Drainage - Introduction - Page 1
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Separate and Combined Systems
A separate
drainage system is one were the foul water
and the surface water are always kept
separate.
This is shown in the two
previous diagrams.
When a separate system is used then the sewerage
treatment plant will not get overloaded in periods of wet weather.
A combined
system is no longer used and joins some or all
of the surface water into the foul water drainage system.
This means that both surface water and foul
water will discharge into the sewerage treatment plant. To avoid the
treatment plant being overloaded, it may be possible to extract some foul water
at various points in the drainage network. This can be achieved if the surface water is less dense than the foul water and tends to flow at the top in a
drain. A separating device can be used to divert surface
water into a storm water channel or drain.
It is generally agreed that
the installation and running costs of sewerage treatment plant can be minimised
if a separate system is adopted. For
this reason the separate system is
favoured by local authorities.
A typical combined system is shown below but not recommended.
Combined System is not recommended. The Separate
system as shown on the previous page is now used.
