which it was proposed to utilise a flap valve on the outlet so
as to render the discharge of the sewage automatic. That is to
say, the sewage was proposed to be collected in a reservoir at
the head of, and directly connected to, the outfall pipe, at
the outlet end of which a flap valve was to be fixed. During
high water the mouth of the outfall would be closed, so that
sewage would collect in the pipes, and in the reservoir beyond;
then when the tide had fallen such a distance that its level
was below the level of the sewage, the flap valve would open,
and the sewage flow out until the tide rose and closed the
valve. There are several objections to this arrangement. First
of all, a flap valve under such conditions would not remain
watertight, unless it were attended to almost every day, which
is, of course, impracticable when the outlet is below water. As
the valve would open when the sea fell to a certain level and
remain open during the time it was below that level, the period
of discharge would vary from, say, two hours at neap tides to
about four hours at springs; and if the two hours were
sufficient, the four hours would be unnecessary. Then the
sewage would not only be running out and hanging about during
dead water at low tide, but before that time it would be
carried in one direction, and after that time in the other
direction; so that it would be spread out in all quarters
around the outfall, instead of being carried direct out to sea
beyond chance of return, as would be the case in a well-
designed scheme.

When opening the valve in the reservoir, or other chamber, to
allow the sewage to flow through the outfall pipe, care should
be taken to open it at a slow rate so as to prevent damage by