306 Ground Water, Wells and Farm Drainage. 



9,000 feet of 3 inch tile are laid 100 feet apart ; but follow- 

 ing the third system only 3,000 feet of 4 inch and 15,300 

 feet of 3 inch render the same service with a saving of 

 about $33.00 for tile. 



Usually no single system can be followed but the slope 

 and shape of the land will require a combination of two or 

 more. 



381. Intercepting Surface Drainage. In very many cases 

 where drainage is required the necessity is caused by 



the collection of surface 

 waters from the surround- 

 ing higher lands. It may 

 often be possible in such 

 cases to avoid a large part 

 of the expense of under- 

 drainage by intercepting 

 and controlling the sur- 

 face waters, collecting 

 them into surface drains 



and leading them away as 

 represented in Fig. 126. 

 In this case the water is 



Fio. 126 -Method of intercepting surface Collected into a Surface 



(Frcm ditch before it reaches the 

 low area and is carried 

 around on the higher ground. It is specially important to 

 use this method in cases where low areas are surrounded on 

 all sides by a rim of land high enough to prevent the con- 

 struction of underdrains. 



drainage. A, B, surface ditch. 

 Irrigation and Drainage.) 



382. Construction of Surface Drains. Where surface 

 waters are to be handled as in (381) it can usually best be 

 done by constructing broad and comparatively shallow 

 runways, which can be kept in permanent grass, the width 

 and slope of the ditch being such that a wagon and mower 

 can readily be driven along and across it. Such waterways 

 should usually be 1 to 2 feet deep and 10 to 15 feet wide 



