Supply Chain - Flood Alleviation - Protection of Assets

The works were undertaken by JBA-Bentley, a joint venture between designers, JBA Consulting, and principal contractor, JN Bentley. This was through the EA’s £2.5 billion Water and Environment Management (WEM) Framework - Asset Delivery. The project was delivered under an NEC 3 Engineering and Construction Contract (ECC) Option C Contract.

The project was funded by key partners including Hull City Council, East Riding of Yorkshire Council, Highways England, Humber Local Enterprise Partnership, Northern Powerhouse, and DEFRA.

Climate resilience and adaption was at the heart of the design as evidenced by a 20% overdrive capability built into the East Hull controls, temporarily increasing pumping outputs to 12m3/s, delaying the need for future pump upgrades.

At Castlehill, multiple social, environmental, and economic benefits have been realised, increasing flood storage within the catchment, delivering new woodland habitat, and integrating ‘access for all’ walking routes around the site. This solution reduced the peak pumping requirements at East Hull and created a valuable social space for the community in dry periods, improving biodiversity.

Existing flood resilience was impacted by 3 key factors:

The project faced significant delivery challenges:

As such, JBA-Bentley were contracted to design, build and commission a replacement pumping station 50m North of the confluence of the Holderness Drain and the Humber Estuary (50-year life). This was a multi-disciplinary scheme, requiring civil, structural, MEICA, geotechnical and hydrological/hydraulics inputs. Completing this scheme as a joint-venture allowed an expedited programme through increased design-construction integration and buildability efficiencies.

The new pumping station consisted of four 2.5m3/s pumps (13T each) operating in a duty-assist-assist-assist configuration, two per wet well. A gravity channel was constructed for flows outside of tidal-locking scenarios, which can be isolated using new tidal pointing doors and a penstock sluice gate for secondary containment (see Figure 4 below). This improved reliability of the failing tidal defences in conjunction with new floodwalls.

The pumps were controlled by a motor control centre (MCC) kiosk, which is part of the site’s MEICA Village: MCC; NPG substation, providing a DNO mains connection; an EA Switchgear room; and a 2000kVA step-down transformer.

Rock armour, gabions and reno mattresses were installed for scour protection in-channel and on the drain’s banks, preventing the pumping station’s foundations from being undermined. An access causeway was constructed for safe crane access, up to 250T (see Figure 5 above). The pumping station and access causeway were founded on steel H-piles and concrete CFA bearing piles to minimise settlement.

To deliver the works effectively and safety, a large central 30m x 25m cofferdam was formed and incorporated a bypass channel. The bypass was sized to convey all river flows up to 30-40m3/s seen in winter months. As seen in Figure 6 (below), these temporary works would eventually be integrated into the permanent works saving time, cost, and carbon.

The complexity of the solution - particularly the phasing of the combined temporary and permanent works - led the team to deploy various digital delivery tools to aid the process. A 3D federated Revit model was created for the scheme that facilitated collaboration between JBA-Bentley and the many sub-contractor design packages and ensured effective clash detection was possible and that client and landowner input was communicated and captured.

Construction on East Hull Pumping Station started July 2020. During the works, the site and design team responded to many external challenges and worked closely with stakeholders to resolve them. For example, one of the existing tidal pointing doors sea defences protecting the drain from the Humber failed mid-works, requiring an emergency response to prevent an increase in flood risk.

This was not the most challenging issue faced. Nearing completion, a decommissioning process was required to remove parts of the cofferdam and return gravity flows to the new central gravity channel – closing off the bypass channel. Dry working options were preferred, but a new option emerged when JBA Bentley approached Yorkshire Water for use of their pluvial pumping station to redirect the Holderness Drain into the Humber directly (something they already did in emergencies). This option created a dry working area using temporary dams and stoplogs at the upstream listed Hedon Road bridge, allowing potential for 24/7 working to reduce the programme. This method was safer than alternatives like pontoon working in low neap tides, additionally preventing water stagnation and silt build-up from impacting the protected Humber. It was also less carbon-intensive than sheet piling across the whole drain, and allowed for more rapid demobilisation of temporary works if there was a storm event during the decommissioning.

24/7 working saved 3 months of planned programme time, reducing cost and carbon by 48%. However, it left the catchment completely controlled by pumping.

4D time and motion modelling (Synchro 4D) was used to garner stakeholder agreement for this. 4D modelling simulated a digital twin of the real life works, aiding virtual planning of the complex decommissioning phase. This significantly reduced construction risk by highlighting plant clashes and working room restrictions and became a critical stakeholder engagement tool.

Initially Castlehill formed part of the existing Holderness Drain floodplain, forming a buffer between the drain and local communities. The area was predominately agricultural, and its topography left it wet and inaccessible throughout the year.

Castlehill now delivers a multi-functional site. The scheme’s primary purpose was to deliver a more climate resilient solution by delaying overspill into the floodplain and making use of untapped storage within the drain itself. Secondarily, through consultation, the scheme created new social spaces, ‘access for all’ walking routes and a link-up with the TransPennine Trail. The local community were key stakeholders in this scheme, helping to form requirements for these social areas and participating in tree planting initiatives.

New woodland planted could sequester more than 6000T of carbon and will offset the Castlehill construction emissions within 10 years. Some 15 years later, it will also have absorbed 50% of the East Hull capital carbon - this provided not only new habitats, but also a direct resilience benefit. The table below compares capital carbon emissions to woodland sequestration.

The scheme worked directly to improve protection of neighbouring properties through re-alignment of Sutton Cross Drain further North-East (further into the floodplain), and through installation of over 140m of sheet piling along the length of Sutton Cross Drain and East Carr Drain. This also allowed for the space to create a joint wetland shelf/fish refuge in dry periods along the re-aligned drain’s route.

Overall, the scheme provides biodiversity net-gains for the following protected and priority species:

Another aim of Castlehill was to improve access to and understanding of the historic environment, due to the presence of a Scheduled Ancient Monument on the site. Information boards were installed, and inclusive K-gates and barriers were fitted to provide safe entry and prevent unauthorised site access e.g., by motorbikes etc. This will protect the historic site and preserve it for future generations.

Finally, and in keeping with the requirements for improved resilience, the project also incorporated new elevated gravel laydown areas to assist effective flood incident response, see Figure 9.

To conclude, this multi-faceted design has made provisions for a new online pumping station at East Hull and has increased resilience and social-environmental value of the flood storage area at Castlehill, achieving significant improvements to the Standard Of Protection to properties along the course of the Holderness Drain. These works were technically complex, but thanks to the ‘One Team’ focus of the JBA-Bentley joint-venture, significant design and construction challenges were overcome using innovative temporary works and digital rehearsal/delivery strategies at every step.

The solution became operational in December 2023 and has already supported effective incident response and recovery by protecting properties during six recent and consecutive storm events (Elin, Fergus, Gerrit, Henk, Isha and Jocelyn). The flood alleviation works has delivered significant improvement to the Standard Of Protection afforded to around 1000 properties, increasing from approximately 20% AEP to 0.5% AEP from fluvial and tidal events, in-line with the Humber strategy.

The Don Regulators comprise three regulator gates on the River Rother that are owned, operated, and maintained by the Environment Agency (EA). The purpose of the regulators is to reduce the risk of flooding to settlements within the River Don catchment by attenuating flows in the River Rother. JBA-Bentley has completed the design and installation of the first regulator gate. The detailed design of the second gate is currently being undertaken, while the third regulator is being modelled as part of the optioneering phase. In addition to the installation of the first regulator gate, a bespoke full-channel fish pass has been installed directly downstream to improve migratory fish passage.

The Meadowgate Regulator is located within the Rother Valley Country Park. The historic regulator consisted of a single fish belly bottom-hinged tilting gate, operated by a single electrically powered hydraulic ram.

In 2023, JBA-Bentley replaced the gate with a top-down vertical control gate, improving the resilience of the structure. Alongside the regulator gate, a new control building and EA Office have been constructed. Both buildings have green roofs and EV charging. The gate was commissioned in February 2024 and is ready to operate during a flood event.

The gate is operated to ensure a maximum of 60m3/s forward flow is always maintained. When flows exceed 60m3/s the new gate is lowered and water levels in the Rother rise and begin to spill into the washlands located within the Rother Valley Country Park, which can retain approximately 1.5 million m3.

The removal of the bottom tilting gate provided an opportunity to improve fish passage on the River Rother through the installation of a unique full-channel width fish pass. This fish pass is designed with 4-tonne reinforced concrete ‘fish tiles’ featuring varied-height upstands supplied by Craven Concrete Ltd.

The tiles were designed with the aid of computational fluid dynamics modelling to ensure they influenced the nature of the flow to allow for varied fish species to migrate upstream while also withstanding hydrodynamic forces during extreme events. The fish species focused on are coarse fish, European eels, brown trout, large migratory salmonids, and lamprey.

The 40m long stilling basin has been removed by building up the existing concrete channel bed and grading out the levels to create a uniform slope. The ‘fish tiles’ have been laid onto the regraded channel. This is the first fish pass of its kind in the world.

The fish pass installation required the full channel as a dry working area. To achieve this, an innovative syphon system, designed by Dutch water specialist Vanderkamp UK, was installed. The solution involved complex temporary works and contingency planning.

To form the upstream dam, the new regulator gate was dropped to bed level, allowing upstream water levels to build up. The gate was designed to operate this way; hence no further calculations were required. Four syphon intake pipes were installed upstream of the gate to divert up to 12m3/s of flow out of the channel for 115m, around the working area.

The syphons were primed using electric vacuum pumps which expelled all the air from the system to draw water through the pipes. By utilizing the existing gate and power supply, the syphons had a far lesser environmental impact than a typical cofferdam and over-pumping solution. The total embodied carbon associated with the syphon solution was 464 tons.

Due to the scale of the flows being diverted, the loads imposed on the riverbanks by the pipes when full were considerable. JBA-Bentley and Vanderkamp UK worked together to design a temporary support system involving ground-bearing improvements, steel and timber supports, and retaining structures. Checks were also carried out on the existing channel wall where the forces from the syphons acted upon it.

In addition to work to ensure the stability of the syphons, an energy dissipation system was designed and installed at the syphon outlets to combat scour, and a bubble curtain was installed upstream to deter fish from entering the syphons. The installation of the system was done via a temporary crane pad. Due to the nature of the site and its space constraints, this was a challenging design. JBAB worked closely with the landowner, Rother Valley Country Park, to balance the desire to allow continual access into the park with ensuring the crane was safe to carry out the required lifts. To achieve this, the crane had to be placed in close proximity to the riverbank. Slope stability modelling and bearing capacity calculations were undertaken to ensure the crane could be operated safely.

Recent storm events have recorded flows higher than the syphon capacity. To manage the risk of this occurring during the programmed works, a contingency plan was developed.

The basis of the plan was developed from a bespoke JBA flow forecasting system, which forecasted the flow over a 2-day period. Using the data from the forecasting system, flow monitoring data provided by Vanderkamp UK, upstream gauge data, and the storage capacity of the washlands upstream of the gate, JBAB could make informed decisions on whether the gate needed to be raised to allow flow to pass forward.

This decision was made with the aid of hydraulic calculations and decision flow charts within the contingency plan, allowing for quick and effective decision-making, ensuring flood risk was not impacted upstream and the safety and well-being of the site team working in the channel was never put at risk.

The Canklow Regulator is the furthest downstream of the three Regulators, approximately 3.5km upstream from the confluence of the River Rother and the River Don at Rotherham.

The existing structure consists of a single electrically powered vertical lifting sluice gate operated by an electric wire rope hoist, comprising a drive motor gearbox assembly, cross shaft with integral rope drums, and support bearings.

To improve resilience and the operation and maintenance of the asset, JBA-Bentley is completing the detailed design and build of a new vertical regulator gate and associated MEICA and civils infrastructure.

The MEICA structure consists of a 20.3-ton vertical gate, mounted on a new steel bridge and working platform, which shall also house 13.5 tons of drive equipment for operating the gate.

Two 4kW motors, working in a duty/standby configuration, will provide drive to the gate via bevel and gearboxes, which turn a single driveshaft spanning the width of the gate. On this driveshaft, one at either end of the gate, are rack and pinion gear assemblies, which convert the rotation of the driveshaft to the vertical motion of the gate. The total gear ratio from motor to driveshaft is an approximate reduction of 4410:1, allowing relatively small motors to be specified.

To support the new gate structure over the next 50 years, a new anchor restraint system has been designed. A buried sheet-piled ‘dead-man’ wall will be installed with ten 36mm anchor rods, evenly spaced, connecting to a waling beam on the wet side of the existing channel wall. This will be mirrored on both riverbanks.

The new infrastructure replicates the existing system, which has been determined to be past its design life and insufficient in supporting the new gate.

The existing superstructure of the control houses will be demolished, the foundations will be retained and extended where required to support the new gate structure using cast-in bolt sets.

A new permanent crane pad will be constructed on the south bank for the construction, maintenance, and decommissioning of the gate. This will double as parking spaces for EA operatives when not being used by a crane.

The JBA-Bentley team worked collaborative to optimise the delivery. This meant that site constraints were identified, and the design was completed with buildability and safety as the focus. A key constraint on the scheme is the proximity of the Northern Power sub-station and overhead power lines. The design of the dead-man walls, crane pad, and steelwork platform was completed to ensure that the plant and temporary works required for construction and installation were outside of the powerline exclusion zones.

The Woodhouse Mill Regulator is situated between Canklow and Meadowgate. It uses a single electrically powered vertical lifting gate to retain water. This gate is operated by an electric wire rope hoist, which includes a central drive motor and gearbox assembly, half shafts, spur and pinion driven rope drums, and support bearings, all counterweight assisted.

JBA-Bentley is currently carrying out hydraulic modelling on behalf of the EA as part of the optioneering phase. The options include passive solutions, such as a baffle or orifice plate spanning the width of the channel to continue to utilize the upstream storage. Due to the size of the Don catchment, the modelling required three individual models to be run together:

Multiple return periods are being considered, resulting in hundreds of models runs. The modelling also uses a continuous simulation approach, which adds to the complexity of the model runs.

The upgrading of infrastructure of the Don Regulators will ensure continued flood risk benefits into the future for the Don Catchment and surrounding area with improved resilience and reliability of the new assets. Alongside the reduction in flood risk, the environment and biodiversity will improve in the River Rother as a result of the Meadowgate Fish Pass.

“Flood Control International, a trusted subcontractor to MWH Treatment, brought the expertise and professionalism required to review the proposed solutions through collaboration, and offered opportunities during the design phase which led to both cost and time savings to the programme.”

Torrential rain in 2017 led to flash flooding and power outages across Northern Ireland, with the North West suffering badly. The River Faughan overflowed causing major damage to bridges, roads, water mains and flooding to some Northern Ireland Water sites including Faughan Raw Water Pumping Station (RWPS), the sole source of raw water to Carmoney WTW outside Eglinton village.

Danson Park Lake is situated within a densely populated area of southeast London, near Bexleyheath. The lake receives water from a small catchment, which is entirely urban, apart from the immediate park, which bounds the lake to the north and south. The watercourse downstream of the dam is culverted for a considerable length, through housing, before emerging in Bexley Woods, approximately 600m downstream of the dam.

To comply with Section 10 of the Reservoirs Act 1975, reservoir inspections are required at intervals not exceeding 10 years. During the last inspection it was identified that an increase in the spillway capacity was required to meet new legislation. The existing capacity was limited by the discharge pipework to approximately 2m3/s, whilst the probable maximum “safety check” flood is estimated at 45m3/s. A subsequent flood study indicated that it was not feasible to prevent overtopping of the dam. Instead, it recommended that the proposed works should include measures to protect the dam against overtopping flows.

The client considered the options on the basis of hydraulics, associated civil design, environmental impact and cost. The modification of the left bank, to function as a second auxiliary spillway, was identified as the preferred design option. This included installing a new floodgate on the crest road adjacent to the spillway, to prevent flow spilling south from the additional spillway during operation, as well as installing a second floodgate at the southern end of the dam adjacent to the existing (secondary) spillway, to prevent flow spilling north from the spillway during operation.

Lift hinge floodgates were specified, due to the need for maintaining a flat walkway for pedestrians and cyclists. This was a particularly novel project, as it was the first time Flood Control International’s floodgates have been used as flow diversion gates to protect an existing dam spillway.

The clients’ objective, working closely with their insurance partner, was to find a way to protect key assets at the site, that would keep the plant running in the event the local river level rose such that the site becomes inundated. It was clear that it would have been uneconomical to protect the whole expansive site, so the team identified key areas and assets at risk of flooding and at what depth they needed to be protected to. A risk value versus cost outlay exercise was conducted on everything below the flood defence level, to help define the risks to factory output and provide a list of areas where options to prevent/mitigate exposure could be considered.