Farm drainage / The Principles, Processes, and Effects of Draining Land with Stones, Wood, Plows, and Open Ditches, and Especially with Tiles

by Henry F. French

In another place, he says:

"The very general concurrence in the adoption of the line of greatest descent, as the proper course for the minor drains in soils free from rock, would almost lead me to declare this as an incontrovertible principle."

Allusion has been made to cases where we may have to defend ourselves from the flow of water from higher undrained lands of our neighbor. To arrest the flow of mere surface water, an open ditch, or catch-water, is the most effectual, as well as the most obvious mode. There are many instances in New England, where lands upon the lowest slopes of hills are overflowed by water which fell high up upon the hill, and, after passing downward till arrested by rock formation, is borne out again to the surface, in such quantity as to produce, just at the foot of the hill, almost a swamp. This land is usually rich from the wash of the hills, but full of cold water.

To effect perfect drainage of a portion of this land, which we will suppose to be a gentle slope, the first object must be to cut off the flow of water upon or near the surface. An open ditch across the top would most certainly effect this object, and it may be doubtful whether any other drain would be sufficient. This would depend upon the quantity of water flowing down. If the quantity be very great at times, a part of it would be likely to flow across the top of an under-drain, from not having time to percolate downward into it.

In all cases, it is advised, where our work stops upon a slope, to introduce a cross-drain, connecting the tops of all the minor-drains. This cross-drain is called a header. The object of it is to cut off the water that may be passing along in the subsoil down the slope, and which would otherwise be likely to pass downward between the system of drains to a considerable distance before finding them. If we suppose the ground saturated with water, and our drains running up the slope and stopping at 4 feet depth, with no header connecting them, they, in effect, stop against 4 feet head of water, and in order to drain the land as far up as they go, must not only take their fair proportion of water which lies between them, but must draw down this 4 feet head beyond them. This they cannot do, because the water from a higher source, with the aid of capillary attraction, and the friction or resistance met with in percolation, will keep up this head of water far above the drained level.

In railway cuttings, and the like, we often see a slope of this kind cut through, without drying the land above the cutting; and if the slope be disposed in alternate layers of sand or gravel, and clay, the water will continue to flow out high up on the perpendicular bank. Even in porous soils of homogeneous character, it will be found that the head of water, if we may use the expression, is affected but a short distance by a drain across its flow. Indeed, the whole theory as to the distance of drains apart, rests upon the idea, that the limit to which drains may be expected effectually to operate, is at most but two or three rods.

Whether, in a particular case, a header alone will be sufficient to cut off the flow of water from the higher land, or whether, in addition to the header, an open catch-water may be required, must depend upon the quantity of water likely to flow through or upon the land. An under-drain might be expected to absorb any moderate quantity of what may be termed drainage-water, but it cannot stop a river or mill-stream; and if the earth above the tiles be compact, even water flowing through the soil with rapidity, might pass across it. If there is reason to apprehend this, an open ditch might be added to the header; or, if this is not considered sufficiently scientific or in good taste, a tile-drain of sufficient capacity may be laid, with the ditch above it carefully packed with small stones to the top of the ground. Such a drain would be likely to receive sand and other obstructing substances, as well as a large amount of water, and should, for both reasons, be carried off independently of the small drains, which would thus be left to discharge their legitimate service.

Where it is thought best to connect an open, or surface drain, with a covered drain, it will add much to its security against silt and other obstructions, to interpose a trap or silt-basin at the junction, and thus allow the water to pass off comparatively clean. Where, however, there is a large flow of water into a basin, it will be kept so much in motion as to carry along with it a large amount of earth, and thus endanger the drain below, unless it be very large.

DISTANCES APART, OR FREQUENCY OF DRAINS.

The reader, who has studied carefully the rival systems of "deep drainage" and "thorough drainage," has seen that the distance of drains apart, is closely connected with that controversy. The greatest variety of opinion is expressed by different writers as to the proper distances, ranging all the way from ten feet apart to seventy, or even more.