CONSTRUCTION NOTES 241 



Areas Requiring Drainage and General Problems of Each. 



(a) Roads. Roads are usually crowned for drainage of their surface- 

 This crown will usually approximate a half inch to each foot of width 

 between the middle line and the side line for macadam roads, one-fourth 

 inch for smooth impervious surfaces. On roads which are comparatively 

 flat (2% to 5%) the crown may be as slight as three-eighths of an inch to 

 each foot, while on roads of steeper grades (7% to 12%) the crown may 

 be increased to three-fourths of an inch to each foot or even more in order 

 to ensure the prompt removal of surface water to the gutters and thereby 

 eliminate washing of the road surface through streams of water which might 

 find their way over the road surface from some distance before finally reach- 

 ing the gutter. This applies to macadam roads. For smooth impervious 

 surfaces the crown is not increased with the gradient. There are various 

 types of gutters which are not discussed in these notes. The types of inlets 

 and catch basins to meet the requirements of road drainage are shown on 

 Plate 107. 



In the heavier clay soils it is extremely desirable that the subgrade of 

 the road should be thoroughly drained. This may be accomplished either 

 by crowning the subgrade and removing the water through four-inch tile 

 drains (similar to figure 3 on Plate 108) installed within the road area and 

 along the immediate side of the road, or by one single similar tile drain 

 installed in a depression in the subgrade under the middle line of the road. 

 The usual depth of these tile drains under the road approximates twelve 

 inches below the surface of the subgrade. 



(b) Walks. It is quite essential that the surface of walks of all kinds 

 should be so graded that the surface water will be promptly carried to the 

 sides, and it is equally essential that the surrounding surface of the ground 

 on either side of the walk should be so graded that the minimum amount 

 of surface water will find its way to the top of the walk. 



Walks constructed on the clay soils are usually drained with a line of 

 four-inch tile installed under the middle line of the walk in a trench approx- 

 imating twelve inches in width and twelve inches below the subgrade of 

 the walk, and filled with cinders to cover the tile. Such underdrainage 

 removes promptly all surplus water which would cause damage in the 

 presence of freezing conditions and which might also cause a soft condition 

 of the walk surface, especially on gravel and turf walks. 



(c) Lawns, garden areas, farm areas. The modeling of the surface of 

 lawns and gardens is a question of practical and aesthetic grading too long 

 to discuss here. Subdrainage of all these areas is similarly largely a horti- 

 cultural or agricultural question. Tile drainage for lawns is shown in figures 

 i, 2 and 3 on Plate 108; for gardens in figures I and 4 on Plate 107. 



