Full resolution (JPEG) - On this page / på denna sida - IV. Forestry - 2. Forest Industries. By E. Arosenius - Floating. By Th. Örtenblad
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floating.
207
timber which can be expected to be floated down it, and on the costs of
regulation. As a rule, it may be said that it pays to adapt even quite small
water-courses to this purpose.
In the main waters of a large river the work of making a floating-way
consists principally in blasting away rocks which form obstructions, building wooden
troughs to regulate streams or waterfalls or to narrow the water-course, building
facings along such river-banks as are specially liable to get washed out, and
placing booms to guide the floating timber in the desired direction, thus
protecting low meadows, mills and other water-works, bridge-piers, and the
like. In these large rivers, and also in such smaller watercourses as flow
direct into the sea, sorting-booms are placed at the mouths, where the
floated timber is sorted according to the marks it bears, after which it
is delivered to its respective owners. In the smaller rivers, besides the above
arrangements, it is frequently necessary to build dams to regulate the depth of
the water, as, since these water-courses, unlike the large rivers, are not fed by the
melting snow in the high mountains, they would otherwise contain sufficient
water for floating only during the spring floods. The dams are built either at
the outflow of these rivers from some lake or tarn, which by damming can
be used as a reservoir (which is the most usual manner), or at the lower
end of some swamp, which is then made to serve the same purpose, or else
in some part of the water-course that runs more slowly (dead water). The dams,
as a rule, consist of stone coffers, strengthened in the front by banks of earth. In
the dam there are made openings, which, by means of hatches, can be entirely
or partially closed, whereby the height of water can be regulated. A special
opening (the outlet-sluicer or "shoot") is made in the dam for the escape of the
logs. Like the other openings it is provided with timbered walls and a
somewhat sloping floor of round timber.
Floating-channels (flumes) can, as a rule, not be dispensed with in the smaller
floating-ways. A precipitous stream with small water-supply, a large fall, an irregular
river-bed with large stones at the bottom, — such conditions make floating
channels indispensable. The trough or flume is made of timber and is either
supported by trestles or by beds of timber or stone, the latter being employed
when the flume lies low. In certain places (in Dalarne) the wooden channels
have been superseded by flumes of sheet iron, which have proved very practical.
— To ensure good floating, a tolerably equal depth of water should be maintained
all through the channel, and, consequently, the channel must be made narrower
where its slope is greater. The width should be relatively large at the
beginning of the channel and then decrease somewhat, because part of the water
is always lost by evaporation and leakage. The width and depth of the channel,
too, are adapted to the supply of water and the quantity of timber to be floated.
An incredibly large quantity of timber can be conveyed in a well-built
floating-channel, even if the dimensions of the flume are not considerable.
In front of the inlet of the channel there are leader-booms, so that the
timber is carried forward by the current toward the opening, where there are
always workmen posted, however, to regulate the entrance of the logs, which
should enter the channel evenly and so slowly that they do not accumulate in
such numbers as to burst the channel. By means of a system of signals
it . is possible to give notice, if necessary, from any part of the channel
when the feeding-in of the logs is to be interrupted. The lower end of the
channel has a slight slope, so that the logs will not strike against the
bottom when they leave the flume. If the water-course is shallow here, there
is built below the trough of the channel a "sliding bottom", of round timber,
over which the logs slide; this flooring, consequently, receives the first shock
of the issuing logs.
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