Journal of Irrigation Sciences and Engineering
Year:2011 | Volume:34 | Issue:1|Papers Count:13

Runoff is one of the important parameters in hydrologic cycle and water resources management of basins. In this research, Remote Sensing (RS) and Geographic Information System (GIS) techniques were used for runoff potential estimation in Khosro-Abad watershed, located in the Hamedan region. In this regard, first, the various thematic maps layers such as Digital Elevation Model (DEM), land use and land cover, slope, soil hydrologic groups and sub-basins location were prepared. Then, based on the prepared thematic layers, a weighting method was developed to runoff potential estimation of the area. To spatial runoff variability investigating, the classifieds estimated runoff potential (low, medium, high and extreme classes) was evaluated using the SCS method. The SCS method was estimated based on three previous soil moisture conditions (dry, normal and wet). The results showed that the weighting method is enable to runoff potential estimation. This method can be proposed for runoff potential estimation especially in the cases that the needed data were missed. The results also showed that with the previous soil moisture increasing (from dry to wet conditions), the CN increase about 30%.

Salt and drought stress is one of the main problems of Agricultural production in many parts of the world, especially in arid and semi-arid area. Therefore, this study was conducted to investigate the effect of both stresses (individually and simultaneously) on yield and yield component of tomato (Super Strain B) in order to program irrigation management in Karaj. The experiment was carried out as Factorial on base of complete randomized design with three replicates including two factors: Salinity and irrigation water. Salinity and irrigation water factors consisted of four levels (S1=0.7, S2=4, S3=8 and S4=12 dS/m) and three levels (W1=100, W2=75 and W3=50 percent of water requirement), respectively. The soil texture was sandy loam. The results of this study showed that the yield production reduced by increasing salinity and drought stresses. The maximum yield (240.7 g) was corresponded to W1S1 treatment and the minimum yield (48.58 g) was corresponded to W3S4 treatment. Salinity, deficit irrigation and their interaction had significant effect (p<0.01) on dry weight, root length and tomato evapotranspiration, but they did not have any significant effect on the number of fruits. The combined impact of salinity and deficit irrigation did not have any significant effect on plant height and dry weigh. W1S1 and W3S4 treatments had maximum and minimum growth respectively during the growing season.

The amount of daily rainfall for a solitary wet day (Class 0) is normally less than the rainfall for a wet day that is enclosed by wet days on either side (Class 2). The same characteristics hold true for the case of the first or last day of wet spells (Class 1) and there fore the rainfall here is found to be smaller than the Class 2 rainfall. In many regions, there exist large differences between these rainfall classes. In this study, the daily rainfall data from 5 rain gauge stations in the north and northwest of Iran are classified to classes 0, 1 and 2 according to the number of adjoining wet days. To examine the impact of adjoining wet days on the distribution of rainfall amounts, different distributions were tested with 3 different data sets: (1) all rainfall classes grouped together, (2) solitary wet days fitted separately from other wet days, and finally (3) all rainfall classes separately. The results showed that the models which treat the rainfall classes separately are a better fit for all the 5 stations. The Akaike Information Criterion (AIC) values are significantly reduced as the rainfall data are split into rainfall classes. Also, among 4 different distributions considered (Gamma, Lognormal, Mixed Exponential and Weibul), mixed exponential distribution in most cases and lognormal distribution in one case showed better performances.

Vertical and horizontal extension of cities and growing trend of industrial activities in them has resulted in wide changes on ground physical properties, released energy, air pollution, temperature and as a result change of local climate in metropolises. Cities are often warmer than their environment. This phenomenon is determined by the difference between cities' energy and their environment's energy. Synoptic climatology data of Ahvaz and Dezfool in a 44- year period was surveyed and studied to specify these changes in Ahvaz metropolis. The results showed that annual average minimum temperature of Ahwaz in this period has a total increasing trend of 3.375oC and (0.077oC/lyr) yearly, whereas the corresponding parameter was without any changes in Dezfool. Temperature increasing trend in Ahwaz in comparison with Dezfool as indicated by the results which is resulted by the heat island effect in Ahwaz and the lack of development of Dezfool with time. The greatest increase rate of Ahwaz average minimum temperature is 4.14oC and (0.094oC/lyr) yearly in Azar monthly in this period and the smallest is 2.07oC and (0.047oC/lyr) yearly in Esfand monthly. Usually the extent and extension of the city are known as the most important factors in the severity of heat island effect, and population growth is among the serious factors which cause the increase of its severity and finally result in the change of local climate of metropolis. Population is considered as parameter which is explanatory of city's size. In this study, a relationship has been developed for the average intensity of heat island effect in Ahwaz and the logarithm of population.

There are many conditions in open channel flows where the steady flow of water passes through a cluster of vertical cylinders. These vertical cylinders may represent piers of bridge, jetty or vegetation on the floodplain of rivers. Where flow passes from a cylinder, periodic vortex shedding occurs downstream from the cylinder. In this study the wooden circular cylinders with different diameters were screwed into the bed of the flume at different setting up patterns and spacing. The waves were produced from the periodic forces created by the vortex shedding from the cylinders. The transverse waves with maximum amplitude appear, when natural frequency of water waves equals to frequency of vortex shedding. The major purpose of this study is to compute of Strouhal Number in flow of water passes through vertical cylinders. The values of Strouhal Numbers calculated from Fitz-Hugh's graphs and Lienhard's graphs were not equal to the measured Strouhal Numbers. Thus dimensional analysis is used for this proposition. To find a proper equation for Strouhal Number in water, the effective parameters on Strouhal Number are recognized and analyzed. Finally new equations are proposed for determination of Strouhal Number in open channels flow.

Estimation of flood due to rainfall has been always a main subject in hydrology science. According to the importance of unit hydrograph for river flood forecasting and design of hydraulic structures and being not sufficient data at hydrometry stations of Khuzestan watershed, necessity of using artificial unit hydro graph for estimating of flood in rivers with no data is obvious. Moreover, because of the importance of rainfall in producing runoff, evaluation of the effect of loss models in production of water surface is important. In this research, two different models were evaluated: Initial- continues loss and SCS loss. So two direct runoff models include SCS and Snyder were applied for simulation of flood hydrograph due to excess rainfall. Therefore with 15 series rainfall- runoff data of Abolabbas watershed, HEC-HMS model was applied to calibrate and validate selective models. Three statistical indexes (mean relative error, root mean square error and coefficient of correlation) are applied to estimate the errors. The results of mean relative error of flow peak and time of flood peak in evaluation models show that the best estimation of flow peak and time of flood peak obtain in SCS loss model with Snyder unit hydro graph and in initial- continues loss model. Comparison of the average values of root mean square error show that minimum value of RMSE is related to SCS loss model with Snyder unit hydrograph and in initial- continues loss with SCS unit hydrograph. This show that these models the best results among other models for their ability in separation of excess rainfall. Finally, the occurrences that are simulated by SCS unit hydro graph and SCS loss models have the best correlation with actual conditions. Therefore these methods are able to accurately simulate the flood extent within a poorly gauged basin.

Emitter is the key component in drip irrigation system; it is designed to let out the water in pipe to drop into the soil slowly and uniformly. Uniformity of emitter discharge is dependent on some parameters such as water temperature. Temperature variations influence water properties, especially viscosity. This may be a significant factor affecting flow through emitters. Field and laboratory study on this object is time-consuming and expensive. Computational fluid dynamics provides a promising tool to help in study of flow behavior of water passing through the channel of labyrinth. In this study, the flow in labyrinth channels was simulated by using the method of Computational Fluid Dynamics (CFD) to calculate temperature effect on emitter discharge for three sample of one type emitter. For this purpose, emitter discharge for the six pressures: 2, 4, 6.1, 9.2, 12.25 and 16.33 mH20 and six temperature: 5, 15, 20, 25, 35, 45 and 55oC was simulated. Samples were destroyed and longitudinal and latitudinal cuttings for the samples were obtained and sizes of the channels were calculated by photography with Scanning Electronic Microscope (SEM). To simulate pressures and temperature effect on rate of discharge using CFD, laminar flow model and turbulence model was applied. Verification of Results showed that the simulated data had a good agreement with the experimental data and also emitter discharge is insensitive to temperature variations and CFD provides a promising tool to reduce the cost and time of study on emitters.

Recent studies regarding dam failure show that most dam failures are due to unsuitable conditions of foundation and insufficiencies depth of bed rock. Seepage, uplift pressure and piping phenomenon under the foundation of dam cause disastrous failures in dams that exit gradient is an important criterion for safety against piping. Therefore, finding methods will be to reduce seepage flow, exit gradient and uplift pressure will be very important. In this study, ANSYS software is employed for analysis and modeling water flow in foundation dam. This study determines the flow characteristics (flow rate and exit gradient) and quantities of uplift pressure in an impervious dam with sheet pile. Extensive analyses were performed for different condition, including dam width and sheet pile depth. The results have been presented in simple charts. These simple charts allow designer to predict seepage problems and perform an optimum design in short time.

Effect of cutoff curtain on phreiatic seepage line position and seepage discharge in earth dams has a great importance. Therefore in this research, a mathematical model has been developed in which general equation of fluid flow in nonuniform and anisotropic soil was discretized by finite volume method. The position of phreiatic line is determined with iteration and deformed mesh method. As a verify model, experimental results of earth dam model in a seepage tank was used. Calculated and measured position of phreiatic line and seepage discharge for different condition of upstream water head shows high accuracy of model. Effect of different position and length of cutoff curtain on seepage discharge and phreiatic line position were investigated after model verification. The results showed maximum seepage discharge exists when cutoff curtain is constructed under center of dam bottom. By moving the cutoff curtain location from center of bottom toward toe and hill of dam seepage discharge can be reduces even to 20%. When cutoff curtain location moves from hill toward toe, phreiatic seepage line moves to higher situation. Saturated mass volume of dam will increase to 49% when cutoff curtain location moves from middle of dam bottom toward toe of dam. On the other hand if cutoff curtain is constructed in the hill of dam, saturated mass volume decrease only 17.9%. Comparison to no cutoff condition, by increasing cutoff curtain length from 0 to 90% of permeable layer thickness seepage discharge reduces up to 22.8%, but if length of cutoff curtain is equal to total thickness of permeable layer seepage discharge will reduce more than 99 percent.

Determination of the volume and depth of scour hole around a bridge pier placed on a river bed has been considered as an important issue from the view point of stability. Hence, broad investigations are carrying out in order to control and reduce the local scour. The current paper with the goal of reduction in local scour has investigated the slotted pier and double-pier close to each other. Different widths of slots in a single cylindrical pier are investigated under clear-water flows in an experimental flume. The depth, volume and iso-depth of scour hole in different models are examined. The results of experimental works have shown that in a slotted single pier extended below the bed level with w/D=0.3 (in which w is the width of slot and D is the pier diameter), the depth and volume of scour hole are reduced up to 72.5% and 83.8% respectively. In other slotted single- pier models with w/D=0.3 with the slot length limited to the bed level and 0.2 with the extended and limited slot to the bed level the depth of scour hole are reduced up to 58.1, 51.2 and 44.2% respectively. In pier groups, the depth of the normalized depth of scour ds/D at w/D=0, 0.25, 0.5, 0.75 and 1 are equal to 2.9, 2.5, 2.3, 2.2 and 2.0 respectively. Among the double- pier models it is said that at w/D=1 , depth and volume of scour hole in comparison to the single solid pier, 13.2 and 15.3% are reduced which shows the appropriate behavior of such models in reduction and control of the scour depth in comparison to the single solid pier.