فصلنامه مهندسی منابع آب
پیاپی 10 (پاییز 1390)

In this paper, a numerical model has been presented to investigate the scour and deposition in channel confluences. Finite-volume method, which is an acceptable and effective approach, has been used to discretize the governing equations. The effect of turbulence has been considered in the model via an eddy-viscosity approach. The continuity and momentum equations and the sediment continuity equation have been coupled by a fully-coupled method. It is assumed that the flow is two-dimensional and only the bed load transport has been considered in the model. The sediment transport formula of Grass has been utilized to estimate the rate of bed load transport. To evaluate the numerical flux at the cell interface, the method of HLLC has been employed. A 90o channel confluence has been simulated by the model and the results have been compared with experimental data, which show satisfactory agreement. The model can successfully predict the scour hole, the formation of bar at mainstream channel after the confluence and the penetration of scour hole into the tributary channel. To accomplish a quantitative comparison, the maximum scour depth, maximum height of the bar and maximum penetration of scour hole into tributary channel, have been compared with those of experiments

Accurate and suitable design of spillways as major parts of dams is very important in the stability and safety of dams. Hydraulic characteristics of flow are determined by benefiting from physical models, however, they are expensive and time-consuming to construct. These difficulties maybe overcome by the development of mathematical models using the numerical methods. The potential flow model is one of the mathematical flow models which used in this research. In this model, flow is assumed incompressible, non- viscous and irrotational. Flow characteristics over an ogee spillway were analyzed using the finite element method to develop a mathematical model. The results of numerical method compared with experimental values and the amount of error estimated. A good agreement was reached between the theoretical and experimental values

Subsurface travel time is, in fact, the response time of the subsurface flow of complex hillslopes corresponding to rainfall infiltration, used to estimate the subsurface hydrograph of watersheds. Due to Dunne-Black mechanism, it is the subsurface flow which is conducive to determination of surface flow as well as runoff mechanism. In this work, we studied the influence of factors such as soil depth, soil hydraulic conductivity, shape and geometry of complex hillslopes (plan shape and profile curvature) on subsurface flow travel time. It is seen that lower soil depth or less hydraulic conductivity leads to a more quickly saturation, whereby, the travel time decreases. Also, decline in travel time emerges with increasing rate of convergence of the hillslopes, and vice versa. Moreover, increase in travel time happens with a curvature deformation of hillslopes from concavity towards convexity. Taking the shape and geometry of hillslopes as between half and twice, may help grow their travel time

The most important factors about rainfall are its frequency, intensity and amount. The main goal of this study was estimating the time distribution of rainfall in some climatic regions of Iran. There are different methods in estimating time distribution of rainfall. Two of these are the Huff and Pilgrim methods in which real rainfall data are used to estimate rainfall temporal patterns. As the first step statistical analysis was performed to estimate the PDF curves. Then the minimum range for storm selection in each station was investigated. The results showed that the optimum rainfall range in each of the selected stations (Bam, Tehran, Shiraz and Gorgan) were 7.0, 10.5, 12.0 and 10.0 mm, respectively. Then the rainfall temporal pattern of the four climatic regions of Iran including sever arid (Bam), arid (Shiraz), semi- arid (Tehran) and semi humid (Gorgan) was identified applying the Huff and Pilgrim methods. Dimensionless curve fitting of the temporal patterns of the rainfall of each statin was also investigated. Comparison of the patterns of the two selected methods with the collected data indicated that the Huff method was superior to the Pilgrim method results

Rising concentration of greenhouse gases will affect both the amount and characteristics of agricultural products. Decreasing the crop's growing period, increasing the evapo-transpirations and variation in nutritional characteristics of plants are the outcomes of global warming. Currently, the general circulation models (GCMs), are widely used to anticipate future fluctuation and trend in temperature and precipitation. Since these models are in coarse scale, they may not represent the precise features of local characteristics and therefore, needed to be downscaled to be compatible with local attributes and reality. The present study was motivated to evaluate temperature and precipitation conditions in Fars province for the period 2011-2040. For achieving this goal, two distinct statistical downscaling approaches were used to downscale the outputs of the ECHAM5 model. For two scenarios of this model including 20C3M and 1PTO2X, the outputs were downscaled for the period 1951-2005. As a reasonable relationship between observed data and the simulated time series derived for this period, the obtained regression models were applied to downscale the data for the period of 2011-2040. According to the given results by 20C3M scenario, Fars province fasces 0.55OC increase in temperature by 2040. This increase was estimated to be around 2.35 OC using 1PTO2X scenario. Also precipitation in 20C3M and 1PTO2X scenarios, respectively, will decrease around 14 percent and increase about 19 percent for next 30-year

In this study, the relationships between deficit irrigation with optimal cropping pattern was studied. This technique has been used widely, especially in regions facing water deficit. Since Fasa City of Fars Province is placed in warm climate and affected by water stress more than other climatic regions of the province, this city was selected as the study area. A nonlinear programming model with an aim to maximize net revenue was used subject to the yield response functions to water and other limitations. The results showed that there is the possibility of increasing income of representative farm by applying full irrigation instead of deficit irrigation in the current pattern and reducing cultivation to use the available water. In addition, in drought conditions, depending on the severity of the crisis and water restrictions, how to decide strategy for irrigation and land is different to the way if the level of water supply reduce to more than half of the current available water, the deficit irrigation strategy is the best options for optimal use of land and minimum available water. In this regard, farmer can reduce his gross margin reduction to a minimum by adopting yield reduction for some crops and changes in their cropping pattern in accordance with their marginal revenue of each unit of water consumption

A research was done to investigate the effect of the supplementary irrigation in different wheat phonological steps in rain fed condition on biomass, wheat yields, KW, nitrogen, wheat protein with three times experimental treatment and one control for a tillage year in Abhar’s fields in 1388. The experimental treatments were: I1) one time irrigation at heading stage (500 m3/ha); I2) two times irrigation at heading and grain stages (Total 500m3/ha); I3) one time irrigation at grain stage (500 m3/ha); I4) the control (without irrigation). The results of the research showed that the effect of supplementary irrigation on biomass, yield, KW at 1% level and on nitrogen and seed protein percent at 5% level was significant so that the maximum amount of aforementioned qualities of supplementary irrigation at the beginning of heading state were biomass 6.888, yield 2.442ton/ha, KW 42.32 ton/ha, N 1.977%, protein 11.53%. The control (without irrigation) illustrated the minimum amount. All of these qualities in these groups were placed in “a” class. The treatment in supplementary irrigation was in better condition than the control group. According to the obtained results of the study through the investigation of qualitative and quantitative features, with one time irrigation can increase 30 percent of harvest in the beginning of heading stage that is when the negative effects of dryness stress in rain fed condition start

Water and nitrogen are two of the most important factors that affect plant growth and yield. Nitrogen is also one of the important nutrients. Extra use of chemical fertilizer in recent decade, especially nitrogen fertilizer, causes soil, water and environment nitrate pollution. This study was carried out to investigate the effects of different water regimes (40, 60, 80, 100 and 120 percent of water requirement) and different amounts of nitrogen (60, 120 and 180 kg/ha) as well as their interaction on nitrate gathering in root environment of tomato (variety of Early Urbana) as an important food production in the world. The experiment was performed in research farm of agriculture faculty of Tehran University (semi-arid area) in a clay–loam soil, using a split plot design with three replications (irrigation treatments as main plots and different amount of nitrogen as sub plots). The results obtained from statistical analysis indicated that the different treatments of irrigation and nitrogen as well as their interactions have significant effect (in 1 percent level) on nitrate gathering in soil. The maximum nitrate gathering in soil obtained in 40% water regime with 180 kg/ha nitrogen. The minimum nitrate gathering in soil occurred in 120% water regime (complete irrigation) with 60 kg/ha nitrogen. Also different tomato yield measurement was done. Finally, by considering our conditions of the test place and tomato variety, it is recommended to use 100% water requirement with 120kgN/ha for optimization of nitrate gathering in soil. An important result of this study is that less nitrogen fertilizer should be used in deficit irrigation situation