نشریه پژوهش های حفاظت آب و خاک
سال شانزدهم شماره 3 (پاییز 1388)

A detailed description of the behavior of cohesive fine-grained sediments is a very complicated task. Simulation of cohesive sediment movement has been successfully treated in the past using the macroscopic properties of the water-sediment system. In this study, a 1-Dimensional equation of cohesive sediment has been proposed for deposition term and dispersion coefficient of mass transfer equation. This equation has been solved by Control Volume method and calibrated with laboratory data. The tests have been done in a flume with 0.3m diameter, the slope 0.00008, discharge between 3~5.7 liter per second and the concentration of 4~8 gram per liter. The model shows that the dispersion coefficient is a function of Reynolds number and rate of velocity to shear velocity.

Submerged vanes are plane structures placed on river bed with an angle to the approach flow which cause secondary flow. They can be used to reduce sediment entrainment to water intake structures. Studying the effect of submerged vanes on the strength of secondary flow and possible sediment diversion near the bed are the goals of this paper. The simulation includes two cases, one in which submerged vanes are placed in front of the intake and the other for no vanes. Therefore, three-dimensional Reynolds-Averaged Navier-Stokes equations for turbulent flow in front of intake in 180° bend was solved numerically. The CFD solver FLUENT was used to solve equations and the results of numerical models were compared with available experimental data. Investigations showed that the secondary flow around vanes was at the same direction of main secondary flow. Therefore by intensifying, it causes more deviation of near bed streamlines toward the inner bank and surface streamlines toward the outer bank. Furthermore, it causes more water diversion with less amount of sediment. The separation zone at main channel is widening near the surface of inner bank and the vanes prevent the formation of the saddle stagnation zone and reverse flow toward the intake in main channel, so that less sediment enter into the intake.

Life in Esfahan province is dependent on Zayandeh Rud. Therefore, sustaining the quality and quantity of Zayandeh Rud water is of much importance. The first step for adopting correct management decisions is to have continuous awareness of water quality and quantity, temporal changes, and spatial variations and, eventually, specification of main source of pollution. One of the models being used worldwide in such studies is SWAT. The first step in using this king of models is to prove their ability to simulate hydrologic cycle in a the watershed. The main goal of this study was to assess SWAT performance in Zayandeh Rud watershed in order to simulate river flow rate values. Model Calibration and validation were done using average daily flow in four stations named Ghal’e Shahrokh, Zayandeh Rud Dam, Pole Kole and Varzaneh. Observed and simulated values were compared by statistics including R2, NS and COE values to evaluate the model predictions against the observed values. The results of these values for flows at four stations for calibration process ranged between 60.2 to 80.1, 59.4 to 79.0 and 72.6 to 82.0, respectively. According to previous studies and the quality of the data used in this study, these values seem acceptable. The values for validation period were 60.4 to 72.0, 60.1 to 69.1 and 64.7 to 70.8, respectively. Among these four stations, measured and simulated flows at Pole Kole and Ghal’e Shahrokh matched well and weak, respectively. In general, the results showed that SWAT could be a proper tool for simulating the flow rate values of the river.

The release rate of non-exchangeable K (NEK) plays a significant role in supplying necessary K for plants, particularly in soils containing K bearing minerals. Information about NEK release rate in Golestan soils is limited. Kinetics of non-exchangeable potassium release, therefore is necessary in management and optimum use of soil resources. Laboratory experiment was conducted on NEK release of saturated soil sample by calcium from 2 to 1844 (h) duration in 12 dominant soil series of Golestan province. Different soils indicated various responses in successive extractions. The rate of K released was lower in CaCl2 than organic acid. The mean of the potassium release by oxalic acid was 2.33 times higher than potassium release by CaCl2. K release was faster in earlier periods in all soils followed with a lower release rate. The Elovich and Parabolic diffusion equations described well the NEK release kinetics by organic acid and power, first order and Elovich equations were suitable to describe the NEK release kinetics for CaCl2, based on their highest coefficient of determination, and their lowest value of the standard error of the estimate. Therefore, NEK release kinetics of soils were found to be influenced by diffusion, indicating that NEK release rate was controlled by K diffusion out of the mineral interlayer.

Soil hydraulic conductivity is a crucial parameter in modeling flow process in soils and in decision making on water management issues. In this research by using 41 soil samples with 11 different soil textures covering sandy, loam, and clay from the UNSODA database, an investigation was conducted on the applicability of specific liquid-vapor interfacial area around the soil particles concept for predicting soil hydraulic conductivity function fitted by van Genuchten model. The results showed that the specific liquid-vapor interfacial area (Aws) meniscus around the soil particles does not monotonically increase as suction increases for all soils. Soil moisture corresponding to the maximum Aws is not equal to residual water content but its value depends on soil characteristic curve. The results showed that between FC and PWP, variable viscosity of water around soil particles did not have a marked effect on unsaturated hydraulic conductivity computations. Variable weight of water in the soil, as compared with constant water weight, had a marked effect on the results.

Estimating runoff from ungauged catchments has been an important subject for experts in planning, development and operation of various water resources projects. Focus of this study was on application and evaluation of Clark instantaneous unit hydrograph in predicting direct runoff hydrograph of Jafar-Abad watershed, Golestan Province. Isochron map and time-area histogram were extracted using GIS technique and IUH of study area was also simulated by Clark IUH model. The direct runoff hydrograph was simulated for six storm events. Time of concentration and storage coefficient were considered for sensitivity analysis of Clark IUH model. The efficiency of Clark IUH model in predicting direct runoff hydrographs was evaluated by Nash-Sutcliffe, relative error of peak discharge, time to peak and volume, and root mean square error criteria. The results showed that Clark IUH model just predicted time to peak and peak discharge with good accuracy. Sensitivity analysis of input parameters (storage coefficient and time of concentration) indicated that model outputs were strongly affected by value of calculated time of concentration for watershed.

The recent research es indicate that irrigating with mean values of crop reference evapotranspiration (ETo) level will only provide about 50% of plant water demand. In such cases, irrigation level may not provide optimum water for plant and plant may face with water stress or water excess. With respect to the impact of ETo estimation methods, irrigation schedule period, and optimal probability level on plant water requirement, accurate evaluation of each case seems necessary to be studied. Using climatologies (1977-2006) of daily meteorological data, the daily ETo is estimated by means of five commonly used evapotranspiration methods (Blaney-Criddle, Penman, Penman-FAO24, Penman-Montieth and Penman-Montieth FAO-56). To evaluate the influence of each ETo models on actual plant water requirement, the daily evapotranspiration values were determined for wheat (ETc) during the period of study (1977-2006). The dates of starting and ending of maximum water requirement (MWR) were determined by means of moving average approach. Using the extracted dates, mean daily ETo values were plotted for different periods from one day to 30-days of MWR and different probability levels. The results indicated that if we apply the mean daily ETc values in designing irrigation systems (7-day period), at 50% probability level and Blaney-Criddle, Penman-Montieth FAO-56, Penman, Penman-FAO24 and Penman-Montieth ET0 methods, the water capacity of irrigation system will respectively be 12%, 10%, 18%, 14%, and 15% less than the corresponding values of 75% probability level. The statistical analysis of daily (ETc) data also showed that by increasing the MWR period, the estimated mean daily evapotranspiration would decrease. In addition, for a specific period, using higher probability level causes more crop water requirement values.

Groynes are structures constructed at an angle to the flow in order to deflect the flowing water away from critical zones. They serve to maintain a desirable channel for the purpose of flood control, improved navigation and erosion control. One of the most important problems for designers is the estimation of the maximum local scour depth in the vicinity of groynes. Due to contraction of streamlines, the local shear stress increases and the scouring around groynes will be developed. Underestimation of the maximum scour depth may lead to collapse. Most of the Previous studies were performed on the straight groynes and little information exists on local scouring around L-head groynes. Usually in practical case, the series of groynes (three groynes) are used for protecting the region subjected to scouring. In this study, the experiments were carried out with three different types of grain size, four various distances between groynes and three flow discharge in clear water condition. The results showed that the maximum depth of scour occurred in vicinity of first groyne and by increasing the grain size, the maximum depth of scour decreased. Also in a specific bed grain size, by increasing the distance between groynes, the descending trend of maximum depth of scour was observed especially in greater froude number.

The purpose of this study was to, investigate the changing trend of precipitation in Hamedan province by considering its temporal and spatial variability, and determining regions where these changes were at their maximum for long-term water resource management. In this research, the annual rainfall was collected at 23 different meteorological stations situated throughout Hamedan Province. The collected data were analyzed to determine the probable climate change during period from 1982 to 2006 (24 years), based on the Mann-Kendall method. The results showed that Aghajanboulaghi, Touserkan and Ghahavand had a significant increasing trend and the others did not show any trend. The sudden variations of annual rainfall presented at the stations illustrated fluctuations of climate of the region. These different results indicate the spatial irregular rainfall variability of the region. Therefore, more complementary investigation is necessary. Using more stations and longer rainfall data and application of the method based on the temperature characteristics of region could be effective for climate change identification of the region.