In addition to the above reasons for preferring covered drains, it has been asserted by one of the most skillful drainers in the world (Mr. Parkes), "that a proper covered drain of the same depth as an open ditch, will drain a greater breadth of land than the ditch can effect. The sides of the ditch," he says, "become dried and plastered, and covered with vegetation; and even while they are free from vegetation, their absorptive power is inferior to the covered drain."
Of the depth, direction, and distance of drains, our views will be found under the appropriate heads. They apply alike to open and covered drains.
BRUSH DRAINS.
Having a farm destitute of stones, before tiles were known among us, we made several experiments with covered drains filled with brush. Some of those drains operated well for eight or ten years; others caved in and became useless in three or four years, according to the condition of the soil.
In a wet swamp a brush drain endures much longer than in sandy land, which is dry a part of the year, because the brush decays in dry land, but will prove nearly imperishable in land constantly wet. In a peat or muck swamp, we should expect that such drains, if carefully constructed, might last twenty years, but that in a sandy loam they would be quite unreliable for a single year.
Our failure on upland with brush drains, has resulted, not from the decay of the wood, but from the entrance of sand, which obstructed the channel. Moles and field-mice find these drains the very day they are laid, and occupy them as permanent homes ever after.
Those little animals live partly upon earth-worms, which they find by burrowing after them in the ground, and partly upon insects, and vegetation above ground. They have a great deal of business, which requires convenient passages leading from their burrows to the day-light, and drains in which they live will always be found perforated with holes from the surface. In the Spring, or in heavy showers, the water runs in streams into these holes, breaks down the soft soil as it goes, and finally the top begins to fall in, and the channel is choked up, and the work ruined. We have tried many precautions against this kind of accident, but none that was effectual on light land.
The general mode of construction is this: Open the trench to the depth required, and about 12 inches wide at the bottom. Lay into this poles of four or five inches diameter at the butt, leaving an open passage between. Then lay in brush of any size, the coarsest at the bottom, filling the drain to within a foot of the surface, and covering with pine, or hemlock, or spruce boughs. Upon these lay turf, carefully cut, as close as possible. The brush should be laid but-end up stream, as it obstructs the water less in this way. Fill up with soil a foot above the surface, and tread it in as hard as possible. The weight of earth will compress the brush, and the surface will settle very much. We have tried placing boards at the sides, and upon the top of the brash, to prevent the caving in, but with no great success. Although our drains thus laid, have generally continued to discharge some water, yet they have, upon upland, been dangerous traps and pitfalls for our horses and cattle, and have cost much labor to fill up the holes, where they have fallen through by washing away below.
In clay, brush drains might be more durable. In the English books, we have descriptions of drains filled with thorn cuttings from hedges and with gorse. When well laid in clay, they are said to last about 15 years. When the thorns decay, the clay will still retain its form, and leave a passage for the water.
A writer in the Cyclopedia sums up the matter as to this kind of drains, thus: