SURFACE AND TILE DRAINS. 



275 



A great saving of water at the side is made by a ditch above 

 the slope of a cut on the upper side, taking the surface-water 

 to the side of the next fill. The dimension of these surface 

 ditches will depend upon the amount of water to be provided 

 for, and their depth may be diminished by depositing the earth 

 taken out on the lower side next to the top of the slope. 



The following cross-section shows the plan of a cut, with 

 width of road-bed at twenty feet. 



Cross-section, of same cut as above, without a substratum of 

 pebbles, and a line of tiles in the centre, showing a saving in 

 width of cutting and depth of side ditches. 



Where no gravel or pebbles can be obtained, the under- 

 draining will undoubtedly make the best road at the least cost. 



In cities and villages it is desirable to be able to drive to the 

 edge of the sidewalk ; and this will not allow a depression for 

 surface-drainage exceeding one foot below the crown, depending 

 upon the width of driveway, and in many cases it should not 

 exceed six inches. Hence, in such cases, a system of under- 

 drainage becomes indispensable, unless there is a very deep 

 substratum of clean gravel or sand. 



An increased width of road-bed may make two lines of tile- 

 drains necessary, one towards each side ; and even in the ordi- 

 nary width of twenty feet it may be expedient in some very wet 

 places. 



On the other hand, the under layer of pebbles will not gener- 

 ally be necessary on banks of three feet and upwards, though it 

 will diminish the heavings of frost, and make a dryer road in 

 the spring. 



In side-hill cuts, where much water comes from the upper 

 side, culverts beneath the road should be placed at short inter- 



