of 20 field Samples and studying Socio-Economic factors, using Analytical Hierarchy Process, the proper pressurized irrigation system for Dehgolan plain region has been selected. Main impressive factors have been divided in two groups of field physics and socio-economic. Consequently solid-set sprinkler system was introduced as a proper system for fields used in the study. Results show the analytical hierarchy process has acceptable usage in irrigation system selection topics.