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convey, and dispose of the sewage of Southgate. Only one
length of sewer, apart from culverts, is now constructed of
brickwork, that length being the southern main joining the
Edmonton sewers.
The sewers are laid principally in open trenches, but as their
depth is in some cases as much as 30 feet below the surface, the
driving of short tunnels as headings is occasionally resorted to
Pymmes Brook is crossed in several places by means of inverted
syphons. These have been constructed with iron pipes from
special designs, which permit the smallest area of sewage being
exposed in the manholes, and have worked very satisfactorily.
The sewers are also carried at several points under the New
River, and a few years ago the late New River Company insisted
upon a special system being adopted, by which large cast-iron shield
pipes are forced by means of powerful hydraulic jacks through
the soil under the river, thus forming tunnels in which the
sewage pipes are laid.
In the case of new streets, no new sewers are permitted
to be covered up until the work has been thoroughly inspected
and tested with water. The pipes used have special joints,
are made of the strongest stoneware clays, and laid upon a
thick bed of cement concrete. In addition, they arc laid to
absolutely straight lines from point to point, and by means of
manholes can be examined and seen through from end to end.
At the head of every branch sewer means for Hushing are
provided by lampholes and flushing chambers, through which
thousands of gallons of clean water are systematically delivered
in order to prevent any deposit within the sewers. There are
upwards of 100 of these flushing chambers within the district.
Fortunately, all the sewers may be said to be self-cleansing, and
within an hour or two of any foul matter being discharged into
a drain or sewer it is delivered at the Edmonton Sewage Works.
The sewers are ventilated by means of gratings over the
manholes and by upcast shafts ; but the gratings intended to be