SuDS in London - a guide

Natural capital
Natural assets which include geology, soil,
air, water and all living things within an
ecosystem.
Net present value (NPV)
The difference between the discounted
costs and benefits over the appraisal period.
NOx PM
Oxides of nitrogen particulate matter,
especially atmospheric pollutants as a
result of fuel combustion.
Opportunistic retrofitting
Where the opportunity to retrofit storm
water management arises on the back of
other drivers, such as regeneration or small
scale improvements. These may occur
within a neighbourhood, or locally on a
plot level.
Orifice control chamber
A chamber within a drainage system which
controls discharge rates.
Pathway
The route by which potential contaminants
may reach targets or by which water (and
pollutants) are conveyed either below or
above ground.
Pavement
The road or car park surface and
underlying structure, usually asphalt,
concrete or block paving. Note: the path
next the road for pedestrians is the
‘footway’ (the UK colloquial term being
'pavement').
Percentage runoff
The proportion of rainfall that runs off
a surface.
Permeability
A measure of the ease that fluid can flow
through a porous medium. It depends on
the physical properties of the medium, eg,
grain size, porosity and pore shape.
Permeable pavement
A permeable surface that is paved and
drains through voids between solid parts
of the pavement.
Permeable surface
A surface that is formed of material that
is impervious to water but, by virtue of
voids formed through the surface, allows
infiltration of water to the sub-base through
the pattern of voids, eg, concrete block paving.
Phytoremediation
Use of living plants to clean up soil,
air, and water contaminated with
hazardous chemicals.
Pluvial flooding
Flooding that results from high intensity,
extreme rainfall-generated surface
water flow.
Pollution
A change in the physical, chemical,
radiological, or biological quality of a
resource (air, water or land) caused by
man’s activities that is injurious to existing,
intended or potential uses of the resource.
Pond
Permanently wet depression designed
to retain storm water above the
permanent pool and permit settlement of
suspended solids and biological removal of
pollutants.
Porosity
The percentage of void space in
a material.
Porous paving
Surfacing material that contains voids,
allowing water to pass through it.
Potable/mains water
Water company/utility/authority drinking
water supply.
144 Appendices