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I i ,.--1 It') ,::; ~ 8 ...1 ~._.', ~.~ Spills and Crop Surface Total Irri- Seepage fro Irri- Runoff & Water gated Canals & Farm gation Deep Per- Canal Dvrtd. ATea Laterals Delivery Use colation (Ac.Ft. ) (Ac. ) (Percent of Total Water Diverted) Government Highline Canal 272,000 21,600 43 5'T 20 3'T Mesa Canal 21,000 1,000 13 8" 13 74 Mainline Canal 96,000 10,400 30 Independent Ranchmen 29,000 2,000 19 Improved water management is needed throughout the conveyance, distribu- tion, application, and return systems. Total system emphasis should be placed on diverting the amount of water needed for good system manage- ment, soil leaching, cultural practices, and unavoidable seepage and spillage losses. Because the source of salt pickup i3 from the under- lying shale formation and alluvial acquifer, overall 3ystem emphasis should be placed on reducing deep percolation and maintaining positive control over return flows to eliminate mixing with th," ITll>l'e saline ground water. Within this overall system approach the improvement 0:' laterals, on-- farm irrigation systems, drainage and cultural practices can playa significant role. An estimated 55 percent of the salt pickup frGITl the irrigated area is attributed to seepage and runoff from farm ""plication of irrigation water. Another 20 percent is attributed to St".,"ige from lateral canals and 25 percent is from canal seepage and spi:U. The degree of contr~l over seepage losses from off-farm conveyance and return flow systems and from on-farm systems is being studied. Lined canals and surface drainage ditches could be utilized throughout the off-farm systems; whereas on-farm, the water has to be applied to the land thereby providing opportunity for some deep percolation and salt piCkup even under high management practices. The principles that must be applied in securing a high farm irrigation efficiency involve, (1) installing lined ditches or pipelines; (2) installing and using proper control structures and measuring devices; (3) using the irrigation system best adapted to the soils and crops grown; (4) utilizing soils information in design and layout of irrigation and dra:lnage systems, and (5) applying the proper amount of water at the proper -eime to meet crop consumpt:lve use plus cultural practice requirements.