study of design discharge for pressurized irrigation systems based on probability analysis

a design discharge is an important issue in the design process of pressurized irrigation networks. underestimating the desing discharge affect, the required pressure and offtake discharge, increase the cost of the network. because of the lack of a standard and reliable method for this propuse, usually different approches are used by designers. the network fails to provide the required flow rate and pressure if the design discharge is understimated, while overestimating, it influences the network cost drastically. accordingly, many studies were accomplished and some models were proposed for this purpose, which determine the design discharge based in users’ freedom in choosing irrigation periods. therefore, the currently available models usually overestimate the discharges, which increase the cost of the irrigation network ad the pumping station. in this study, based on probability analysis a method for discharge estimation was proposed which determined the design discharge that satisfies the demand variations. however, it restricts the users’ freedom in selecting the irrigation time to some extend. a classical case was used to evaluate the model results. in this case the users were considered free in determining the irrigation time. the model provide satisfactory results compared to the traditional models, however, its advantage is that it accept rational limitation in order to present more economical design.