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<br />,tv <br />00 <br />'0 <br />t;\J <br /> <br /> <br />~ <br /> <br />SECTION 2 <br /> <br />CONCLUSIONS <br /> <br />Desalting is a very expensive but nevertheless feasible <br />salinity control alternative. Unit costs are inversely pro- <br />portional to plant capacity and feedwater salinity and pro- <br />portional to land, energy, and material prices. It appears a <br />reverse osmosis system having feedwater in the 7,000-10,000 <br />mg/~ range will offer the most cost-effective system for a <br />regional salinity management application. The capital costs <br />(l976 base) for such a system are approximately $320 for a 30 <br />year removal of one metric ton annually. <br /> <br />Desalting cost estimates are affected by several site- <br />specific conditions like land costs, environmental concerns, <br />climatic conditions, energy availability, and labor. The supply <br />of feedwater and the removal and disposal of brines are also <br />serious considerations in desalting system designs. In the <br />Upper Colorado River Basin or others of a similar nature, these <br />factors would not significantly alter the unit cost noted above. <br /> <br />Because irrigated agriculture is a large contributor to <br />most western salinity problems, the feasibility of desalination <br />depends on the cost-effectiveness of improving irrigation <br />efficiency. The reduction of salinity concentrations in irri- <br />gation return flows is primarily a matter of minimizing the <br />subsurface component of the hydrology by lining conveyance <br />systems to reduce seepage, increase on-farm irrigation efficiency <br />to diminish deep percolation, and utilize field relief drainage <br />to intercept deep percolation. Desalting the return flows is <br />generally a more cost-effective alternative than relief drainage <br />and compares favorably with large canal linings in low seepage <br />areas, However, most on-farm improvements such as head ditch <br />linings, automation of surface irrigation, conversion to <br />sprinkler systems, or better water management practices (irri- <br />gation scheduling) have better cost-effectiveness characteristics <br />than desalting. Conversion to trickle irrigation and desalting <br />return flows have comparable cost-effectiveness. It should be <br />emphasized that the relative feasibilities of these technologies <br />are highly dependent on site specific factors and can change <br />measurably from location to location. <br /> <br />Salinity control strategies involve complex, constrained <br />and nonlinear mathematics when reduced to their most elemental <br /> <br />4 <br />