Journal of Irrigation Sciences and Engineering
Year:2012 | Volume:35 | Issue:3|Papers Count:13

Dams are one of the most common structures to make a reservoir for water accumulation. Sediment deposition in reservoirs not only reduces the storage capacity of a reservoir but also decreases its useful life. Also, in many cases sedimentation creates problems for bottom outlets. In this study simulation of sediment deposition in Jiroft Reservoir is investigated with the aids of GSTARS3 model. At first the measured data of Jiroft Reservoir are used to calibrate the mathematical model. The Manning coefficient and the sediment transport equations are used for this proposed. After calibration, existing data are used for verification of the model. Finally, the time variation of reservoir volume is calculated. The results showed that the mean annual volume reduction of the reservoir is approximately equal to 1.27 percent of initial volume. Also, the trap efficiency of the reservoir is computed and it was equal to 87 percent.

Increasing demand of water resources in the world, especially in arid and semi-arid regions, has forced farmers to use low quality water, such as drainage water and saline groundwater. In order to evaluate the effects of saline water management on corn yield and salt distribution in soil profile, five management methods were conducted in a lysimetry study in Karaj. Therefore, the experiment was performed as a randomized complete block design with three replications by Furrow irrigation including five treatments: irrigation with non-saline water (M1=0.7 dS/m), irrigation with saline water (M2=5 dS/m), irrigation with mixed water (M3=2.85 dS/m), alternative irrigation with non-saline and saline water (M4) and alternative furrow irrigation simultaneously with saline and non-saline water (M5). In the latter one a furrow was irrigated with saline water and side furrow with non-saline water constantly. The results showed that highest yield and measured characteristics were corresponded to irrigation method with non-saline water (6988.12 kg/ha) and the least one with saline water (4090.76 kg/ ha). Yield decreased 20.59, 16.34 and 8.77 percent in M3, M4 and M5 treatments respectively as compared to the control treatment (M1). The average soil salinity in top 30 cm layer was 3.66, 2.66, 2.36 and 2.15 dS/m in M2, M3, M4 and M5 treatments, respectively. Therefore, it can be concluded that the best management practices among proposed treatments is alternative Furrow irrigation simultaneously with saline and non-saline water.

Generally, the influence of temporary rain fall on runoff response may be simulated by a hydrograph. In this research study, based on statistical model, for evaluating the temporary rain fall hydrograph on run off peak, by considering two specified rain fall and producing a runoff model, simulation has been done in a small basin. The mathematical model, namely SEBRM, derived from primary data of two rainfall events and produced runoff of SepidroudBasin, reconstructed and a hyetograph is simulated by two certain rainfalls and calibration of obtained data would be the basis of evaluating of future runoff. The results show the SEBRM model in low and moderate rainfalls intensity, submits very closely convergence between actual and predicted data for describing the role of rainfall volume in producing runoff in small basins. So, in this research study, the error in computations, for maximum 60 mm/h rainfalls intensity, was 13% for SepidroudBasin approximately.

Discharge of emitters changes by various factors such as pressure, manufacturing coefficient of variation, clogging and the temperature of water irrigation. In order to study the effects of temperature on discharge of emitters, 10 types of emitters have been tested in irrigation laboratory in Faculty of Water Sciences Engineering Ahwaz, Shahid Charm University. In this research, the effect of 4 different temperatures i.e.10, 20, 30, 40°C under 4 pressures i.e.5, 10, 15, 20 m was reviewed. By calculation of manufacturing coefficient of variation and based on American Society of Agricultural Engineers Standard, qualitative classification of emitters was done. Finally, four type were excellent, two of them unusable and the others were between both conditions. For experiments in temperature of 10°, the ice and in temperatures of 30° and 40°, a tank equipped with an electric heater and controlling unit for temperature was used respectively. With regard to obtained results by raising temperature of irrigation water, the discharge of non-compensating emitters was increased. In compensating emitters, the temperature didn't have significant effect on discharge of emitters in 3 cases, but in two types cause discharge was decreased and in one, discharge was increased. In final, result showed that temperature doesn't have a significant effect on manufacturing coefficient of variation and water emission Uniformity.

Rivers have always a significant role in foundation, evolution and development of human civilizations and societies. Along a river, different organizations construct many longitudinal and transverse hydraulic structures for different purposes that these type of structurs cause many changes in morphology and dynamic of such rivers. In this research study, the effect of the transverse structures to the flow direction built on Barajin River in Qazvin province on flood zone and land uses has been investigated. For this purpose the river plan, longitudinal river profile and cross sections were provided using topographic and land use maps. In the next step, flood hydraugraphs different and the peak discharges were provided using different methods such as SCS with different return periods. The geometric data of river and its hydraulic structures were then collected using surveying information. HEC-RAS and GIS Softwares, which are popular for river engineering, were applied in this research. Flood mapping zones were provided with and without structures for different return periods. The predicted results were then compared with the corresponding meansured values and these comparisons showed the accuracy of those softwares.

The present study has been conducted in a 90 degrees sharp bend to investigate the effect of bank roughness on flow patterns. Tests conducted under two different flow conditions, with Froude numbers equal to 0.17 and 0.4 and two different roughness sizes of 0.5 and 5.0 mm. In each test three components of flow velocity at 576 point were measured. Plot of flow velocity vectors and stream lines were done by SURFER and TECPLOT softwares. The results show that the region of maximum flow at the beginning of bend occurs at the inner bank then gradually shifted toward the outer bank at the end of bend. Comparison of flow patterns in two different roughnesses shows that by increasing the roughness height, the strength of secondary flow decreases while the number of smaller rotational cells is increased. In general it may be said that in a sharp bend up to cross section of 70, the region of high shear stress is very closed to the inner bank and from that place to the downstream, it shifted to the outer bank. The increases of bank roughness causes that the maximum shear stress is decreases. The location of maximum and minimum shear stress at two roughness of 0.5 and 5.0 mm are at 20 and 90 respectively, their values have been calculated to be 1.47 and 0.54 N/m2 for 0.5 mm roughness and 2.2 and 0.46 N/m2 for 5.0 mm roughness, respectively

Heavy rainfalls are one of the crisis couses. The crisis of heavy rainfall in arid area are strong.in this study Zayandehrood basin as a arid area have storng floods in recent years. Statistical analysis in this period (1972-2010) indicate March flood that is ocured with 646 m3/s discharge and standard indicis SFI=10.47, is the biggest flood. In this study thermodinamic and synoptic conditions are anylyzed by Raklif and Bradbari indices. The SKW-T chart and upper air data in 500 mb are used. Bradbury and Rackliff Index show values of -1.58 and 33.6 that indicated a high instability in basin region. In addition, pressure synoptic analysis showed that 500 mb synoptic conditions are favorable for the occurrence of flooding is in accordance with expanding Atlantic – Europe down words polar shift. The dominant meridional pattern over the Mediterranean region and Middle East is formed over the Mediterranean and the West, with an intense fall over Iran. Bradbary and Radcliffe the indexes are fit for forecasting heavy rainfall that may lead to flooding.

Attention has been paid for many years to the problem of sedimentation in river intakes of irrigation and drainage projects, hydro-electric installations and water treatment plans. One of the methods to control sediment deposition at the entrance of intakes is the application of Submerged Vanes. But their efficiency is restricted to a particular hydraulic condition. In other word at the straight river reach, using submerged vanes in the low value of relative discharge (Qr<0.2) eliminates sediment uptake. Beyond this value, the effectiveness of the vanes reduces. The sediment-control performance of the vanes was enhanced by introducing different structures, modifying vane shape and changing intake geometry. In this research, Current Deflecting Wall-Sill (CDW-Sill) was used as a new method to control sediment at the lateral intake. The sediment-control performance of its various parameters was investigated. Primary and secondary CDW channel width, sill height and the angle of secondary CDW were also investigated using three different relative discharges. The results obtained showed that, when the angle of installation of the secondary CDW is 63 degree the sediment transport was low. The results also showed that up to relative discharge of 0.4, the primary CDW channel width equal to 14 cm has the best performance for different secondary CDW channel widths and eliminates sediment uptake. However increasing the Sill height reduces the performance of CDW-Sill.

Despite of many researches on bank erosion mechanism, there exists an incomplete understanding of one of the basic mechanisms governing sediment loading to streams which is namely erosion by concentrated lateral, subsurface flow which causes river bank failure after undercutting process and removing sediment into the river. The objective of this research is to study seepage erosion (piping) in river banks in two cases of presence of a cross structure (e.g. drainage pipes or gas transport pipes, …) and without cross structure by measuring the depth of undercutting hole induced by seepage erosion in sand layer with three different grain sizes under different hydraulic gradients in a laboratory flume. The results show that under equal hydraulic gradients length of erosion hole depends on river bank sand layer grain size and presence of cross structures.

For determining homogeneous regions and estimation of maximum flood in various return periods, cluster method and regional frequency analysis using linear moments are used in areas without hydrometric stations. Results showed that using Cluster analysis in the under study region was detected suitable to 5 homogeneous regions with k-means clustering method in Urmia lake basin. Discordance test has conducted and two stations such as Sahzab and Bokan were found as discordant stations and frequency analysis has implicated at-site. With elimination of discordant stations, all regions was found homogeneous using heterogeneity test. In this research, maximum annual flood fitted to eleven distribution functions. Using goodness-of-fit the Generalized logistic distribution were selected for three regions of A, B and C, Log normal 3 parameters for D, Generalized extreme value for E and for Sahzab and Bokan stations Log normal 2 and 3 parameters were chosen respectively. Besides, Generalized extreme value distribution was found appropriate for all of the regions.

Sedimentation occurs at the entrance of reservoir in the form of delta, and coarse particles create delta. In this research, the effect of non-uniformity of sediment particles on the progression and shape of delta in steady and unsteady flow is studied. Results show that in experiments with non-uniform particles, the progression of delta is more 2dimentional than in experiments with uniform sediment particles. Symmetry in final pattern of delta doesn’t depend on non-uniformity of sediment particles, and in all experiments a good symmetry can be observed. In experiments with non-uniform particles in steady flow, the power of Swenson equation for the toe is calculated 0.788 that shows slower progression for delta because this power in experiments with uniform particles is calculated 0.85. This is also correct in unsteady flow. After flood, the foreset slope of delta is decreased in experiments with non-uniform particles.