LAYING OUT THE SYSTEM 



177 



installed without taking account of these conditions is 

 likely to be inefficient and expensive. 



Laying out the System. After the preliminary survey 

 is made the system can be laid out and the location and 

 depth of each drain determined. The district should be 



FIG. 25. METHOD or ESTABLISHING GRADE OF 

 DRAINS 



mapped in such a way that the data obtained in the pre- 

 liminary survey will show the contour of the surface, the 

 texture of the soil and subsoil, and the ground-water 

 condition. On this map the drainage system may be 

 drawn in such a way that intersecting joints, the sizes of 

 tile, and other data can be preserved for future use. These 

 data are extremely valuable in locating trouble. The 

 memory is not sufficiently accurate to be relied on for this 



