DRAINAGE 



225 



to it. This cannot be determined by the effects of 



drainage wells upon other similar strata, but only by a 



knowledge of the very 



same bed of material 



which receives the 



drainage for which 



disposal is sought. 



Sewers used to drain 

 lands. In some situa- 

 ations outlets for open 

 drains can be secured 

 only with difficulty. 

 The water must be car- 



Figure 124. The dotted lines mark the cross- 

 section of a deep, narrow ditch made with a ditch- 

 iug Plow, and the wavy line the angle of repose 

 sought by the banks when they have fallen in. 



Figure 125. Cross-section of ditch through soil 

 which tumbles or is wasiied in easily. 



ried long distances 

 through neighboring 

 fields or along road- 

 ways, and possibly the 

 fall is insufficient to 

 allow the water to run 

 off freely. A deep drain 

 through an adjacent 

 portion of higher land, 

 with a low area on the 



OppOSltC side, may pH)- 

 A L 



vide a short but ex- 



pensive outlet in the 



form of an open ditch 



or a covered sewer. In 



this case, the sewer is 



not only less expen- 



sive, but sometimes 



better than the 



wide open ditch, 



the tiles and narrow ditch costing less than the 



open ditch. Either drain tile or sewer tile may 



be thus used to receive surface water at the 



Figure m Cross . section 

 spade through eaty soil - 



ditch made 



