Journal of Irrigation Sciences and Engineering
Year:2013 | Volume:36 | Issue:1|Papers Count:13

In this study, dynamic pressures due to impact of a ski jump out of a flip bucket downstream of a chute spillway model have been studied. Experiments were performed for five discharge (0.11, 0.18, 0.25, 0.32, 0.39 m3/s per unit width) and four jet impact angles (00, 300, 600, 900). Fluctuation of dynamic pressure was measured using a 250 mbar pressure transducer. Discharge (q), horizontal and vertical distance from the peak to jet impact location (L, H-h) and angle impact in downstream (q) were considered as the main parameters affecting the dynamic pressure. Results showed that pressure coefficient is highly sensitive to horizontal and vertical distances to impact location as well as to the impact angle. Using dimensionless parameters, a power function was correlated for calculation of the dynamic pressure for variable impact angle.

Sedimentation is one of the most important issues of manmade reservoirs and directly case reduction in useful life of dams. Density or turbidity currents are commonly occurs in reservoir especially when the inflow associated with high sediment load. Fresh water entrainment into density currents is directly affected its transportation and other hydraulics parameters. There are some parameters that may effects water entrainment.Changing in successive cross sections is one of the parameters that may affect this parameter. In this research water entrainment of density current in converging sections is studied. Experiments were carried out in a flume with variable bed slope, with three convergence angle, three discharge, three concentrations and three bed slope.The results show that with increasing of converging angle water entrainment will be increase. And finally by using the data and the equations proposed by other researchers for fixed sections, an equation is presented for water entrainment of density current in both fixed and converging sections.

Removal of toxic heavy metals from wastewater is an important environmental challenge. In this work, the nano particle of zizyphus spinachristi fly ash is used as a fit adsorbent for the removal of Zn2+ from aqueous solutions and industrial wastewaters. Bath experiments were used to determine the best adsorption conditions. The experiment showed that the adsorption capacity of nano particle of zizyphus spinachristi fly ash is a function of pH, contact time, amount of adsorbent and initial concentration in solution.Maximum adsorption of Zn2+ was obtained at pH of 5, contact time 30 min, amount of adsorbent 20 g/L and initial concentration of 2 mg/L. The Ho et al. and Lagergern kinetic models were used to determine the correlation among the experimental data. The correlation coefficients obtained for Ho et al. (R2=0.9979) and Lagergern (R2=0.9925) models showed that the Lagergern model described better the experimental data. Metal adsorption onto adsorbent was evaluated by Langmuir and Freundlich isotherms. Results indicated. the Langmuir isotherm model (0.9645) is the most suitable one for the adsorption process using sheep gut waste.

Excessive use of water for irrigation has lowered underground aquifers and has deteriorated the quality of underground water for irrigation causing agricultural production and water use efficiency to decrease. To study the effect of salinity of irrigation water and application of nitrogen on yield and water use efficiency of pomegranate a split plot experiment with 15 treatments and three replications was performed in city of Saveh in 1389. Treatments were factorial combinations of five levels of salinity (2, 4, 6 and 8 dS/m) for irrigation water and three rates (0, 150 and 300 g) of nitrogen for each tree. The salinity levels of irrigation water were located in main plots and nitrogen rates were considered as subplots using a randomized complete block design. The results showed that the salinity of irrigation water decreased plant yield when it was higher than 4 dS/m. When the salinity levels of irrigation water were less than 4 dS/m reduction in yield was not significant and this salinity level was considered as threshold salinity for pomegranate. At higher salinity levels the yield of pomegranate decreased at the rate of 3.3 percent per each unit of EC of irrigation water.Application of nitrogen increased plant yield at salinity levels lower than 4 dS/m but it decreased pomegranate yield when the salinity levels of irrigation water were higher than threshold salinity. The 34 relative yield of pomegranate at different salinity levels was estimated by an equation and reported in this paper.

one of the most basical issues in groundwater resources management is the estimation of water table from observation well network data. The purpose of this study is estimate the groundwater level using the combination algorithm of the geostatistics and Artifical Neural Networks method. Shahrekord plain was selected as a case study of this work. After selected February 2007 and September 2009 as the months with the maximum and minimum groundwater level (during the studied period of 2003 to 2009), using Co Kriging, Kriging and Inverse Distance Weights, groundwater level has been estimated. The results showed that CoKriging with semi-variogram Gousian model had the best statistical validation (R2=0.816 and MAE=16.54 for February 2007, and R2=0.854 and MAE=11.87 for September 2009). So this approach with combination Artificial Neural Networks give the best results. Also two types of Neural Networks layers, Multi Layer Perceptron (MLP) and generalized feed forward (GFF) were used with combination Kriging method. The results showed that Multi Layer Perceptron network was effective to estimate groundwater levels with statistical indicators of (R2=0.906 and MAE=12.73 for February 2007, and R2=0.924 and MAE=8.75 for September 2009).

Sediment deposition is the principal problem affecting the useful life of reservoirs. Here we quantify the physical properties of sediments deposited in Dez dam reservoir by field investigations and empirical methods. Upon field investigation performed in the reservoir, 79 undisturbed sediment samples were taken from 12 cross sections of a 25 km of the reservoir upstream dam body where the sediments deposited have always been submerged. Results showed that grain size and bulk density of sediment deposited in the studied reach (up to 25 km upstream Dez dam body) are almost uniform and empirical methods for calculating bulk density in comparing of field data has averagely an error of 30%. This shows that the empirical methods aren't capable accurately to predict bulk density of fine sediment in Dez reservoir. Analysis of the results showed that the error mostly refer bulk density calculation of the clay sediments.

Difficulties like production, transportation, performance and etc in sandy envelopes which have been used in subsurface drainage projects have innovated artificial envelopes At this research performance of the artificial envelope PP450 produced in two Iranian factories (called A and B) came under close observation and compared with the same foreign grade. For these reasons first with Komo Standard Tests the artificial envelope came under loading process and the amount of sand passed into every artificial envelope measured.Results of soil/sand tank showed the out flow fluctuation on the first second and third day was high but it decreased after that and got stable (94, 66, 72 ((mlit/min) /m) respective related to the foreign envelope, envelope A and envelope B). Total maximum and minimum average of the out flow discharge related to the foreign envelope and the envelope A. Comparison of water resistance around the drainage pipe showed that the foreign artificial envelope has the minimum entrance resistant (2.03 day/m). Minimum and maximum amount of sediment in the pipes related to, putting in order, the foreign envelope and envelope A. but in sum there was no major difference on the amount of sediment, the maximum difference 20% is its indication. Finally this research passes and confirms the envelopes produced inside but recommends more study on them, specially envelope A, in order to get a better quality.

The aim of this study is to assess the consequences of coincidence of water and salinity stress on yield of a popular local rice variety. A factorial pot experiment using a randomized complete blocks design with three replications was carried out at the Rice Research Institute of Iran, Rasht. Five different levels of water salinity and five irrigation regimes were considered in this study i.e. water salinity treatment: fresh water (1 dS/m, as control), 2, 4, 6 and 8 dS/m and irrigation regimes: full irrigation, AWD (Alternative Wetting and Drying), and irrigation at 100, 90 and 80 percent of field capacity (FC). Yield and yield components were determined at the end of the season. The result showed that salinity stress has a severe effect on rice yield and yield components. The results showed that when the irrigation water salinity is lower than 1 dS/m, intermittent irrigation is relevant.

Hydraulic jump is one of the important phenomena in rapidly varied flow. Due to this phenomenon the energy loss, the upstream flow velocity significantly decreases. In the present study, hydraulic jump on a new roughened bed -with half cylindrical shape bars with three heights (r) and four different longitudinal spacing (s=1D, 2D, 3D, 4D) were investigated. In total 238 experiments were performed for a range of Froude numbers from 4.6 to 7.4 on horizontal bed and two adverse slopes of 1 and 1.5 %. The results showed that the sequent depth decreases and energy loss and bed shear stress increases as the height, spacing of the rough bars, adverse slope and Froude number increased. In hydraulic jump on adverse slope of 1.5% and rough bed with half cylindrical roughness, sequent depth 36% decreases and the bed shear stress coefficient is 16 times of its corresponding values on smooth and horizontal bed. Some empirical relations for sequent depth ratio, relative energy loss and bed shear stress coefficient were introduced.Totally, the results obtained show that, rough bed with adverse slopes may be used to achieve better performance in stilling basins.

Groundwater in many parts of the world is the main source of drinking water. The Shahrekord aquifer (Iran) supplies the drinking water to the residents of Shahrekord. The aim of this research was to geostatistically analyze and map nitrate and phosphate concentrations in this aquifer. For this purpose, 100 agricultural wells, located in the Shahrekord plain, were sampled on three different dates during 2010 and water samples were analyzed for nitrate and phosphate. The results presented here are based on the average concentrations of the three samples. The mean concentrations of nitrate and phosphate were 25.9 and 0.09 mg/L, respectively. Comparison shows that these mean concentrations have increased since 2007. The spatial variability of nitrate and phosphate were better described by spherical semivariogram models. Examination of maps shows that the southeast of the aquifer had the highest concentrations of both nitrate and phosphate. In some wells, located in the southern part of the aquifer, the concentration of nitrate sometimes exceeded the permissible level of 45 mg/L. This may be attributed to the presence of the Shahrekord municipal wastewater treatment plant, the shallower water table in this part, and also due to the inflow of groundwater.