TILE DRAINAGE. 



67 



faces down hill. It will be seen that the surface of the 

 ground crosswist- of each drain will be level ; and as the strata 

 of soil and subsoil in bowlder clays that need drainage are 

 usually nearly horizontal (the slopes being made in the past 

 largely by erosion and wash), the water readily follows these 

 strata sidewise, and a little forward down the slope until it 

 finds the tiles and enters them. But, now, suppose the drains 



Fig. 19. Cross-section of tiles improperly laid, crosswise of the slope. 

 Now, as water- can soak only downward, by gravity, and only half way 

 between the drains it laid at the proper distance with reference to the 

 porosity of the soil, it will follow that a considerable part of the land 

 down t he slope from each drain (A, B, C, D, and F, G, H, I, in the figure) 

 will not be properly drained. That is, the "suction range " of a tile 

 drain is about as great on level ground as down the slope, while up the 

 slope it has almost none, owing to the opposing force of gravity. 



are laid crosswise of the slope, as in Fig. 19. As the soil 

 strata are practically horizontal, if the slope is at all steep then 

 almost no water enters the drain from the downhill side see 

 Fig. 19. The darts in each figure indicate the lateral flow of 

 the water under hydrostatic pressure from above. But in 

 Fig. 19, only the water between A and D, and that between 

 F and I can enter the two drains from below, since water can 

 not flow up hill. This is all wrong. There should be no 

 d<>wn hill and practically useless side to a tile drain; that is, it 

 should run straight down the slope, and then the water can 



