The height, above absolute low water, at which the outlet should be placed, will depend on the depth of the outlet of the land drain, and the depth of storage room required to receive the drainage water during the higher stages of the tide. Of course, it must not be higher than the floor of the land drain outlet, and, except for the purpose of affording storage room, it need not be lower, although all the drainage will discharge, not only while the tide water is below the bottom of the gate, but as long as it remains lower than the level of the water inside. It is well to place the mouth of the trunk nearly as low as ordinary low-water mark. This will frequently render it necessary to carry a covered drain, of wood or brick, through the mud, out as far as the tide usually recedes,—connected with the valve gate at the outlet of the trunk, by a covered box[pg 206] which will keep rubbish from obstructing it, or interfering with its action.
When the outlet of the land-drains is below low-water mark, it is of course necessary to pump out the drainage water. This is done by steam or by wind, the latter being economical only for small tracts which will not bear the cost of a steam pump. Formerly, this work was done entirely by windmills, but these afford only an uncertain power, and often cause the entire loss of crops which are ready for the harvest, by obstinately refusing to work for days after a heavy rain has deluged the land. In grass land they are tolerably reliable, and on small tracts in cultivation, it is easy, by having a good proportion of open ditches, to afford storage room sufficient for general security; but in the reclaiming of large areas, (and it is with these that the work is most economical,) the steam pump may be regarded as indispensable. It is fast superseding the windmills which, a few years ago, were the sole dependence in Holland and on the English Fens. The magnitude of the pumping machinery on which the agriculture of a large part of Holland depends, is astonishing.
There are such immense areas of salt marsh in the United States which may be tolerably drained by the use of simple valve gates, discharging above low-water mark, that it is not very important to consider the question of pumping, except in cases where owners of small tracts, from which a sufficient tidal outlet could not be secured, (without the concurrence of adjoining proprietors who might refuse to unite in making the improvement,) may find it advisable to erect small pumps for their own use. In such cases, it would generally be most economical to use wind-power, especially if an accessory steam pump be provided for occasional use, in emergency. Certainly, the tidal drainage should first be resorted to, for when the land has once been brought into cultivation, the propriety of introducing steam pumps will become more apparent,[pg 207] and the outlay will be made with more confidence of profitable return, and, in all cases, the tidal outlet should be depended on for the outflow of all water above its level. It would be folly to raise water by expensive means, which can be removed, even periodically, by natural drainage.
When pumps are used, their discharge pipes should pass through the embankment, and deliver the water at low-water mark, so that the engine may have to operate only against the actual height of the tide water. If it delivered above high-water mark, it would work, even at low tide, against a constant head, equal to that of the highest tides.
CHAPTER X. - MALARIAL DISEASES.
So far as remote agricultural districts are concerned, it is not probable that the mere question of health would induce the undertaking of costly drainage operations, although this consideration may operate, in connection with the need for an improved condition of soil, as a strong argument in its favor. As a rule, "the chills" are accepted by farmers, especially at the West, as one of the slight inconveniences attending their residence on rich lands; and it is not proposed, in this work, to urge the evils of this terrible disease, and of "sun pain," or "day neuralgia," as a reason for draining the immense prairies over which they prevail. The diseases exist,—to the incalculable detriment of the people,—and thorough draining would remove them, and would doubtless bring a large average return on the investment;—but the question is, after all, one of capital; and the cost of such draining as would remove fever-and-ague from the bottom lands and prairies of the West, and from the infected agricultural districts at the East, would be more than the agricultural capital of those districts could spare for the purpose.
In the vicinity of cities and towns, however, where more wealth has accumulated, and where the number of persons subjected to the malarial influence is greater, there can be no question as to the propriety of draining, even if nothing but improved health be the object.
Then again, there are immense tracts near the large cities of this country which would be most desirable for residence, were it not that their occupancy, except with certain constant precautions, implies almost inevitable suffering from fever-and-ague, or neuralgia.