JWSS - Journal of Water and Soil Science

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A computer model (SprinklerMod) was developed to simulate hydraulics of sprinkler irrigation systems. The objective of this paper is to describe mathematical background of this model for simulating pressures and discharges of sprinklers along the laterals. The model is capable of designing two types of laterals: laterals with fixed sprinklers and laterals with portable sprinklers. The model shows the simulation results in the forms of tables and graphs. Laterals with one or two diameters on uniform or non-uniform slopes can be designed. The model provides graphical presentation of percentage of sprinkler pressure variations for different lateral inside diameters. The Hazen- Williams equation was used for the calculation of friction losses. The required input parameters for lateral simulation are lateral type, desired sprinkler operating discharge and pressure head, spacing between sprinklers, distance of first sprinkler from lateral inlet, number of sprinklers operating on the lateral, riser height, Hazen- Williams pipe friction coefficient and lateral longitudinal slope or field elevations at each of the sprinklers on the lateral. Laterals are simulated such that average sprinkler pressures and discharges become equal to the values requested by the designer. Iterative procedures were implemented to simulate sprinkler pressures and discharges on laterals and the Newton- Raphson iterative method was used for calculating pressure of each of the sprinklers on the laterals with portable sprinklers. In order to evaluate the model, some example results of the model were compared with classical design results. Since there is no formula for the calculation of the required lateral inlet pressure in classical design of laterals with portable sprinklers in the scientific references, a new formula was developed. Averages of absolute percentage of variations of lateral inlet pressures for laterals with fixed sprinklers and with one or two-size diameters ranged from 0.3 to 0.7 percent, respectively. This value for laterals with portable sprinklers was 0.1 percent. 

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Global solar radiation (Rs( on a horizontal surface in the estimation of evapotranspiration of plants and hydrology studies is an important factor. Average daily global solar radiation on a horizontal surface was estimated by artificial neural networks (ANNs) and five empirical models including FAO (No.56), Hargreaves-Samani, Mahmood-Hubard, Bahel and Annandale. The weather data was selected from Karaj, Shiraz, and Ramsar weather stations, which have arid, semi arid and very humid climates (based on De Martonne classification). Daily solar radiation was measured at the three sites selected. The ANN, with actual duration of sunshine and maximum possible duration of sunshine as input parameters, generated daily solar radiation estimates with highest level of accuracy among all models tested. Rs estimates by ANNs with only temperature indices as input and by Hargreaves-Samani, Annandale and Mahmood-Hubard, which are all temperature oriented models, had lower accuracy at all three sites. In contrast, ANNs with actual duration of sunshine and maximum possible sunshine hours as inputs in Karaj, Shiraz and Ramsar station with root mean square error (RMSE) of 2.08, 1.85 and 2.05 Mj m-2 day-1 respectively were the best models. After ANNs, FAO-56 model which is based on sunshine hours produced results closer to the measured values. Rs estimates by ANNs with only temperature indices as input and by Hargreaves-Samani, Annandale and Mahmood-Hubard which are all temperature oriented models, had lower accuracy at all the three sites. These models are not appropriate for estimating daily global solar radiation.