criteria. However ^ the cost of construction still plays an 

 Important part In determining the final design. Many tile 

 systems are Installed In a piecemeal fashion. That is, 

 laterals are added whenever it is economically feasible for 

 a farmer to do so. 



In the San Joaquin Valley, two basic tile system designs are 

 generally used: (l) the "interceptor" type, which is a 

 single-line drain placed on the periphery of a field to 

 intercept or reduce lateral movement of water, and (2) the 

 "total relief" type, which consists of a large number of 

 closely spaced laterals (distances vsiry from 200 to 400 feet) 

 designed to alleviate existing high water table conditions 

 within an entire field. 

 These two types of tile 

 system layouts are illus- 

 trated in Figures 2 and 3. 

 Modifications of inter- 

 ceptor type drains have 

 led to the use of other 

 terms, such as "partial 

 relief", which refers to 

 single-line or interceptor 

 drains in which one or two 

 laterals are added to 

 alleviate specific high 

 water table conditions 

 within a field. Distances 

 between laterals in these 

 systems usually exceed 

 400 feet; 600- to 800-foot 

 distances are common. 



FIGURE 2 

 INTECEPTOR SYSTEM 



FIGURE 3 

 TOTAL RELIEF SYSTEM 



The term "perimeter interceptor" is applied to fields 

 surrounded by a single-line drain, several of which exist in 

 the area studied. 



Various design modifications have been made to adapt tile 

 systems to pstrticular drainage conditions or economic situa- 

 tions. Consequently, many systems cannot be adequately 

 described by the above terminology. 



Materials, Construction, and Installation 



The sustained performance of a tile system is governed to a 

 great degree by the type of materials used in construction 

 and the methods of Installation. Materials used in construc- 

 tion of tile systems in the San Joaquin Valley have been 

 somewhat limited to those products available from local 

 manufacturers. The selection of materials depends mainly on 

 recommendations made by local work unit offices of the Soil 



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