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[H11247 . CHAPTER IV IHPROVEHKNT AND EXTENSION Installation of Pipe and LininR Lining of project canals and laterals would improve the general appearance of the area, and would reduce conveyance losses, operation and maintenance costs, and the salinity of streams draining from the area. In areas of intensive use, particularly the residential areas, replacement of open canals and laterals with buried pipe is desirable to eliminate safety hazards and interference with other developments. Water conveyance losses are generally high and are known to be excessive in certain reaches of the canals and laterals. Little quantitative data is presently available, however, concerning the magnitude of the losses in individual reaches of tne system More definite information might show that losses in some reaches are sufficiently low that providing of pipe or lining could not be justi- fied from tbe standpoint of water savings or salinity reduction_ More detailed studies mignt also show a justification for realignment of reaches of canals and laterals or discontinuation of irrigation service to certain segments of the project with accompanying reduc- tions in lengths of the distribution systems. For purposes of this report, however, it has been planned that all existing canals and laterals would be lined or placed in pipe. . Present cost estimates are generally based on earth lining of all canals and laterals with capacities in excess of 100 c.f.s. and concrete lining of the smaller canals and laterals. Exceptions to these criteria include concrete lining of reaches of the larger canals and laterals having steep gradients, and placement of pipe in all reaches through residential or other highly developed areas. Combined lengths of canal and lateral reaches total 88 miles for earth lining, 425 miles for concrete lining, and 31 miles for pipe installation. Construction of the pipe and lining would also provide additional conveyance capacity in canal and lateral reaches that now restrict necessary deliveries. Minor Canal and Lateral Structures Deteriorated or obsolescent canal and lateral structures are replaced by the water users association when the structures are no longer operable, are in imminent danger of failure, or can otherwise be replaced as part of the regular maintenance program. Because of the great number of structures involved, it will require many years before they can be replaced under the maintenance program of the association. The number of structures that should be replaced under a Federally-financed improvement program would depend upon the timing of the improvement program and the condition of the structures at that time . 50