Walthamstow Wetlands Redevelopment
Structural & Civil Engineering Consultants
London, United Kingdom
Kinnear Landscape Architects for Waltham Forest Council
Kinnear Landscape Architects
Witherford Watson Mann
The Walthamstow Wetlands is a 200-hectare Thames Water reservoir site that is the main source of water supply for 3.5 million people. It is also a significant nature reserve, providing shelter to a wide range of wildlife.
For this project, Entuitive engineered the facilities necessary for transforming the wetlands site into an urban nature reserve with free access for the public. The redevelopment included the extension and refurbishment of historic buildings, as well as the creation of pedestrian entrances, bridges, a foot and cycle path network throughout the site and connected to the wider Lea Valley, signage and interpretation, a new rangers’ and volunteers’ hub, and a small car park.
We used a high-level of slag in the concrete. This meant we had a high percentage of recycled content in the mix, greatly reducing embodied carbon emissions for cement manufacturing.
The project optimizes human comfort with radiant heating and cooling (with hot water coming from the District Energy building two blocks away) while minimizing the need to condition outdoor air thanks to a dedicated outdoor air system (DAS). The system supplies outdoor air to the space at a low level and low velocity, known as displacement ventilation, which efficiently removes unwanted heat and contaminants as the supplied air rises through the space.
The nodes of the 55-metre truss consist of five piles of 100-mm-thick plate. The largest node weighs the same as some battle tanks at 12 metric tonnes. The two diagonal web members, which support the largest compression forces of 33 and 38.5 meganewtons, comprise four piles of 100-mm solid plate. These were welded using partial joint penetration welding along the edges in the shop, requiring high pre-heating and careful post-heating to minimize potential weld-induced stress concentrations and indicators. The site welding required for connecting the truss web members to the largest node took approximately 150 man hours to complete over multiple days, with induction heaters running 24 hours a day.
The library’s entryway is designed to resemble a Chinook arch cloud formation. The three-storey, 18-metre-tall trusses feature architecturally exposed web members, with the largest members comprising four built-up piles of 4” thick plate. The largest truss spans 55 metres, is curved, and supports another truss spanning 30 metres.
The library sits over Calgary’s busiest light rail transit (LRT) line. This presented many unique structural challenges. The curved shape of the LRT line helped achieve the library’s distinctive shape by mirroring the curve along its longitudinal axis. Cost-effective structural solutions involving long-span floor framing and long-span, mega-trusses provided large, column-free spaces at the main entrance and oculus.
Each truss was too long, too tall, and too heavy to ship as one piece. As such, each piece was individually shipped and erected 10 metres above grade and temporarily braced back to the concrete cores that were advanced first. A temporary bracing system was used to stabilize each truss as additional floors were cast. Welded in shop along the long edges in partial joint penetration, the truss pieces required careful pre- and post-heating to minimize potential weld-induced stress and steel cracking. Two-end dialog b members support the largest compression forces of 33 and 38.5 meganewtons.
Meet the Team
Europe’s Largest Urban Wetlands
The existing locally-listed Engine House and the grade II-listed Coppermill Tower were robust brick boxes built to house the engines that pumped water up to the city. The goal was to adapt these integral buildings for public use while maintaining their heritage and significance.
The Engine House was built in 1894 for a giant triple expansion engine and extended in 1908 to house steam turbines. A cluster of rooms, it is squeezed into a triangular riverside plot. Its 30-metre tall chimney had been demolished in the 1960s, leaving the structure feeling lopsided and diminished.
The Coppermill, at the southern end of the Walthamstow site, is a remnant of a watermill built in 1806. The tower was re-built in 1865 to house a Cornish beam engine.
As multiple undersized beams had to be replaced, the structural team worked closely with the contractor to ensure that the means and methods were the most economical and feasible, while ensuring that the replacements would not adversely impact the new building envelope components that would be installed overtop.
The extensive decay to the timber framing required much of it to be replaced in-situ, including corrections to poorly executed carpentry work found once the walls were fully revealed. Some of the decay was so severe that tools were not required to remove the affected components. (The team could remove them by hand.)
At the Coppermill Tower, the challenge was to achieve a stair and viewing platform within the Italianate tower while working around existing window openings and the historic iron frame that had held the beam engine in place. The stair touches the original walls very lightly to emphasise the verticality of the tower and distinguish the old and new structure.
Entuitive engineered a visually exposed steel stair and viewing platform from flat steel plate with carefully detailed connections supported in just a handful of places on in-situ visual concrete padstones.
The existing structure comprised a boiler room, turbine room, and a 15-metre high triple engine room. In order to adapt the house to public use, it was necessary to unblock bricked-up openings, deal with flooded below-ground chambers, and create new doorways so that the central boiler room would provide access to all the other rooms, as well as create an interesting and appealing space for visitors. Renovations also included the addition of a single-storey kitchen, a galleried internal balcony and boldly cantilevered external terrace, as well as the reconstructed chimney/bird and bat house.
Entuitive also designed all steel connections for this system, ensuring that the solution not only respected the integrity of the existing structure but also that a harmonious aesthetic was achieved.
The off-site, prefabricated nature of the steel meant that it was possible to prepare the existing building and foundations in advance, dealing with the typical unexpected issues encountered with an historic building, and then bring the steel to site for a swift installation.
Many of the elements requiring fire protection were assembled from components bolted together. This allowed fire protection to be applied only in the specific locations required, such as the loadbearing elements, which minimized the requirements and allowed the raw steel to be widely exposed.
The two heritage buildings were the disused Engine House and the grade II-listed Coppermill Tower, which were adapted for visitor use, providing an exhibition space, an education room, a café, washrooms, and a viewing platform.
One significant feature of the Marine Engine House was the reconstruction of the long-since demolished chimney. Built entirely in brickwork in the traditional fashion, this structure acts both as a beacon for the building and houses roosts and nesting boxes for birds and bats.
Reflecting the environmental significance of the site and the structures on it, it was fundamental to the vision of the project to conserve and enhance the site’s natural and built heritage.
RIBA National Award, 2018
RIBA London Award, 2018
Structural Steelwork Merit Award, 2018
The gallery was built around the edges of the boiler room, served by stairs and a new lift, and providing further space for the café customers.
The steel framing of the gallery and balcony is supported entirely off the existing masonry and so the new steel beams were carefully positioned to make best use of the stronger areas of masonry and the existing structure, verified by testing the bricks and mortar. Entuitive also engineered the architectural metal work, such as the solid but delicate raw-steel balustrade guarding the gallery floor edge above the café and the edge of the cantilevered terrace.
An advantage of this approach, other than the aesthetic appeal, was to allow the structure to be assembled from a kit of parts from within the tower itself with no onsite welding. Structurally, the stair is suspended from the viewing platform by steel rods to the half landings while the treads slot into notched plates in the stringers and the balustrade is in folded flat plate with angle uprights and a channel to which the wreathed wooden handrail is fixed.
To prevent lateral movement and vibration of the suspended landings, the edge beams are embedded into the supporting padstones, which are in turn dowelled into the surrounding masonry to prevent pull-out. The stair treads are folded steel plate set within and bolted to the flat plate steel stringers.
BSc(Hons) CEng MIStructE