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8
Separate system
for surfacc
water.
be desirable that an arrangement should be made, between
the two Boards, to adopt similar regulations, as to the
drainage of roads and gardens, as well as of houses.
This raises again the important question of how far a
double system—a sewer or drain lor the sewage, and a
separate conduit for clean water is to be carried, as regards
both existing and future roads, houses, and gardens.
To separate entirely the storm-water from the sewage, the
double system must be carried to each street and house, as a
large portion of the rainfall descends on the houses and
gardens. This system if applied to a district already drained,
and especially where water-courses have been converted into
sewers, would cause a very large outlay, and a great amount
of interference with private property; but its application to
future roads and buildings would not involve such serious
consequences, and deserves consideration.
Unless some arrangements be made to separate the surface
water from the sewage, the portion of rainfall seeking an
outlet through the main sewer, will be augmented by the
construction of sewers and drains from new roads and houses,
as the process of converting agricultural land into building
land goes on.
The Alexandra Cottages, about 160 houses in the
ham Sewerage Area, have a double system of drains ; but I
know of no other instance in the Sewerage Area, or Penge,
where the system is applied to any considerable number of
houses.
I am of opinion that, apart from the question of cost, the
separation of the rainfall and land water from the sewage
and house drainage, may, under some circumstances, be
crriedd too far; as the want of sufficient water to cleanse
sewers and drains where the gradients are flat, would cause
evils, which, although difficult to measure, may be far more
serious than occasional floodings, the effects of which are
apparent.
Values to
house drains
Among the works carried out at Penge for the Lewisham
Board, I have fixed self-acting valves or flaps in the sewers,