HIGHWAY CONSTRUCTION 



apart, more or less, depending on the contour of the ground. Tin* 

 cross drains into which they discharge should be of ample dimensions. 

 On these longitudinal lines of tiles the introduction of catch basins 

 at intervals of f>() feet will facilitate the removal of the water. These 

 catch basins may be excavated three or more feet scjuare and as deep 

 as the tiles are laid. After the tiles are laid the pit is filled with gravel 

 and small stones. 



Fall of Drains, It is a mistake to give 100 much fall to small 

 drains, the only effect of which is to produce such a current through 

 them as will wash away or undermine the ground around them, and 

 ultimately cause their own destruction. "When a drain is once closed 

 by any obstruction no amount of fall which could be given it will 



Fig. 1 



again clear the passage. A drain with a considerable current through 

 it is much more likely to be stopped from foreign matter carried into 

 it, which a less rapid stream could not have transported. 



A fall of 1 inch in 5 feet will generally be sufficient, and 1 inch 

 in 30 inches should never be exceeded. 



Fig. lf>. 



Side Ditches are provided to carry away the subsoil water 

 from the base of the road, and the rain water which falls uj>on its 

 surface; to do this speedily they must have capacity and inclination 



