R. Moazenzadeh; B. Ghahraman; K. Davary; A.A. Khoshnood Yazdi
Abstract
Soil moisture retention curve (SMRC) is an important soil property which expresses reaction between matric potential and moisture of soil. Direct measurement of soil matric potential and moisture is labour- and time-consuming. In order to prevail this problem, indirect methods are used for SMRC prediction. ...
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Soil moisture retention curve (SMRC) is an important soil property which expresses reaction between matric potential and moisture of soil. Direct measurement of soil matric potential and moisture is labour- and time-consuming. In order to prevail this problem, indirect methods are used for SMRC prediction. Pedotransfer functions (PTFs) are one of these indirect methods. This study was carried out to evaluate three internal pedotransfer functions, first and second models of Ghorbani and Homaee (1381) and Sepaskhah and Bondar (2002) derived in Iran, to predict SMRC in some Iranian soils. Also we tried to develop new different PTFs with better performance using the available information. Therefore 42 soil samples with spatial distribution from northern region of Iran, Amol, Babol and Karaj were selected and divided in Loam (20 samples) and Clay Loam (22 samples) texture classes. In evaluation of all existing PTFs, all 42 soil samples, and in developing new PTFs, 36 soil samples were used. The remaining six samples (three samples in each texture class) were used for validation of the new developed PTFs. In evaluation of the existing PTFs, results showed that the first and second models of Ghorbani and Homaee had alike and appropriate prediction of moisture in whole range of matric potential, whereas Sepaskhah and Bondar did not show an appropriate prediction. By the way, none of these PTFS had noticeable preference in specific texture classes in comparison with the others. New developed PTFS were highly significant (p
M. Sadeghi; B. Ghahraman; K. Davary
Abstract
Abstract
In recent years, many researchers have attempted to estimate the soil hydraulic functions (e.g. soil moisture characteristics curve, and hydraulic conductivity function) using particle-size distribution (PSD) curve. In these studies, an accurate mathematical representation of PSD is required ...
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Abstract
In recent years, many researchers have attempted to estimate the soil hydraulic functions (e.g. soil moisture characteristics curve, and hydraulic conductivity function) using particle-size distribution (PSD) curve. In these studies, an accurate mathematical representation of PSD is required for fitting the observed data. So far, some mathematical models were developed with different limitations. The goodness of fit is directly related to the number of the model parameters. However, estimating the parameters for higher-parameter models which have no mathematical or physical significance is a problem. Among the current models, 2-parameter Log-normal distribution model with mathematical significant parameters has been considered as a basis for many studies. In this study, it is indicated that the 2-parameter Log-normal distribution model can not be very accurate for representation of the PSD for all of soil textural classes. As an alternative, 2-parameter Gamma distribution model is proposed for more accurate representation of the PSD that its two parameters also are mathematical significant and readily computable. These two models have been compared in fitting the observed PSD data of 461 soil samples from UNSODA soil database. Gamma distribution model indicated a pronounced improvement in representation of the PSD. Based on Coefficient of determination (R2), in 362 samples and based on RMSE, in 323 samples, Gamma distribution model showed a better representation of the PSD than Log-normal. To evaluate the significance of the difference between two models, a t-test was performed. The results showed that, at confidence level of 1%, the R2-values of the Gamma model are significantly greater than those of Log-normal model. Also, at confidence level of 5%, a significant difference between the RMSE-values of two models was shown. Therefore, 2-parameter Gamma distribution model is judged to be better than 2-parameter Log-normal model for representation of PSD.
Key words: Particle-size distribution (PSD), Log-normal distribution, Gamma distribution, UNSODA
M. Khayami; Sh. Danesh; S.R. Khodshenas; K. Davary
Abstract
Abstract
In this research the thermal stratification of the water in the Torogh Dam Basin and the resulted changes in its quality with respect to temperature, salinity and dissolved oxygen was investigated using the Dynamic Reservoir Simulation Model. The results indicated that in wet years such as ...
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Abstract
In this research the thermal stratification of the water in the Torogh Dam Basin and the resulted changes in its quality with respect to temperature, salinity and dissolved oxygen was investigated using the Dynamic Reservoir Simulation Model. The results indicated that in wet years such as 1998, when the average annual precipitation and the resulted inflows to the basin is higher than its long-term average, the water level in the basin reaches above 50 m. Under such conditions, thermal stratification starts from mid-spring and lasts to the end of summer, and establishes through the total depth of the basin. Consequently, considerable changes in water quality occur through the depth. However in dry years such as year 2000, the water level in the basin diminishes considerably (16 to 20m in depth) and thermal stratification either does not establish or if establishes, it is incomplete, starts much earlier and persists for much shorter periods of time. On the basis of the model’s results, the differences observed in the average temperatures of the surface and deep layers of the basin during the spring and summer seasons of 1998 were 10◦C and 11◦C, respectively while in the spring of 2002, the observed difference was only 1.5◦C. The results of the study also showed concurrent occurrence of salinity stratification with thermal stratification which results in increase in salinity with increase in depth. The difference between salt concentration of the surface and deep water layers of the basin was observed to be 43 mg/lit in the spring of 1998 and 10 mg/lit for the summer of the same year. In regard to the dissolved oxygen concentration, the simulation results showed a difference in the range of 0 to 9 mg/lit between the surface and deep water layers. With the start of stratification, oxygen concentration decreases gradually with depth., such that in July the lowest 10m layer of the basin becomes completely anaerobic, providing conditions for production of undesired odors, tastes and color. During the period of 1998 to 2004 (period of data analysis and simulation run), the water quality of the basin was observed to be uniform in autumn and winter months indicating a complete mixing condition in the basin.
Key Words: Water Quality Models, Thermal Stratification, Water Salinity, Dissolved Oxygen, Dam’s Basin.
H. Shamkoeian; B. Ghahraman; K. Davary; M. Sarmad
Abstract
Abstract
Natural disasters threatening and endangering human communities has resulted in the study and research of such disasters through the related sciences and present methods of forecasting their behavior with time and place and also from a qualification and quantity viewpoint. To this end, numerous ...
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Abstract
Natural disasters threatening and endangering human communities has resulted in the study and research of such disasters through the related sciences and present methods of forecasting their behavior with time and place and also from a qualification and quantity viewpoint. To this end, numerous methods for the determination of the maximum flood in various return period has been made available which can be refered to as flood frequency analysis methods. One of these methods is the regional flood frequency analysis in which instead of using the data from a single station, it considers the data and characteristics of a group of similar stations. In the case under the research this method uses L-Moments and Index Flood in North, Razavi and South Khorasan water basins and MATLAB software. Maximum annual flood statistics were used from 68 Hydrometric stations with minimum and maximum statistical periods of 6 and 39 years. Using Cluster analysis the region under study was divided to 7 partitions. Discordance test has conducted and only one station in region C was found as discordance station. Because of knowing the homogeneity of the regions, the parameter of Kappa distribution were estimated and with using the simulation method of Monte Carlo with 500 times, the homogeneity measure was tested in 7 regions. Using homogeneity test all regions was found homogen. Using goodness-of-fit measure z and Kolmogrove-Smirnov the Log normal 3 parameters distribution were selected for two regions of A and B, GEV for C, Generalized Pareto for D and E, Generalized logistic for F and Pearson III for G. Besides, GEV distribution was found appropriate for all of the regions, only their parameters are different in any regions. For estimating of index flood a logarithmic model has found for each region with 4 variables of area, height, average slop and form factor. Using of these models, the index flood can be estimated in each region and it can be used for standardize the statistics of maximum flood values.
Keywords: Regional flood frequency analysis; L-Moments; Index Flood; Cluster analysis; Khorasan
B. Ghahraman; K. Davary; A.R. Astaraei; M. Majidi; S. Tamassoki
Abstract
Abstract
Irrigation planning and management requires continious monitoring and measurements of soil moisture content. Application of Gypsum blockes (GB) are common in soil moisture measurements. GB readings are subjected to its geometry and soil solution concentration. This study was carried on 90 ...
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Abstract
Irrigation planning and management requires continious monitoring and measurements of soil moisture content. Application of Gypsum blockes (GB) are common in soil moisture measurements. GB readings are subjected to its geometry and soil solution concentration. This study was carried on 90 GB in research greenhouse of Faculty Agricultural, Ferdowsi University of Mashhad. At the begining, all GB were calibrated in distilled water. Further, readings were collected in four solutions of 2, 6, 10 and 18 dS/m salinity. Then, three soil media with different textures (sandy loam, loam, clay loam) at 5 levels of salinity rate (trace, 2, 6, 10 and 18 dS/m of saturated extract) were studied, as 15 treatments. GB readings, at different soil moisture contant, were made by ELE-5910A. For each treatment, readings vs. soil moistures were plotted. These curves were compared with that of standard (same soil texture with trace salinity). Finally, some corrector functions were developed to eliminate the salinity effects from GB readings.
Key words: Gypsum block, Salinity, Salinity effect correction, electrolytic concentration of soil solution
S.R. Khodshenas; B. Ghahraman; K. Davary; H. Nazerian
Abstract
Abstract
Sediment load-discharge data of hydrometric stations in the north of Great Khorasan province were studied. Twenty nine stations were selected and the mean annual sediment yield was computed using sediment rating curves. The total annual sediment yield for these catchments (61.5 to 16800 km2) ...
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Abstract
Sediment load-discharge data of hydrometric stations in the north of Great Khorasan province were studied. Twenty nine stations were selected and the mean annual sediment yield was computed using sediment rating curves. The total annual sediment yield for these catchments (61.5 to 16800 km2) varied between 4.8 to 19500 M ton/year and the specific sediment yield varied between 62 to about 4000 ton/year/km2. Due to large variations in the total and specific sediment yield, 29 selected catchments were divided in two groups: 17 large catchments (area>500 km2) and 12 smaller ones (area
A. Emami; B. Ghahraman; K. Davary; M. Hashemi nia; S. Tamassoki
Abstract
Abstract
Deficit irrigation is a method to promote water use efficiency (WUE) in a farm under water shortage conditions, however, the consequences is that yield per area decreases. To determine production functions for three cotton cultivars, an experiment was conducted during 1381 growing season on ...
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Abstract
Deficit irrigation is a method to promote water use efficiency (WUE) in a farm under water shortage conditions, however, the consequences is that yield per area decreases. To determine production functions for three cotton cultivars, an experiment was conducted during 1381 growing season on a silty clay loam soil in HashemAbad Agricultural Research Station in Gorgan. This study was performed using a split-plot design with 3 replications on three cotton cultivars. A line-source sprinkler irrigation system was used with 54 plots in each side of the line (3cultivars* 6treatments* 3replications). To estimate root zone water deficit, climatic data and cotton crop coefficients during the growing season were used. For each cultivar second order equations were derived to relate yield and applied water. However, linear relationships were established to relate yield and evapotranspiration. In addition, based on Doorenbos and Kassam formula yield response factors were found to be 1.02, 0.96 and 1.01 for Sahel, Say Ocra, and 818-312 cultivars, respectively. Such yield response factors can be used to optimize irrigation planning under water shortage conditions.
Key words: water production function, yield response factor, line source irrigation, Gorgan
M. Sadeghi; B. Ghahraman; K. Davary
Abstract
Abstract
The rate and duration of downward flow during redistribution process determines the effective soil water storage at any time. This property is vitally important, particularly in arid and semi-arid regions where plants must rely for long periods of time on the remained soil water of the root ...
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Abstract
The rate and duration of downward flow during redistribution process determines the effective soil water storage at any time. This property is vitally important, particularly in arid and semi-arid regions where plants must rely for long periods of time on the remained soil water of the root zone. In this study a new approach for scaling of soil moisture redistribution process based on the Green-Ampt redistribution theory was developed. Using the scaled results of numerical solution of the general flow (Richards’ equation), an empirical equation for predicting the soil moisture profile during redistribution process was derived. An important advantage of the empirical equation is adopting the effect of hysteresis in soil retention curve on redistribution process. To validate the proposed empirical equation, its outputs were compared with those of Richards’ solution for 11 soil textural classes (from sand to clay). The comparison showed negligible amount of error for all of the 11 soil textural classes and for a wide range of initial conditions. However, some deviations from results of Richards’ solution were observed under high initial infiltrated water depth and/or high initial soil water content. Therefore, a model which can estimate the soil moisture content at any depth and time during redistribution phase with accuracy of numerical models and simplicity in application of analytical models was obtained.
Key words: Scaling, Soil moisture profile, Redistribution phase, Green and Ampt equation, Richards’ equation
