Designing Furrow-Irrigation Systems for Improved Seasonal Performance

Abstract

ABSTRACT Atraditional approach to furrow irrigation system design was evaluated to determine its effect on the seasonal performance of a typical farmer-managed system. Results indicate the need for an improved design approach that better accounts for seasonal changes in field conditions. Recently, attention has been focused on the need for more wise and efficient use of water on the farm. Irrigated agriculture, in particular, is faced with the dilemma of using a diminishing supply of water to meet an increasing demand for food and farm income. Much of the responsibility to meet this challenge falls upon the agricultural engineering profession. Traditional methods of system design and operation need to be evaluated and new methods developed that will help to strengthen irrigated agriculture as an economically justifiable, productive, and socially responsible endeavor. Surface irrigation (used here to refer to surface flooding by gravity flow) is the method used on most of the world's irrigated land (Goldberg, 1974). Improving irrigated agriculture on a worldwide scale must address the problems related to surface irrigation. Many surface irrigation systems ideally can supply crop water needs at field application efficiencies of 70 to 85 percent (Willardson, 1972; and Merriam and Keller, 1978). Studies conducted around the world indicate typical efficiencies to be only 40 to 50 percent (Bos and Nugteren, 1974; Clyma and Ali, 1977; Kruse and Heermann, 1977; Clyma et al., 1975). Solving the problems of inefficient surface irrigation practices requires the use of good system design. A good irrigation system design is the product of a reliable design procedure and the appropriate application of that procedure. The design procedure should be based on a model that adequately predicts system hydraulics and performance. It is used to select the values of system and operational (or management) variables that constitute the right conditions for achieving a specified level of performance. If the system is built and given to the operator without instructions as to how the system should be operated, the system cannot be expected to function to produce the desired results. Traditionally, design procedures for surface irrigation have specified operational variables based on field conditions during the period of peak consumptive use of the crop (USDA, 1979; Corey and Hart, 1974; Withers and Vipond, 1974). Thus, the design does not account for the change in field conditions during a cropping season. In the case of the SCS method and various other empirical methods of furrow irrigation system design, operational variables are explicitly selected in the design process. However, when system and operational variables are specified and implemented based upon conditions existing in the field at one point in time, the resulting system performance may be poor. How do furrow intake rates and required water application depths vary on a typical farmer managed furrow irrigation system? What system performance would result if each irrigation, as scheduled by the farmer, were operated with the flow rate and inflow time designed for the peak capacity period? If seasonal variations in field conditions are considered in design, what changes in the system or its operation might be needed to achieve acceptable performance through the season? This study was conducted to address these questions.