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w o I-' N SECTION 2 CONCLUSIONS The salinity control cost-effectiveness associated with each alternative improvement is the basis for determining the formu- lation of an implementation policy. Studies reported in the technical literature indicate that the salinity damages in the Lower Colorado River Basin range from $150 to $350 per metric ton per year when extended to the Grand Valley. Local benefits to the project such as increased crop yields, reduced irrigation system maintenance costs, increased land values and other factors were not evaluated as part of this report and are not included in the cost-effectiveness of the various alternatives. In terms of dollars per unit of annual salt load reduction achieved, the most cost-effective measures were: 1) Concrete slip form or low head PVC plastic conduit lining of laterals. The two methods are almost equal in cost-effectiveness and can reduce salinity at substantially less cost than the $150/metric ton value. Concrete slip form linings offer the advantages of easier and less frequent maintenance than pipelines, and they are more acceptable to 10cal irrigation. Pipelines, on the other hand, are ea~ier and more rapidly installed and can be instal lId by the farmer as part of his matching requirements. 2) Use of high-head PVC pipe or concrete pipe is not a cost-effective alternative to concrete linings or low- head PVC and should be discouraged. Attendant problems with the use of low-head pipe can be overcome by giving particular attention to design and installation specifications. 3) Field head ditch lining by concrete slip form or gated pipe have comparable cost-effectiveness values, and while costing more than twice as much as lateral linings to remove a unit of salinity, they still cost consid- erably less than the $150/metric ton value. 4) Automation of irrigation systems through automated cut-back surface irrigation, sprinkler or trickle irrigation are somewhat more costly than the 14