فصلنامه علوم و مهندسی آبیاری
سال سی و هفتم شماره 2 (تابستان 1393)

Already many studies have been done on the mechanism of scour around hydraulic structure especially bridges and methods for control or reduction of scour around them have been investigated and evaluated. In the field of scour around bridges, researches are more focus on scour of piers in compare with abutment. While the review of available information on the bridge required cost, the major problems are related to abutment. There fore most costs has spent in this part. One of the methods used to reduction of scour is collar. Collar is the flat plate with small thickness that can be installed around the piers or abutment. In this research 93 set of experiments are performed to find the effect of different dimensions of symmetrical and unsymmetrical collars on reduction of scour around bridge abutment. Results show that increasing dimensions of both collars will increase the efficiency of performance. Comparing of both collars indicated, when the upstream width of collar was larger than its downstream width, its performance will be better than the symmetrical collar with uniform area. The influences of installing elevation of symmetrical collars were also investigated. The results show that the collars installed bellow the bed level have less scour in compare with the one installed on the bed or above the bed.

Hydraulic conductivity coefficient of saturated soil as one of its important physical properties indicates water movement in soil. However Guelph permeameter method is very simple, it has a robust theoretical fundamental. The main difficalty of the Guelph method is the double depth experiments which causes negative or irrational results in some of Kfs values because of its heterogeneous equations This difficalty can be resolved by single depth analyses of Guelph equation set. This research is based upon the results of single and multiple depth analysis of Guelph method in comparison to inverted auger hole method at three different depths. Hydraulic conductivity depth variation was assessed by both inverted auger hole and Guelph permeameter methods. The experiments were performed in 30 holes at three different depths of 60, 90 and 120 centimeters and simultaneously the samplings were done at the holes for exploration experiments. The experimental results show that Guelphpermeameter analyses estimates three times at 60 centimeter depth and five times at 90 and 120 centimeters depth less than the results got by inverted auger hole method. Laplace analysis gets higher values and the results made by basic regression analysis of Richards have the least variations and were close to the two depth analysis. The variation of hydraulic conductivity had a decreasing trend with depths This lands. But, this variation was not constant and its gradient decreases through depth.

Natural disturbances as well as man-made activities may cause an increase in sediment supply to rivers. Rivers naturally react to these changes to reach a new balance between imposed conditions. This accordance always lasted until the new dynamic equilibrium regains. The objective of this experimental study is to show the most remarkable features of the morphological responses of alluvial sand-bed channels reacting to changes in sediment supply. The observed results of this research indicate that for a constant rate of sediment concentration, the increase in flow discharge may be followed by channel section increasing. Also, channel widening trend with flow and sediment supply is steeper than no supply condition while increasing in sediment concentration increases the rate of change of widening. It was concluded that the stable channel width is greater with sediment supply than that of no supply conditions.

Variability on soil properties along a furrow and through a growth season causes the variability in infiltration rate and eventually leads to the variability on irrigation efficiencies. The aim of this study is to find if infiltration rate variability along a furrow affects irrigation efficiencies, i.e., Distribution Uniformity (DU), Application efficiency (Ea), Deep Percolation Ratio (DPR) and Tail Water Ratio (TWR), and how does the infiltration change spatially and temporally through a growth season. Soil had sandy clay loam texture. To achieve the goal of this study, two furrows with 140 m length and 1.83 m width were selected in Amir Kabir unit by Product Company in spring and summer Evaluation measurements were made in six furrows with 140 m length and 1.83 m width, grouped in two sets of three furrows each. The middle furrow in each set was used to conduct measurements and the other used as buffers. In the first group (uniform assumption) irrigation performances were calculated assuming uniform soil infiltration properties along the furrow, but the middle furrow of the second group (variable assumption) was divided to four sections each of which was 35 m and infiltration was calculated for each section separately, to calculate irrigation performances accounting for infiltration variability along the furrow. Also irrigation performances were simulated by both above mentioned assumptions. Then calculated irrigation performances were compared with performances simulated by the model, through growth season. Results indicated that if (CVf0) along a furrow is considered in estimating irrigation performances, DU will change significantly in compare to other performances. In which applying (CVf0=0.28), Du decreased 33% from uniform to variable assumption. But, the reduction of Ea was %6. DPR increased 26% from uniform to variable assumption, and TWR showed no changes by the change of the coefficient of variation of final infiltration.

In this research study the effect of different widths of baffles, different distances of baffles rows and bed slopes on structure's energy dissipation was investigated using the physical models of baffled apron drops with 3 different widths (7.5, 11.25 and 15cm), and 3 different row spaces (15, 22.5 and 30cm), and three bed slopes of drop (21.8, 25.6 and 35 degrees). In total a number of 120 experiments were carried out with different combinations of baffles size and spaces, bed slope and different discharges (15, 20, 25 and 30lit/s). The measured energy losses show that increasing of baffle width and row space increases the energy loss. Also the bed slopes of 25.6° and 35° have the maximum and the minimum energy losses, respectively. According to these experiments the model with the largest width and row space on the 25.6° bed slope has the maximum energy dissipation, when compares with the other considered models.

Maroon irrigation and drainage network is located in the south east of Khuzestan province of Iran where the most regions the soils are chalky. In this research, the very specimens were gathered in the destroyed canal locations of existing irrigation network. Then, the various engineering tests were performed to determine of the physical, chemical and mechanical properties of the soil samples. The results showed that often destruction have occurred due to poor geotechnical condition of embankment such as swelling and dissolving of gypsum soils. In this research, the lime was used to rehabilitation of problematic soils which the content of lime in per cubic meter was 50, 100 and 200 kg. The consolidation tests were performed in order to investigate of mechanical properties of clay–gypsum soils. Findings showed that all contents have a significantly effect on decreasing the rate of soil consolidation. So that the calculations showed that at the maximum and minimum cases, the consolidation coefficient decreases to 50 and 4 times for 100 kg content of lime respectively. Moreover, findings showed that the 50% time of consolidation in the first loading, increases to 26 times rather that natural soil of zone for 50 and 100 kg content of lime. In addition, the results showed that the compression index 180 times decreased for 50 kg content of lime. While, the swelling index in rehabilitated samples were smaller than the natural soils also. For 50 kg content of lime, this index decreased to about 7 times.

Today, the drought and increasing water demand faced groundwater sources to challenge. Hence the need of the optimized water sources management has indicated its specific importance. This study has been implemented in order to manage the aquifer exploitation of the Nourabad plain in the drought conditions and this has been done by the finite differentiation modeling. To provide the conceptual model of the plain the geological log, observation and exploration wells, geological aspects, and the well’s hydrograph were used and after that, the model was provided. Then, the aquifer’s condition for October 2012 to October 2014 was predicted. The plain prediction hydrograph indicates the decrease of the groundwater level (-1.55m) for two next years. The model implementation in drought conditions shows that in these conditions the groundwater level decreases with the average of (-2.05m) which with the 20 % decrease of the discharge of the exploitation wells in these conditions this amount decreases to (-1.3m) and the aquifer balance improves with the average of 3.5 million cubic meters.

Stilling basins of sudden expansion are one of the energy dissipater structures which can dissipate most of the kinetin energy of the flow through hydraulic jump. In this structure the sequent depth ratio is less and the jump length is more than in classical jump. Since the roughening on the stilling bed can reduce both sequent depth ratio and jump length and its effect have not been investigated before, this study was conducted. In this study many tests are conducted in a relatively large flume size of 80 centimeter wide and 12 meter length. The sudden expansion ratio was 0.33 and tests were conducted for Froude numbers in the range of 2-10. The final results of this study show that for roughened bed sudden expansion stilling basin, the sequent depth ratio is 53 percent and the jump length was found to be 25 lower than in classical jump.

Agriculture development and improvement of soil and water resources productivity mainly depends on irrigation efficiency and reduction of water losses. This research was conducted in Borougen, Khanmirza and Shahrekord plain during 2010 growing season in order to evaluate the furrow irrigation systems. Evaluation of furrow irrigation systems were carried out in Potato fields in Borujen and maize fields in Khanmirza and Shahrekord plains. According to the results, application, conveyance, adequacy and overall irrigation efficiencies of Borujen plain were calculated 49.27, 83.65, 98.22 and 41.53 in percent, respectively. Such values for Khanmirza plain were 55.41, 77.11, 60.2 and 41.58 percent and those of Shahrekord plain were, 61.41, 88.43, 84.24, 54.67 percent, respectively. The results show that the application and adequacy efficiencies of furrow irrigation systems in these plains are acceptable. The overall irrigation efficiency was low mainly due to conveyance efficiency. Lining the transmission canals, using the standard structures and using of gated pipes, instead of traditional methods especially in furrow irrigation, is recommended and can be useful for improving distribution efficiency on farm.

Behaviors of cohesive sediments are influenced by many physicochemical properties. In this study in order to investigate salinity effects on time variation of suspended cohesive sediment concentration some experimental tests were conducted in an annular flume. Sediment samples were composed 63.2% of clay, 36.1 %of silt and 0.7% of sand. Velocity and shear stress profiles were measured by ADV velocimeter. Duration for each experiment was 360 minutes and the equilibrium condition was occurred in ranging of 40 min to 2 hours, for different tests. The results showed that different level of salinity has similar effect on flocculation of cohesive sediments. In a higher value of shear stress (i.e. 0.593 N/m2) the salinity hadn’t significant effect on reaching of suspended cohesive sediment to an equilibrium condition, but in a lower value of shear stress (i.e. 0.299 N/m2) the salinity had more significant effect. The results also showed that in flocculation processes of cohesive sediments shear stress was an effective parameter comparing to salinity.

Most processes of soil and water in the field occur in unsaturated conditions.In the field, It’s possible to estimate soil hydraulic properties by measurement of soil water content and soil water pressure head in different times, using inverse method. In the other hand, it’s difficult, time consuming and costly to measuring soil water content and water pressure head simultaneously. So, in this paper, the possibility of predicting soil hydraulic properties by measurement of soil water content or water pressure head separately were studied. To do this job, ESHPIM2, an inversion approach computer model, has been used. In this model, soil hydraulic parameters are optimized to reach the minimum value of objective function (Summation of squared differences between measured and predicted soil water content or water pressure head) using genetic algorithm. Soil hydraulic parameters of four soil series at Agricultural College of Shiraz University were studied in three cases. In the first case, the ESHPIM2 model with the objective function based on measuring the soil water pressure head and in the second case, the ESHPIM2 model with the objective function based on measuring the soil water content are used. Moreover, in the third case, soil hydraulic parameters are estimated by measuring soil water content and soil water pressure simultaneously. The results show that soil hydraulic parameters are predicted more appropriately by measuring soil water pressure head than soil water content in studied soils by inverse method using ESHPIM2 model.

Shock waves are often occurring during passage of supercritical flow in the non-prismatic channels. In the present study, values of height and instantaneous velocities were measured in various points of shock waves observed in two contractions with fixed convergence ratio and convergence angles of 7.6 and 21.3 degrees for four Froude Numbers (models 1 and 2). RNGk-ε and RSM turbulence models were used for 3-D simulation. The average relative errors of wave profile calculation for Fr1=7.0 using the mentioned turbulence models were 1.82% and 1.06% for the model 1, 3.46% and 2.67% for the model 2, respectively. Also, wave velocity values were 2.35% and 1.44% for the model 1, 5.75% and 3.23% for the model 2, respectively. The results showed that the RSM model performed slightly better than RNGk-ε model in simulating of shock waves.