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230
HARBOUR ENGINEERING.
Training-works.
For the purpose of training navigable channels, any or all of the following
measures may be adopted.
(1) Training by means of Groynes. —Groynes are narrow jetties
generally of timber, occasionally only of stone or conerete, projecting from
the bank into the bed of the river at right angles to the direction of its flow.
In some cases, the groyne is formed by sheet-piling driven continuously and
bound together by horizontal runners; in other cases, detached piles are
driven in a straight line so as to form, with longitudinal walings, a series of
bays or panels, ranging in extent from 5 feet upwards to 20 feet or more.
These bays are filled in with planking, laid horizontally on edge, and spiked
Fig. 211. —Timber Groyne.
to the piles, or by means of bundles of brushwood bound with wire, the
interstices between the bundles being packed with clay and shingle. Bags of
sand may be used for the same purpose.
The piles for groynes need not be of any great length ; a depth of from
10 to 20 feet into the ground will generally suffice. As regards height, they
will advisedly be brought at least to the level of the river bank, and as much
above it as will serve to indicate the position of the groyne in times of flood.
The body-work of the structure need not be carried higher than ordinary high-
water level, if indeed so much as tbat.
Groynes are spaced at varying distances apart: sometimes at intervals
equivalent to their own length, sometimes more or less than that standard,
according to the special requirements of each case. They have the effect of