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

Whether drains should run up and down the slope of the hill, or directly across it, or in a diagonal line as a compromise between the first two, are questions which beginners in the art and mystery of drainage usually discuss with great zeal. It seems so plain to one man, at the first glance, that, in order to catch the water that is running down under the soil upon the subsoil, from the top of the hill to the bottom, you must cut a ditch across the current, that he sees no occasion to examine the question farther. Another, whose idea is, to catch the water in his drain before it rises to the surface, as it is passing up from below or running along on the subsoil, and keep it from rising higher than the bottom of his ditch, thinks it quite as obvious that the drains should run up and down the slope, that the water, once entering, may remain in the drain, going directly down hill to the outlet. A third hits on the Keythorpe system, and regarding the water as flowing down the slope, under the soil, in certain natural channels in the subsoil, fancies they may best be cut off by drains, in the nature of mains, running diagonally across the slope.

These different ideas of men, if examined, will be found to result mainly from their different notions of the underground circulation of water. In considering the Theory of Moisture, an attempt was made to suggest the different causes of the wetness of land.

To drain land effectually, we must have a correct idea of the sources of the water that makes the particular field too wet; whether it falls from the clouds directly upon it; or whether it falls on land situated above it and sloping towards it, so that the water runs down, as upon a roof, from other fields or slopes to our own; or whether it gushes up in springs which find vent in particular spots, and so is diffused through the soil.

If we have only to take care of the water that falls on our own field, from the clouds, that is quite a different matter from draining the whole adjoining region, and requires a different mode of operation. If your field is in the middle, or at the foot, of an undrained slope, from which the water runs on the surface over your land, or soaks through it toward some stream or swamp below, provision must be made not only for drainage of your own field, but also for partial drainage of your neighbor's above, or at least for defence against his surplus of water.

The first, and leading idea to be kept in mind, as governing this question of the direction of drains, is the simple fact that water runs down hill; or, to express the fact more scientifically, water constantly seeks a lower level by the force of gravitation, and the whole object of drains is to open lower and still lower passages, into which the water may fall lower and lower until it is discharged from our field at a safe depth.

Water goes down, then, by its own weight, unless there is something through which it cannot readily pass, to bring it out at the surface. It will go into the drains, only because they are lower than the land drained. It will never go upward to find a drain, and it will go toward a drain the more readily, in proportion as the descent is more steep toward it.

To decide properly what direction a drain should have, it is necessary, then, to have a definite and a correct idea as to what office the drain is to perform, what water is to fall into it, what land it is to drain.

Suppose the general plan to be, to lay drains forty feet apart, and four feet deep over the field, and the question now to be determined, as to the direction, whether across, or up and down the slope, there being fall enough to render either course practicable. The first point of inquiry is, what is expected of each drain? How much and what land should it drain? The general answer must be, forty feet breadth, either up and down the slope, or across it; according to the direction. But we must be more definite in our inquiry than even this. From what forty feet of land will the water fall into the drain? Obviously, from some land in which the water is higher than the bottom of the drain.

If, then, the drain run directly across the slope, most of the water that can fall into it, must come from the forty feet breadth of land between the drain in question, and the drain next above it. If the water were falling on an impervious surface, it would all run according to the slope of the surface, in which case, by the way, no drains but those across, could catch any of it except what fell upon the drains. But the whole theory of drainage is otherwise, and is based on the idea that we change the course of the underground flow, by drawing out the water at given points by our drains; or, in other words, that "the water seeks the lowest level in all directions."

Upon the best view the writer has been able to take of the two systems as to the direction of drains, there is but a very small advantage in theory in favor of either over the other, in soil which is homogeneous. But it must be borne in mind that homogeneous soil is rather the exception in nature than the rule.