Heritage and Conservation
Case study
Heritage and Conservation
Heritage and conservation works in sensitive environments
Scope
successfully achieved our goal within 6 weeks Phase 1 — to reduce criticality of the situation by the working 2 shift patterns. installation of a long term cofferdam to reduce flood Heritage risk to Howden and surrounding properties and Once designs for the new door were complete and businesses (End of 2019) signed off, the installation phased commenced.
However, during installation, excavation works
Phase 2 — to install new wooden penstock valves uncovered issues regarding previous works that and install replacement new flood gates forming had taken place in the 1950’s, external to the brick outlet to tidal River Ouse (Due for completion Feb archway culvert, which required immediate 2021) consultations/remediation measures to be taken.
Flood gates prevent tidal and/or flood waters
Given the original arch feature was constructed in
flowing back inland into low lying agricultural, the 1750’s, brickwork required sympathetic re- residential and commercial areas with potential for pointing at various locations and fallen pier caps re- significant flooding damage. The river at this seating. location is 268m wide with varying tidal depths from
Road Closures
0.0m up to 5.29m and infrequent surges topping
Urgency acknowledged - it was necessary to close
7.4m. Obviously, any works involving tidal/flood the public highway for access as machinery was gates generate considerable concerns for local operated directly from the road under an residents and companies. emergency road closure. All necessary permits and statutory obligations were fulfilled and consultation
Key Aspects
with the local residents/business were carried out
Design
throughout the duration of the workings. Other
The state of the existing wooden door structure was
obligations regarding utilities, access, diversions, surveyed using 3D point cloud survey laser school transport, council run services and full traffic scanning and was deemed to be in a critical state. management system to Chapter 8 regulations.
Urgently working with our designers, liaising with
Community liaison in post and person also formed
the Environment Agency, Internal Drainage Board part of our remit. and Local Authority, we developed a plan. A large
Client Requirements
scale cofferdam t was designed such that it could
We also were challenged by the client to make an
be used to mitigate all flood risk posed by the allowance for the cofferdam to allow some water to damaged doors for a long duration. With the time be able to run by gravity through the temporary line of the project being across 12 months we had cofferdam. We achieved this by using a steel frame to ensure that the top of the cofferdam reached at in the base and fixing 6 x450mm diameter non- least the height of the existing flood embankment return flap valves. This element did add cost but making the cofferdam 6.18m tall. A lot of structural allowed for greater capacity during wet times when calculations had to be conducted to ensure the the doors would normally be operating along side a 3D Point Cloud Survey Images from within the 1750’s Brick Built Arched Culverts
Project Images
Challenges
Flood risk Health & Safety
By far the biggest issue and key at every stage; a Working in the base of the existing culvert structure lot of consideration and design work for temporary the River Ouse bottom is a very difficult works had to be put in place before removing any environment to keep clean and dry and posed existing infrastructure to ensure that we did not significant risks to the health and safety of our cause any flooding. Large volumes of water coming workforce. In order to maintain safe working through the drainage network had to temporarily practices, it was necessary to excavate silt and dammed off to make the workings dry. This was debris and boulder rock to create a level platform to managed with 3 pumps one 8” and two 6” to cope work from. A concrete foundation was cast in situ to with the volume of water that needed to be over build the new cofferdam on. To initially keep the pumped for the duration of the works 24/7. workings dry had to over pumped with a 4” high pressure pump.
Tides
Public Interest
The tidal nature of the River Ouse meant that works
had to be planned and executed at key windows of Works of this nature typically engage both public opportunity around the best tide which meant some interest and concern particularly from residents and night working. We overcame this with portable site businesses that are affected by flood gate removal lighting but due to the proximity of residential works and possible flooding. A great deal of time properties, screening was necessary to deflect light went into communicating with local residents, East away from the residential properties and only the Riding of Yorkshire Council and other stakeholders quietest of tasks was undertaken during the night to throughout the duration of the works to alleviate minimise noise disturbance. A lot of consultation concerns regarding the weather, anticipated was carried out with 3 residential properties flooding, lengths of work, progress and difficulties specifically. and inevitably frustration at road closures.
A fully Chapter 8 compliant traffic management
programme was implemented and adapted to
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