LAND DEAINAGE 41 



then need to be united, namely, a regular system coupled mtli 

 spurs and side lines to reach the wetter sjoots. 



Springy lines on the side of a slope or at its foot may often 

 be intercepted by a drain across the slope near the upper side 

 of the wet area and cutting fairly deep or down to the imper- 

 vious layer that is forcing the water to the surface. Sometimes 

 two or more such intercepting lines are necessary, and on a 

 springy hillside diagonal drains may be best. 



Muck soil areas, esjiecially small pockets, should generally 

 have a di-ain along the border at the foot of the slope. It should 

 be added that for muck soils the first drains should usually be 

 open drains until the muck has settled and the nature of its 

 subsoil and the sources of water have been determined. 



Pronounced springs should be tapped by the most direct route 

 and if they spread over a considerable area spur drains on one 

 or both sides should be arranged like a funnel to intercept the 

 flow. These spurs should cut fairly deep. 



Two or three feet is a good average depth for drains. 



Plant roots and under drains. — The penetration of the roots 

 of trees or other jjlants into tile drains is not determined by the 

 depth of the drain so much as by whether water flows continually 

 in the drain. In dry periods the roots are likely to be led 

 toward the tile where it carries a continual flow of water. Cer- 

 tain types of trees, such as the elm, poplar, willow and even the 

 apple, may be especially troublesome in this way. Tight joints 

 formed with cement in the neighborhood of such plants is the 

 only available protection. Ordinarily, plant roots do not much 

 interfere with field drains. A\Tien the land is uniformly drained, 

 roots do not enter the tile. 



Size of tile. — The size of drains should be determined by 

 several factors. The more important of these are (a) the rain- 

 fall, which will determine the amount of surplus water in the 

 soil, (b) the slope of the drain, (c) the porosity of the soil and 

 the manner in which the rains occur, whether as ordinary show- 

 ers and rain periods only or very heavy downpours, (d) the 

 occurrence of springs and surface flow which would increase 

 the volume of water in the soil over that due to rainfall on the 

 local area, (e) the texture of the soil in relation to the grade. 

 Soils having silty or quicksand (very fine sand) properties 

 require the larger tile. 



The capacity of a tile to carry water depends mainly on two 

 things: These are its diameter and the slope at which it is 

 laid. The capacity varies with the square of the diameter rather 



