sections of pipeline has often shown that systems Installed 

 without filter material and backfilled with soil were 

 "silted in" or were grossly restricted by crop roots. 

 Similar conditions have also been reported for systems which 

 have been improperly vented. Vented systems are those which 

 have vertical sections of pipeline installed at intersec- 

 tions of laterals and the mainline. Cases have been 

 reported where tile system laterals without vents develop a 

 vacuum condition that hastens silting, root growth, and the 

 formation of bacterial sludge. All tile systems monitored 

 during this investigation had sand or gravel filter 

 materials; only a few of the systems monitored were provided 

 with vents . 



Installation . The drainage pipelines sire usually buried at 

 a predetermined depth and gradient from 5 to 9 feet below 

 the surface of the soil. The specific depth at which pipe- 

 lines are installed, which is believed by some Soil Conser- 

 vation Service engineers to be quite critical, vatries from 

 one strea to another, depending upon soil conditions (texture, 

 stratigraphy, and topography). 



Most of the tile systems in the Gustine-Mendota area have 

 been installed at an average depth of about 7 feet . In the 

 Byron-Westley area, many tile systems have been installed at 

 9-foot depths . One tile contractor claims that deeper 

 drains allow more distance between laterals because of 

 greater drawdown, which permits a lower water table and a 

 more consistent drainage between irrigations . 



Tiling operations may differ greatly depending on the type 

 of conduit materials being used. During the installation of 

 concrete pipeline, constant mechanical pressure is applied 

 to the segmented pipe by tiling machines to minimize deforma- 

 tion of the pipe during backfilling and during later subsi- 

 dence. Some tiling machines employ the use of a television 

 camera to monitor the placement of conduit (center of photo- 

 graph. Figure 4). 



Plastic conduit is now installed with the same basic 

 machinery used to install concrete conduit . The use of 

 hydraulic equipment has been eliminated because alignment is 

 not as critical a factor in the installation of plastic pipe 

 as in the installation of concrete pipe. Therefore, instal- 

 lation time is decreased. New methods of plastic pipeline 

 installation are being developed wherein long strings of 

 conduit are fed into preformed tunnels made by a large 

 subsoiling device. 



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