Some writers advocate the use of a line of tile near the surface, on each side of the trackway. The object of placing the tile in this position is to secure a rapid drainage of the surface; but very little, if any, water from the surface will ever reach a tile so placed, since the road surface when wet is puddled by the traffic, which pre vents the water percolating through the soil. It is certain that in clay or loam the drainage thus obtained is of no practical value. Many farmers have tried to drain their barns-yard by laying tile near the surface, but always without appreciable effect. The deeper the tile the better the drainage.
One writer advocates digging a trench in the middle of the road and filling it nearly full with broken stone or poles, and then filling the remainder with earth. This drain is to be connected with both side ditches by cross drains 50 feet apart. Such construction would be very expensive and practically useless.
The rapid surface drainage sought by putting a tile or its equiva lent near the surface, can best be secured by giving the surface of the road a proper crown and keeping it free from ruts and holes (see § 194).
While a line of tile on one side of the road is usually sufficient, there is often a great difference as to the side on which it should be laid. If one side of the road is higher than the other, the tile should be on the high side to intercept the ground water flowing down the slope under the surface. Sometimes a piece of road is wet because of a spring in the vicinity, or perhaps the road is muddy because of a stratum which brings the water to the road from higher ground; in either case, the source of supply should be tapped with a line of tile instead of trying to improve the road by piling up earth.
If the road is tiled as above recommended, the side ditch need not be very large; but it should be of such a form as to permit its construction with the road machine or scraping grader (§ 142) or with a drag scraper (§ 137), instead of requiring to be made by hand.
On comparatively level ground, the proper form of side ditch is readily and cheaply made with the usual road machine. An exam ple of this form of ditch is shown in Fig. 9, page 85. If a larger and deeper ditch is required, it can still be made chiefly with the drag-scoop scraper (I 137). For an example of a deep ditch of this form, see Fig. 10, page 85.
A deep narrow ditch is also expensive to maintain, since it is easily obstructed by the caving banks, by weeds, and by floating trash. Fortunately the shallow ditch is easy and cheap to construct and also to maintain. If it is necessary to carry water along the side of the road through a rise in the ground, it is much better to lay a line of tile and nearly fill the ditch than to attempt to maintain a narrow deep ditch. A tile is much more effective per unit of cross section than most open ditches.
110. The side ditch should have a uniform grade and a free out let into some stream, so as to carry the water entirely away from the road. No good road can be obtained with side ditches that hold the water until it evaporates. Much ostensible road work is a positive damage for this reason. Piling up the earth in the middle of the road is perhaps in itself well enough, but leaving undrained holes at the side probably more than counterbalances the benefits of the embankment. A road between long artificial ponds is always inferior and is often impassable. It is cheaper and better to make a lower embankment, and to drain thoroughly the holes at the side of the road. Public funds can often be more wisely used in making ditches in adjoining private lands than in making ponds at the roadside in an attempt to improve the road by raising the surface. It is cheaper and better to allow the water to run away from the road than to try to lift the road out of the water.
When the road is in an excavation, great care should be taken that a ditch is provided on each side to carry away the water so that it shall not run down the middle of the road. Every road should have side ditches, even one that runs straight down the side of a hill. Indeed, the steepest road needs the side ditch most, although it often has none. Frequently the water runs down the middle of the road on a side hill and wears it into gullies, which are a discom fort, and often dangerous, in both wet weather and dry.