SSDA 2018 A W A R D
18 NSC
October 18
The Leeds Flood Alleviation
Scheme (FAS) is led by Leeds
City Council in partnership with
the Environment Agency. It will
provide the city centre and over 3,000 homes
and 500 businesses with protection against
flood events from the River Aire.
It will also enable key regeneration
opportunities along the river’s south bank,
while another key objective of the scheme is
the provision of new routes for pedestrians
and cyclists.
Forming an integral part of the FAS
improvements, a replacement weir needed
to be constructed on the Knostrop site.
Leeds City Council was made aware of the
opportunity of combining this structure
with a bridge across the river
Despite the technical challenges and
a complex construction programme, this
innovative plan was achieved through
careful planning and engineering. The
final design uses the new weir walls as pier
foundations for the bridge above, providing
significant savings in budget, time and
resources.
The client recognised the wider value
for the design to be of high quality and
identifiable with its place. A free flowing
and curved concept was preferred, but any
double curvature in the bridge’s form would
be prohibitive in cost and time.
Despite the apparent complexity of the
final design’s appearance, it only requires
a single curvature in the fabrication of the
steel plate elements. This served to simplify
fabrication and enabled the bridge to be
delivered within budget and programme.
A curved soffit combines with the
changing deck width to translate the varying
plan width into a rippling deck edge detail,
producing a dynamic ‘sinuous’ quality,
which is said to mirror the noise and
movement of the falling water beneath.
Another unique feature of the design is
that in elevation the piers are only 50mm
thick and almost invisible in long views,
creating the illusion of a floating deck.
When viewed on closer approach, the
appearance of the piers change, emerging as
dramatic projecting cantilevers, springing
from the weir below. Lookout points have
been positioned above each pier enabling
people on the bridge to stop and enjoy views
over the weir and along the river.
Steel was the obvious material of
choice to achieve the required aesthetic
and minimise the significant construction
challenges of working over water. The 70m
long bridge was fabricated in S H Structures’
facility which is situated just 17 miles from
the Knostrop site and treated at a local
facility, minimising the environmental
impact of the works.
In addition, wherever possible, local
suppliers were used to provide materials
and services which ranged from bolt supply,
on-site Non-Destructive Testing and site
surveying.
Construction over a river creates
numerous challenges in order not to harm
the waterway and its ecology. Minimising
the time and extent of temporary works
in the river was an essential aspect of the
design. The prefabricated superstructure
sections and piers were installed over two
weeks using a single crane.
At the abutments, special eel bypasses
have been incorporated to allow for
migration, while a dedicated fish bypass is
included in the weir.
When considering flooding events,
Knostrop Weir Foot and
Cycle Bridge, Leeds
Knostrop Foot and Cycle Bridge serves to
reconnect the Trans Pennine Trail, following the
removal of a section of island between the River
Aire and the Aire and Calder Navigation.
FACT FILE
Architect: Knight Architects
Structural engineer: Mott MacDonald
Steelwork contractor: S H Structures Ltd
Main contractor: BAM Nuttall
Clients: Leeds City Council and
Environment Agency
All images on this spread © Paul White
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