Author
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Ayars, James |
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Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 10/1/1997 Publication Date: N/A Citation: N/A Interpretive Summary: This chapter summarizes studies related to managing irrigation systems in the presence of shallow ground water and to designing systems which include management of shallow ground water. Factors affecting the design and management include soil salinity, crop salt tolerance, leaching, ground water quality, depth to ground water. New criteria proposed for the design of subsurface drainage systems included reducing the depth of drain installation and permitting the water table to come closer to the soil surface. Studies demonstrated that it was possible to regulate the depth of the water table under an irrigated field using valves on the laterals and weirs on the submain of a subsurface drainage system. Regulation of the water table resulted in reduced irrigation and increased use of water from the water table by a crop. Scheduling irrigation using a crop coefficient which accounted for crop water use, increased the water consumption by a cotton crop from the water table and reduced the required irrigation application. Application of the methods proposed in this chapter will result in improved irrigation efficiency, reduced demand for water by agriculture, and reduced drainage flows. Technical Abstract: In the past, irrigation and drainage systems were designed as separate and distinct entities and as a system with two interactive components. The irrigation system was designed and a management established for the system based on the soils, cropping pattern, and water quality. A value of deep percolation, estimated from the irrigation system design and management, was used to design the subsurface drainage system. The drainage design assumed that all the drainage water was discharged and the mid-point water table height reached the maximum value by the end of the irrigation season. No interactive management was assumed to occur between the drainage and irrigation system. Irrigation management assumed that deep percolation was lost from the system, and the crop was not using water from the shallow groundwater. Ideally integrated management of irrigation and drainage systems will start with the design of new irrigation and drainage systems. If this is not possible, modifications to existing irrigation and drainage systems and management techniques will have to be developed. The objectives of this chapter are to review the factors considered in the design and operation of an integrated irrigation and drainage system; to provide examples of new procedures for the design and operation of drainage systems; and to summarize results of field studies using new concepts. |
