|Grismer, Mark - UC DAVIS|
|Guitjens, John - UNIVERSITY OF NEVADA RENO|
Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 17, 1996
Publication Date: N/A
Interpretive Summary: Drainage is an integral part of irrigated agriculture, however, with increased environmental awareness, the ability to discharge subsurface drainage water containing salt and trace elements is being severly restricted. These restrictions resulted in new methods being developed to integrate the management and design of irrigation and drainage systems. A new subsurface drainage system design procedure was proposed which uses the drainage water quality as one of the design criterion. In the proposed design procedure, the drain installation depth was reduced, the depth to the water table at the mid-point between the drains was reduced, and crop water use from shallow ground water was also included. These modifications resulted in a reduction in the calculated salinity of the drain water while maintaining a lateral spacing approximately equal to that calculated using the old methods. Adoption of this proposed procedure has the potential to result in reduced drainage flow and salt load being discharged into surface water. Since this was a theoretical study, the concepts still need to be thoroughly tested in the field.
Technical Abstract: In the past, irrigation and drainage systems were designed and managed as separate entities. As water supplies become scarce and environmental restrictions increase, there will be a demand for the integrated design and management of irrigation and drainage systems. This type of system will make optimum use of existing water supplies and should reduce the impact of return flow on the environment. Modifications in current drainage design practice are presented which will facilitate integrated management. Recommended modifications include changing the design minimum water table depth from 1.2 to 0.9 m and the depth of drains from 2.4 to 1.5 meters. These changes coupled with either improved irrigation management or incorporating crop water use from shallow ground water will result in approximately the same drain spacings as calculated using the USBR transient design procedure. Adopting the new drain depth criterion should result in less drain water and lower salt loads being discharged. These concepts were demonstrated with simulations using a drainage system designed for a cotton crop growing in the presence of shallow ground water.