مجله مهندسی آبیاری و آب ایران
پیاپی 8 (تابستان 1391)

Constructing stilling basins usually are expensive، so reduction of stilling dasins length is economically important. The dimensions of the stilling basin depend on the length and sequent depth of hydraulic jump. Therefore، increasing the energy loss in dam structure decreases the length and sequent depth of hydraulic jump and as a result reduces the stilling basin cost. Also in designing of diversion dam، in order to prevent the agricultural land flooding during the flood season، a smaller height of diversion dam is designed and this may produce many difficulties for upstream intake structures. In this research study a combination of two jets in ogee dam was used، in order to increase the energy loss along the dam structure and to reduce the hydraulic jump length and sequent depth. The laboratory models of ogee dams were designed and built based on the USBR standards with a designed slot near to the toe of the dam. In these experiments the directions of the flow out of the slot were 0، 45 and 90 degrees in respect to the horizontal line. The effect of six discharge ratios (discharge from the slot to the total discharge) for each angle was investigated on the hydraulic jump length and sequent depth. The Froude Number was measured 1. 5 to 4. 5. The results showed that the angle 45 degrees has the maximum effect on reducing the hydraulic jump length and sequent depth، with an average discharge ratio of 26% the hydraulic jump length being reduced about 50% in comparison with the classic jump. This structure is also able to increase the total discharge coefficient.

Soils due to different properties have a range of infiltration rates (IR). This study investigates the influence of soil properties on infiltration rate at the field conditions. Infiltration studies were conducted using double ring method (constant head of 5 cm) at 15 sites with 3 replications. The results showed that final IR ranged between 0. 8 – 34. 6 cm/h and the time required to achieve steady state IR varied from 20-80 min. The texture of soils had significant effect on IR. Increasing clay and silt percentages by 6 and 14. 4 times، final IR decreased 5. 1 and 38. 7 folds، respectively. Reversely، increasing 8 times in sand fraction، final IR increased 14. 8 times. Also، among soil chemical properties، lime had the most effect، which increasing 3. 6 times in lime، final IR decreased 10. 2 times. This result was attributed to lime particles size which is placed in clay and silt fractions. The results indicated the higher important role of physical characteristics، especially particle size distribution than the chemical properties in soil permeability. The findings of his study reveal the important role of lime in arid and semi arid regions.

The effect of suspended load on friction coefficient has been studied widely by different researchers، yet vast disagreement exists among them which call for further studies in this area. In this study، the effect of suspended load on flow friction coefficient on smooth and rigid beds was experimentally studied. The experimental setup that was used for this study، consists of a 0. 2m wide، 20. 4m long and 0. 3m deep flume، a water reservation tank and sediment mixture tank. A special sediment sampler has been developed for this study and the discharge was measured by using an orifice that was previously calibrated. The compiled data of this study indicated no impact to decrease friction coefficient. Also it is shown that the variation of the friction coefficient depends on particle Reynolds number. The obtained results was compared with that of other researchers results and which revealed that Parker-Coleman''s relationship could be considered as the most appropriate one for determining the effect of suspended load on flow friction coefficient.

This study fulfilled to assess the moisture in soil profile over the study period with LEACHM model and estimation of leaching، denitrification and nitrogen uptake with sugarcane. Irrigation treatments consisted of full irrigation (I1) and others were 85 (I2) and 70 (I3) percent of I1. Experimental fields irrigated with hydroflumes. Nitrogen application were concluded of 150 (N1)، 250 (N2) and 350 (N3) kg/ha. Moisture measured from Soil samples collected from field plots in 0. 3 m depth increments to 1. 2m on a periodic basis. LEACHM model Efficiency (Willmott''s index) to simulation soil moisture changed from 0. 78 to 0. 95 and best regression coefficient occurred in I2 treatment. Simulation of nitrogen losses and uptake indicated that Mean of highest and lowest of leaching was observed in I1 and I3 with 17 and 8 percent. These results showed with leaching and increase of irrigation had a close relationship. High and low rate of denitrification occurred in I1N3 and I1N1 treatment with 19 and 38 percent. Maximum rate of nitrate uptake with 63 and 56 percent in I2N1 and I1N1 and minimum rate with 35 and 37 percent was observed in I1N3 and I3N3 respectively، full irrigation showed the nitrate leached from root zone and couldn’t uptake by plant and deficit irrigation with composing the stress decreased the root uptake.

Accumulation of anions and cations in soil solution prevents growth of plant. The main problem in saline soils is related to soluble salts. Saline soils have a large amount of salts; therefore the leaching from these soils is important. This study was conducted to evaluate the movement of solutes using soil columns picked from Azizabad of Bam. Leaching experiments were conducted on columns of five soil textures (clay loam، loam، sandy clay loam، sandy loam، loam sandy). The soils were filled in columns to achieve uniform bulk density of 1. 5 g cm-3. The columns were leached with approximately 5 pore volumes (pv). Effluents from each leaching were collected for chemical analysis. Leachate samples were analyzed for soluble cations (Ca2+، Mg2+، Na+ and K+). After completion of the leaching the soil columns were split open and cut into 3 sections، each 10 cm. Soil samples at different column depths were analyzed for EC، Na+،Ca2+ and Mg+. The results showed using water in leaching experiments could reduce solutes concentration and it following saline soils and these soils do not need any amendant. Generally the effect of coarse textured soil on the ion movement is more than in the case of fine textured soil. The solute arrival in effluent solution is ahead when soil texture is coarse. The amount of clay plays an important role for retaining and ions removal from soil. The difference between the amounts of irrigation water needed for salinity removal depends on soil texture. The most common of such reactions is cation exchange.

Weirs and gates are frequently used as measuring devices because a simple stage-discharge relationship can be deduced. Weir and gate system is a plate that seated at end of canal and the flow current from over an under it. In this paper، the discharge relationship of Weir and gate system is deduced by a theoretical analysis، based on the application of the -theorem of the dimensional analysis، coupled with an experimental investigation carried out by using a laboratory flume.

Yet، the estimation of critical shear stress for cohesive sediment erosion as a function of degree of consolidation and elevation of exposed layer of the bed sediment is under consideration around the world. Sediment shear strength in the vicinity of the interface can be a good delegate of critical shear stress. Because one can relate this parameter to some parameters such as volumetric concentration and effective stress which are function of time and space and can be modeled analytically. Moreover one can measure the coefficients such as fractal Dimension، effective stress coefficient، Creep coefficient، lateral stress coefficient، internal friction angle and cohesion coefficient، using experimental techniques. Some of these coefficients are used to be measured by soil mechanical laboratorial experiment. However for measurinf of fractal dimension and effective stress coefficient، there is not any documented method. In this paper، an experimental method has been developed using a settling cylinder for bed sediments of Sefidrud Dam reservoir. Experimental results have shown that every fractal dimension has always been jointed with specific effective stress coefficient. Moreover the best value for fractal dimension is the mode of its frequency distribution. Therefore the best value for effective stress coefficient is its average between the pairs with the same selected fractal Dimension. In General، critical shear stress is very sensitive to fractal dimension and it has been shown that the less fractal dimension، the less rate of critical shear stress with respect to volumetric concentration.

AbstractOne of the usual methods for river banks protection is using Gabion groyne structures. A local scouring phenomenon is one of the important problems in hydraulic design of groynes. Due to constriction and downward flow، the scouring can occur around the groynes. In this investigation a laboratory movable bed flume with 18m length، 1. 5m width and 0. 8m depth was used. To study local scour near the head of unsubmerged Gabion groynes، the groynes were constructed perpendicular to the flume''s wall. Two shapes of groyne (straight and T shape)، two constriction ratios (20% and 30%) and four ratios of space to length (S/L)، were used with one constant bed material and one constant bed slope with three different discharge. Based on the experiment results، for straight S/L=3 and for T shape S/L=4 is recommended the suitable S/L ratios. Regarding the type and shape of groyne، T shape groyne indicated the least scouring and the scouring depth of Gabion groyne was less than of impermeable groyne.

The most common cause of embankments failures is erosion due to water flowing over tops of of them. Specifications and compaction effort used in construction of the embankments affect significantly in erosion rate during overtopping. The objective of this research is investigation the effect of clay percentage، compaction effort and water content on the erodibility of cohesive soils. The soils used consist of sand mixed with Bentonite in proportions varying from 10% to 20% by weight. Soil samples are compacted in the standard compaction mold at different water contents and compaction efforts، then they are tested by a closed conduit in varying discharges and obtain erosion parameters for each of them. The results indicate that the sample compacted at optimum water content creates a structure with the most resistant to erosion. The erodibility of samples compacted dry of optimum water content is less than samples compacted on the wet side of optimum، critical shear stress of wet side of compaction curves is minimum 1. 2 and maximum 1. 6 times dry side. The higher compaction effort at given water content in dry side increases critical shear stress and decreases erosion rate.