24 IOWA DEPARTMENT OF AGRICULTURE. 



adapted for the purpose than that found where first located. For instance, 

 soils adjacent to the beds of streams or in morasses and swamps, being 

 close and pervious, are very difficult to surface and subdrain, but routes 

 over such ground can often be avoided by locating the road upon higher 

 ground, where the natural drainage is better. 



Another consideration in choosing the line of travel is that roads on 

 slopes having a southern or western exposure can be much more satis- 

 factorily and economically maintained than those located on eastern or 

 northern slopes. 



DRAINAGE. 



Water is the most destructive agent to a road, and yet if a few sim- 

 ple principles are followed it can be easily dealt with. Earth is more 

 susceptible to the action of water and more easily dissolved and moved 

 by it than any other road material, and for this reason too much atten- 

 tion can hardly be given to the drainage of roads. Drainage alone will 

 often change a bad road into a good one, while, on the other hand, the 

 best road may quickly go to ruin for lack of drainage. 



Most country roads are too flat on top to shed water; indeed, a great 

 many of them are not only flat but concave, the center being the lowest 

 part; in other words, their crowns are inverted. The sides of the roads 

 are often square shoulders (Fig. 2) which obstruct the water on its pas- 



Fio. 2. — Improper cross section contrasted with proper cross section. 



sage to the side drains, and as a result the water lies on the surface until 

 it is absorbed by the material or evaporated by the sun. It is often al- 

 lowed to stand in the traveled way until the material softens and yields 

 to the impact of the horses' feet and the action of the wheels of the ve- 

 hicles; the holes and ruts rapidly increase in number and size; wagon 

 after wagon sinks deeper and deeper, until the road becomes utterly bad. 

 (Fig. 3.) 



The importance of drainage has been emphasized in the statement 

 that the "three prime essentials to good roads are, first, drainage; second, 

 better drainage; third, the best drainage possible." On open or pervious 

 soils, surface drainage, in connection with heavy rolling, is usually quite 

 satisfactory, provided the slope is good and the traffic is not too heavy; 

 but for the close, impervious, alluvial and clayey soils subdrainage is 

 sometimes necessary. With heavy traffic, narrow tires and long-continued 

 rains, freezes and thaws, the surface of any dirt road is liable to be com- 

 pletely destroyed, and in this case the only remedy is a consolidated mass 

 or crust of gravel or broken stone, forming a roof to keep out and carry 

 off the water. This, of course, constitutes "the best drainage possible." 



