Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 10, 2010
Publication Date: N/A
Interpretive Summary: As the world’s population increases to 9 billion people by 2050 the demand for food from irrigated agriculture will increase from 35 to 40% of the total production. Subsurface drainage will be required if irrigation is to be sustained. This chapter discusses the need for drainage to insure a well aerated root zone, timely operation of agriculture and salinity profile that will sustain production. The steps required for the design from the determination of the need for drainage, to the preliminary field investigations and the steady state and transient design methodologies are discussed. The impact of subsurface drainage on water quality and the new criterion to restrict the depth of placement of the drains to minimize the environmental impact are highlighted. The importance of improved irrigation design and management to minimize the deep percolation losses was identified as the critical part of the design process. It is no longer acceptable for irrigation and drainage systems to be designed independently of each other. Future water management in irrigated agriculture will require an integrated approach to the design and operation of irrigation and drainage systems.
Technical Abstract: This chapter was written for publication in the 6th Edition of Irrigation being published by the Irrigation Association of the United States. The need for drainage is discussed and the implications for the design of irrigation systems are highlighted. It provides the outline of the steps needed to be considered for the design of a subsurface drainage system of irrigated agriculture. These include: determining the source of the excess causing the problem; identifying the area to be drained; conducting field studies to characterize soil conditions; characterizing the water flow; developing drainage criteria, and completing the design. Drainage provides a well aerated root zone, timeliness of operations and in irrigated agriculture manages salinity in the crop root zone. Salinity management is done traditionally by leaching, which is the application of excess water to move through the root zone and thus transport salt. To meet this requirement, the irrigation designer must provide the appropriate design and management plan for the soils and crops being irrigated. There are significant environmental impacts associated with drainage water discharge and the need to modify the drainage design criterion and to include active management of the drainage system is discussed. The critical message is that drainage is not the solution to poor irrigation system design and management. Irrigation system designs must include a well developed management plan that corresponds to the designed irrigation system.