Drainage ix New York. 259 



through coarse textured soil than through fine textured ones. Third, 

 that natural surface or underground drainage water should be intercepted 

 at the point where it arises. Fourth, that on flat clay soil the trouble 

 is more likel}- to be in the surface accumulation of water and there- 

 fore a matter of removing surface water, while on sandy soil, if it is 

 wet, the subsoil must be drained as well as provision made for surface 

 water, which will be less in amount and more closely related to the 

 subsoil water than on clay soil. Fifth, the tile should be arranged at 

 the depth where the water flows most readily and most largely. Sixth, 

 on heavy clay soil note carefully the presence or absence of an extensive 

 stratum of well drained gravel or sand at a reasonable depth beneath the 

 clay. It is sometimes possible to drain such soil by means of wells or 

 permeable media by ' which the surface water can reach the porous 

 stratum. Seventh, the size of the tile must be adapted to the area of 

 land drained by the system and the volume of water to be handled, also 

 to the fall of. the drains. Eighth, in very fine sands and muck soils, the 

 land should first be permitted to settle somewhat after the removal 

 of the water by open ditches before the tile are laid. In the case of 

 the sand, precautions against its running into the tile must be taken. In 

 muck soil, precautions must be taken against the shrinkage of the muck 

 after drainage, which may throw the tile out of line and destroy the 

 grade. 



a. Kinds of systems. 



There are two general types of drainage systems. These are : 

 1st. The natural or irregular system which follows the natural de- 

 pressions in the surface and seeks only to remove the water from the 

 low places. Probably the greater part of the land needing drainage in 

 this State requires only this type of drainage system. The system shown 

 in Fig. 195 is an example of this type. 



2d. The gridiron or regular system by which lines of tile are arranged 

 at uniform distances apart throughout the extent of the land drained. 

 This is necessary only in very uniform soil of uniform physiographic 

 features where the excess of water is widely and somewhat uniformly 

 distributed. The Yoemans system shown in Fig. 193 is an example of this 

 type. 



b. Laying out tile drain systems. 



On very level land where the fall is small and the outlet question- 

 able, it is always advisable to employ careful leveling instruments and 

 in such cases it is often necessary to employ an experienced engineer 

 to plan the system, to locate the drains, to determine the fall in differ- 

 ent parts of the system and to indicate the cuts necessary. Where 



