During the progress of the works the location of the sea
outfall will be clearly indicated by temporary features visible
by day and lighted by night; but when completed its position
must be marked in a permanent manner. The extreme end of the
outfall should be indicated by a can buoy similar to that shown
in Fig. 33, made by Messrs. Brown, Lenox, and Co. (Limited),
Milwall, London, E., which costs about L75, including a 20 cwt.
sinker and 10 fathoms of chain, and is approved for the purpose
by the Board of Trade.

[Illustration: FIG 33 CAN BUOY FOR MARKING OUTFALL SEWER.]

It is not desirable to fasten the chain to any part of the
outfall instead of using a sinker, because at low water the
slack of the chain may become entangled, which by preventing
the buoy from rising with the tide, will lead to damage; but a
special pile may be driven for the purpose of securing the
buoy, at such a distance from the outlet that the chain will
not foul it. The buoy should be painted with alternate vertical
stripes of yellow and green, and lettered "Sewer Outfall" in
white letters 12 in deep.

It must be remembered that it is necessary for the plans and
sections of outfall sewers and other obstructions proposed to
be placed in tidal waters to be submitted to the Harbour and
Fisheries Department of the Board of Trade for their approval,
and no subsequent alteration in the works may be made without
their consent being first obtained.