8/12/2019 10255 Drainage Philosophy
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Additional percolation testing will need to be carried out in
the vicinity of the new
extension to confirm infiltration rates and the feasibility of a
new soakaway in that
location. If infiltration rates are good we would propose
permeable paving for the
external works with sufficient below ground attenuation to also
deal with storm water
run off from the extension building. If infiltration rates in
this area are not adequate,
then we will consider the construction of a new soakaway in the
area of the MUGA to
the rear of the school. This will require storm water drainage
from the newdevelopment to be positively drained to the location of
the proposed soakaway.
The new on site surface water drainage will also be designed in
accordance with the
Building Regulation: Part H: Drainage and Waste Disposal 2002
Edition. All pipe
sizes and gradients will be determined taking into account the
catchment area draining
to each length, and a self cleaning velocity of 0.75m/s based
upon a 50mm/Hr rainfall.
The network will be modelled and upgraded where necessary to
ensure that it has
sufficient capacity to deal with the 100 Year design Strom + 20%
in peak rainfall
intensities to allow for climate change.
Following detailed design, full details of the surface water
drainage can be provided
to discharge any storm water drainage Planning Conditions
attached to a PlanningApproval.
Foul Water Drainage
A new foul water drainage network was constructed to serve the
new school. This
foul water drainage network discharged into a new on site foul
water pumping station
that then pumped foul water drainage off site into the South
West Water foul water
sewers at the junction of Poole Park Road and Savage Road.
Building Regulations require the foul water receiving chamber to
be sized to contain
24Hr inflow to allow for disruption in service. At this time we
have no information on
any available spare capacity within the receiving chamber. At
detailed design stage
the additional inflow will be calculated and the storage volume
checked. If necessary
the receiving chamber storage will be increased to serve the
additional flows from the
new development. As foul water drainage is pumped off site at a
controlled rate and
the rate of discharge will not increase there will be no
capacity issues within the
receiving South West Water sewer.
On site the new foul water drainage will be designed in
accordance with the Building
Regulations: Part H: Drainage and Waste Disposal 2002 Edition.
This details
acceptable pipe sizes and associated pipe gradients all of which
will be applied to thedesign.
Mike Quigley
Airey & Coles Consulting Engineers
