Supply Chain - River Work

The Severn Estuary is renowned for its tidal range of 12-14 meters, the second largest in the world, and as such poses significant challenges for civil and marine works. In late 2024, a critical infrastructure upgrade project was completed near Nash, Newport, replacing a long sea outfall pipeline originally constructed in 1960 to extend its operational life. The project involved installing a 1.4km 560mmØ high-density polyethylene (HDPE) outfall pipe to replace the deteriorated concrete-coated steel pipe. Situated within one of the UK’s most ecologically sensitive regions and a Site of Special Scientific Interest (SSSI) in the Severn Estuary, the project not only secured infrastructure integrity but also adhered to stringent environmental protection measures. Project challenges and environmental safeguards

Kaymac Marine & Civil Engineering Ltd was appointed as the principal designer and contractor for the £8.4m outfall replacement project.

The Severn Estuary is designated as a Site of Special Scientific Interest (SSSI), which protects its tidal flats, salt marshes, and diverse wildlife, which required the project team to introduce and adhere to comprehensive environmental safeguards.

[caption id="attachment_19920" align="alignnone" width="1200"] The in-land RC chamber connecting the new and existing pipe (during construction) - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

Sediment control measures such as careful selection of plant and equipment, implemented in collaboration with National Resources Wales (NRW), minimised water quality impacts during the excavation and pipe-laying activities.

Kaymac Marine & Civil Engineering Ltd drew upon its deep industry expertise and practical experience to drive the design direction and successfully secure all necessary permits and permissions for the project. Working closely with the local council and NRW, Kaymac led the process of obtaining the required Marine License, Environmental Permits, and Planning Permissions, ensuring full compliance with all regulatory requirements.

Through comprehensive site investigations and advanced geophysical and bathymetric surveys, Kaymac Marine & Civil Engineering Ltd identified critical site-specific characteristics that directly influenced the project’s design. This informed approach allowed the team to craft tailored solutions that addressed regulatory concerns while optimising project outcomes.

Kaymac’s practical experience played a crucial role in addressing the expectations of the environmental regulators. By proactively collaborating with NRW and other stakeholders, the team was able to satisfy stringent environmental requirements, demonstrating how the proposed designs minimised ecological impacts while maintaining structural and operational integrity.

[caption id="attachment_19919" align="alignnone" width="1200"] New valves within the inland chamber - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

This expertise and experience, coupled with a solutions-focused mindset, not only streamlined the approval process but also ensured that the final design adhered to both regulatory standards and the project’s overarching goals.

To maintain quality standards and to ensure the works could be undertaken within the licencing timeframes, Kaymac Marine & Civil Engineering Ltd engaged suppliers early on, securing essential equipment and materials; whilst conducting regular necessary quality visits and inspections to ensure technical and Quality compliance.

Severn Estuary LSO Replacement: Supply chain - key participants Principal Designer & Contractor: Kaymac Marine & Civil Engineering Ltd Designer: Pebble Engineering Ltd Specialist design: Morek Engineering Ltd Specialist design: H2NA Ltd HDPE pipe: Pipelife Norge AS Precast concrete collars: Poundfield Precast Precast concrete mattresses: Subsea Protection Systems Duckbill check valves: Measurit Technologies Valves: Scott Parnell Landside temporary works & shoring MGF Ltd Huennebeck Construction materials Scott Parnell Neal Soils Wright Readymix Stone Supplies IPP Floating plant Jenkins Marine Kraken Marine Services P&D Environmental Construction plant hire Land & Water Plant Hire Flannery Plant Weldex RW Christopher Crane Hire Ltd United Rentals Atlas Winch & Hoist Services Ltd A1 Surveys MTK Breakers LGS Gap Hire Services HV Fusion Severn Environmental Services ABP Newport & Barry [caption id="attachment_19913" align="alignnone" width="1200"] Trench excavation prior to the first section of pipe installation - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Detailed design & planning

A comprehensive understanding of the physical forces that dominate the ocean environment, their origins, and the likelihood and intensity of these forces over the lifespan of an outfall is critical to its effective design, regardless of the construction materials used.

These forces can compromise the outfall’s integrity either directly or indirectly, such as through seabed erosion or by destabilising its foundation. Additionally, sediment transport can obstruct diffuser orifices, potentially leading to system failure. These factors were considered and mitigated during the planning and design phases to ensure the long-term functionality for this particular environment.

Kaymac Marine & Civil Engineering Ltd appointed Pebble Engineering Ltd as designers and worked collaboratively to develop the construction methods and subsequently the detailed design of the outfall.

Both the construction method and the detailed design needed to align and complement each other, with regard to compliance of the aforementioned environmental and planning regulations, the seabed conditions present on site and the anticipated physical conditions (such as sea, wind, wave, tidal and current) of the works location.

Delivery & preparation of HDPE pipe

The new high-density polyethylene (HDPE) long sea outfall pipe, measuring 1.4km in length and 560mm in diameter, was manufactured by Pipelife Norge AS in Norway and was towed 1,134 nautical miles to Newport in 11 sections under a single trip.

Upon arrival at ABP Newport Docks, each pipe section was stringently inspected, tested and then later prepared for installation.

The preparation works involved the installation of over 260 bespoke precast concrete ballast collars that were designed to ensure stability of the pipeline against the hydrodynamic forces of the watercourse and the natural buoyancy of the HDPE material, once it had been sunk to its installed position within the trench.

[caption id="attachment_19915" align="alignnone" width="1200"] Pipe being prepared for connection - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Innovative installation techniques in a tidal environment

The use of specialised low pressure bearing amphibious excavators handled intertidal trenching at low tide, while a GPS-equipped dredging vessel undertook the offshore trenching requirements. The installation spanned an approximate 28-day period, working shift patterns under challenging tidal conditions, with trenches reaching depths of approximately 1.5–2 meters.

A key milestone involved towing the first 250 meter section of the pipe from ABP Newport, navigating the currents and flows of the Severn Estuary, to the installation site, approximately three nautical miles away. This segment, equipped with 50 concrete collars, was positioned over the trench as the tide receded, sunk under the guidance of divers from Kaymac Marine & Civil Engineering Ltd to ensure accuracy, before being backfilled with the previously excavated spoil.

Finally, the precast articulated concrete mattresses from Subsea Protection Systems Ltd were installed by utilising a crane barge to provide additional scour protection and stability to the outfall. Such mattresses have been used successfully for decades to protect oil and gas pipelines and since the early 1990s, they have been increasingly used to protect ocean outfalls.

Throughout the project, Kaymac employed a flotation and submersion technique whereby each 250 meter long section was towed into position and the seaward end of the previously installed pipe length was recovered to the working platform, before connecting to the new length and then sinking within the new pre-excavated trench.

[caption id="attachment_19916" align="alignnone" width="1200"] First section of the pipe within the trench during low tide ahead of backfilling - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption]

Ensuring an accurate and safe sinking procedure in the Severn Estuary required considerable planning efforts from the delivery team, taking into consideration tidal movements and slack water periods. Each sinking activity was planned meticulously to ensure that a constant submersion rate could be implemented, assisted by a number of key specialist vessels being present to position and secure the pipe section in place whilst the slack water period approached.

Slack water periods in this location are relatively short and as such, the rate of pipe submersion needed to be planned and controlled by adjusting both the water inflow and air release rates. To avoid a bending radius that could become smaller than its allowable minimum and further, to prevent the pipe wall buckling, the rates needed to be carefully monitored and controlled, all whilst considering the load imposed by the ballast weights, the varying tidal water depth and the pulling forces applied to the outfall by the marine plant.

The pipe installation continued in four separate sections, totalling 1.47km, with a diffuser head separately installed through diving operations at the seaward end. A backhoe dredger was used to place the previously excavated material on to the pipe.

Following the backfilling, approximately 210 of the precast articulated concrete mattresses in total, each weighing 8.3t in air, were laid over the installed lengths of pipe from the crane barge. The backfilling and mattress installation were monitored and supervised by Kaymac Marine & Civil Engineering Ltd’s dive teams, ensuring the accuracy and efficiency of both activities throughout the scheme.

Civil operations, plant isolations and final connection

To prevent disruption to the client during their day-to-day operations, the marine activities to install the replacement outfall were carried out alongside the existing operational outfall. Simultaneously, inland operations were undertaken by the skilled civils teams from Kaymac Marine & Civil Engineering Ltd, who installed a temporary sheet piled cofferdam to excavate and expose the existing valve and land-based outfall arrangement.

Two short operational isolations were required; the first to replace the existing land based valve and connecting pipes, and the second to connect the new replacement outfall to the existing infrastructure. Again, these isolations were planned precisely around suitable tidal windows, to maximise working efficiency and to minimise interruption to the plant operations.

During the first isolation, the existing land-based single non-return valve was replaced with new valves and a T-piece arrangement system that would permit future inspection and maintenance requirements.

Once the land based replacement and connection works were complete, the replacement valve arrangement was housed within a newly constructed reinforced concrete chamber, built alongside the normal operations of the plant. The chamber was designed to permit safe future access around the valve arrangement and to retain a section of the existing flood defence embankment.

The second isolation took place while the land-based civil works were underway to construct the new chamber. Working at low tidal periods, a bespoke HDPE pipe section was fabricated that considered both the vertical and horizontal changes in direction to align with the newly installed outfall. This section was installed to connect the newly installed outfall to the existing pipeline ahead of removing the isolation.

[caption id="attachment_19918" align="alignnone" width="1200"] Old pipe being removed during low tide - Courtesy of Kaymac Marine & Civil Engineering Ltd[/caption] Conclusion

The long sea outfall replacement project stands as a model of responsible marine engineering within sensitive ecosystems.

By balancing complex engineering requirements with rigorous environmental protection, Kaymac Marine & Civil Engineering Ltd are proud to have played a key role in improving Newport’s existing infrastructure; blending innovative marine engineering techniques with stringent environmental safeguards to protect and enhance the unique ecology of the Severn Estuary.

According to the European Commission, scientists estimate less than 1% of UK rivers are free from barriers to fish and eel migration. There has been a concerning decline in eel populations in recent years, and although the exact reasons for this are unknown, the government’s Water Industry National Environment Programme (WINEP) aims to help restore populations by requiring water companies to create vital passages for fish and eels at sites of obstruction. This project involved the construction of an 18m-long fish and eel pass at Langford Weir on the River Blackwater, about 50m downstream of an abstraction point used to abstract around 160 megalitres of water per day. The project enables aquatic species to migrate past the weir that was built to maintain the river’s water level to maximise abstraction availability. Site description

The River Blackwater is an Environment Agency (EA) designated main river and runs through the centre of Langford in Essex. The Blackwater intake, operated by Essex & Suffolk Water (ESW) provides raw water for transfer to Hanningfield Reservoir. A smaller abstraction, which feeds the Langford Water Treatment Works (WTW), takes place at the Langford Mill intake approximately 150m downstream.

The River Blackwater splits into two channels at Langford Weir. The main River Blackwater flows westwards over the weir to a pond and continues to its confluence point with the River Chelmer, at Beeleigh, just north of Maldon Golf Club. Flows around the Langford Mill intake are conveyed in an eastern Blackwater channel to Beeleigh. The site is in a designated Conservation Area.

[caption id="attachment_21943" align="alignnone" width="1200"] Site overview prior to construction of the pass - Courtesy of Stonbury Ltd[/caption] Project scope

A summary of the works undertaken is as follows.

Survey and design (by Stantec UK). Site preparation and groundworks. Construction of retaining wall to the River Blackwater. Construction of an in situ cast concrete fish pass structure including stop log isolation to both ends of the structure. Fish baffle and eel tile installation. Flow restrictor installation (in conjunction with the Environment Agency). Bespoke camera box installation. Design

Prior to Stonbury’s involvement in the programme, Stantec UK undertook the detailed design of the structure for ESW. A design was selected to suit both the asset geography and the species likely to use the pass. The pass design featured two specialised channels: one with multi-sized eel tiles and the other with Larinier fish baffles, featuring a resting pool halfway along the fish side. The tiles in both channels of the gravity-fed system were engineered to optimise water flow and facilitate easy passage for aquatic species.

[caption id="attachment_21944" align="alignnone" width="1200"] Tree stump removal as part of site preparation - Courtesy of Stonbury Ltd[/caption] Environmental management

A project site environmental assessment sought to register and mitigate site-specific environmental impacts such as noise, land and watercourse pollution, waste materials and damage to local ecology. Identified environmental risks were controlled through measures detailed in risk assessments and method statements.

A preliminary ecological appraisal was undertaken during the pre-construction phase to determine the presence of dedicated nature conservation sites and protected species in proximity to the site. During assessment, the toxic plant hemlock water dropwort was identified, and specific H&S protocol was put in place to protect workers.

The Client worked closely with the EA during the flood risk activity permit (FRAP) application and continued a close dialogue throughout the project. This included a collaborative visit by several EA staff to view project progress and discuss potential improvements and initiatives.

Site preparation

As the site is in a conservation area which has a high potential for archaeology, the programme methodology included special measures to avoid breaking ground unless it was essential. Therefore, to install a safe access route to the working area, timber bog mats were laid to create a firm access road without excavating the ground.

Suppliers with a specialist machine were mobilised for the removal of two large tree stumps that were obstructing the location of the new pass.

[caption id="attachment_21941" align="alignnone" width="1200"] Portadam system in place at the start of construction - Courtesy of Stonbury Ltd[/caption] To dewater the site and create a dry working area, a temporary Portadam system from OnSite Central Ltd was installed. One dam was installed on the river side at the top end of the pass, and a second in the pond at the lower end of the pass. Temporary pumping was used to drain the area behind the Portadams and maintain drainage throughout the programme. Once the working area was dry, a piling mat was laid to allowed access for the installation of steel sheet piling to prevent water from undermining the pass structure and provide additional foundation support. Langford Weir Fish Pass: Supply chain - key participants Principal contractor: Stonbury Ltd Principal designer: Stantec UK Ecological appraisal: Essex Ecology Services Ltd Archaeologist: Wessex Archaeology Ltd Civils construction subcontractor: GMP Projects Ltd Piling contractor: GM Piling Ltd Portadam: OnSite Central Ltd Temporary pumping: Selwood Concrete delivery: G&B Finch Fish baffles: Aquatic Control Engineering Eel tiles: Berry & Escott Engineering Services Stainless steel: Wickham Engineering Construction

While the working area was being dried, the team began excavating for the new fish pass. Initial excavations were supervised by the Client’s archaeologist, as stipulated in the planning conditions for excavation works. To avoid the necessity for the archaeologist to attend over several separate days, the site team carried out all excavations under one watching brief and backfilled before re-excavating while building the pass.

[caption id="attachment_21939" align="alignnone" width="1200"] Construction components; clockwise from top left: Gabion baskets, specialised fish and eel tiles, soil reinstatement, and safety railings - Courtesy of Stonbury Ltd[/caption] Sheet piling was installed at both ends of the pass to enable secure anchoring of the finished structure. This was achieved by driving piles into the riverbed at varying depths to create a stepped finish for the base, which was filled with a lean mix concrete to create a suitable foundation for the rest of the structure.

Bespoke steel supports were built and formwork was erected. A new concrete river wall was formed at the top of the pass to integrate with the existing structure. Formwork was then filled with concrete to create the main pass structure which included both fish and eel channels, a resting pool part-way up the fish pass, and cut-outs for stop logs and the new camera monitoring system.

After casting the concrete pass structure, the team installed an engineered wall on the river side of the structure and gabion baskets on the pond side to support the bank and backfilled behind the baskets with clean stone. The lower gabion on the southern side (nearest the bank) was placed to prevent pooling in what would otherwise be a ‘dead end’ for the fish and eels looking for a way into the pass. The banks and ground around the structure were then reinstated with the previously excavated material.

To complete the pass, the team lined the inside of the channels with bespoke Larinier fish baffles and tiles suitable for eels and elver. On the eel side, GRP mesh flooring was affixed on top of the channel. A handrail was installed around the structure to allow safe access for operatives to maintain the pass and remove debris, and a debris deflector was installed at the head of the eel pass to reduce debris entering the system.

[caption id="attachment_21940" align="alignnone" width="1200"] Completed concrete channels – Courtesy of Stonbury Ltd[/caption] Finally, Principal Contractor, Stonbury Ltd, worked with the Client and the EA to form experimental flow restrictors to control flows on the eel channel to maximise its operation, and with specialist suppliers to fabricate a bespoke waterproof camera box to monitor the number and diversity of fish using the pass. Challenges

The project posed two main challenges. First were the restrictions caused by the small working area constricted by two water courses and proximity to several protected trees. As there was only one access route to the working area, excavations and sheet pile installations had to be completed in stages, using an excavator with a Movax attachment, working backwards along the single access route.

Second, persistent heavy rain led to multiple major flood events which breached the Portadam and forced the team to reset the site and reinstate the working area before recommencing work. This was successfully managed by monitoring river and rainfall data to identify opportunities to reset and pump the area dry.

Video: Langford Weir Fish Pass - Courtesy of Stonbury Ltd

Sustainability

Addressing Stonbury’s and ESW’s commitment to deliver low-carbon, environmentally restorative infrastructure, each element of the project was completed using the most sustainable method practically available.

These included:

Using low-carbon, or ‘low-C’ concrete to form the main pass structure. Reuse of materials when possible - no excavated material was removed from site. Minimising on-site waste. Minimising fuel usage by ensuring pumps were switched off when not required. Conclusion

The team’s dedicated persistence achieved delivery despite the site constraints and setbacks due to unprecedented wet weather. The project will help facilitate the successful migration of fish and eels, re-connecting previously isolated populations and enhancing breeding opportunities. These benefits are highly likely to result in a significant increase in biodiversity.

The Outstrays to Skeffling Managed Realignment Scheme (OtSMRS) is a major coastal flood risk management and habitat creation project located on the north bank of the Humber Estuary, East Riding of Yorkshire. Developed by a joint initiative of the Environment Agency (EA) and Associated British Ports (ABP), the project is being delivered by JBA Bentley, and it forms part of the wider Humber Flood Risk Management Strategy. The project was developed to address several needs including compensating for intertidal habitat losses from coastal squeeze, new flood defences and future port developments, reducing the risk of flooding for properties and land around the villages of Patrington, Welwick, Weeton and Skeffling, and creating a more resilient land drainage system capable of responding to long-term climate change pressures. Project background

As the managed realignment altered the lower catchment drainage regime, a planning condition stipulated that the total pumping capacity of the fluvial pumping station needed to be increased to maintain effective drainage performance. Hydraulic modelling showed that the existing asset could not provide the required standard of protection during a 1-in-100-year fluvial event with climate change allowances.

The scheme includes the construction of a new managed realigned coastal flood embankment, controlled breaching of existing defences, habitat creation and replacement of the existing Skeffling Pumping Station.

[caption id="attachment_32168" align="alignnone" width="1200"] Breach facing the intertidal habitat and set back embankment - Courtesy of JBA Bentley[/caption] Client & stakeholders

The project is being delivered for the Environment Agency, working in partnership with Associated British Ports as the funding partner. Key stakeholders included the South Holderness Internal Drainage Board (IDB), East Riding of Yorkshire Council in its role as Lead Local Flood Authority, and Yorkshire Wildlife Trust, the Wildfowling Association, Natural England, the RSBP, Wildfowl and Wetlands Trust, and local naturalists for input on access and environmental considerations.

Climate-resilient flood defence & intertidal habitat creation

The Outstrays to Skeffling Managed Realignment Scheme fundamentally restructures the coastal defence line by constructing set-back embankments  and allowing tidal inundation of previously defended agricultural land.

The intent of the design was to create 169 hectares of new intertidal habitat and 75 hectares of complementary freshwater habitat (wet grassland) on the north bank of the Humber Estuary.

The new flood defence comprises approximately 5.5km of earth embankment designed to provide improved protection against tidal flooding, incorporating allowances for climate change. This required over 2 million tonnes of site-won material to be excavated, transported and placed to form embankments, habitat features and drainage infrastructure. The use of indigenous materials eliminated the need for imported fill, reducing both cost and embodied carbon.

The embankment design incorporated climate change allowances, providing protection against a high fluvial 1-in-200-year storm event including 2080 climate change projections.

[caption id="attachment_32166" align="alignnone" width="1200"] 3D model used for design and communication throughout the project displaying access arrangement, the new Skeffling Pump Station, the eel pass and realigned embankment - Courtesy of JBA Bentley[/caption] Drainage & hydraulic infrastructure

The OtSMRS required a complete reconfiguration of the drainage and hydraulic network to accommodate both river flows and tidal influences following the creation of intertidal habitat. Approximately 4.1 km of open drainage channels were constructed to convey inland flows around the realigned landscape and maintain effective catchment drainage.

As a result of the revised drainage strategy, flows reach Skeffling Pumping Station (SPS) more rapidly than under the previous arrangement. Hydraulic modelling showed that the existing pumping capacity of 2.40m3/s would be insufficient to maintain flood protection standards under future climate change scenarios, requiring an increase to 2.85m3/s.

To address this, a new pumping station was constructed 250m west of the existing facility, where modelling demonstrated improved hydraulic performance and operational resilience. Located behind the new eastern embankment, the station is protected from tidal flooding and provides a robust long-term solution for managing catchment drainage and reducing flood risk.

Supply chain - key participants Principal designer & contractor: JBA-Bentley JV Designer: JBA Consulting Contractor: JN Bentley Hydrodynamic modelling: ABPmer Steel sheet piling & CHS bearing piles: Ivor King the Piling People Pumps & weedscreen (subcontractor): Aquatic Control Engineering (ACE) Weedscreen, cleaner & gantries (supplier): Landustrie Stoplogs & flap valve: Waterfront Fluid Controls Metalwork: APT Engineering MCC: RSE Control Systems (TCS) MCC kiosk & wiring: Southern & Redfern Systems integration: Actemium Automation Electrical subcontractor: Bradshaw’s Electrical Ltd OSA subcontractor: Hesselberg Erosion Protection Geotechnical testing & validation: Professional Soils Laboratories Ground investigation: Central Alliance Pre-Construction Services Ltd Ground investigation: Lankelma Ltd Archaeology: York Archaeology Trust Fencing: Burn Fencing Ltd Bird hides: Gilleards Brothers Landscaping: Lowthers Forestry Group Road surfacing: Til-Ex Pumping station design & replacement

The installed solution comprises three Archimedes screw pumps, selected for their suitability in low-head, high-flow land drainage applications and their inherent compatibility with eel passage requirements. The pumping station discharges into the newly created intertidal habitat area, representing a significant change from conventional outfall configurations and requiring careful hydraulic integration with tidal conditions.

[caption id="attachment_32169" align="alignnone" width="1200"] Skeffling Pumping Station view from inlet channel - Courtesy of JBA Bentley[/caption] Innovations, cost savings & carbon reduction

The scheme incorporates several practical innovations through eel-friendly Archimedes screw pumps, an open stone asphalt (OSA) eel pass, a site-won wave bund, virtual reality (VR) stakeholder engagement, and GPS-enabled digital earthworks.

Results included improved buildability, reduced carbon, supported ecological compliance and created repeatable solutions for future EA schemes.

Material reuse and carbon reduction

The extensive use of site-won material for embankment construction reduced the need for imported fill. Sacrificial wave bund constructed from site-won material which avoided approximately 40,000t of rock armour saving approximately 23,000 tCO2e (90% less carbon than rock armour). Haul road materials were re-purposed through site-won materials with carbon saving of approximately 116.5 tCO2e.

Eel pass innovation

Suitable for erosion protection in tidal and river environments, with the capability to withstand flow velocities of up to 8.5m/s, the scheme incorporates a purpose-built eel pass integrated within the new embankment.

Constructed using open stone asphalt (OSA), the eel pass was selected for its permeability, flexibility and rough surface texture, which provide favourable conditions for eel migration while accommodating ground settlement and reducing hydrostatic uplift forces.

The design was developed to comply with the Eels (England and Wales) Regulations 2009, ensuring the safe upstream passage of eels between the Humber Estuary and inland watercourses while maintaining the resilience and performance of the wider flood defence infrastructure. The use of OSA for eel passage is the first of its kind in the UK, and possibly globally.

[caption id="attachment_32167" align="alignnone" width="1200"] OSA formed eel pass integrated within the new embankment on the left - Courtesy of Hesselberg Erosion Protection[/caption] Digital delivery

Digital engineering played a significant role in scheme delivery. The collaborative 3D modelling platforms such as VR, 360° imagery, drone footage and coordinated 3D models to walk through the design, enabled the coordinated and multidisciplinary design team to resolve clashes and support construction sequencing and stakeholder engagement.

This digital approach improved quality control and provided a clear audit trail, particularly important for a scheme involving multiple interfaces between civils, geotechnical, hydraulic, structural and environmental disciplines.

Programme & cost performance

Integrated delivery, digital tools, early stakeholder engagement and material reuse improved buildability, reduced change and strengthened cost certainty. Re-purposed materials and alternative haul road methods saved approximately two weeks.

Early option appraisal and collaborative workshops with the Environment Agency, Natural England, the Internal Drainage Board and other stakeholders helped reduce risk, streamline approvals and manage ecological, seasonal and weather constraints.

Careful phasing, concurrent work fronts and close collaboration enabled the project to be delivered on time and below budget.

[caption id="attachment_32165" align="alignnone" width="1200"] Typical OSA section for eel pass open channel - Courtesy of JBA Bentley[/caption] Social value

Social value is the wider value generated above and beyond the scope or requirements of a project. At Skeffling, there were no social value targets set at the beginning of the project. However, as the project evolved, the team ‘went the extra mile’ to ensure that social value was still delivered throughout the works.

This was achieved through close collaboration with landowners, farmers, statutory bodies and community stakeholders, helping to reduce disruption, use local knowledge and create a more resilient landscape for communities around the Humber Estuary.

Supporting local businesses

Prioritising local suppliers enabled investment in the local economy, with local farmers efficiently flailing 250ha of land and seeding 20ha of new embankment using their specialist knowledge of the area.

Supporting the environment

Collaboration with local environmental groups helped deliver biodiversity enhancements beyond the project’s original scope.

By trebling its original planting commitment of 4,901 replacement trees and shrubs (five new trees/shrubs for every one removed), the project delivered more than 14,200 trees and shrubs and 700m of new hedgerows. These measures have created a network of interconnected green corridors for wildlife and enhanced the ecological value of the site.

[caption id="attachment_32171" align="alignnone" width="1200"] New set back tidal defence embankment and the intertidal habit area on the left - Courtesy of JBA Bentley[/caption]

Promoting sustainability, educational outreach & supporting early careers

The scheme delivered lasting environmental and community benefits that aligned with long term sustainability goals where more efficient pumping stations have been installed and new embankments created, improving flood resilience, increasing drainage capacity and reducing operational carbon.

The project team supported Blue Carbon research through site sampling conducted by a PhD student. Alongside this, the EA and JBA Bentley dedicated over 100 hours to educational activities with local schools and college students, covering topics such as archaeology, coastal erosion and flooding. Students also helped design new bird hides, with features including sustainable oak sleepers and a cockleshell roof incorporated into the final design.

The project supported a range of apprenticeships and work placements, from engineers to quantity surveyors and general construction operatives. This generated over 15,000 hours of earn-and-learn opportunities.

Community engagement

Community engagement was vital throughout the scheme, from concept to delivery. Regular newsletters kept stakeholders informed on design and construction progress, while local drop-ins and surgeries provided opportunities to ask questions, share feedback and raise concerns. Stakeholder input helped shape the design wherever possible.

During construction, site visits for parish councillors, environmental groups and students, together with drone footage showcased at drop-ins, maintained engagement despite restricted site access.

Local-led design

During the design phase, feedback from residents and local organisations led to the main path being relocated to the embankment crest, improving estuary views. In response to requests from horse riders, the route was also designated as a bridleway. Continued engagement helped shape accessibility improvements, including horse rider-friendly gates, Access for All features and locally informed signage.

Archaeology as an engagement tool

As the project progressed, a strong interest from the local community was noticed in the archaeological investigations. As a result, the project team displayed finds at several drop-ins, allowing people to see and handle them. At the request of community members, the project team created a public exhibition at a local museum, telling the story of settlement in South Holderness and produced a booklet on the history of the area for visitors to take away.

[caption id="attachment_32170" align="alignnone" width="1200"] Open stone asphalt (OSA) implemented on discharge channel replacing conventional hard-engineered materials - Courtesy of JBA Bentley[/caption] Conclusion

The Outstrays to Skeffling Managed Realignment Scheme is a major piece of coastal infrastructure, delivering flood risk reduction, enhanced land drainage, habitat creation and wider community benefits. The scheme demonstrates how traditional engineering can be adapted to meet modern sustainability and environmental objectives, while providing long-term public value through improved climate resilience, new intertidal habitat and lessons that can be applied to future coastal and water infrastructure projects.

Key achievements include:

Large-scale habitat creation exceeding original targets. Delivery of resilient flood defences incorporating climate change allowances. Innovative solutions such as the Open Stone Asphalt (OSA) eel pass and site-won sacrificial wave bund. Measurable reductions in cost, carbon and imported materials through the extensive reuse of site-won resources. Transformation of formal social value targets into a wide-ranging legacy of community, environmental and economic benefits across the Humber Estuary.

Construction has been completed in phases, with pumping station works completed in 2025 and final scheme completion expected in 2026. Despite significant ecological constraints, seasonal working restrictions and challenging weather conditions, the project was delivered on time and below budget through collaborative planning, digital delivery and efficient construction methods.

Northbridge is a key drinking water supply location with a large amount of upstream habitat available for eels. The intake is located 11km from the tidal limit on the right-hand bankside of the River Exe, Devon and is the intake for Pynes WTW. Abstraction occurs all year round, with typical abstraction rate between 30,000-40,000m3 per day with a maximum licenced flow is 66,450m3/day. Water is abstracted via two inlet lanes each consisting of a course and fine screen which feed a total of four pumps with the two lanes being able to be operated independently. All four pumps can be operated whilst one lane being closed if flow must be diverted around the closed lane using the actuated penstocks. Background

The existing screening has coarse (9mm aperture) and fine (5mm aperture) screens within the pump house, which discharge debris and eels back to the river via a chute through the side wall.

The current screening will not meet 2025 statutory requirements and South West Water are addressing the issue now to ensure future compliance.

This project will deliver improved screening at the Pynes WTW intake with Eel Regulations compliance, which is required by the end of AMP7, ensuring continued operational abstraction at the site. There is a need to improve the exclusion of the freshwater stages of the critically endangered European eel from river intakes and abstractions allowing lifecycle completion at sea. Additionally, there is need for protection of downstream migrating salmonids. This includes both Atlantic salmon and brown (sea) trout.

[caption id="attachment_12976" align="alignnone" width="1200"] Existing intake structure (external screens at and below river level behind the debris boom with the access platform above) - Courtesy of South West Water & Fishtek Ltd[/caption] Northbridge design considerations

The proposal was to install two 2.352m wide Hydrolox S1800 rotating band screens within the existing bankside infrastructure to replace the existing screening. This will reduce fish and eel entrapment at the intake and ensure compliance for continued operational transfer to Pynes Water Treatment Works. These screens also offer health and safety benefits, as well as OPEX and TOTEX cost benefits.

To allow the planned work to be undertaken, the inlet lanes had to be closed one at a time for the new screens to be installed and the old screens removed whilst still allowing for the 46,000m3/day abstraction. High water demands during the summer months had to be considered along with other consents and approval conditions, so the earliest date restrictions could be imposed was early September 2023. The work was therefore initially planned for a 4-month duration between September 2023 and January 2024.

During the installation period, South West Water had to allow for ‘recharge periods’ where both lanes could be open to allow for the 60,000m3/day abstraction. This would be over a weekend (Friday-Monday), and this allowed for a total of 50% of the installation period where recharge could be undertaken.

To be able to produce a feasible design, various surveys and reports had to be undertaken. These included dive surveys, ecological surveys, protected species surveys, GPR surveys, existing infrastructure surveys, 3D scans of the pump house building and underwater intake bays, and crane lift surveys.

The results of the surveys found the existing intake structure was structurally sound to be re-used for the new Hydrolox screens, which removed the need for using ‘wet’ concrete to construct the work, which would of entailed using a cofferdam. This removed a hazard from the new work within the design stage, benefitting both programme and cost savings.

[caption id="attachment_12977" align="alignnone" width="1200"] New debris return launder chute - Courtesy of South West Water & Fishtek Ltd[/caption] Hydrolox screen selection

Hydrolox S1800 rotating band screens were chosen for this scheme as they are considered an industry best practice solution by the Environment Agency. Benefits included:

Through management and coordination between South West Water Operations and the contractor Fishtek Ltd, this option carried less programme risks than alternatives because the ability to abstract river water during construction was retained. The solution was considered to be ‘riverside’ and therefore applicable for reduced screen sizes compared to the options available if they were to be set back from the riverbank. Being installed above-ground, inspection and maintenance of the screens removed the hazard of requiring confined space access. Being an accepted best practice solution, notably less consultation would be required with the National Eel Service Helpdesk, so this solution carried significantly less risk towards compliance. Restricted site

The work site was approximately 330m from an unclassified single vehicle access road, and having to navigate down this road and track with oversize vehicles, along with having to contend with a section of Japanese knotweed was an early challenge. The rutted access track had to be regraded to accommodate the large vehicles and crane attendances along with protection of the knotweed to prevent cross contamination of the area across the area.

The site was extremely restricted and a 90t crane was required and had to be set up in a small area constrained by the existing building, the Network Rail mainline, 11Kva overhead power cables, outbuildings and mature trees.

Because the location was restricted and unsuitable for larger vehicles, the contractor had to change their methodology and bring the new structural elements in as individual components. These components were transferred onto smaller flatbed vehicles away from the site and reassembled in the small working area.

[caption id="attachment_12988" align="alignnone" width="1200"] (top left) Crane setup within restricted location & approach track, (top right) structural steelwork components being fixed ready for lifting and installation, (bottom left) silt removal prior to installation of steelwork, and (bottom right) accommodation work installing new concrete apron at landowners access gate to provide turning for reversing delivery vehicles - Courtesy of South West Water & Fishtek Ltd[/caption] Construction phase

One of the first tasks was to remove the existing course trash screens and decking area over the River Exe intake in a safe and controlled manner, utilising a dive team to prop open the existing penstocks which remained in place until the scheme was complete and the equipment removed.

Upon successful removal of the existing equipment, the galvanised steel platforms (as required under DWI Regulation 31) were assembled on site and lowered into position within the existing reinforced concrete inlet structures and fixed with galvanised mechanical fixings. The steel platforms would house the two Hydrolox screens.

Other work streams involved mechanical and electrical interfaces, where decommissioning and removal of existing redundant equipment including the two sets of fine and coarse screens, wash water booster set, pipework and obsolete electrical equipment and cabling, all of which had to be phased in agreement with the Operations team.

Electrical scope included the installation of the instrumentation required to control the new screens and four ultrasonics, including a temperature sensor, and temporary isolation and installation of actuators for the external penstocks so that the new steel decking could be installed. This required good communication and agreement with the South West Water Operations team and the control centre.

[caption id="attachment_12980" align="alignnone" width="1200"] (left to right) Hydrolox screen installation, (i) steel support frame, (ii & iii) screen being lowered into position (note proximity to the building), and (iv) final positioning of the Hydrolox screen - Courtesy of South West Water & Fishtek Ltd[/caption] Northbridge Eel Regulations Compliance Project: Supply chain - key participants Client: South West Water Principal designer & contractor: Fishtek Ltd Diving & civils contractor: Teignmouth Marine Services Ecological supervision: Colmer Ecology Supplier of eel screens: Intralox Ltd Instrumentation & controls contractor: SWW O&T Dept M&E contractor: A&T Electrical Structural steel supplier: Milestone Communications Ltd Wash water booster pumps: Xylem Water Solutions Trash screens, launder chute & deflector boom: TWS Ltd Lifting contractor: Spence Crane Hire Ltd Transportation contractor: ACE Crane & Transport Ltd Value engineering

The contractor, Fishtek Ltd, worked efficiently, continually keeping the project team informed with progress and any issues that arose to agree a solution to keep the project momentum. During the time that the contractor was on site, value engineering principals were applied. Examples of this include the reuse of existing equipment such as the launder chute where a partial section was manufactured and installed which reduced the material usage by some 80%.

Another example of the value engineering approach was to take most of the removed equipment to Pynes WTW, which would be available to be re-used for spares and parts replacement.

This benefitted South West Water from disposal costs and the costs of new parts.

Another positive outcome of the project was that Fishtek Ltd, engaged South West Water’s O&T team to undertake the instrumentation and controls scope. This worked extremely well to the benefit of all parties, setting a precedent for future collaborative working.

Third party relationships

Good engagement with all stakeholders (EA, Network Rail, National Grid, landowners and South West Water’s Asset & Operational team) was maintained throughout the programme and there were zero complaints.

To get equipment and cranes onto site, the team required access via a landowner’s property so good relationship was developed and maintained throughout the project. By way of thanks, a new reinforced concrete slab was constructed at the field entrance as a good gesture for the landowner’s cooperation. Upon project completion, a final re-grading of the 330m track was undertaken, and the Japanese knotweed protection was kept in place.

[caption id="attachment_12979" align="alignnone" width="1200"] (left) Complete Installation of the S1800 Hydrolox screens and decking system, and (right) new wash water booster set which provides high pressure cleaning of the screens removing debris - Courtesy of South West Water & Fishtek Ltd[/caption] Conclusion & successes

Though the project was completed in an agreed revised programme due to several issues outside of the contractor’s control, the scheme was still completed almost one year ahead of the regulatory compliance date (March 2025).

The contractor demobilised from site in April 2024, with all that remains to be undertaken being the removal of one fine screen which was left in place at the request of the South West Water Operations team until the new screens had sufficient bedding in time, and after five river spate conditions of the River Exe had been experienced.

While on site, the contractor adopted a ‘see it, sort it’ ethos and several site operational safety improvements were identified and acted upon. Despite this additional work, the project scheme still came in 9% under budget.

Good health and safety was managed throughout the programme and the project was delivered with zero incidents or accidents.

The overall objective of the project was achieved and exceeded, gaining valuable lessons learnt for all involved so future schemes can be optimised throughout the project life cycle from conception through to construction and handover. This will allow for improved programme durations and activities, increased risk identification, improved tender scope and work information, as well as logistical restrictions and operational interface requirements.

Starting on site in 2022, the conceived project was to construct a new fish passage around the Holme Sluice Gates on the River Trent, allowing bi-directional travel of all breeds of fish from salmon to coarse river fish. The existing gates were constructed in the 1950s and are currently operated by the Environment Agency to maintain navigable river levels within the Nottingham area. This paper follows up on one published by Water Projects in 2022, and looks at the construction and commissioning elements of the project. Background

When the Holme Sluice Gates structure was constructed, the River Trent was diverted from its original path around the Country Park through a newly excavated 80m wide cut channel. At the side of the sluice gates is the Holme Canal Lock with a further adjacent water structure of the Holme Pierrepont canoe slalom course; all of which create barriers for migratory fish back up the River Trent.

Project summary

As the sluice gates will remain in operation, the fish pass channel requires two bridges rated to 40t to be built to maintain access to that area. The channel is to be protected at the intake via a single floating boom and the water isolated from the channel by a combination of removable stop logs and an automated radial gate system.

[caption id="attachment_12348" align="alignnone" width="1200"] Aerial view of the completed fish pass - Courtesy of Jackson Civil Engineering Ltd[/caption]

The design of the fish pass has been provided by the Environment Agency’s designer, TEAM Van Oord (TVO), with Jackson Civil Engineering Ltd (JCE) undertaking design elements for the temporary works and the Mechanical, Electrical, Instrumentation, Control and Automation (MEICA) elements.

The fish pass design has a total flow rate of 4.4m3/s - 4.9m3/s with a varying water depth of 1.5m- 1.7m. Although the velocities within the vertical slots have a flow rate of 2m3/s, the pools created at each stanchion bay slows this to >1m3/s; allowing fish to rest as they travel through the pass.

Where we left off……

This paper follows on from an initial case study published by Water Projects in August 2022. In the time since, the piling works (which started in April 2022) were completed by Ivor King The Piling People, following a period of ground pre-auguring to ensure that the circa 10m AZ700-36 sheet piles could be driven with relative ease.

A total of 350 sheet pile pairs with a number of singular piles were driven into the ground to produce the working cofferdam.

Due to the inlet and outlet elements of the fish pass having to be installed within the river flow, it was imperative that the works hit the allowable in-river works period to avoid damage to spawning fish and suitable breeding grounds. This period ran from 15 June 2022 to 2 October 2022; these dates forming an X5 Contract Key Date. Work on the inlet/outlet sections started nine workdays after the period started, and all piling works were completed by the end of August 2022.

There were some significant challenges throughout this period, the depth and complexity of excavating safety behind the sheet wall to install tie piles at a depth of 4-5m requiring a significant portion of the river bank (50m3) to be removed stored and reinstalled and for a number of the tie bar being at a level below the surface of the river, meant a design change was needed to a welded beam solution on the backside of the piles.

[caption id="attachment_12352" align="alignnone" width="1200"] Modular wall shuttering in place for wall pour - Courtesy of Jackson Civil Engineering Ltd[/caption] Channel design concept

In summary, the channel concept included a full height channel wall at the inlet and outlet, joined on both sides by a 2m high dwarf FRC sheet pile wall. Around the top of the sheet piles, a non-structural concrete pile capping beam (chainage 24m - 150m) was required, at which point the design changed to a structural capping beam.

This design was driven by the ground pressures seen on the sheet pile walls in that the channel floor would act as the only prop needed in the non-structural sections, however, due to the increasing depth of the channel towards the discharge end the top of the channel would also need to be permanently propped as well as using the base slab.

The start of earthworks & FRC

Originally the staging for construction was to temporarily prop the sheets at the top throughout the channel run, excavate down to design invert level, cast the base slab and the install the capping beams. This would require the need for significant soffit support systems and working at height.

Through detailed project discussions with the principal designers and supply chain, the decision was made to excavate only the area needed for the capping beam and use the ground formation to act as the soffit support there for removing a significant health and safety risk. To allow access throughout the construction period a section of capping beam was left out (5m of the 400m required) which would require a conventional support system for install.

Earth removal started in earnest in mid-August 2022 reducing the ground to install 26 (No.) SBS 400-185Hyd struts and 300m linear lengths of SSB wailing beams provided by Mabey Hire Ltd.

[caption id="attachment_12345" align="alignnone" width="1200"] Excavated fish pass awaiting FRC works - Courtesy of Jackson Civil Engineering Ltd[/caption] Groundwater challenges

From the provided geotechnical report it was noted that groundwater was expected circa 2m below the ground surface and from engaging with a dewater drainage specialist it was possible that installing a dewatering system would require a significant number of well points discharging 25 l/s. The larger issue was that these wells would need to be installed through the capping beam (not aesthetically pleasing) or would be placed in the way of the bulk earthworks removal.

A number of trail pits were excavated to 4m to assess the realistic nature of the groundwater. Little groundwater was evidenced during these tests, therefore the project proceeded without the use of dewatering, with a mitigation measure that a local sump would be created to allow groundwater to be pumped our using a 6” end suction over pump, to aid in the drainage and working surface a 100mm thick layer of gravel (350 tonnes) was installed in the bottom of the channel to allow the water to flow beneath and work plant. The risk of significant groundwater did not materialise.

The installation of the temporary struts and excavation of bulk material were done in sections therefore allowing manoeuvrability of the excavator to reach between the piles. M2 Civils Ltd, the earthworks contractor, removed on average 24 road wagons of earth per day, totalling 1458 loads or 27,935 tonnes (13,760m3).

Holme Sluice Fish Pass: Supply chain - key participants Client designers: Team Van Oord Principal contractor: Jackson Civil Engineering Ltd Temporary works design: Waterman Group Mechanical design: KGAL Consulting Engineers Ltd Eel passes: Fishtek Ltd FRC: STAM Construction Ltd Groundworks: M2 Civils Ltd Piling works: Ivor King The Piling People River works: Red7 Inshore Diving Ground support: Mabey Hire Ltd Electrical design & control equipment: IMAC Ltd Radial gate system & stop logs: Centregreat Engineering Ltd Eel tiles: Berry & Escott Engineering Services Fish monitors: FishTrack Precast concrete beams: Banagher Precast Concrete Ltd Tarmac & surfacing: CR McDonald Surfacing [caption id="attachment_12347" align="alignnone" width="1200"] Non running fish pass mid-distance - Courtesy of Jackson Civil Engineering Ltd[/caption] FRC

The FRC works was undertaken by STAM Construction Ltd and started in October 2023 with the installation of base slab using cut and bent reinforcement steel throughout the construction. This would then allow the high-level shoring props and wailing beams to be removed. Due to the nature of the design being effectively three straight runs of dwarf walls, the wall shuttering system (9m long by 2.5m high) was constructed on an adjustable wheeled cart, thus allowing the shutters to be installed, retracted, moved, and redeployed reducing the use of timber and removing significant lifting and manual handling risks.

To facilitate this the project teams worked on providing a solution to allow the shuttering system to fly past the starter bars required for the wall and floor stanchions. This was achieved by utilising a ‘Startabar’ product whereby the RC bars are encased under a steel cover which is then removed, and the bars bent out to the correct position after the wall concrete has been poured.

To construct the wall and floor stanchions, conventional shuttering systems were employed. In total 329 tons of steel reinforcement was used and 2,250m3 of concrete were pumped.

Bridges

The construction of the fish pass has created an island of the operational sluice gates requiring 24 hour. To service this asset, two permanent 40T rated road bridges were designed and installed. A major project challenge was to sequence the bridge construction start for after the bulk excavation had past the bridge locations and have them finished before the temporary access created across the sheet piles needed to be excavated out. This includes the bridge abutments, deck and on/off ramps. The bridge construction utilised MY3/MY3E precast concrete beams spanning 12.6m utilising seven beams per bridge and used scaffold soffit support system to all for cast in situ sidings and deck. The MY3 beams were planned and delivered in a ‘Just in Time’ strategy allowing a direct lift and install from the wagon to their installation location.

Construction started September 2022 and finished October 2022 including the installation of the vehicle restraint system, notably the bulk earth movement completed by removing the temporary access to the island in December 2022.

MEICA

The water passage through the pass is controlled by an automated radial gate system, using local river levels and area flow gauges. The gate opens when the flow is greater than 49m3 and the level is above 20.34m AOD; should either of these readings become false the gate will close.

The gate spans the full width of the channel with a radius of 3.5m and stands closed at a vertical height of 1.9m. Using a single actuator the gate (10 ton self-weight) is lifted and lowered via a steel cable winch system with a full extent of travel being circa 4m vertically.

The radial gate solution was chosen by the designers as the best suitable control mechanism due to the following benefits:

Requiring less infrastructure than a vertical gate (no need for structures/lifting frame/gantry above the channel) all reducing the civil reinforcement design in those areas. Less energy to operate as loads are transferred through the pivots and the geometry of the gate means upwards water pressure will assist with lifting. Longevity of the seals as loads transferred through the pivots and not into guides and seals. No need for channels/slots in the walls/base of the channel which could become blocked with debris and would also affect hydraulics.

Even though the size of the fish pass requires significant volume of water to achieve a steady state, this is realised in approximately 90 seconds from the start of the gate opening even though the gate takes 8 minutes to fully clear the pass/river surface.

The isolation of the fish pass for maintenance purposes is undertaken by the installation of five 6.8m long stop logs. These are deployed using an 18m long lifting gantry with dual lifting hoist with a SWL of 2.5T and a hand cranked moveable storage cart.

While the pass is in operation there will be free bidirectional passage for aquatic life, however during non-operational periods eels are still likely to try and pass and with the water during non-operational period only filling the last third of the pass, there is the potential for the eels to become stranded in the pass. Therefore, the pass has been designed with eel chute compliant with the Eels Regulations 2009. The chute and subsequent rebates along the edges of the pass have been fitted with fixed plastic eel tiles therefore providing purchase to aid the eels in their journey. To assist the chute, which is connected to the radial gate and is lifted out of the water during gate operation, while the gate is closed there is a constant flow of water covering the eel tiles guided by the fall of the channel base and surface mounted fixed plastic lumber sections.

[caption id="attachment_12351" align="alignnone" width="1200"] Completed fish pass - Courtesy of Jackson Civil Engineering Ltd[/caption] Pass/river interfaces

Extensive riverbank and river bend modifications were needed to ensure that the pass joined and exited the river and was engineered to prevent erosion. During the in-river works period of 2022 and detailed as a key date within the contract, specialist dive services were employed to dredge out the riverbank/bed and place 80-100T of scour protection amour using 5-300kg sections of rock.

This was all achieved using bank-side long reach excavators; therefore being more environmentally friendly, with greater efficiency than deployment of float pontoon platforms.

Due to the in-river works, stringent protection measures were placed on the project with regards to fish protection and silt migration. The project team deployed 100m of silt bubble curtains around the river work areas to reduce the any sit mitigation as well as undertaking on-site water quality monitoring for turbidity and dissolved oxygen both upstream and downstream, and within the works area. Data showed that the work area was a factor of 10 higher than the up/downstream areas, which remained within agreed permissible limits.

Further dive works included underwater cutting and removal of the cofferdam end sections to open the fish pass to the river. This solution was chosen as it reduced the risk of delays and damage to permanent structures during a vibration extraction method.

Monitoring fish usage

The fish pass is fitted with state of the art near-field communication hardware (passive induction transmitters) to facilitate the monitoring of fish passage. When the electronics are installed, the system will allow the client to understand how effective the pass is, the direction of fish travel and time spent within the pass.

[caption id="attachment_12350" align="alignnone" width="1200"] (left) Completed fish pass looking towards the intake structure and (right) fish pass in operation showing control radial gate - Courtesy of Jackson Civil Engineering Ltd[/caption] Conclusion

The project completed on 14 May 2024 having run for 27 months. The following is a statement from Simon Ward, Fisheries Specialist with the Environment Agency.

“After two years in construction, and several years of planning and design, the Colwick (Holme Sluices) Fish Pass on the River Trent is now complete and ready for fish to use enabling them to reach their spawning and feeding grounds. This flagship project opens up the River Trent and its tributaries for migratory fish, including salmon, trout and eels, making more habitat accessible for fish. Whilst a complex task the construction ran smoothly throughout and the partnership of designer, constructor and EA Fisheries technical staff working together is an exemplar of what can be achieved for the environment.

“The fish pass is part of the Environment Agency’s work to improve fish passage across the country and provides a significant step in restoring the River Trent catchment to its former glory for salmon and other coarse and migratory fish. The project also includes an eel pass to help support the critically endangered European eel; and a public viewing platform above the water, with highly visual interpretation boards to inform and advise visitors about the local wildlife in and around the river, including the fish that are expected to use the pass.”

The Don Regulators comprise three strategically important 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 Don catchment, by attenuating flows in the River Rother. JBA-Bentley, in a joint venture relationship, are working on the replacement of the three regulators, each being at a different stage of design or construction. Figure 1 illustrates the locations of the three sites. Canklow 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. It is located approximately 50m downstream of the A630 Rotherway near junction 33 of the M1. The existing structure, consists of a single electrically powered vertical lifting sluice gate operated by an electric wire rope hoist, comprising drive motor gearbox assembly and cross shaft with integral rope drums and support bearings. To improve resilience and the operation and maintenance of the asset, JBA-Bentley were required to provide a new guillotine gate and associated MEICA and civils infrastructure. The Canklow Regulator is usually the first of the three gates to operate and is activated when trigger levels are reached elsewhere within the catchment. Operating the regulators on the Rother during a significant flood event allows the flood peak on the river to be delayed until the peak on the River Don has passed Rotherham and prevents flooding from the Don. Lowering the gate at Canklow can hold back over 1.5 Mm3 of flood water across seven washlands. [caption id="" align="alignnone" width="1200"] The existing Canklow regulator gate - Courtesy of JBA-Bentley[/caption] Canklow is currently in the detailed design phase of works. Alongside the gate design some additional civil engineering works are required. This includes some remedial works to the existing sheet piled channel walls including new anchors, a new crane pad to be utilised during construction and to facilitate future gate maintenance as well as the substructure for the new motor control centre (MCC). One of the key constraints of the site are high voltage overheads; therefore, the crane pad location and the siting of the EA’s compound with MCC had to carefully considered. To assist in undertaking the design and developing the business case for the project, 3D survey was undertaken to create a 3D Matterport tour of the site. It allows the user to quickly navigate around the site and view all the infrastructure remotely. This proved particularly useful during the pandemic when restrictions were in place and site visits were limited. Woodhouse Mill The Woodhouse Mill Regulator is located on the Rother between Canklow and Meadowgate, upstream of the B6200 Retford Road. It retains water using a single electrically powered vertical lifting gate. It is operated by an electric wire rope hoist, comprising a central drive motor and gearbox assembly and half shafts, with spur and pinion driven, counterweight assisted, rope drums and support bearings. The proposal at this site is to decommission the current regulator and replace this with a passive solution, such as a baffle or orifice plate which spans the width of the channel, to further utilise some of the upstream storage in the washlands. JBA-Bentley are currently undertaking modelling of options for Woodhouse Mill regulator to inform the next phase of the project and the viability of the proposed solution. [caption id="" align="alignnone" width="1200"] The existing Woodhouse Mill regulator gate - Courtesy of JBA-Bentley[/caption] Meadowgate The Meadowgate Regulator is located within the Rother Valley Country Park. The existing regulator consisted of a single fish belly bottom hinged tilting gate, operated by a single electrically powered hydraulic ram. As per Canklow, the new gate will be a top-down vertical control gate improving resilience of the structure; as per the model above. When the new gate is lowered, water levels in the Rother rise and begin to spill into the washlands that are located within the Rother Valley Country Park, which can retain approximately 1.5 Mm3. Temporary set up The civils elements of the scheme have included demolishing the existing buildings and installing new control building. To ensure the gate remained operational during this time a temporary control centre was established during the early part of the scheme; once the gate has been commissioned this will be removed from site. River Don Regulators: Supply chain - key participants Project delivery: JBA-Bentley JV JBA Consulting JN Bentley Principal designer: Callsafe Services Ltd Gate design: Aquatic Control Engineering (ACE) Electrical Installations: IMAC Ltd Building design: JP Chick & Partners Building design: Peter Wells Architects Supporting ECC Supervisor with new gate & associated equipment: KGAL Consulting Engineers Ltd Precast fish pass tiles: Craven Concrete Ltd In situ concrete works : Bells Construction Ltd Metalwork fabrications: Fabtek Green roof: ABG Geosynthetics Ltd [caption id="" align="alignnone" width="1200"] Model of the new Meadowgate regulator - Courtesy of JBA-Bentley[/caption] HAZOP Working closely with the Environment Agency’s Operational and Maintenance teams the gate design and associated infrastructure has been developed to ensure it allows safe access and operation; a Hazard & Operational Study (HAZOP) was undertaken during the early design stages to ensure all requirements were included. Full channel fish pass By removing the bottom hinged tilting gate, there was an opportunity to improve fish passage on the River Rother. Currently, there is a stilling basin immediately downstream of the gate approximately 40m in length, 12m wide and up to 3m deep at the upstream end. Through design development a unique full channel fish pass has been developed which removes the stilling basin by infilling to grade out the bed levels before installing reinforced concrete fish tiles with upstands of varying heights. Computational fluid dynamics (CFD) modelling of fish pass Due to the engineered nature of the channel in this location and the operation of the gate, the fish pass is required to withstand high velocity flows up to 8m/s during extreme events. This proved challenging to the more traditional fish pass construction leading to a heavily engineered solution. [caption id="" align="alignnone" width="1200"] (left) Screenshot of fish pass model - Courtesy of JBA-Bentley, (top right) fish tile mould - Courtesy of Craven Concrete Ltd, and (bottom right) the Meadowgate site - Courtesy of JBA-Bentley[/caption] To refine the design and prove passability for a range of species, the proposed arrangement was modelled using CFD. This allowed the upstand heights to be adjusted to provide the optimum depth and velocities through the range of design flows. Fish pass tiles Once the height and arrangement of the upstands was agreed with the Environment Agency’s National Fish Pass Panel, the structural design of the fish pass tiles began. Each tile measures 2.5m x 2.0m and weigh 4 tonnes; therefore, the design not only had to withstand hydrodynamic forces but also the lifting requirements for construction. In total, 80 fish pass tiles will be manufactured and placed into the channel, within a dry working area. [caption id="" align="alignnone" width="1200"] Precast fish pass tiles - Courtesy of Craven Concrete Ltd[/caption] Temporary works consideration To allow the fish pass to be installed within a dry area of channel, the full river channel needs to be dewatered. This will be achieved by installing an upstream dam and fluming the flow through the working area. The decision to install precast units reduces the risks of in-channel pours and to reduce programme duration for the in-channel works. Summary The replacement Don Regulators will protect Rotherham and the surrounding area from flooding, improve resilience, and ensure the gates can be operated as required both now and as we see the effects of climate change.

Duston Mill Pumping Station in Northampton is a critical Anglian Water asset supplying raw water to Pitsford Reservoir, a primary water source for nearby communities and industries. The pumping station plays a pivotal role in water abstraction and distribution, ensuring the consistent and reliable supply of water resources to meet the growing demands of households, businesses, and agricultural operations. Nestled in an area rich in biodiversity, the station’s surrounding environment is home to numerous aquatic and terrestrial species. Among these is the European eel (Anguilla anguilla), a species classified as critically endangered due to a significant decline in population over the past few decades. Background

The river system around Duston Mill is part of a vital migration route for eels, making the preservation of this habitat a key priority for ecological conservation efforts.

In addition to its ecological significance, Duston Mill’s location within a dynamic river system presents unique operational challenges. Seasonal variations in river levels, potential flooding events, and the need for uninterrupted water supply create a complex balancing act between operational efficiency and environmental responsibility. These factors make Duston Mill a prime candidate for innovation in water management infrastructure.

[caption id="attachment_19464" align="alignnone" width="1200"] Hydrolox eel screen installation - Courtesy of Anglian Water’s @one Alliance[/caption] The issue

The European eel population has experienced an alarming decline of up to 95% since the 1970s, attributed to a combination of factors including overfishing, habitat loss, climate change, and barriers to migration. These barriers, which include water intake systems and hydropower facilities, are a significant threat as they hinder the eels’ natural life cycle by preventing migration and causing injury or death during intake processes.

To combat this crisis, the Eels (England and Wales) Regulations 2009 were introduced, mandating measures to protect eel populations, particularly at water abstraction points. Therefore compliance with these regulations are critical, as failure to address the requirements can exacerbate the decline of eel stocks and result in penalties for the water companies.

Existing intake structure

At Duston Mill, the existing intake structure was assessed and found to be non-compliant with these regulations. The intake consists of two channels, each equipped with angled baffles, flat bar coarse screens, and fine mesh cup screens.

While these components provide basic screening functionality, they do not meet the stringent standards required to prevent eel entrainment and impingement.

Time-limited exemptions granted by the Environment Agency allowed continued operation while plans for compliance were developed. However, these exemptions are set to expire, necessitating immediate action.

Adding to the complexity, the station is the sole source of water supply to Pitsford Reservoir, requiring that abstraction operations continue uninterrupted during the upgrade. This dual challenge of maintaining operational continuity while implementing a compliant solution underlines the importance of careful planning and execution.

[caption id="attachment_19461" align="alignnone" width="1200"] Hydrolox eel screen installation - Courtesy of Anglian Water’s @one Alliance[/caption] Duston Mill Pumping Station: Supply chain - key participants Project delivery: @one Alliance Mechanical/electrical PSSC works: Waveneys Eels screens: Hydrolox Steel access metalwork: Global Energy Group MCC: Paktronic Engineering Co Ltd Roof survey: Claret Civil Engineering Ltd The solution

To address these challenges and bring the station into compliance, a robust solution was developed by the Anglian Water’s @one Alliance. The centrepiece of the project was the installation of a modern positive exclusion screening system, that meets the Eels (England and Wales) Regulations 2009 and supports broader environmental conservation efforts.

The solution involved replacing the outdated coarse and fine screens, with two high-performance Hydrolox traveling band screens. These were designed to operate with a 2mm slot size and an approach velocity of ≤0.4 m/s, ensuring optimal protection for yellow and silver eels.

The screens will operate in a duty/duty configuration, allowing each to handle 50% of the design flow and maintaining redundancy and reliability. To support the new screens, a steel structure was constructed on the intake frontage, providing a secure foundation and incorporating access platforms and handrails to facilitate maintenance and inspections. Additionally, an automated wash water system, powered by duty/standby submersible pumps delivering 5.94 l/s of water at 4 bar pressure, will ensure uninterrupted performance by efficiently clearing debris from the screens.

[caption id="attachment_19460" align="alignnone" width="1200"] Dive operations - Courtesy of Anglian Water’s @one Alliance[/caption]

The solution also included integrating the new system with existing automation and telemetry controls through a new motor control center (MCC) and human-machine interface (HMI). The installation was carried out in phases to maintain the continuous abstraction, with one intake channel remaining operational while the other is upgraded, ensuring a steady water supply to Pitsford Reservoir throughout the project.

To minimise disruption to the aquatic environment, environmental safeguards were included like air-lifting localized silt deposits and removing existing coarse screens and baffle plates to prepare the site for installation. These measures ensure that the project aligned with both regulatory compliance and ecological preservation goals.

Environmental & operational benefits

From an environmental perspective, the new screening system will play a critical role in supporting eel population recovery. By preventing the impingement of eels, the from Hydrolox system allows these species to continue their natural migration and life cycles.

Compliance with the Eels (England and Wales) Regulations 2009 will contribute significantly to reversing the severe decline in eel stocks, promoting ecological balance and enhanced biodiversity.

The protection of eels and other aquatic species fosters a healthier river ecosystem, benefiting a wide range of wildlife. Additionally, the project aligns with the goals of the Water Industry National Environment Programme (WINEP), meeting regulatory requirements while demonstrating a strong commitment to environmental stewardship.

Operationally, the project brings improved efficiency, reliability, and adaptability. The advanced design of the new system, combined with automation, will streamline operations by reducing energy consumption and minimising Anglian water’s maintenance costs. The automated wash water system ensures debris buildup is efficiently managed by maintaining optimal flow rates. The duty/duty operational configuration offers redundancy, allowing abstraction to continue uninterrupted during maintenance or equipment failures.

The robust design, with a 40-year horizon for civil structures and a 15-year horizon for mechanical components, guarantees long-term resilience and reliability. Furthermore, the system’s ability to accommodate peak abstraction flows of up to 1,053 liters per second, and its scalability for higher river levels, ensures adaptability to future demands.

[caption id="attachment_19463" align="alignnone" width="1200"] Hydrolox eel screen installation - Courtesy of Anglian Water’s @one Alliance[/caption] Community & economic benefits

From a community and economic standpoint, the benefits are equally significant. Continuous abstraction during construction ensures an uninterrupted water supply to communities and industries dependent on Pitsford Reservoir. The phased installation approach minimised disruptions, maintaining trust and reliability among customers and stakeholders.

Proactively addressing compliance during AMP7 also provides a cost-effective solution, avoiding the potential for higher expenses and operational constraints in AMP8 and beyond.

The project enhances public perception by showcasing a clear commitment to environmental sustainability, strengthening the organization’s reputation among regulators, local communities, and environmental advocates. These collective benefits highlight the comprehensive value of the project in achieving environmental, operational, and societal goals.

Conclusion

The £2m upgrade at Duston Mill Pumping Station represents a landmark initiative in integrating ecological responsibility with operational excellence. By addressing the non-compliance issues and implementing cutting-edge eel protection measures, the project ensures adherence to legal requirements while contributing to the conservation of a critically endangered species. Beyond regulatory compliance, the initiative highlights the broader benefits of sustainable water management, from enhanced biodiversity to improved operational resilience and community trust.

As Duston Mill transitions to this new system, it sets a benchmark for similar projects, demonstrating that sustainable practices and technological innovation can coexist to meet both human and environmental needs. This forward-thinking approach not only safeguards the future of the European eel but also exemplifies the role of modern water management in creating a harmonious balance between development and conservation.

Sandown Surface Water Abstraction (SWA) is a pumping station abstraction from the River Yar on the Isle of White, which feeds raw water into the Sandown WTW. The pumping station is several hundred metres from the water treatment works, and sits alongside the popular and busy Red Squirrel Trail walking route and cycle path. Along with many other water intakes throughout the UK, Southern Water had to upgrade the water intake screens to be compliant with the Eel Regulations, which meant a bar-spacing that did not exceed 2mm and an approach velocity that did not exceed 0.25 m/s. The existing intake structure was built in the early 1980s and consisted of interlocking steel sheet pile walls, capped with a concrete slab. Manholes on top of the slab provided access to the sump pumps, valves and pipe/cable ducts. The river bed in front of the structure is a flat concrete slab, which could provide a good base for the eel screens to sit on if needed. [caption id="" align="alignnone" width="1200"] (left) Concrete slab on top of the sheet-pile pump and valve enclosure and (right) sheet-pile walls that make up the pump enclosure[/caption] [caption id="" align="alignnone" width="1200"] (left) View inside the pump chamber, looking at the sheet piling adjacent to the river. Below the waterline is the 0.2m high x 3m wide slot where the river water is drawn through. (right) close-up of intake drawing showing ‘letterbox’ slot[/caption] The existing intake did not have any screening; hence fish, eels and other objects could potentially enter the pump chamber. CMDP was the main contractor for the project, and GoFlo worked closely with them from the early design stages to the final commissioning to ensure an optimal solution was developed. With a maximum abstraction flow rate of 0.278 m3/ second, the approach velocity through the existing intake slot in the sheet pile wall would exceed the maximum specified in the Eel Regulations. This meant that would it would not be possible to install the GoFlo screens inside the existing pump building and would have to be installed externally to the existing building. An added complication was that the intake could not be shut down for more than 8 hours without severely disrupting the water supply to the Isle of White, which would not be acceptable, so the solution had to be designed to be installed into a working intake using divers. GoFlo had a similar issue at another Southern Water site (Springfield), and for that site designed a fabricated ‘intake box’ system that could be installed by divers. This system worked well, so the principle was used for Sandown, even though the water depth at Springfield was 4.5m, whereas at Sandown it is typically only 600mm. The width of the screens at 3.55m has been determined by the minimum depth of water in the river (0.438m) while still having to meet the 0.25 m/s approach velocity under the Eel Regulations while abstracting the maximum flow rate. Site survey The design process started with a detailed survey of the intake area. As is the case with many sheet-pile structures, nothing was exactly plumb or square, so because the fabricated intake box we would have to manufacture had to fit perfectly, first time, we had to enter the river and make plywood templates that fitted the profile of the existing structure perfectly. At the same time a detailed level-survey was conducted on the river bed concrete slab. We took the wooden templates away and turned them into precise profile data points that could be used to build an accurate 3D model of the existing structure in our CAD system. Based on that, we could design the intake box to fit perfectly. Design Due to how the in-pans and out-pans of the sheet piling were positioned, the bolted connections onto the Intake Box at the upstream end was on an out-pan and at the downstream end on an in-pan, so the left and right-hand intake box sides being different widths (1560mm and 1450mm). [caption id="" align="alignnone" width="1200"] (left) Intake box side drawing and (right) plan drawing showing new intake box attached to existing sheet-pile structure[/caption] The intake box is a stainless steel fabricated box made up of the two sides and a baseplate that were assembled into a finished box on-site. The structure is designed to be a rigid structure so it could support the screens in the inclined ‘operating’ and vertical ‘service’ positions. The Intake Box structure also had the walkways fixed to it, which in turn have the security fencing fixed to them, so had to be designed to be very strong. A course bar screen with 50 mm bar-spacing was incorporated into the intake box, just upstream of the screens. This bar screen will protect the fine GoFlo screen meshes from large debris which could deform or puncture the screen face during flood flow conditions, but also keep any swimmers away from the moving parts! An advantage of having the screens perpendicular to the river flow will reduce the possibility of the bar screen collecting debris; the river passing flow tending to pull material away from the bars. [caption id="" align="alignnone" width="1200"] (left) Drawing of intake box with course bar screen attached to upstream face and (right) drawing showing GoFlo screens, debris trough and intake box attached to existing structure[/caption] The debris captured by the screens is returned to the river via the debris trough and return channel, but about 5m downstream, so the likelihood of material being pulled back into the screens is minimised. The walkway structure incorporates davit sockets and removable winches. The winches are used for pulling the screens from their inclined ‘operating’ position to the vertical ‘service’ position. From here, the screen’s motor/gearbox and drive system can be accessed safely. Should a motor need to be taken off the screen, a portable davit can be mounted in a dedicated floor socket and the motor lifted up and over the handrail onto a trolley for transport away from the area. [caption id="" align="alignnone" width="1200"] Complete 3D model of proposed GoFlo system attached to the historic structure[/caption] Installation This started with the river bank and floor being cleared of any silt and stones etc. Next, the intake box was assembled, including adding some temporary diagonal braces to keep the sides an baseplate square and to prevent the structure flexing during lifting. Once the intake box was in the river and fixed in position the diagonal braces were removed. The intake box was fixed down to the concrete apron using stainless steel M16 resin-fixed anchors, and to the vertical sheet pile wall by drilling a tapping M12 bolted fixings. Installing such a structure in a flowing river was a hazardous operation, especially with divers in the water to guide it into position, drill and install the fixings into the wall and river bed. Underwater visibility was very poor due to unseasonal heavy rainfall and increased river flow. The divers had to be in constant radio contact with the dive support team on the bank. The divers also had a live video feed to the team in the control room so they could be guided to the fixing locations. [caption id="" align="alignnone" width="1200"] (left) Lifting the intake box into the river and (right) lifting the first of the GoFlo screens into the intake box[/caption] Once the intake box was fixed in place the two GoFlo screens were lifted into position. This is a relatively quick operation due to the integrated ‘pivoting frame’, which are guide rails allowing the screen to be lifted in vertically and accurately guide the screen into position, even when the intake is flooded with zero visibility. At this point the screens were connected to a temporary control panel and a wooden debris trough was constructed to allow the screens to be put into operation. The screens had to be put into service immediately because of the looming deadline to make the Intake Eel Regulations compliant. [caption id="" align="alignnone" width="1200"] (left) The first screen in position on the intake box and (right) both GoFlo screens in position in the intake box[/caption] A few months later the walkways, debris trough and security fencing were fitted, which all bolted directly to the intake box. The assembly was all designed in detail using 3D CAD software by GoFlo, then the constituent parts laser-profiled and CNC folded, finally being welded together. The walkways were installed in two days, and the debris trough in a similar time, which is testament to the accuracy of the design and fabrication undertaken by GoFlo. [caption id="" align="alignnone" width="1200"] Completed GoFlo screen installation[/caption]   For more information: GoFlo Screens Ltd | +44 (0)1453 884400 | www.gofloscreens.co.uk  

Springfield Surface Water Abstraction (SWA) is a Southern Water pumping station located on the banks of the River Medway in Maidstone, Kent and transfers water to Eccles Lake. The intake is positioned flush with the riverbank and consists of two openings into an underground concrete intake structure, with a busy riverside towpath on top. The picture above is before any works started. There are two coarse bar screens, one in front of each opening and a fixed timber boom in the river in front of the intake to deflect large debris. The flow travels approximately 25m by gravity into the pump house building, then is pumped to Eccles Lake and from there under gravity to Burham Water Supply Works. To comply with The Eel Regulations, Southern Water had to upgrade the intake so that the maximum bar-spacing on the intake was 2 mm and the velocity of the water approaching the screen did not exceed 0.25 m/s. This is to prevent juvenile ‘glass eels’ from being sucked into the intake which would prevent them from moving upstream into the Medway catchment and beginning the long and complex life cycle of the European eel. The 0.25 m/s approach velocity could be achieved by using only half of the existing intake, with the other half blocked up using a concrete stop-log. GoFlo Screens were awarded the contract to supply and assist with the installation of the eel screens at this location, by Trant/BTU Utilities Ltd. The site is particularly complicated because it is in use 24/7, and cannot be turned off for more than a day or two before disruption to Burham Water Supply Works would occur. Coupled with this, the site cannot be de-watered, so would have to be installed by divers in water that is 4.5 metres deep, with very low underwater visibility. The new GoFlo screens are too large to fit inside the existing concrete structure, so had to be accommodated outside of the existing concrete structure, in a prefabricated stainless steel ‘intake box’ that sits on the existing underwater concrete apron. GoFlo designed and manufactured the GoFlo screens, intake box, walkways and debris trough. Everything had to be designed to be simple and modular so that the underwater elements could be installed by divers. The elements supplied by GoFlo are shown below along with the basic specification: Screen drive: 2.2 kW 3-phase WIMES-spec motor/gearbox Maximum bar spacing: 2mm (Single) screen mesh area: 4.652m2 Angle of inclination (from horizontal): 72.5° Construction material: 304 stainless steel [caption id="" align="alignnone" width="1200"] GoFlo 3D CAD model of the proposed screens, intake box and walkways[/caption] Proposed design The overall design of the system was developed collaboratively between the main contractor (Trant/BTU), the client (Southern Water), Atkins Global who were the M&E designers working for Trant/BTU and GoFlo Screens. GoFlo also worked closely with Commercial and Specialised Diving Ltd to incorporate their ‘diver design friendly’ feedback into the design to make it easier for the divers to install, which was especially important considering it would be installed in the middle of winter. Before the detailed design could begin, the intake and apron area in front had to be cleared of silt and debris. Once in the water the divers found a tangled mess of silt, fishing line, a large quantity of steel railing, two motorbikes, a pushbike and various other debris! Once the debris was cleared, a detailed site survey was undertaken to determine how flat the apron was, the exact profile of the vertical concrete piers which the GoFlo intake box would fix onto (a special 5-metre-long profile gauge was manufactured to achieve this), and check how far the apron extended out into the river. A number of differences were found between the original construction drawings from the 1960s and what was actually built. Following the site survey, a detailed 3D model of the intake was constructed in Inventor software which formed the basis of the GoFlo design. The principle of the GoFlo design was a modular construction, comprising of: A fixing frame that fixed to the concrete structure and was used as a template for drilling the fixing holes. A sacrificial ‘measuring frame’ which bolted to the fixing frame to allow all of the key levels to be measured (hence adjusted) from above-water. 2 x intake box sides which bolted to the fixing frame (assembled above-water, after the fixing frame fixing holes had been drilled and the fixing frame removed). The standard GoFlo baseplate and pivoting frame (guide rails), 2 off. The standard GoFlo screen(s). Coarse debris screen/walkway that integrated with the Intake box/debris trough and return channel. The modules were pre-assembled in our workshop to ensure that everything fitted together, prior to arrival on-site. The individual items, and the complete assembly are shown below. [caption id="" align="alignnone" width="1200"] (i) The fixing frame (ii) the temporary measuring frame, fixed to the fixing frame (iii) an intake box side - two are required, and (iv) the baseplate and pivoting frame[/caption] [caption id="" align="alignnone" width="1200"] (i) Course debris screen (ii) the walkway assemblies (iii) debris trough and return channel with covers (iv) the completed design[/caption] The whole design was based on simplifying the works on site, particularly in regard to making the works as straightforward as possible for the divers. Key design features include: Two reference brackets installed on the above-water concrete upstand, which provided two precise reference points for the fixing frame to locate onto at top end. [caption id="" align="alignnone" width="1200"] (left) Reference brackets fixed to existing concrete structure and (right) fixing frame in position against existing structure[/caption] The fixing frame, which once positioned acted as a drilling template for all of the fixings into the concrete structure. At each fixing position there is an 18.5 mm diameter hole, to allow an 18 mm masonry drill bit to pass through which was used as a guide for drilling. These 18 mm diameter holes, once the fixing frame was removed, had Hilti HKD-SR stainless-steel M16 fixings installed. For precise positional adjustment, the fixing frame had 2 x M16 height adjusting bolts close to the toe of the intake apron, 2 x M16 stand-off adjusting bolts at the bottom of the vertical and two temporarily-fixed adjustment blocks at the bottom of the vertical frame members to allow the frame to be pushed/pulled both laterally and longitudinally, and once in position locked in that position for the fixings to be drilled. These were removed once the intake box was finally installed. [caption id="" align="alignnone" width="1200"] (left) Close up of the baseplate of the fixing frame, showing the levelling bolts and (right) temporary adjustment blocks used for positioning the fixing frame[/caption] The fixing frame was designed to stand-off the concrete by a nominal distance of 20 mm to allow for unevenness in the concrete structure. This gap was taken-up at each fixing point using a stainless-steel shim stack. The height of the required shim stack was measured after the fixings holes had been drilled, but before the fixing frame was removed so that the shim stacks for each fixing point could be pre-prepared. Fine adjustment was still possible by adding/removing shims later as required. Once the fixing holes had been drilled, the fixing frame was removed, then the intake box sides bolted on, the GoFlo baseplates and pivoting frames attached. This allowed the whole intake box to be lifted in as an assembled unit and fixed in place using the pre-prepared fixings and shim stacks. Apart for the minor adjustments to levels, this saved a lot of complex underwater assembly work. Once the intake box was fixed in position, the coarse debris screen and walkway were fixed onto the intake box, then the GoFlo screens were installed. So, that was the principle – now let’s looks at the actual installation! Construction The photos below show the actual parts being installed on site. Bear in mind that the water is 4.5 metres deep, and the GoFlo screen 6.1 metres long. The first photo shows the fixing frame lying on its back, having the measuring frame bolted to it prior to being lifted in. The second photo shows the assembled fixing frame and measuring frame being lifted into position. You can see that the river was very high after several days of heavy rain. [caption id="" align="alignnone" width="1200"] (left) Fixing frame and measuring frame being assembled and (right) fixing frame and measuring frame being lifted into the intake – note the very high water levels![/caption] The fixing frame and measuring frame in position, ready for the fixing holes to be drilled. The mild steel measuring frame was sacrificial, but provided above-water horizontal references for a spirt level, which was essential during levelling. Once the drilling was completed, the fixing frame and measuring frame were removed from the water, then the intake box sides, GoFlo screen baseplates and pivoting frames assembled together. [caption id="" align="alignnone" width="1200"] (left) Fixing frame and measuring frame in position and (right) the intake box being assembled prior to final installation[/caption] [caption id="" align="alignnone" width="1200"] (left) The fully assembled intake box, (middle) lifting the assembled intake box into the intake with a 60-tonne crane, and (right) the assembled intake box was attached to the concrete structure by divers which took several days[/caption] Next, the coarse bar screen was lifted into position, closely followed by the GoFlo Screens. GoFlo screens are lifted in vertically and use the pivoting frames as guide rails to guide the screen precisely onto the baseplate. [caption id="" align="alignnone" width="1200"] (top left) Lifting the course bar screen into the intake box, (bottom left) lifting the first GoFlo screen into the intake box, and (right) fitting the front part of the walkway structure onto the intake box[/caption] The screens are designed to discharge the collected debris into a dedicated trough behind the screens. The trough is made from stainless steel (as are the screens, intake box and coarse bar screen). The trough has a high back to catch the spray (2.5 bar water pressure) that is emitted from the screen spray-bars behind the mesh belt. Each screen has a spray bar with multiple nozzles fed by a remote water booster pump located inside the main building. Debris on the surface of the screen mesh as it rotates falls off as it runs over the top sprockets, while any remaining ‘sticky’ debris is blasted off by water the jets from the inside of the screen and into the trough. [caption id="" align="alignnone" width="1200"] (top left) Fitting the debris trough and return channel, (bottom left) the spray boom assembly which fits inside the screen mesh, and (right) completed walkway structure attached to the intake box[/caption] The debris trough includes a dedicated water feed (10 litres/second) to flush collected material back into the river downstream of the screens. The green fence posts are to support the security fence to protect the public from the machinery. [caption id="" align="alignnone" width="1200"] (left) The debris flushing flow pipework underneath the debris trough and (right) the security fencing being fitted[/caption] 10 cm bar-spaced coarse debris screen protects the GoFlo screens from large object damage, and keeps swimmers out. Due to the proximity of the screens to the footpath and the possibility of ice formation in winter months, a fully enclosed debris trough was required to confine the spray mist. The covers are hinged to enable full unrestricted access to the trough. [caption id="" align="alignnone" width="1200"] (top left) View from the-screens, looking out towards the river, (top right) the lids covering the debris trough, (bottom left) further lids covering the debris return channel and (bottom right) the completed installation, inside the security fencing[/caption] [caption id="" align="alignnone" width="1200"] The completed installation, looking upstream[/caption]   For more information: GoFlo Screens Ltd | +44 (0)1453 884400 | www.gofloscreens.co.uk