Irrigation & Drainage Systems Engineering

Hydraulics of Linear-Move Sprinkler Irrigation Systems, II: Model Development

Abstract

Zerihun D and Sanchez CA

This manuscript presents a hydraulic simulation model for linear-move sprinkler irrigation laterals equipped with pressure reducing valves (prvs). The linear-move lateral considered here consists of a series of arched spans with a specified geometry and multiple outlet-ports. Lateral diameter, hydraulic resistance characteristics, field slope, spacing between outlets, and sprinkler hydraulic characteristics can be constant or variable along a lateral. Lowpressure sprinklers, or spray nozzles, coupled to pressure reducing valves are used in these laterals to achieve controlled application of irrigation water. Depending on their modes of operations, prvs can have a significant effect on lateral hydraulics. Thus, operating modes of prvs are defined and their effects on system hydraulics are described in a companion manuscript. The basic algorithms of the hydraulic computation functionality of the simulation model, presented here, are developed using computational techniques applicable to hydraulic manifolds. However, the algorithms developed as such are modified to account for the particular conditions that prvs impose on the hydraulics of a linear-move lateral. The iterative solution of the linear-move lateral hydraulic simulation problem (which typically involves multiple lateral-wide hydraulic computations) is formulated here as a one-dimensional optimization problem that seeks to minimize the error, between the computed lateral inlet head and the imposed inlet head, as a function of the distal-end nodal head. The current manuscript is part-two of a three-part article and it describes the formulation and numerical solution of the lateral hydraulic simulation problem. Part-one of the article focusses on specification of the lateral hydraulic simulation problem, statement of assumptions, and system description. Part-three presents results of model evaluation and explores potential applications of the model.