Supply Chain - Flood Alleviation

With limited public funding and the increasing need for multifunctional infrastructure enhancements, the scheme offers lessons in the delivery of multiple benefits. The scheme comprises:

Ammanford is located at the confluence of the rivers Loughor, Lash and Marlas. The rivers respond rapidly to rainfall and their channel capacity is limited. Much of the town is built on low-lying land adjacent to the river and overtopping is predicted at multiple locations. If nothing was done to reduce flood risk, 198 homes and 25 business would remain at risk of flooding from the 1 in 100 (1%) annual chance event.

NRW studies demonstrated a strong case for change. The study area was one of the top communities at risk of flooding from main rivers within Western Wales, and facing one of the largest increases in flood risk as a result of climate change. Flooding in the area was predicted to cost the UK some £7.9m in today’s prices over the next century.

With options to slow flows upstream infeasible, optioneering focused on better containment of flood waters in the river corridor. No single flood defence would be able to meet the project objectives, so a combination of raised defences throughout was adopted as the preferred solution.

The scheme was designed to reduce flood risk up to the 1% AEP event, allowing for the impact of climate change over the scheme’s 100-year lifetime; benefiting 349 homes and 37 businesses.

Separately, NRW had identified the case for improvements to Tir-y-Dail weir at the downstream extent of the scheme. The weir was a partial barrier for upstream migration of adult Atlantic salmon and trout, and a complete barrier to adult lamprey and juvenile European eel. Fish passage improvements would unlock 20km of river to migratory fish. The weir was in poor condition but encased a critical main sewer and enabled upstream river level gauging.

The design phase of the scheme involved comprehensive investigations and modelling to understand flood dynamics and identify effective solutions. Key design considerations and innovations are presented below.

Positive solutions to mitigate detriment

At the outset, the team identified a risk of conflict between the initially separate fish passage and flood scheme objectives. A further challenge was mitigating potential flood detriment to other areas. Flood modelling indicated that raising flood defences and making fish passage improvements to the Tir-y-Dail weir would cause unacceptable detriment elsewhere. Typical measures to mitigate the detriment were investigated but were found to be either ineffective or excessively costly (such as additional raised defences upstream) jeopardising the business case justification for the scheme.

The team identified and developed from first principles an innovative solution to locally address issues in proximity to the weir, including an area of ground lowering within the field adjacent to the existing weir and fish passage pre-barrages. This provided additional conveyance around the existing weir and proposed pre-barrages in more extreme flood events, mitigating potential detrimental increases in flood risk associated with both the flood defence and fish passage improvements.

To maximise the benefits of the ground lowering, soils generated from this area were used within the construction of the Tir-y-Dail flood bund, improving the scheme’s earthworks balance and reducing import volumes. The area was also landscaped to provide additional area of riparian habitat.

Balancing earthworks

Two factors made creating an earthworks balance on the project challenging. Firstly, the nature of the scheme and site constraints resulted in limited areas of fill. Secondly, the engineering and chemical parameters of some of the soils excavated were unfavourable.

To minimise the volume of excavated soils that would need to be disposed of off site, the team first addressed the chemical properties of the made ground. Site-specific risk assessments were undertaken to derive appropriate re-use criteria for human health and controlled waters. These were developed into a material re-use strategy, which considered appropriate legislative frameworks and was able to demonstrate that the majority of made ground was chemically suitable for re-use in appropriate scenarios.

To address the imbalance in volumes, the design of the Tir-y-Dail flood bund was reviewed as the primary fill area within the scheme. Flood bunds are most commonly constructed from a homogenous clayey material. This would need to be imported due to a lack of suitable on-site sources. The flood bund was therefore designed to have a ‘cap’ of imported clay to ensure performance against flooding, while the main core was formed from variable site-won material. Slope stability assessment undertaken under various scenarios demonstrated that, as long as the clay cap material was appropriately controlled, the geotechnical parameters for the core material could be significantly reduced.

To allow the contractor flexibility of the site-won materials placed in the core of the bund depending on the sequencing of their works, a project-specific soil material class was created. This was based on a combination of observational and basic material classification controls. This approach resulted in a reduction of 270 wagon loads of soil movements, reducing carbon and impact on local residents.

Sensitive detailing of flood defences

Measures were adopted to ensure the flood defences were sensitively integrated into the local landscape.

Flood walls in publicly viewable areas were finished with brick cladding, form liner finish and imitation stone copings to match local architecture. Coping stones were designed to be structurally integral to the flood wall to minimise their overall height, as well as reduce maintenance and public safety risk. Pillar features were incorporated into the facing of brick cladding at regular spacings to provide visual interest along the expanse of the wall.

Design of the Tir-y-Dail flood bund was tailored to mitigate its impact on the open views from a nearby public right of way. In plan, a curved alignment was specified to conserve an irregular field pattern. In section, slopes were slackened and rounded at the top and bottom to create a naturalistic landform.

A fundamental element of the scheme design was determination of the alignment and form of the flood defences to minimise tree loss along the riparian corridor. An arboriculturist, who was integral to all major design decisions, was embedded within the design team. Every tree was considered individually so that as many trees as possible could be maintained. The resulting designs/design adaptations included micro-siting of flood walls and localised modifications to flood wall foundations in the vicinity of root protection zones.

The project is in the heart of Ammanford, with interventions required in a combination of residential, commercial and public spaces. Multiple rounds of public engagement supported the scheme development, including:

In line with NRWs strategic objectives, enhancements to public space and ecological habitats were fundamental to the scheme design, in addition to reducing flood risk. To provide biodiversity net benefit through increasing connectivity, diversity and ecosystem resilience of the high value riparian corridor, enhancements delivered as part of the scheme included:

Improvements to public spaces in the vicinity of the flood defence works, but also within the wider community, were also delivered as part of the scheme as summarised below:

Environmental impacts were assessed through the Environmental Constraints and Opportunities Record (ECOR), with mitigation and enhancements integrated at an early stage into scheme development, heavily influencing the design process. Potential impacts upon trees, protected species, local community, archaeology, and local landscape, are some of the many that were assessed and mitigated.

The ECOR informed the Environmental Action Plan which formed part of the works information for the scheme and enabled key environmental mitigation measures to be communicated and tracked during the construction phase. The mitigation and protective measures implemented were comprehensive, covering the local community, protected species and environmental quality.

The works were spread across nine locations in Ammanford comprising residential, commercial and public areas. Each location presented unique challenges and constraints. To ensure that the project was executed safely and efficiently, significant effort was made to tailor methods of construction in each location.

The team’s focus on careful planning and attention to detail ultimately resulted in the successful completion of the project.

Early contractor investigation works captured potential clashes with existing utilities and structures. A collaborative working approach from all parties ensured potential issues were rectified before the main construction works commenced.

Working methodology, plant and equipment choices were tailored to the environment at each location to minimise disturbance. Due to the nature of restricted access in some locations, alternative construction methods were implemented. This included the use of a lightweight shuttering system that could be safely manually handled into position.

Collaborative working between the client, contractor and designers allowed early access for in-river works. Note only did this result in the fish passage works being completed with minimal impact on the ecosystem, but also reduced the overall construction programme by many months.

The Ammanford Flood Risk Management and Fish Passage Scheme is a testament to the importance of comprehensive planning, innovative design, and community involvement in flood risk management. By addressing the unique challenges of Ammanford, the scheme significantly reduces the flood risk for hundreds of properties and unlocks 20km of river to passage, as well as providing numerous other environmental enhancements. This case study highlights the critical role of such projects in building resilient communities and enhancing the environment.

The scheme was successfully tested whilst still under construction in September 2023.

The Stephenson Street Scheme comprises approximately 2km of raised defences (flood bund, sheet pile wall and reinforced concrete stem walls). Additional defences address outflanking, including a 9m-wide floodgate where Corporation Road passes beneath a railway. This required the construction of 0.7km of new highway to provide alternative access and emergency egress when the flood gate needs to be closed.

The design overcame significant constraints including challenging mudflat settlement, access/landowner access requirements and a plethora of congested existing utilities.

The project vision supports the area becoming a visitor destination in its own right. A ‘hidden’ flood defence wall integrates the scheme into its industrial setting. For the trail section, views out to the River Usk from sections of the iconic Wales Coast Path (WCP) were maintained and accessibility improvements delivered.

The scheme also improved community green spaces. Enhancements to Coronation Park comprised new accessible footpaths with regular resting and seating areas to offer views across the River Usk and to the restored Newport Transporter Bridge in a circular route. 1,600 trees were planted to form an area of urban forest, as well as shrubs, wildflower, grassland, and reedbed areas. In response to suggestions during community engagement, a linear seating feature was incorporated into the design to support the adjacent community football team pitch.

Ground conditions at the site are dominated by around 14m of very soft tidal flat deposits. The soft material is highly compressible and exhibits long-term secondary creep behaviour.

In Coronation Park, the historical embankment was raised by about 1m and widened, maximising reuse of site-won material, then capped with imported clay, with allowance for the bund crest to settle a predicted 0.4m over 50 years.

The highway runs up and over the flood wall on an embankment. Innovatively for a flood defence scheme, Arup designed a prefabricated vertical band drain facilitated surcharge solution to drive out the predicted 0.9m settlement within the construction phase rather than over decades.

Surcharge was required to expedite the consolidation process and mitigate against secondary component of consolidation known as creep. This protects the highway pavement and flood walls from excessive settlement post-construction, whilst saving significant cost and carbon over traditional piled methods.

Continuous monitoring and various instrumentation interpretation allowed site team to update actuals vs prediction for effective forward planning of subsequent highway construction. The scheme has gained national interest and featured in Ground Engineering.

With SAC watercourses in proximity and earthwork activities during inclement weather, silt mitigation was a key consideration. Through attenuation ponds, well considered pre-earthworks drainage and silt busters, construction avoided silt-related issues. The scheme was developed in consultation with the Sustainable Drainage Approval Body (SAB) and the Highways Authority, prior to adoption.

The River Usk at this location is a Special Area of Conservation (SAC) and Site of Special Scientific Interest (SSSI) - extending from the river to the crest of the embankment. Parts of the embankment are also Sites of Importance to Nature Conservation (SINC) for their habitats. Shad, a species of fish, are a feature of the SAC and are sensitive to vibration.

Proactive, extensive ecological surveys and consultation with regulators over several years, managed risk with protected and invasive species. Surveys identified potential habitats for water vole, dormouse, badger and great-crested newt but confirmed these are not likely to be found or breeding within the affected works area.

Construction minimised the impact on any sensitive species and habitats to ensure no loss to protected habitats. Techniques such as innovative GIKEN reaction-based piling system minimised noise and vibration, avoiding consenting delays and challenges.

Between Coronation Park and the Felnex Industrial Estate, the existing bund was sandwiched between sensitive saltmarsh and businesses. Early engagement and collaborative design workshops with NRW environmental advisors and ECI partners led to the selection of silent press-piling systems to install 700m length of sheet pile wall; undertaken by Ivor King The Piling People.

Pile transportation, pitching and installation itself are carried out from on top of previously installed piles. This footprint-free method had multiple benefits including:

The 1.7m high and 9m span sliding flood gate across the Corporation Road highway prevents a flow path for flood water beneath a railway overbridge. As the access to industrial premises, the design considered the road is subject to a high volume of Heavy Goods Vehicles and also abnormal vehicles, and the gate was design for deployment in high winds by a single operative. The gate was manufactured by local Port Talbot-based firm MM Engineering.

There are a high number of existing statutory and non-statutory utilities in the carriageway. Construction was delivered through close collaboration with every statutory undertaker without impacts on project programme, minimising construction risk.

Minimising embedded carbon was a key performance indicator for the scheme. An initial baseline embodied carbon assessment by the design team in advance of construction highlighted key areas for potential savings.

The team selected ‘Eco’ sheet piles, produced using recycled steel and 100% renewable energy, delivering a 40% reduction in sheet pile embodied carbon.

The concrete specification strongly promoted carbon reduction with cement replacement materials. Indeed, ordinary Portland cement was not permitted for use.

Creating an earthworks balance was challenging. The nature of the scheme and site constraints offered limited areas of fill. Also, the engineering and chemical parameters of most soils excavated were unfavourable. Facilitated by site-specific risk assessments to derive appropriate re-use criteria, the project team found a use for materials won in the highway construction within the formation of the Coronation Park flood bund. This allowed re-use of 3,500m3 of site-won material otherwise needing off-site disposal.

Educating the next generation of engineers and environmental specialists was an important aspect that was incorporated into the delivery model. Two engineering and one QA apprentices were employed on site. Trips with around 200 site visitors were organised and supported through organisations such as ICE, CIWEM and University of South Wales. The scheme was also an important part of Cardiff University’s Civil Engineer Degree Year 4 module with fifty students attending each year for a site visit and presentation given by the site team.

Stephenson Street represents NRW’s largest capital investment in a singular flood risk management project in Wales. The collaborative engagement between client, designer and contractor throughout development and delivery demonstrates inherent value; particularly through the incorporation of innovative, low-carbon engineering solutions and the early identification and utilisation of a local supply chain.

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.

Bridgend County Borough Council (BCBC) commissioned Arup to develop a business case for investment to reduce coastal flood risk to Sandy Bay, a wide and popular beach in Porthcawl. Analysis revealed that the condition of Porthcawl’s historic Western Breakwater was key to managing coastal risk throughout the bay. As a result, it was agreed with Welsh Government, to include the structure in the project.

The bay is surrounded by more than 100 acres of land identified for regionally significant regeneration. A phased approach was developed so works within the council’s control could be funded without the delay and risk of awaiting future development.

As part of the evidence for the business case, flood inundation modelling, informed by asset condition assessments and wave modelling, showed that 110 homes and 70 businesses were at risk of flooding. However, if the Western Breakwater were to fail, this increased to more than 530 homes and 175 businesses.

Porthcawl’s 182m-long Western Breakwater is 200 years old and Grade II heritage listed. It forms a crucial part of the coastal infrastructure that protects the harbour and Sandy Bay from extreme wave impacts, but a challenging programme of repairs and strengthening measures was needed to maintain its structural integrity.

To protect its legacy, Arup consulted closely with Cadw, the Welsh Government’s historic environment service, as well as BCBC’s heritage specialists, enabling consents to be obtained without programme delay.

The challenge with the Western Breakwater was understanding the existing structural form (as the breakwater had undergone numerous modifications over its lifetime) and the likely failure scenarios associated with that structure. It was essential for the team to uncover its chronological development since its construction in the 1820s and to identify the nature and extent of its defects.

Arup combined historical research with drone, lidar, geophysical and geotechnical survey data to understand its structural weaknesses. Surveys used non-destructive techniques such as ground-penetrating radar, supplemented by trial pits and horizontal cores. Using the information gathered, the team devised a plan to help maintain the breakwater’s original character while reducing flood risk and improving its structural integrity.

The design included repairs to masonry and concrete, raising parapets, installation of a precast concrete cut-off wall and new rock armour. The design thus reduced the risk of voids and the impact of waves. Stone was sourced from the local quarry used in the original construction to replace a failed seaward sloping wall, and the voids were grouted to prevent water leakage and corrosion. A cut-off wall was constructed to provide a protective layer to reduce scour risk and future washout of fine material.

To strengthen the slender parapets without damaging the heritage-listed historic masonry, Cintec reinforcing anchors were added. This is a system that uses grout contained in a fabric sock mesh, combined with steel anchors. It helped to preserve the breakwater’s original character, as well as minimising carbon impacts and overall project costs.

By repairing the existing breakwater, rather than building a new one, the project reduced embodied carbon, and using locally quarried materials reduced transport impacts. The choice of prefabricated mass concrete blocks instead of reinforced concrete for the cutoff wall reduces future maintenance needs for the Western Breakwater. During construction it also reduced the health and safety risks of deep-water working, as the blocks acted as permanent shuttering.

Early engagement with Knights Brown contractors providing early supplier engagement was key; it ensured that the team’s designs could be safely implemented during periods of low tide and in challenging coastal working conditions.

As well as repairing and improving the listed breakwater, the project extended to the Eastern Promenade, located on the west side of the popular Sandy Bay beach. Initially, a secondary wall to stop waves overtopping the promenade was planned, but Arup’s placemaking design sought to ensure the promenade would be attractive for visitors and residents in years to come, and overtopping studies showed that the wall could be replaced with multifunctional planters. This added more green space, integrated terraced seating and minimised service diversions and disruption to the public.

The team also improved cycling and walking routes, ensuring the promenade was more functional and appealing for visitors and locals.

Where previous proposals would have seen the sand dune habitat protected by concrete terraced defences, ABPmer’s study for Arup into coastal processes showed that the dunes could be preserved and restored using nature-based solutions, minimising costs and carbon emissions. For the restoration of the dunes to create a natural buffer, the team proposed 285m of low-level fencing to encourage the build-up of new dunes. These simple measures, combined with a growth and stability monitoring plan, will help maintain the coastal pathway. This approach has enhanced coastal resilience and revitalised the beach ecosystem, benefiting both residents and tourists.

To help support marine biodiversity, the team worked with CubeX Industries Ltd/BlueCube Marine and Swansea University to test innovative modular textured panels used to form an artificial reef and rock pools.

The project, known locally as the Settlers of Porthcawl, gained community support for eco-engineering interventions. Through questionnaires, the team established the public’s preferences for patterns imitating natural textures, and for a mixture of designs on the seawall. The project gained popularity among local schools and hosted over 200 students to teach them about climate change, biodiversity and sea-level rise.

Monitoring for a year revealed colonisation disparities across the sites due to wave exposure. This emphasised the significance of submergence and exposure. It was found that the most successful patterns to help foster colonisation were those with protruding ledges and rough microstructures, as opposed to smooth designs.

Knights Brown was appointed principal contractor under a NEC3 Engineering and Construction Option A contract, reflecting a commitment to cost acuity and risk mitigation.

In the high-risk environment, reducing construction risks meant minimising drilling, concreting and grout injection times to suit three-hour tide windows. Design and construction teams worked collaboratively on site, for example to minimize grout loss due to residual post-survey uncertainty around structural void volumes and locations. Cradle solutions extended working times. Precast standardised mass concrete blocks and redesigned Cintec anchor applications all supported installation.

Extensive consultation with users of the infrastructure and development of a phasing plan (including measures such as avoiding construction at Rhych Point during peak tourist season and phasing construction to retain public access to Eastern Promenade) was crucial to mitigate negative impacts during construction. This enabled community and sporting groups to access the promenade and maintained RNLI lifeboat access to the slipway. Project information boards and use of local media raised awareness of the scheme and kept users informed of progress.

Community benefits emphasised local employment and training opportunities, including five new-entry apprenticeships, engagement with local supply chain and support of local initiatives for young people not in education, employment or training. A bespoke schools engagement programme based on ‘The Tale of the Sea Monster’ educated and raised awareness of the need for improvements in a child-friendly, engaging way.

Construction was hit by several large and powerful storms; evidenced by modelling to be impacted by climate change. In response to damage from a May 2021 storm, repairs employed hydro-demolition of concrete around reinforcement bars, repairing the corroded bars and spraying concrete to repair panels. The resilience of these repairs was proven in December 2021 when Storm Barra halted construction work but caused no damage to repairs.

Despite the impact of the COVID-19 pandemic, as well as multiple severe storms, the Porthcawl Sandy Bay Coastal Scheme was completed in the agreed time-frame and within budget in Summer 2023.

Beyond its primary objective of reducing flood risk, the scheme has delivered substantial economic benefits to the local community and the wider region. By safeguarding critical infrastructure, residential properties and commercial assets, the scheme protects livelihoods and preserves the vitality of the coastal economy. Moreover, the enhanced recreational opportunities and improved coastal aesthetics will attract tourists and investors, stimulating economic growth and enhancing the town’s resilience to future shocks.

Janine Nightingale, Director of Communities, Bridgend County Borough Council commented:

“... [the scheme] forms a vital part of the infrastructure for defending the town against flooding and will also help to secure future development in the area.”

The scheme was highly commended for the Environmental Project of the Year and shortlisted for the National Infrastructure Commission’s Design Principles Project of the Year at the British Construction Industry Awards 2023.

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 Living With Water (LWW) Partnership was formed following the 2007 floods when 16,000 properties in Hull and East Riding were flooded. It became clear that no single agency accepted any responsibility outside of their own term of reference, but that each had a part to play in maintaining the waterways in the city of Hull which contributed to the floods. The partnership brings together Yorkshire Water, Hull City Council, East Riding of Yorkshire Council, Environment Agency and University of Hull to enable them to collaboratively deliver flood alleviation schemes in the city. The first of its kind in the UK, the partnership aims to reduce flood risk in high-risk areas, while combining blue-green principles to deliver sustainable, low carbon solutions, encouraging knowledge share between all parties, building community resilience, improving local areas by providing biodiversity net gain.

The principles of the project are to allow exceedance flows from heavy rainfall, for which there is no capacity in the sewer network or nearby watercourses, to flow above ground via existing road accesses between properties, into detention basins retrofitted into existing green spaces in the area. The stormwater can be retained away from properties and returned to the sewer network once there is available capacity and the network is no longer surcharged.

The road access, or ‘10fts’, between properties are lowered to create a channel for stormwater to flow from the highway into the Aqua Green. A headwall and return sewer are installed from the low point of the Aqua Green, connecting into the existing sewer network in the main highway. Flows leave the Aqua Green under gravity, meaning that no mechanical or electrical elements are required for the operation of the solution. The lowering of the 10fts meant that property protection measures were required to the properties adjacent to the 10ft to prevent the solution resulting in them to be at greater risk of flooding. Existing boundary fences were replaced with new fence panels installed on concrete gravel boards to provide a waterproof barrier between the 10ft and the property.

Across the three Aqua Greens, over 1800m3 of storage has been proved. With a traditional grey infrastructure project, providing the same storage would have had a much higher embedded carbon measure, could not have been constructed in the small areas that were available and would have required some form of M&E installation with associated ongoing maintenance and running costs.

The concept design was carried out by Stantec, who produced a full hydraulic model of the whole area to determine where the highest flood levels are seen, to identify the green spaces that would provide the most benefit if they were developed. A total of 11 green spaces in the area were investigated, with cost benefit analysis carried out to establish which of those spaces would provide the most benefit for the community. Three sites were selected to be developed in the first Work Package (WP1) with a further three sites to be developed in Work Package 2 (WP2).

The overall project programme meant that long term groundwater monitoring could not be carried out prior to the design process for WP1. For design calculations, groundwater therefore had to be assumed to be at ground level, which resulted in flotation of the liner and as a result, an additional drainage later needed to be installed below the liner to prevent flotation.

During the construction of WP1, it was observed that the Aqua Greens were retaining water before the liner was installed and that the as clay of very good quality. For WP2, permeability testing and longer-term groundwater monitoring were able to be carried out. This determined that the natural clays were of higher impermeability than the geosynthetic liner and that the groundwater was not as high as was believed during the design phase for WP1. It was therefore discussed and agreed with all relevant parties that the additional geosynthetic liner did not need to be included on site. This saved a total of two weeks on the programme for WP2, approximately 60 tonnes of carbon, material costs of approximately £60,000 and removed the risk of delays associated with the liner install in wet weather.

Construction for WP1 was from October 2023 to December 2024, with works still progressing on the WP2 sites. Sole access to the green spaces via 10ft wide access tracks introduced some difficulties to the construction. Only small plant could be used and the 5m wide liner had to be cut to 2.5m for delivery to the greens. Limited space on site also meant that excavated materials could not be stored at the greens and had to be stockpiled at the site compound, requiring a significant number of dumper loads of materials to be moved on the local road network. The nature of the project and works commencing in winter meant the Aqua Greens frequently flooded during the construction, with water regularly needing to be pumped to the drainage network before further progress could be made.

Due to the location of the Aqua Greens in such close proximity to residential properties, significant community engagement was needed throughout the project, during both design and construction phases, to ensure that the community were kept up to date with what the project would deliver, how the construction works would impact them and ultimately how the SUDs solution would operate and be maintained into the future. Over 30 engagement sessions have been held with the community to date, from the start of the design development to the end of the construction phase. This has been coupled with regular letters and updates on the LWW website, providing the residents with an opportunity to raise any concerns about the works as well as to help to convey the importance of flood alleviation in the area.

To aid conversations with the local community about the Aqua Green developments, computerised visualisations were produced which showed how the Aqua Greens would look upon completion. While the existing greenspaces were mainly neutral grassland before works commenced, the solution was to plant wildflower seeds in the greenspaces upon completion, to increase biodiversity of the area. To provide habitat for wildlife, wildflower areas are maintained less frequently than grassland spaces and this therefore needs to be portrayed to the residents.

The visualisations also helped the MMB team to discuss the proposals with the residents to see if there was anything additional, they would like to see of change as part of the design. Some residents said that they particularly liked the shrubs at the back of one of the green spaces as they provided them some security for their garden, so these were retained as part of the design. Others suggested that the proposed parking areas would not be used and that they did not want to encourage parking on the green spaces, so these were reduced in width to just passing places on the narrow roads.

Continued engagement with the community has been needed throughout the construction phase to answer any queries that the residents had about the works and rectify any problems they had been experiencing. Upon completion of the Aqua Greens, permanent notice boards have been installed at each of the sites to inform the residents of the benefits of the Aqua Green.

The University of Hull have installed testing and monitoring equipment at all three of the Aqua Green sites in WP1 to understand how these Aqua Greens perform. The testing and monitoring equipment included soil moisture probes located above and below the liner; conductivity, temperature, and depth (CTD) probes in the return sewer and a weather station at a local school. The aim is that this data will be analysed and used to improve the design to enhance these assets for future installations. The weather station data is also accessible by the local school so that the data can be used for educating the students about the weather and flood risk of their local area and how we can safely live with water.

The intention is that further testing and monitoring equipment will be included on the WP2 sites so that a comparison can be made between the lined and unlined solutions to see if one of them is more effective at providing the required storage or improving the quality of the water that enters the sewer network.

Since the installation of the first three Aqua Greens was complete, the benefits provided by the Aqua Greens has been visibly clear during periods of heavy rainfall, with quantitative data expected from the testing and monitoring installations within the next few months. These large-scale SuDS basins have provided flood protection to hundreds of properties in an area which otherwise would be at very high risk. Providing the protection via blue-green methods rather than traditional grey infrastructure has resulted in a solution with a much lower carbon impact, while also providing the areas with an improved biodiversity, making it a much more sustainable solution. The blueprint of this project, along with that of the Living With Water partnership, can be applied to other areas across the UK where properties are at high risk to deliver more types of these projects in the future.