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By Rear-Admiral Campbell of
Barbreck. [Premium—The Gold Medal.]
The following report has
reference to the drainage, &c, on the farms of Leregychonie and Barvullen.
This is a plain of about
130 acres in extent, from 28 to 38 feet above the level of the sea, having
the advantage of all day sun even in winter. It was, eight years ago,
waste land, so soft as to be dangerous, and even sometimes fatal to cattle
and sheep.
At the lower extremity a
rude dyke was thrown across, to form a mill-dam, which was fed by mountain
streams; and in very wet weather a great part of the land was submerged.
On the water subsiding in spring, sheep from the neighbouring mountains
died in great numbers from eating the herbage which had been under
stagnant water.
The bases of the
surrounding hills (for the plain is so surrounded) had afforded the only
arable ground on the respective farms, and these were cropped to the edge
of the morass, so that the best of the land, probably for ages, had been
washed down to the plain below, where the sour and stagnant water of
course prevented any healthy vegetation; and a deep bed of the richest
possible loam lay there worse than useless.
Throughout this plain, with
the exception of about 20 acres (where the moss is deep), the subsoil is
gravel, and is covered by from 3 to 5 feet of loam and moss.
It was found that the
levels admitted of the mill-dam being-placed close to the mill, instead of
a quarter of a mile from it, and below the place chosen for the outfall of
the drainage of this singularly valuable subject; and the whole plain was
open drained preparatory to thorough drainage.
After two years the ground
became solid enough to admit of this, and a leading drain 3 feet wide was
taken up through the bed of the old dam (now dry rich land) for a mile and
a quarter, gradually narrowing towards the head, but from 5 to 6 feet deep
throughout, so that the sub-leaders have a clear drop into it. The small
drains (4 feet) have a similar drop into the sub-leaders, and are carried
up so as to terminate in the base of the hills, where the subsoil is very
open gravel. By thus raising the heads of the drains a constant scour is
secured, and that by the purest water. This open subsoil before the
drainage was so full of water, which was kept on dam by the close loam
below, that it used to rise to the surface as the only outlet, and sour
the whole plain. The advantage of having the heads of the drains carried
up as I have described has proved so great that fewer drains effect the
same object, and not only is much outlay saved, but the pipes are kept as
clean as gun-barrels. Of course, this advantage can only be attained in
hilly districts, but in such districts it never should be overlooked. An
additional advantage may be attained, as in the case I refer to, by
placing field stones over the pipes to within 18 inches of the surface,
for about 12 feet from the heads of the drains, the throw of water being
much increased thereby.
The leading drain for so
considerable an extent of ground must of necessity require a large duct
(in this case its capacity at the outfall is nearly 3 feet by 15 inches),
and it was found that pipes of the required size would be very expensive ;
the plan was therefore fallen upon of joining open-ended boxes made of old
larch, in the faucet joint form. These boxes are not only fastened with
nails, but with wooden pins. The idea of using wood was taken from finding
a plank under the foundation of an old bridge perfectly fresh, after being
there upwards of 100 years.
The main outfall is upon a
flat rock 2 acres in extent, over which the main stream runs, and the
spread of the water being so great, the run from the great drain is never
stilled even in the heaviest floods.
At the head, this drain is
2˝ feet below the level of the bed of the main stream, and by a few large
pipes connecting the two, the whole of the water from the stream can in
dry weather be turned in to scour out the leading drain.
This land had been let in
very small farms, and most of the tenants had fallen into hopeless
difficulty, which obliged the proprietor to take it into his own hands for
improvement. The drainage was not quite finished when one of the largest
sheep farmers in the country (without the lands being advertised) offered
to take the greater part, at a slight increase of the old rent, and to pay
6˝ per cent. on the gross outlay, and he now holds them on these terms.
The fall in this plain from
end to end is only 10 feet, so that in former days the water, after
souring the ground, went off chiefly in evaporation. It is therefore not
surprising that the air, which used even in summer to be cold and damp for
a great distance round, is now warm and genial; the ground, which was as I
have described it, being now perfectly dry.
The cost of a portion was
L.6, 16s., and a portion L.6, 4s., so that the average was about L.6, 10s.
per acre.
This outlay is large, but
there were several causes of expense which do not commonly occur; for
instance, a new course had to be cut for one of the mountain streams, and
the main or centre stream widened from 7 to 14 feet. The large and deep
leading drain, which takes all the drainage water on both sides of this
stream, was of course expensive. There are two sub-leaders passing under
the stream, one falling in about 1000 yards up the main drain, the other
100 yards from the outfall. The former is 2˝ feet under the bed of the
stream, and is composed of fireclay glazed pipes, over which the gravel is
merely filled in, the joints being perfectly tight; for where there is no
shifting, gravel is as tight in a short time, if always submerged, as any
puddling. The latter is one foot under the bed of the stream, and is
carried across by 9-inch fire-clay glazed pipes, so that these are about
level with the bed of the stream when placed. In laying them, the stream
above the crossing was temporarily turned into the great drain, and the
pipes were made perfectly water-tight by being enclosed in a casing of
Portland cement concrete 5 inches thick. When this was hard, the stream
was returned to its course, and now flows over the cement, which is harder
than most kinds of stone. This sub-leader, before crossing the stream,
passes through 30 yards of rock from 1 to 2 feet deep, the only rock met
with during the progress of the work except on first breaking ground.
In the course of the work,
some very heavy springs were found; one in particular, in the deep moss,
throwing after heavy rains a body of water (enough to fill a 2-inch pipe)
about a foot high above the surface, as if on force. When a drain was
taken through this spring, it was found to have made a large and very deep
hole under the 4-feet cut, and before it could be laid with pipes, a
number of cart-loads of gravel and small stones were put in until a run
for the water was got suiting the rest of the drain, which was laid with
8-inch pipes. Over these, for about 4 yards on each side of the spring,
6-inch pipes were put about half an inch apart, forming a drain within a
drain. These pipes were then covered with field stones to within a foot of
the surface, and turfed over to prevent earth getting down, and all heavy
springs were dealt with in this way. This expedient has never been found
to fail, either in the case of springs or old stone drains so often met
with in old arable ground. If something of the kind is not done, the soil
closes round the pipes, and the water must come to the surface as before.
The value of the land
before drainage could not be more on an average than 4s.; but it must be
remembered that on a great part of it, at certain seasons, the stock were
subject to disease and accident. The present value is at least 25s. per
acre, the flow of grass last summer on part of it, which was before the
most wet and sour, having been beyond anything I have ever seen in the way
of unsown grass. If it were not for the few acres of moss being of
comparatively little value, this average might be stated considerably
higher.
I make these few remarks to
account for the heavy expense, but feel convinced that money could not be
more profitably laid out. |
