DESIGN AND ECONOMIC ANALYSIS OF PRESSURIZED IRRIGATION SYSTEMS

Abstract

Nile river and groundwater are the main sources of water supply in Egypt. Agriculture consumes the bulk of the available water supply. Agriculture is an important sector of the Egyptian economy, and represents about 20% ofGDP, 40% of total civilian employment, and 12% of merchandise export earnings. The dearth of agriculture land (0.13 fed/capitafarid tlie rapid population growth (2.8 %) in Egypt have made land reclamation a high prioritY activity for the Government of Egypt. The primary constraint to agricultural-growth-is the:very limited availabilitY of water (880 3 - . -- ·-·· - . m /capita/yr). Therefore, it is necessary to optimize the use of the national water resources to save water for these new lands and upgrowing water needs. A considerable effort is being made to redm::e- water-losses at the field level. The government prohibits surface irrigation on the sandy soils in New Lands areas, in order to reduce water use. Pressurized imgafion systems are well-known irrigation methods for agricultural purposes and widely use(i"to satisfy crop water requirements with minimum wastage. Although, farmennrre offered low interest loans for irrigation equipment and repayable over 20 years, pressul:ized irrigation ethods are used only on 13 % ofthe irrigated area in Egypt. In reality these savings may be only achieved where the resources to ensure accurate design,-insfalhition and operation of irrigation system equipments are available. · · · . There are many pressurized irrigation systems and configurations. Therefore, it is necessary to have an efficient procedure for selecting the most promising, adaptable system or systems and their configurations for each specific site for meeting development goals and satisfy the field criteria. Then, it is necessary to know what must be done to select from the many candidates the 'best type and configuration'. Insightful selection of the system type and layout that best meet the goals and objectives of an irrigated agricultural development is of primary importance in the overall design process. There is not a blueprint for the design process, but all the available in literature are suggestions. These suggestions help in the search for an image of the system and the engineering solutions to be achieved. Also, pressurized system design is somewhat of an iterative procedure in which a successive adjustment to the design may be made to correct the deficiency that may be shown up in checking the system design. The purpose of the optimal system is to develop assemblages of individual components that will fit together to make a workable and optimized system for a specific site. Therefore, it is important to computerize the appropriate kinds of techniques for the common systems to ensure accurate design. The main goal of this study is to develop· a manual method to select the set of most promising, adaptable system types and their configurations that may satisfy the field and design criteria. The selection procedure focus on economic and physical parameter associated with the different system types and configurations. Then, the preselected systems and configurations could be designed in detail by the developed model for all possible conditions of application rates, outlets and lateral spacings, outlet types, alignments (strips or subunits' sizes), laterals' directions, and pipe specifications. The design techniques use numerical solutions rather than requiring graphical and interpolation from charts, as in the past. After completing the design, a full economic analysis for each system is made to make the comparisons and final selection. This economic analysis is completed on an annualized cost basis. The costs of a system include; installation, energy, maintenance, labor, and water and land costs (if any). The returns of the project are computed for the grown crops. The final selection that best meets the goal based on the economic analysis, determines the system that either returns the greatest net benefits and/or provides the best return on investment. This study covers the common pressurized irrigation systems for agricultural crop production (solid-set, move-stop, center-pivot, and line-source and point-source drip systems). Published farms' designs were used for the model validation and evaluation. The evaluation is concerned with studying the existing systems and comparing it with the model design to assess the benefits of the developed model. The outcome of this work is, basically, a practical computer software, DPIS, that was built to fulfill the needs of irrigation agencies and engineers involved in the field of irrigation systems. Also, a trial to develop a new simple method was made to identify the set of most promising, adaptable system types and configurations that could potentially meet the desired economic goal in a quick manner. The model consists of the main program and twenty-two subroutines. It was coded in FORTRAN language as it is a practical language, with input provided by user created ASCII text files. The executable model was produced by using FTN77/486 Version 2.51 compiler (University of Salford, 1991). The model was developed to be executed by IBM- PC or IBM compatibles under DOS.