Il6 ENGINEERING FOR LAND DRAINAGE. 



with light grade, in which case good judgment must be 

 used in determining the size of the receiving-main 

 drain. Ditching contractors who dig ditches and lay 

 tile by the rod usually prefer to take the surface with- 

 out any preliminary work of the plough. 



Outlet Protection. 



Every system of tile diains must have a discharge 

 through some main into a natural stream or open ditch. 

 The banks of these streams or ditches are continually 

 subject to erosion, so that it is often difficult to maintain 

 a permanent position for the outlet of the tile drain. 

 The ends should be protected in such a way that ani- 

 mals cannot enter when both ditches and tile are nearly 

 dry. While many thousands of drains are not pro- 

 tected in any way, instances of the obstruction of drains 

 by animals entering and not being able to get out oc- 

 casionally occur, so that it is wise to secure the drain 

 against accidents of this kind. In the first place tile 

 which are used near the outlet should be stoneware or 

 vitrified pipe, as the ordinary red-clay pipe which is 

 serviceable when buried will decompose and crumble 

 when exposed to the freezing and thawing which takes 

 place at the outlet of a drain. Better than this, use 

 good sewer pipe with sockets for 1 5 feet back from the 

 outlet and cement the joints with cement mortar. The 

 use of stone for an abutment for the outlet, while desir- 

 able in some localities, is not practicable in others. The 

 foundation should be deep and it should be set well 

 back into the bank so that the water of the stream 

 will not wash behind it. The stone' should be laid in 



