GPSJ Autumn 2024 ONLINE - Flipbook - Page 24
GPSJ
FORMA - COVER STORY
By Jack Shuttleworth, Director of Forma
Airport group takes advantage
of innovation in attenuation
A need to control costs while delivering demanding sustainability
improvements is changing thinking about water attenuation.
The conventional approach, to
install large tanks to hold water
captured in gullies and slot drains,
is proving, in many instances, to
be no longer 昀椀t for purpose.
Climate change, causing more
volatile weather, the subsequent
need to reduce carbon emissions,
a need to redevelop live and
brown昀椀eld sites with complex
ground conditions, and a strong
imperative to control costs are
stacked against tank systems that
have held sway for decades.
Most optimised attenuation
It is why Manchester Airports
Group (MAG), the UK’s largest
airport group, selected a di昀昀erent
approach to attenuation when it
upgraded one of its main sta昀昀 car
parks.
Forma has been designed
to streamline attenuation. It
does it by keeping drainage
shallow, creating a hugely 昀氀exible
and scalable way to manage
stormwater at source, without
large tanks.
It is the most comprehensive
and optimised subbase
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attenuation system on the market,
and is simpler, quicker, less costly
and safer to install.
Forma is also much more
sustainable, with a carbon
footprint a fraction of the size of
traditional tank-based attenuation
systems.
Forma ‘ticked all boxes’
MAG’s project perfectly
demonstrates the advantage of
shallow drainage. It needed to
resurface and upgrade one of
its largest park-and-ride sta昀昀 car
parks at Manchester Airport.
The project was designed by
AECOM, the main contractor was
Allied Infrastructure Management,
part of Colas, and the attenuation
installation contractor was SEL
Environmental.
MAG had found the existing
drainage and tank attenuation
system was not holding water
consistently.
Replacing it like-for-like would
have represented a big proportion
of the cost, time and risk
associated with the project. So
MAG was open to new ideas.
When we presented Forma, it
recognised an ideal solution.
Daniel Wilmer, Capital Delivery
Project Manager at MAG, said:
“My brief was to come up with
a solution. We’re all about
innovation and sustainability and
Forma ticked those boxes.
“I would like to use it across
other sites. They’ve taken a lot of
stress away and have been really
reassuring in terms of what we
require.”
Void space to hold water
Central to the Forma solution for
MAG’s car park is a product called
Formavoid. It’s a modular system
made from recycled plastic, here
in the UK, designed with extremely
strong columns and arches.
Quickly clipped together, 昀椀ll
material can be poured on top
of the Formavoid raft, while 60%
open ‘void’ space remains below
for source control water storage
and management.
The interlocked Formavoid
modules – just 100mm deep – are
positioned on top of a very strong,
wedge-welded puncture-resistant
GOVERNMENT AND PUBLIC SECTOR JOURNAL WINTER 2024/2025
geotextile membrane, called
Formatextile.
The in situ car park surface and
drainage system was removed
with a 450mm-deep excavation.
The Formavoid enhanced
subbase attenuation system
was installed across an area of
8,500m².
The system was designed
to manage around 1,000 cubic
metres of water. It was also more
than capable of withstanding
loads created by thousands of
car movements and bus journeys
every day.
Innovative water system
The Forma system was installed in
昀椀ve months by just six operatives
in the second half of 2024.
Formavoid modules were
integrated with 160mm-diameter
plastic transport pipes. Just 100
metres of pipework were needed
to collect water from across the
carpark and take it to an outfall
point.
A key innovation for this project
was the use of checkdams within
the subbase. This maximised
