244
DOCK ENGINEERING.
intended, but in view of the increase in depth continually demanded by
modern shipping, a concrete floor to a basin is a feature which cannot be
considered free from inconveniences. No deepening of the basin is possible
without its removal, which must prove a costly and troublesome under-
taking.
Sluicing is carried on daily at the Canada Basin, but the maximum
effect is obtained at low water of spring tides, a time when the basin is
very shallow, and when the inner docks can afford to part with a considér-
able amount of the water impounded on the flood tide. The water in the
docks is always levelled with the incoming tide two hours before high
water, within which period the operations of docking and undocking are
carried on.
ENLARGED SECTION THROUGH OUTLET.
i n. Soa^, IZ Feet^lTnohj.
^^f 1 lyt f________y________'i5 ___^ 'F^H.
Fig. 174.
Sluicing on a large scale is a prominent feature of ports bordering on
the English Channel. The method usually adopted is that of impounding
a quantity of water during the flood tide, in a basin specially constructed
for the purpose. At high water the sluice gates of this basin are closed,
and the contents retained until a suitable period about low water, when
the gates are opened again. The discharge of a large volume of water is
found to be absolutely essential to the maintenance of entrance channels
so subject to the introduction of sand by a littoral current, with its
attendant deposition. The rate of discharge provided at Dunkirk and
Calais is about 500 cubic yards per second, and the effective duration
about three-quarters of an hour.
The recent improvement works at the port of Ostend (fig. 175) com-
prise a considerable enlargement of area in the sluicing enclosure there,
concerning which M. Van der Schueren * makes the following obser-
vations :—
“ Ships drawing much water will be able to enter the port by favour of
* Van der Schueren on “Travaux exécutés récemment et en cours d’exécution au
port d’Ostende,” Int. Nav. Cong., Paris, 1900.