EAKTH, SAND-CLAY, AND GEAVEL ROADS. 7 
DRAINAGE. 
The subject of road drainage has been discussed at considerable 
length in other bulletins of the Office of Public Roads and Rural 
Engineering, and therefore will be given only brief mention here. 
Effective drainage usually should be the very first consideration in 
connection with the location and design of any road. This state- 
ment requires no explanation, because the action of water in chang- 
ing clay into mud and in causing all kinds of soils, except sand, to 
give way when a load is applied, is familiar to every person living in 
SIDE DITCH 
R OADWAY | 
Fig. 2. 
a humid climate. The following summary supplies a few suggestions 
as to how water may best be removed from a road bed : 
1. The road surface should be crowned so as to shed water off 
to the side ditches as rapidly as it falls on the road. The typical 
cross sections (shown in figs. 15, 20, and 22) indicate the amounts 
of crown advisable under different conditions. These figures are 
supplemented by a discussion on page 9. 
2. Wherever the road is in an excavation, suitable side ditches or 
gutters should be provided along the sides so that the water may 
SIDE DITCH 
Pig. 3. 
be conducted to some point where it may be turned off from the 
road. Figures 2, 3, and 4 show typical cross sections for earth side 
ditches. The cross section shown in figure 2 is suitable for steep 
grades where the depth of water in the side ditches must be kept low 
in order to prevent washing of the soil. Figure 3 shows a modified 
section which gives a greater capacity for the same widths of ditch 
than the cross section shown in figure 2, but which can be employed 
only on comparatively flat grades if washing is to be prevented. 
Figure 4 shows a cross section adapted especially to flat grades where 
a considerable volume of water must be carried. Ditches of the 
