Journal of Irrigation Sciences and Engineering
Year:2016 | Volume:39 | Issue:1|Papers Count:19

Weirs are one the most important hydraulic structures for flow control, water measurement and regulating of upstream water elevation in canals, irrigation networks and rivers. For a given of channel width, duckbill and oblique weirs have longer effective length in comparison with the usual rectangular sharp crested weirs, and this could be effective on their discharge coefficients and efficiency. Discharge coefficient is a function of weir geometry and hydraulic conditions. Therefore, in this study discharge coefficients were specified for duckbill and oblique weirs with three different wall angles and three weir heights and were compared with the corresponding measured values in usual rectangular weir. Three mathematical dimensionless equations were finally developed for these weirs, describing the relationship of discharge coefficients with the weir geometry and hydraulic conditions. It was found that for all types of weirs the discharge coefficient decreases with increasing discharge or upstream head. However, this reduction has sharp slope for the weirs with higher angles. For duckbill weirs the discharge coefficients were measured 0.5-0.7, 0.4-0.73, and 0.3-0.75 for the angles of 45, 60, and 75 degrees, respectively.For oblique weirs the measured discharge coefficients were 0.66-0.9, 0.64-0.95, and 0.54-0.9 for the angles of 15, 30, and 45 degrees, respectively. The results of this research show that the duckbill and oblique weirs have more efficiency for low head in upstream and are able to pass more discharge with lower upstream head.

In many cases the collection of obstacles stand against water flow direction and by passing water through these obstacles, vortexes are created in downstream of them and by overlapping of these vortexes, surface waves perpendicular to the flow direction are formed. In this study the impact of obstacle shape on the characteristics of transverse waves are investigated. For this purpose, cylindrical obstacle and cubic obstacle are used. Discharges 5, 15 and 25 l/s and insertion of obstacles in parallel with ordering of 60´60, 60´120, 120´120 and 180´180 are considered. Totally 36 experiments were performed. The results showed that the shape of obstacles has high impact on the formation of transverse waves. The maximum amount of relative amplitude (A H) (A: The maximum wave amplitude, H: depth of flow) was occurred for cylindrical obstacle with amount of 61.10% in arrangement of obstacles of 60´120 and discharge equal to 5 l/s and the minimum value of A H was occurred for cubic obstacle for side current collision with amount of 6.00% in arrangement of obstacles of 180´180 and discharge equal to 25 l/s. Equations for estimating of Strouhal Number were presented, using SPSS software developed. According to presented equations, Strouhal number has direct comparison with P D (P: Distance between obstacles, D: Diameter of obstacles) in cylindrical obstacles and has inverse comparison in two situations of cubic obstacles.

To study the effect of water salinity in sprinkler irrigation, the system should be improved for saline levels requirements and a uniform water distribution. In this research, the distribution uniformity and saline gradients were evaluated for a double line source sprinkler irrigation system in Ahvaz in dry and hot climate. During the spring and summer growing season of maize, the data were collected in three farms with similar conditions and different managements, so as daytime (D), nighttime (N) and daytime irrigation with a post short fresh water for foliage washing (F), in three replications. For the two growing seasons, distribution uniformity for each irrigation event in all treatments was defined between 59 to 89% (mostly greater than 75%). Cumulative distribution uniformity for D, F and N treatments were 91, 85 and 87 % in spring, 93, 88 and 93% in summer for saline treatments area, and 88, 82 and 88% in spring for whole irrigation system and 91, 85 and 87% in summer for whole irrigation system, respectively. The coefficient of variation for all treatments during the two growing seasons was less than 3%. Uniform and proper gradient of water salinity and parallel iso-saline lines were observed throughout the field, along with high regression coefficients for liner equations. The results showed that the experimental sprinkler irrigation system provided an appropriate condition for the system throughout the field with low cost and easily management. With avoiding irrigation in windy conditions, increasing wetted radius of sprinkles, increasing the side sprinkler numbers and regulation of them, the improvement of irrigation uniformity must be considered.

One of the most serious consequences of climate change is how it will affect droughts and water resources. This study aims at investigating the impact of climate change on droughts conditions in Dezfool-Andimesh Plain using the Standard Precipitation Index (SPI). To achieve this objective, output of four general circulation models (GCMs) under the A2 scenario were downscaled for two climate stations in the period of 2060-2084 compared to the baseline period (1985-2009). Regarding the dominant crop grown in the study area, a 6-month SPI for the baseline and future periods were estimated under the four GCM-scenarios. Results revealed that there is an increase in the duration of severe and mild droughts while there is a decrease in the duration of moderate droughts. This implies that droughts will be a concern in the future during the growing season (for the dominant crop) which should be considered in water resources management.

In the present paper the Triangular Shape Vane (TSV) attached to the bank of a flume bend for the purpose of introducing a new measure for reducing bank erosion has been experimentally investigated. Tests carried out at 90-degree mild flume with ratio of radius to width equal to 4. For main tests, nine triangular vanes with fixed distance of 70 cm equal to 5 times the effective vane length at angle of 20 degree to the upstream was attached to the outer bank and tested under four different flow conditions of which Froude number was equal to o.24, 0.26, 0.29 and 0.32. Tests also were carried out using regular Rectangular Shape Vanes (RSV) for Froude number equal to 0.26. At the end of each test, bed topography was measured. Plots of bed topography and longitude bed profile show that the scour hole at the noise of both vanes are developed with its maximum depth increases as the flow conditions is increased. Comparison of the scour depth for both TSV and RSV proved that the scour depth for TSV are 80% less than the scour depth of RSV.

In this research, in order to study the effect of deficit irrigation on the physiological indexes of maize (single cross 704), an experiment in randomized complete block design with three replicate, was performed in the experimental field of Shahid Chamran university during the 2013.The Irrigation treatments included 100, 75 and 50 percent of the maize water requirement that was calculated through the evapotranspiration of the reference plant (grass). Volumetric lysimeter were used for the cultivation and the depth of the groundwater table was held at 70 centimeters from the soil surface. A lysimeter with complete irrigation and without the presence of water table was used as control treatment. The amount of the physiological indexes was measured 60, 74 and 88 days after sowing for Determination of Stomatal conductance, photosynthesis speed and chlorophyll's density. The results showed that with increasing of water stress, the amount of the physiological indexes decreased. The maximum and minimum amount of chlorophyll's density was 55.38 and 39.66, obtained from the treatments with 100 and 50 percent of maize water requirement irrigation, respectively. The maximum and minimum amount of Stomatal conductance and photosynthesis speed obtained from treatments with 100 and 50 percent of maize water requirement irrigation, respectively. The alteration process of these three indexes during the infancy showed that from the eighth week after the cultivation till the end of the maize infancy the maize petal loophole conduction, photosynthesis velocity and the chlorophyll's density will decrease. also, the results showed that the maximum maize biomass was 4.63 ton/ha obtained from the treatment with 100 percent of maize water requirement irrigation and the minimum maize biomass was 3.72 ton/ha obtained from the treatment with 50 percent of maize water requirement irrigation.

Most rivers have bend routs that the quite complex flow pattern is dominated on them. It is necessary to study the behavior of a river, the flow pattern is well known that the dominant bend. Numerical models as a powerful instrument for the prediction of such areas can provide a good understanding of them. In the present study using three-dimensional numerical model Flow-3D, Parameters of U/Uc the flow pattern at a 90 degree arc of the moving bed is placed. The results were compared with experimental data. Analysis of results relevant to flow pattern in cross sections and different plans are among other points introduced in this paper.

Shallow groundwater with different quality could be replaced of irrigation water for crop as a cheap water resource in some semi-arid region of world. But salt rising to the root zone due to capillary flow from shallow groundwater is a limiting factor for underground irrigation method. In this study, an experiment in a completely randomized factorial design was conducted with four water treatments include of common water (Gorgan city drink water with 0.6 dS/m of electrical conductivity), 7.5, 12.5 and 17.5 dS/m that were prepared with mixing common water and Caspian Sea water. Two water table treatments also considered include 70 and 100 cm depths. All treatments had 3 replications. Totally 24 lysimeters with 150 cm height and 15 cm diameter were filled with silt clay loam in Gorgan agriculture science and natural recourses university. Ground water injected from some scaled water reservoirs through porous pipes into the soil and water table was created by a floater at stable depth beside of each lysimeter. Soil surface evaporation was measured daily by monitoring the water level changing in each lysimeter reservoir. After a three-month, the water content and electrical conductivity of the saturation extracted samples in four depths including 5, 30, 60 and 90 cm of each soil column were measured. The results of showed that at 1% probability, the rising slat mass in different treatments was significant. In the control treatment, salt accumulation intensity to the soil surface was more than other treatments compare with its groundwater concentration. Comparison of salt rising to the soil surface of treatments for two water tables (70 and 100 cm), showed that the salt rising differences between this two treatments was significant at 1 % probability, and accumulation of salts in the soil profile at 70 centimeters was more than its value at 100 cm water table in all groundwater salinity treatments. Evaporation results showed that the highest evaporation was occurred in 17.5 dS/m salinity treatment. Also as a whole, differences between the evaporation rates of 70 and 100 cm water levels were not significant at 1% probability.

In this article we studied the distribution limits of jet injection in the same phase and dissimilar phase ambient. To achieve the proposes of this research a physical model was set upped consist of experimental flume and related accessories, circular jets nozzles 5, 8 and 15 mm diameter which had various contraction angles. The experiments were conducted at the same phase (clear water) and dissimilar phase (air surrounding) of ambient fluid. According to the results there is a significant effect on the properties of distribution limits on the partially submerged and free jet flow. The results showed that the jet flux has been developed at the dissimilar ambient fluid in the subcritical Densimetric Froude number. While the Densimetric Froude number was supercritical range in the same phase ambient flow. The quantity investigation shows that the maximum of jet flux development in the dissimilar ambient flow in the jet nozzle diameter is about 200 times where in the same phase ambient fluid this development has the nozzle diameter occurred 400 times. The results showed that the effect of dissimilar phase ambient on development of jet flow is much greater than the same phase ambient at the concentrations of 40 to 50 grams per liter. The govern mechanisms of the flux development of free outfall and submerged jet flow and It was found that the slope of the curve of the free jet injection is more of a submerged jet.

Appropriate estimates of flows for different return periods are important for floodplain management in designing canal, bridges, culverts and levees. In general, there are two common approaches to determine design flows at ungaged sites: Rainfall-runoff models, which are often costly and time consuming, and regression models, in which design flows of various return periods are related to watershed characteristics such as drainage area, topographic features, soils and climate. In the present study, bank full-geometry data as well as flashiness index are used as effective independent variables in regression models to evaluate design flows relationships at 41 stream flow-gauging sites in Gara-Gum basin of Khorasan-Razavi province located in an arid and semiarid region. The bank full geometry regression is found to be useful to predict design flows and comparable with flow estimates developed by traditional approaches for ungaged sites in the same basin. As, in three stations in this study area, the error in computations, compared with the method of frequency analysis, was 8% for bank full hydraulic geometry relationship.

In arid and semi-arid regions due to restriction of access to fresh water resources for agricultural production, the major source of irrigation water is salt water. It was argued that the use of magnetic technology and salt water pass through a magnetic field can be helped to improve crop yield where salt water is used. In this regard to investigate effect of salt water passes through the magnetic field on the growth characteristics and yield components of green pepper, an experiment was conducted as completely randomized with split plot design by six treatments and three replications at University of Shahrekord in the summer of 2013. Treatments included two water levels (magnetic and non-magnetic) and salinity at three levels (0.3, 2.3 and 4.2 dS/m). The results showed that magnetic water increases of 12, 19 and 33 percent of the total fruit yield in irrigation water with salinity respectively 0.3, 2.3 and 4.2 dS/m. Also all yield components of the including fresh and dry weight of leaves, stems, roots and root volume of treated water with salinity of 0.3 dS/m highest values than the two others. Magnetic water increases 15 and 11 percent in the weight of stems in salinity of 2.3 and 4.2 dS/m than other non-magnetic levels of its.

The local scour around bridge pier and abutment in recent years has been widely studied by different authors. Scant information exists as to how bridge pier proximity to abutment affects scour depth at an abutment and at a pier. Due to the fact that many bridges have a pier located close to an abutment, therefore, it is necessary to be study. This paper presents the effect of abutment length and pier shape on scour depth of them, by using wing-wall abutments with lengths 25, 37.5 and 50cm and circular, round edge and sharp edge piers in two distance, 17.5 and 35cm from the bank wall at the flood plain. The results of experimental study showed that the proximity pier to abutment, increases scour depth of them and the minimum scour depth related to the circular pier and maximum scour depth related to the sharp edge pier. For example, the sharp edge pier in distance 17.5cm from the bank wall at the flood plain, for abutment with length 50cm, increases scour depth of abutment and pier 50% and 61% respectively, compared with scour depth of them in isolation.

Volume of flooding flow volume in ephemeral streams decreases due to evaporation as well as the channel wall and bed penetration. This process is known as transmission losses. In this study, a model is developed to estimate the transmission losses in irregular sections of rivers, in which a finite difference scheme is used to solve Saint-Venant equations. In this model, for estimating the transmission losses, the Green-Ampt equation is coupled with Saint-Venant equations. After verification of model, the transmission losses at Gharesoo river with 18 KM length and 60 cross sections after 65 hours flood event is evaluated. The results showed that the Green-Ampt equation can predict transmission losses with good accuracy. Using model the transmission losses equal to 1400000 cubic meters is computed which is 2.75% of input flood volume to the reach. Also this model is enabled to evaluate the infiltration rate and cumulative infiltration depth.

Density currents are the most important transport mechanisms and deposition of sediments which causes sediments transportation to the near of dam body. Therefore, Studying of these flows and their affecting parameters are very important in terms of water quality and pollution prediction. According to density current complexity, experimental studies are typically used. In the present research, behavior of the saline density current forehead flowing over artificial vegetation was studied by conducting experiments. Density currents were entered into the flume with four different concentrations. Artificial vegetation was placed in the direction of the flow with four heights and five densities. Velocity and vertical concentration profile were measured in 6 and 3 longitudinal sections, respectively. The results showed that the most effective artificial vegetation density and height in this work can be concluded 1.4 percent and 0.2 meter, respectively. Keolegan coefficient is presented for velocity calculation of flows over smooth bed and bed with artificial vegetation, according to the vegetation density and height. Finally, a relationship was provided to calculate the velocity of flows over the beds with artificial vegetation.

Conjunctional use of saline and non-saline water for reduce the negative effects of osmotic potential in the plant, has gained much attention. The aim of this study is to compare existing approaches and propose a new approach on how to conjunct saline and non-saline water. To do this, an experiment was performed as a randomized complete block design with six treatments and three replications for sorghum in experiment field of Zabol University within 2012-2013. Treatments include; control treatment (100% freshwater), one-third of salty, the alternate time, the alternate place and the mixed. The investigated cropping indices were dry weight of stem, leaf and aerial organs of plant, plant height and leaf area index. The results indicated; both treatments the alternate place and one-third of salty, in all characteristics have been measured, after the control treatment had the highest yield, as the leaf dry weight, plant height and leaf area index did not show significant difference (p≤0.05) and in leaf dry weight and branch dry weight of the control treatment had the highest yield. These two treatments in salts adjusted at the end of the season left acceptable results. It seems local alternative and one-third of salty treatments with their own unique techniques in using saltwater reduce the negative effects of osmotic potential in the plant and compared to the older method (temporal alternative and), they have an advantage.

In order to evaluate the effect of slope on wetting pattern using a linear water supply a study has been taken in research field during the fall of 2014, at Shahid Chamran University of Ahvaz, Iran. In this research two flow rates 6 and 9 liters per hour per unit length, three slopes, including 0, 2 and 5 percent with three replications at the randomized block design were used. The soil texture was silt loam. The results of statistical analysis showed that with increasing discharge and slope, width and depth, area and volume soaked increases. The results showed these differences are significant in 1% level for 2 and 5 percent slopes compared to 0. Increase width soaked in for the rate of 6 liters per hour in slope of 2% with compared to a 0, 10 percent and for slope 5%, was 20 percent. Also the increase for width in the rate of 9 liters per hour respectively was 3 and 13 percent. Increase depth soaked in for the rate of 6 liters per hour in slope of 2% with compared to 0, 12.5 percent and the slope of 5%, was 25 percent. Also the increase for depth in the rate of 9 liters per hour respectively was 17 and 35 percent. Increase area in for the rate of 6 liters per hour in slope of 2% with compared to a 0, 24 percent and for slope 5%, was 56 percent and for flow rate of 9 liters per hour the increase for area, respectively was 28 and 45 percent.