DRAINAGE OF SWAMPS.
Vast Extent of Swamp Lands in the United States.--Their
Soil.--Sources of their Moisture.--How to Drain them.--The Soil
Subsides by Draining.--Catch-water Drains.--Springs.--Mr. Ruffin's
Drainage in Virginia.--Is there Danger of Over-draining?
In almost, if not quite every State, extensive tracts of swamp lands are
found, not only unfit, in their natural condition, for cultivation, but,
in many instances, by reason of obnoxious effluvia, arising from
stagnant water, dangerous to health.
Of the vast extent of such lands, some idea may be formed, by adverting
to the fact, that under the grants by Congress, of the public lands
given away to the States in which they lie, as of no value to the
Government and as nuisances to their neighborhood, in their natural
condition; sixty millions of acres, it is estimated, will be included.
These are only the public lands, and in the new States. In every
township in New England, there are hundreds of acres of swamp land, just
beginning to be brought to the notice of their owners, as of sufficient
value to authorize the expense of drainage.
To say that these swamps are the most fertile and the most valuable
lands in New England, is but to repeat the assertion of all who have
successfully tried the experiment of reclaiming them.
In their natural state, these swamps are usually covered with a heavy
growth of timber; but the greater portion of them have been partially
cleared, and many of them are mowed, producing a coarse, wild, and
nearly worthless grass.
The soil of these tracts is usually a black mud or peat, partly the
product of vegetable growth and decay on the spot, and partly the
deposit of the lighter portion of the upland soil, brought down by the
washing of showers, and by spring freshets. The leaves of the
surrounding forest, too, are naturally dropped by the Autumn winds into
the lowest places, and these swamps have received them, for ages.
Usually, these lands lie in basins among the hills, sometimes along the
banks of streams and rivers, always at the lowest level of the country,
and not, like Irish bogs, upon hill-tops, as well as elsewhere. Their
surface is, usually, level and even, as compared with other lands in the
old States. Their soil, or deposit, is of various depth, from one foot
to twenty, and is often almost afloat with water, so as to shake under
the feet, in walking over it.
The subsoil corresponds, in general, with that of the surrounding
country, but is oftener of sand than clay, and not unfrequently, is of
various thin strata, indicating an alluvial formation. Frogs and snakes
find in these swamps an agreeable residence, and wild beasts a safe
retreat from their common foe. Notoriously, such lands are unhealthful,
producing fevers and agues in their neighborhood, often traceable to
tracts no larger than a very few acres.
In considering how to drain such tracts, the first inquiry is as to the
source of the water. What makes the land too wet? Is it the direct fall
of rain upon it; the influx of water by visible streams, which have no
sufficient outlet; the downflow of rain and snow water from the
neighboring hills; or the bursting up of springs from below?
Examine and decide, which and how many, of these four sources of
moisture, contribute to flood the tract in question. We assume, that the
swamp is in a basin, or, at least, is the lowest land of the
neighborhood. The three or four feet of rain water annually falling upon
it, unless it have an outlet, must make it a swamp, for there can
usually be no natural drainage downward, because the swamp itself is the
lowest spot, and no adjacent land can draw off water from its bottom. Of
course, there is lower land towards the natural outlet, but usually this
is narrow, and quite insufficient to allow of drainage by lateral
percolation. Then, always, more or less water must run upon the surface,
or just below it, from the hills, and usually, a stream is found in the
swamp, if none pours into it from above.
The first step is a survey, to ascertain the fall over the whole, and
the next, to provide a deep and sufficient outlet. Here, we must bear in
mind a peculiarity of such lands. All land subsides, more or less, by
drainage, but the soils of which we are speaking, far more than any
other. Marsh and swamp lands often subside, or _settle_, one or two
feet, or even more. Their soil, of fibrous roots, decayed leaves, and
the like, almost floats; or, at least, expands like a sponge; and when
it is compacted, by removing the water, it occupies far less space than
before. This fact must be kept in mind in all the process. The outlet
must be made low enough, and the drains must be made deep enough, to
draw the water, after the subsidence of the soil to its lowest point.
If a natural stream flow through, or from, the tract, it will usually
indicate the lowest level; and the straightening and clearing out of
this natural drain, may usually be the first operation, after opening a
proper outlet. Then a catch-water open drain, just at the junction of
the high and low land, entirely round the swamp, will be necessary to
intercept the water flowing into the swamp. This water will usually be
found to flow in, both on the surface, and beneath it, and in greater or
less quantities, according to the formation of the adjacent land. This
catch-water is essential to success. The wettest spot in a swamp is
frequently, just at its edge, because there the surface-water is
received, and because there too, the water that has come down on an
impervious subsoil stratum, finds vent. It is in vain to attempt to lay
dry a swamp, by drains, however deep, through its centre. The water has
done its mischief, before it reaches the centre. It should be
intercepted, before it has entered the tract, to be reclaimed.
This drain must be deep, and therefore, must be wide and sloping, so
that it may be kept open; and it should be curved round, following the
line of the upland to the outlet. Often it has been found, in England,
that a single drain, six or eight feet deep, has completely drained a
tract of twenty or thirty acres, by cutting off all the sources of the
supply of water, except that from the clouds. This kind of land is very
porous and permeable, and readily parts with its water, and is easily
drained; so that the frequent drains necessary on uplands, are often
quite unnecessary. Many instances are given, of the effect of single
deep drains through such tracts, in lowering the water in wells, or
entirely drying them, at considerable distances from the field of
operation.
When the surface-water and shallow springs have thus been cut off, the
drainer will soon be able to determine, whether he has effected a cure
of his dropsical patient. Often it will be found, that deep seated
springs burst up in the middle of these low tracts, furnishing good and
pure water for use. These, being supplied by high and distant fountains,
run under our deepest drains, and find vent through some fracture of the
subsoil. They diffuse their ice-cold water through the soil, and prevent
the growth of all valuable vegetation. To these, we must apply
Elkington's system, and hit them _right in the eye_! by running a deep
drain from some side or central drain, straight to them, and drawing off
the water low enough beneath the surface to prevent injury. A small
covered drain with two-inch pipes, will usually be sufficient to afford
an outlet to any such spring.
When we have thus disposed of the water from the surface-flow, the
shallow springs and the deep springs, and given vent to the water
accumulated and ponded in the low places, we have then accomplished all
that is peculiar to this kind of drainage. We have still the water from
the clouds, which is twice as much as will evaporate from a
land-surface, to provide for. We assume that this cannot pass directly
down by percolation, because the subsoil is already saturated; and
therefore, even if all the other sources of wetness are cut off, we
shall still have a tract of land too wet for wheat and corn. If the
swamp be very small, these main ditches may sufficiently drain it; but
if it be extensive, they probably will not. We have seen that we have
some eighteen or twenty inches of water to be disposed of by drainage;
so much that evaporation cannot remove consistently with good
cultivation; and, although this amount might, in a very deep peaty soil,
percolate to a great distance laterally, to find a drain, yet in shallow
soil resting on a retentive subsoil, drains might be necessary at
distances similar to those adopted on wet upland fields. To this part of
the operation, we should, therefore, apply the ordinary principles of
drainage, putting in covered drains with tiles, if possible, at four
feet depth or more, ordinarily, and at distances of from forty to sixty
feet, although four-foot drains at even one hundred feet distance, in
peat and black mud, might often be found sufficient.
Through the kindness of Edmund Ruffin, Esq., of Virginia, we have been
furnished with three elaborate and valuable essays, on the drainage and
treatment of flat and wet lands in lower Virginia and North Carolina,
published in the Transactions of the Virginia State Agricultural
Society, for 1857. The principal feature of his system is based upon his
correct knowledge of the geological formation of that district; of the
fact in particular, that, underlying the whole of that low country,
there is a bed of pure sand lying nearly level, and filled with water,
which may be drawn down by a few large deep drains, thus relieving the
surface-soil of surplus water, by comprehensive but simple means.
We have before referred to Mr. Ruffin as the publisher, more than twenty
years ago, of "Elkington's Theory and Practice of Draining, &c., by
Johnstone;" and we find in his recent essays, evidence of how thoroughly
practical he has made the system of Elkington in his own State. Indeed,
we know of no other American writer who records any instance of marked
success in the use of Elkington's peculiar idea of releasing pent up
waters by boring. Mr. Ruffin, however, has applied, with great success,
this principle of operation, to the saturated sand-beds which underlie
the tracts of low land in his district of country. These water-beds in
the sand lie at depths varying usually from four to eight feet below the
surface. This surface stratum is comparatively compact, and very slowly
pervious to water before it is drained. The water from below, is
constantly pressing slowly up through it, of course preventing any
downward percolation of the rain-water. By running deep drains at wide
intervals, and boring down through this surface stratum with an auger,
the pent up water below finds vent and gushes up in copious springs
through the holes, and flows off without coming nearer to the surface
than the bottom of the drains; thus relieving the pressure upward, and
lowering the water-line in proportion to the depth of the drains.
Mr. Ruffin gives an instance of the drying up of a well half a mile
distant, by cutting a deep drain into this sand-bed, and thus lowering
its water-line.
No doubt in many localities in our country, a competent geological
knowledge may detect formations where this principle of drainage may be
applied with perfect success, and with great economy.
_Is there danger of over-draining swamp lands?_ In speaking of the
injury by drainage, we have treated of this question.
Our conclusions may be briefly stated here. There is an impression among
English writers, that light peaty soils may be too much drained; but
many distinguished drainers doubt the proposition. No doubt there are
soils too porous and light to be productive, when first drained. They
may require a season or two to become compact, and may require sand, or
clay, or gravel, to give them the requisite density; but these soils
would, we believe, be usually unproductive if shallow drained.
In short, our idea is, that, in general, a soil so constituted as to be
productive under any circumstances, will retain, by attraction, moisture
enough for the crops, though intersected by four-foot drains at usual
distances; and that cold water pumped up to the roots from a stagnant
pool at the bottom, is not, either in nature or art, a successful method
of irrigation.
Still we believe that peaty soils may be usually drained at greater
distances, or by shallower drains, than most uplands, because of their
more porous nature; and we should advise inexperienced persons not to
proceed with a lavish expenditure of labor to put in parallel drains at
short distances, till they have watched, for a season, the operation of
a cheaper system. They may thus attain the desired object, with the
smallest expense. If the first drains are judiciously placed, and are
found insufficient, others may be laid between the first, until the
drainage is complete.