Supply Chain - Reservoirs & Storage - Contractors

Loch Katrine, a freshwater loch situated in the Trossachs area of the Scottish Highlands, is not only a natural beauty but also a critical water resource for Glasgow. The Emergency Dam Project was initiated in response to a severe storm in mid-October 2023, which caused significant damage to the dam’s spillway. The loch, approximately 8 miles long and 1 mile wide at its widest point, runs the length of Strath Gartney. The reservoir was originally formed by constructing a dam across the outlet channel at the eastern end of Loch Katrine, raising the natural loch level and significantly increasing its capacity to supply water. History

Victorians considered the supply of clean water to be the cornerstone of a civilised society. Glasgow and other major cities in the UK suffered major outbreaks of Cholera in the middle of the 19th century, which were attributed to polluted water supplies. In 1848, a Public Health Act was passed by Parliament to promote the supply of clean water. At this time, schemes were being prepared to provide clean water supplies to all major conurbations throughout the British Isles.

The eminent engineer John Frederic Bateman selected Loch Katrine as an appropriate source of water for Glasgow, and led a team of engineers who translated the scheme into reality by raising the water height at Loch Katrine, constructing a 26-mile-long aqueduct terminating at the Mugdock (storage) reservoir.

Loch Katrine and associated aqueducts are still as efficient and environmentally friendly now as they were when built due to the fact they take water by gravity from Loch Katrine to Milngavie without the need for pumping, before it is distributed to customers.

[caption id="attachment_14708" align="alignnone" width="1200"] Aerial of the dam repair pre-concrete - Courtesy of Whitehouse Studios[/caption]

On 14 October 1859, the Loch Katrine-Mugdock Waterworks, as they were originally known, was opened by Queen Victoria in a ceremony at the Commissioners’ Cottage. A clean water supply flowed into the north of Glasgow by 1860.

At the ceremony, Queen Victoria said:

“It is with much gratification that I avail myself of this opportunity of inaugurating a work which, both in its conception and its execution, reflects so much credit on its promoters, and is so calculated to improve the health and comfort of your vast population, which is rapidly increasing round the great centre of manufacturing industry in Scotland.

“Such work is worthy of the enterprise and philanthropy of Glasgow, and I trust it will be blessed with complete success. I desire that you convey to the great community which you represent my warmest wishes for their continued prosperity and happiness.”

Later that century, chief engineer James Gale deemed that the storage capacity of Loch Katrine should be increased and that a second line of aqueducts and another storage reservoir should be constructed at Craigmaddie above Milngavie.

The reservoirs represent an outstanding example of Victorian municipal engineering and, as with many feats of engineering from this time, the adventurism, innovation, and quality of workmanship, are outstanding. The engineering design and construction skills employed to supply Glasgow with clean water from Loch Katrine are truly awe-inspiring.

Project drivers

Water that flows through the aqueducts from Loch Katrine goes on to supply 1.3 million people across much of Greater Glasgow and as far east as West Lothian and to areas like Grangemouth and the Ineos refinery; which is crucially important to Scotland and the UK.

The project was driven by the urgent need to repair the spillway to prevent a potential dam failure. The detachment of concrete apron slabs during the October 2023 storm event posed a significant risk, prompting the formation of an emergency recovery team within Scottish Water.

[caption id="attachment_14713" align="alignnone" width="1200"] Detached concrete apron slabs - Courtesy of George Leslie Ltd[/caption] Loch Katrine Dam Repairs: Supply chain - key participants Principal contractor/designer: George Leslie Ltd Designer/technical advisor: Mott MacDonald Drilling works for anchor rods: Albion Drilling Coring of pressure relief holes: Beattie Demolition Joiners for formwork: Beatties FRC Tree clearance: Caledonian Tree Services Concrete pumping: Camfaud Concrete Pumps Reinforcement: Central Rebar Anchor plates: HK Gillies Interlocking blocks: Mellex Group Ltd Scaffolding/access: Peoples Safety Scaffolding Grout for anchor rods: Resapol Pumps: Selwood Welfare buildings: Wernick Hire Project photography/drone footage: Whitehouse Studios Optioneering & design

The design and construction approach focused on ensuring the safety of both workers and the public while addressing the immediate risks. George Leslie Ltd, with the assistance of Mott MacDonald, was engaged to repair the damaged areas.

The main tasks involved installation of Legato blocks, as part of the temporary works design, reservoir drawdown, silt mitigation, drilling and fixing L-Bars, installing mesh and formwork, pouring concrete, and installing pressure relief pipes, all while ensuring safety for workers and the public.

[caption id="attachment_14709" align="alignnone" width="1200"] Installation of fabric mesh and environmental protection - Courtesy of Whitehouse Studios[/caption]

Before full mobilisation, preparations for the crane pad were deliberated and built on-site in anticipation of positioning the 60-tonne mobile crane. Concurrently, during these initial phases, nearby residents received briefings about the projected plan and what they could anticipate in the ensuing weeks. This practice of keeping the local community informed was maintained consistently during the project’s duration.

Regular meetings involving all parties (Scottish Water, George Leslie Ltd and Mott MacDonald) took place every day to review what was needed for the investigation, which would then inform the design stage. Excavation work was carried out to reveal specific areas of the spillway construction. These findings were relayed to Mott MacDonald, contributing to the progression of the design, ensuring a smooth flow from investigation to design, then to planning and execution.

The project’s schedule of work was frequently revised, often in response to planning made during Teams calls. It necessitated regular updates and rebriefing for the onsite team.

Managing environmental pollution was particularly demanding while the reservoir continued to spill over.

On-site logistics posed difficulties with spatial constraints and the necessity to maintain operations at the Loch Katrine steamship workshop throughout the construction period. Careful scheduling of deliveries and the selection of specific transport machinery to accommodate the dimensions and configuration of the access route were vital for ensuring safety and preventing any obstruction in the vicinity of the access path and work zone.

The George Leslie Ltd supply chain team demonstrated exceptional flexibility with the project, expediting delivery schedules, facilitating deliveries outside of normal business hours, and reorganising their work to be on-site for the urgent repairs. Such dedication was instrumental in ensuring the emergency work was completed smoothly.

The project required consultation, inspection, and design to carry out repairs to safeguard the listed structure at the reservoir. This included daily meetings set up by the client for reporting.

[caption id="attachment_14712" align="alignnone" width="1200"] Repairs to concrete apron underway - Courtesy of George Leslie Ltd[/caption] Implementation and Health & Safety

Due to access challenges with a single track road to the site, the size of equipment utilised was limited. The main tasks included the innovative use and the installation of Legato Blocks, to potentially reduce flows over the weir and divert away from the construction area. Reservoir drawdown, silt mitigation, drilling and fixing L-Bars, installing mesh and formwork, pouring concrete, and installing pressure relief pipes was also required.

Health and safety was paramount, with rigorous risk assessments, emergency procedures, safety training, incident reporting, and monitoring compliance forming the backbone of the project’s safety culture.

Impact & benefits

Scottish Water is a public sector body answerable to the Scottish Parliament through Scottish Ministers and our principal activities are the supply of water and waste water services to around 5.4 million customers in homes and businesses across Scotland covering an area of 30,810 square miles.

Our vision is to be trusted to care for the water on which Scotland depends. Reflecting that, our customers expect us to provide excellent customer service by delivering high levels of water quality and environmental performance, all for an affordable price.  Using Scotland’s natural resources and the skills of our people, Scottish Water is committed to improving our services for customers and communities while protecting and enhancing the environment of Scotland.

This project not only restored the dam’s functionality but also reinforced its structure against future threats, ensuring the continued safety and security of water supplies to Milngavie WTW and Balmore WTW. It also addresses the major business risk associated with loss of supply to these strategic assets, which output potable water to a population of approximately 1.3 million people in central Scotland and provides vital water for commercial and industrial use.

This project is important to Scottish Water as it continues to build the trust and confidence of customers and communities across Scotland by maintaining and investing in the company’s assets.

[caption id="attachment_14710" align="alignnone" width="1200"] Katrine Dam: (left) looking north prior to concrete pour and (right) looking west- Courtesy of Whitehouse Studios[/caption] Conclusion

The Loch Katrine Emergency Dam Project stands as a shining example of engineering excellence, showcasing the ability to swiftly and safely respond to emergency situations while maintaining a strong focus on health and safety. The next phase of the work is already underway, promising to further solidify the dam’s role in safeguarding the region’s water supply.

The Saggart Reservoir Expansion Project represents one of the most significant investments in Ireland’s water infrastructure in recent years. The Greater Dublin Area is almost entirely dependent on treated water from Ballymore Eustace WTP. This single facility is Ireland’s largest water treatment works and supplies approximately 70% of Dublin’s drinking water demand. With a daily output exceeding 300 million litres, Ballymore Eustace is a critical asset in the national water network. The Saggart Reservoir plays an equally vital role as a downstream storage facility, ensuring that treated water is available in sufficient quantities to meet demand fluctuations. Background

Over the past decades, water demand in the Dublin region has grown steadily, driven by population expansion, urbanisation, and increasing commercial activity. At the same time, extreme weather events and climate pressures have highlighted the risks of operating with limited storage resilience.

The existing Saggart Reservoir had performed reliably for many years, but its existing capacity was no longer adequate to safeguard against operational shocks or prolonged outages. Its chlorination system was also reaching obsolescence; raising risks for water quality compliance.

The €59m expansion project was conceived to address these strategic risks. By delivering a new 100,000m³ covered reservoir, alongside an advanced OSEC plant, Uisce Éireann sought to secure a resilient, sustainable water supply for the Greater Dublin Area for decades to come. The project also represents an important step in meeting national infrastructure goals for resilience and climate adaptation, aligning with Ireland’s commitments to long-term sustainable development.

[caption id="attachment_25647" align="alignnone" width="1200"] Early stage in development - Courtesy of Coffey[/caption] Project drivers & challenges

Several interlinked drivers made this project essential:

Increasing storage capacity: The need to expand storage was critical in safeguarding against potential service disruption; particularly given Dublin’s reliance on a single treatment works. Chlorination upgrade: The chlorination plant could not deliver the efficiency, energy performance, or operational resilience required for long-term security of supply. Future-proofing: All structures were required to meet a 50-year design life with mechanical and electrical installations designed for serviceability over 20–30 years. Sustainability: Uisce Éireann embedded a requirement for reduced embodied carbon, sustainable construction methods, and environmental enhancement.

The delivery challenges were significant. The new reservoir had to be built adjacent to an operational section of the existing reservoir without disrupting supply. Live connections into existing trunk mains required advanced methods to prevent outages. The confined site added logistical complexity, particularly for deliveries of reinforcement mats, precast roof units, and concrete. Managing the sequencing of works while maintaining strict health and safety standards demanded precise coordination across the delivery team.

Another key challenge was managing the programme to meet strict regulatory timelines. With Dublin’s water supply under pressure, delays could have exposed the region to significant resilience risks. This meant that early procurement of reinforcement mats, precast units, and specialist equipment was critical. By employing standardised design elements, the delivery team achieved economies of scale and streamlined production, reducing the risk of programme slippage.

[caption id="attachment_25640" align="alignnone" width="1200"] Work in progress at Saggart Reservoir - Courtesy of Coffey[/caption] Project scope

The works were divided into three distinct but interconnected stages:

Construction of the new reservoir & OSEC building: Bulk excavation, construction of the reinforced concrete base, erection of internal columns and spine beams, installation of precast roof units, and development of the new chlorination facility. Decommission the existing OSEC facility: Decommission the existing OSEC facility to allow for the operation of newly constructed facility, and refurbish the existing building for future use. Commissioning & operation: A 90-day proving phase that integrated the new infrastructure with the existing live system and validated performance across hydraulic, mechanical and water quality parameters.

The scope also extended to ancillary civil and mechanical works, including installation of GRP access systems, landscaping around the reservoir, and integration of drainage and waterproofing systems to protect the structure over its 50-year design horizon.

[caption id="attachment_25642" align="alignnone" width="1200"] Laying geotextile on roof - Courtesy of Coffey[/caption] Saggart Reservoir: Supply chain - key participants

The programme benefited from strong collaboration across the supply chain, with repeatable design elements and standardisation helping to accelerate delivery and reduce procurement risks.

Project delivery & process & MEICA design: Coffey Civil & structural engineer: Ayesa (formerly ByrneLooby) Precast concrete (reservoir): Banagher Precast Concrete Precast concrete (valve chambers): FLI Precast Solutions Concrete supply: Kilsaran BAMTEC® reinforcement system: Hy-Ten Ltd Shear reinforcement system: Peikko Group OSEC plant: De Nora Water Technologies UK Pumps: SPP Pumps Ltd Chemical dosing tanks: Forbes Technologies Ltd Chemical dosing pumps: Grundfos Pumps Ltd MCC supply & installation: Right Group GRP safety system: Relinea H&S (fall protection system): FreeFalcon [caption id="attachment_25637" align="alignnone" width="1200"] Saggart Reservoir Cell 1 under construction - Courtesy of Coffey[/caption] Reservoir base & reinforcement

The reservoir’s base slab covered an area of 31,500m2, demanding a robust reinforcement strategy to withstand long-term hydraulic loading. Traditional bar reinforcement would have required significant on-site labour, tying, and placement, so instead, Coffey implemented the BAMTEC® Roll-out Reinforcement System, which provided prefabricated mats tailored to the slab design. A total of 1,725 tonnes of BAMTEC® reinforcement were installed in the base, with a further 198 tonnes in the perimeter and internal walls.

This approach reduced site labour requirements, improved safety, and delivered consistent quality. The reinforcement mats were unrolled rapidly, allowing for accelerated concrete placement while maintaining design tolerances. By minimising manual tying, the system also reduced the risk of errors and ensured uniform structural performance.

To address punching shear at column bases, Peikko shear rails were installed, supported by precast pedestals. This avoided the need for local slab thickening, optimising material use and maintaining a uniform slab profile. The combined reinforcement strategy demonstrated how innovative approaches can balance efficiency, safety, and structural performance in large-scale civil engineering.

Floating precast roof structure

The roof was constructed using 879 precast double-tee units, each up to 13m in length. These were supported by a network of 322 reinforced concrete columns and 280 precast spine beams. The modular nature of the roof enabled rapid installation, with Banagher Precast Concrete manufacturing units off-site and delivering them in a carefully sequenced programme.

[caption id="attachment_25636" align="alignnone" width="1200"] Lowering a precast floating roof section - Courtesy of Coffey[/caption] Installation sequencing was critical. The confined site required precise scheduling of deliveries, crane operations, and installation teams. Each roof section was assembled bay-by-bay, with expansion joints incorporated to accommodate thermal movement. Above the roof deck, a fibre-reinforced screed was applied, followed by cold-applied waterproofing and a drainage layer. The final finish was a wildflower meadow roof, which not only provided biodiversity benefits but also reduced visual impact, helping the reservoir integrate into the local environment. On-site electro-chlorination (OSEC) plant

The new OSEC plant from De Nora Water Technologies was designed to replace the aging chlorination system with a safer, more efficient, and more sustainable technology. On-site electro-chlorination eliminates the need for bulk chemical deliveries by generating chlorine through the electrolysis of brine.

The plant achieved an energy efficiency of 5.3 kWh/kg of chlorine produced, surpassing industry benchmarks and reducing operational costs. The system’s modular configuration allows for scalability, resilience, and simplified maintenance. In addition, it provides greater security of supply by reducing dependency on external chlorine deliveries, a factor that has become increasingly important in the context of supply chain disruptions.

[caption id="attachment_25645" align="alignnone" width="1200"] On-site electro-chlorination (OSEC) facility at Saggart Reservoir - Courtesy of Coffey[/caption] Pipework connections & live integration

One of the most technically challenging aspects of the project was the integration of the new reservoir into existing trunk mains, which ranged from 600mm to 1600mm in diameter.

To prevent supply interruptions, under-pressure tappings and live hot-taps were employed. This allowed new connections to be made while maintaining full service to the Greater Dublin Area.

Bespoke reinforced thrust blocks were constructed to support these live connections, ensuring long-term stability under variable hydraulic conditions. This part of the works showcased how innovative engineering methods can provide resilience while avoiding disruption to communities reliant on continuous water supply.

[caption id="attachment_25650" align="alignnone" width="1200"] (left) Internal view of the intake works and (right) internal view of the outlet works - Courtesy of Coffey[/caption] Lean & safe construction practices

Coffey applied Lean Construction methodologies to optimise programme delivery. The Last Planner System was used to coordinate tasks across disciplines, reducing downtime and eliminating rework. This collaborative planning approach also enhanced transparency across the project team, allowing risks to be identified and mitigated earlier.

Safety innovations included the deployment of GRP handrails, ladders, and platforms, selected for durability and corrosion resistance. The FreeFalcon mobile fall protection system was introduced, allowing workers to operate at height without the need for permanent anchor points. This significantly reduced fall risks while improving flexibility in sequencing roof construction. By embedding these safety systems into the project from the outset, Coffey and Uisce Éireann ensured that worker welfare remained a central priority.

Commissioning & integration

The final stage involved a 90-day Operations Period, during which the reservoir and OSEC facility were integrated into the live network. Comprehensive testing was undertaken, including hydraulic performance, water quality monitoring, and system resilience under varying demand conditions. This ensured that the new infrastructure operated seamlessly alongside existing assets before full handover.

[caption id="attachment_25649" align="alignnone" width="1200"] Benefits of the solution - Courtesy of Coffey[/caption] Summary

The Saggart Reservoir Expansion and On-Site Electro-Chlorination Project expansion represents a landmark in Ireland’s water infrastructure. Delivered by Coffey on time and within its €59m budget, the project secures the Greater Dublin Area’s water supply for decades to come.

By implementing advanced construction methods such as BAMTEC® reinforcement, precast floating roof systems, and an energy-efficient OSEC facility, the project achieved a balance of resilience, sustainability, and innovation. The successful delivery of live connections without service interruption demonstrated meticulous planning and technical excellence.

Through the collaboration of Uisce Éireann, Coffey, Ayesa, Banagher Precast Concrete, and Kilsaran, the Saggart Reservoir Project set new benchmarks for efficiency, safety, and sustainability in Irish water infrastructure.

It provides a model for how investment, innovation, and partnership can deliver infrastructure that is fit for the future, environmentally responsible, and socially valuable.

King George V Reservoir (KGV) is an operational raw water storage reservoir located in the Lea Valley at Walthamstow and is a Site of Special Scientific Interest (SSSI) with restricted access. It is controlled by Thames Water’s Lea Valley/North London Abstraction Group based at Coppermills AWTW. Seepage through the clay core at the north-east of the reservoir was identified by a Willowstick survey in 2020. MWH Treatment was awarded a contract to address the seepage issue, with the works taking place 1.4km north of the main entrance from Lea Valley Road to the north of the tidal break on the east side of the reservoir. History of the site The reservoir was conceived as part of an overall plan for the Lea Valley and was laid before the Royal Commission of Water supply in 1893. At this time, the responsible authority was the East London Waterworks Company. Construction took place between 1908 and 1912, and the reservoir was opened by Their Majesties, King George V and Queen Mary in March 1913. At the official opening there was a ceremonial guard of honour review, and The King signed a Grant of Arms to the Metropolitan Water Board (owners and operators at the time). [caption id="" align="alignnone" width="1200"] Google Maps - Location of King George V Reservoir[/caption] Description of the current facility The reservoir was formed by the construction of a continuous embankment on the floodplain of the River Lea. An earth embankment divides the reservoir into two compartments that are connected by three large diameter culverts. The external grassed embankment supports a central puddle clay core. The reservoir has a maximum capacity of 12,492 ML at its top water level (TWL) of 20.18m AOD. It is normally operated on a ‘put and take’ basis which at typical through‐flows of 60 to 100 MLD gives a theoretical retention period between 100‐150 days. The crest level is 22.50m AOD with a length of approximately 7km. The reservoir is operated in conjunction with other local reservoirs to provide a continuous supply of raw water to Coppermills AWTW and Hornsey WTW. The embankment, wave wall and clay core were raised between 1938 and 1941 to restore the 1.5m design freeboard that had been lost due to gradual consolidation settlement. The reservoir was, however, kept 1.5m below original top water level, as a wartime precaution, until February 1945. At the higher TWL leakage occurred at several points, being attributed to dryness of the very high plasticity alluvial clays within the core; consequently, the current TWL was established. A 4.5m deep grout screen was installed along an 800m length of the southwestern embankment in 1983 in an attempt to address the leakage. Access to the reservoir is located at its southeast corner from the Lea Valley Road. This access is shared with a sailing club and activities club. Sheep graze the embankments as an environmentally sustainable way of managing grass growth. Scope of works The key scope of works for the project was the provision of a sheet-pile cut‐off wall. The wall was designed as 15m deep; based on the pile toe being driven into the London Clay a minimum of 0.5m, and 165m long; being installed between crest chainages 1,715m and 1,880m. A low vibration technique of pile driving was promoted to minimise potential for stability issues within the embankment during construction. The scope also included provision of access to the crest and provision of temporary access road, strengthening of existing site roads and protection to existing pipework and services. [caption id="" align="alignnone" width="1200"] Google Maps - location of site compound and works area[/caption] Technical description A survey was carried out late 2019 to early 2020 in the area around chainage 1,750m as this had been identified as an area of interest in a previous survey. Willowstick surveying is a non-intrusive geophysical method used to map and model the subsurface water flow paths. The procedure involves energising the study area with a signature electric current between paired electrodes. The surveying equipment consists of GPS system and an instrument known as a Willowstick which measures the magnetic field response of an electric current. As the electric current flows through the survey area the preferential flow paths are identified, mapped, and modelled. The information gathered can be used in making informed, guided, and cost-effective decisions concerning how to further, monitor, intercept and mitigate seepage. The main findings from the survey were: A weakness zone of preferential flow identified between chainage 1,723m and chainage 1875m. The flow path shows the characteristics of uniform sheet flow and did not indicate a concentrated leakage path, rather a 150m zone where water was passing evenly through the core. The preferential flow was identified at elevation 12m AOD through the foundation underneath the embankment. The preferential flow path strongly correlated to the location of the original stream channel. Its characteristics indicated that seepage was concentrating in flood plain sediments deposited by the original river channel meandering through and beneath the survey area before the dam was built. The survey report recommended remediation works in this area within a short timeframe to reduce any movement or damage to the reservoir embankment. King George V Reservoir: Supply chain - key participants Principal contractor/designer: MWH Treatment Designer: Atkins Temporary works design: Noble Works Ltd UXO survey: 6 Alpha Associates Ground investigation, soil testing: Structural Soils GPR surveys: Technics Group Environmental surveys: Middlemarch Environmental Willowstick survey: Willowstick UK Noise & vibration monitors: RSK Acoustics Silent piling contractor: Sheet Piling (UK) Ltd Piling verticality survey: CMCS Ltd Civil works, labour/plant: Derryard Construction limited Electrical (site setup, gate works): SRS Electrical Ground maintenance: UK Landscapes Scaffolding/access: Clocktower Scaffolding General plant hire: GAP Group Ltd Welfare supply: Wernick Group Supply of Trakway Matting: Sunbelt Rentals Ductile iron pipework: Electrosteel Castings (UK) Ltd Valves: Glenfield Invicta CCTV, timelapse cameras: Wireless CCTV Ltd [caption id="" align="alignnone" width="1200"] Finished temporary road before track matting - Courtesy of MWH Treatment[/caption] Toe road and crane pad Atkins were instructed to advise on embankment loading constraints, construction methodology and the sheet pile solution. They developed the initially suggested remedial works to achieve a detailed solution which was then agreed with Thames Water. The existing track at the toe of the embankment was the only access route to the works area. The track had a loading capacity of 12t and the crest road a 5t weight limit; both limiting machinery and plant selection. A previous project adopted an 8t excavator and 6t tracked dumpers and Atkins used this information within their assessment to complete a slope stability analysis of the embankment. This confirmed that the use of an 8t excavator was acceptable for the works on the crest road. An existing 30” pre-stressed concrete (PSC) pipe main under the road at the toe of the embankment further constrained the size of vehicles to be used during construction and required enabling works. A disused section of pipe was recovered and tested to confirm dimensions and the material characteristics to be used in the loading analysis. Atkins confirmed that the pipe had sufficient capacity to support a maximum axle load of 12t. A temporary road was installed to minimise rutting and dynamic loading on the existing track. Trackway matting was installed from the sailing club ramp to the crane pad to disperse vehicular loading and mitigate impact on the pipe and vehicle speed was restricted to 5mph for all vehicle movements. An emergency plan was put in place to ensure the Thames Water Operations team were made aware of any incident and to cover the eventuality of a pipe burst. The temporary road was designed by Noble Works Ltd and installed by Derryard Construction Ltd over a period of 8 weeks. Over 1km of track matting was hired from Sunbelt Rentals and installed over a period of 2 weeks. Along with the temporary road, a crane pad was installed to facilitate the 200t crane used to lift the piling equipment and sheet piles from the toe to the crest of the embankment. The crane pad was designed by Noble Works Ltd and constructed in MOT Type 1 granular fill by Derryard Construction Ltd. A section of the adjacent aquifer recharge pipeline was dismantled to facilitate construction of the crane pad which also included a concrete protection slab above existing underground HV and telecommunications cables. [caption id="" align="alignnone" width="1200"] Finished installation of the track matting - Courtesy of MWH Treatment[/caption] Piling decision Following previous successful remediation works carried out at Sir William Girling, Staines South, and Island Barn Reservoirs, MWH Treatment selected Giken silent piling. This is a vibration free press-in method that allowed the pile installation to be virtually silent. This technique enables the piling plant to ‘walk’ over the tops of the driven piles. The initial press-in to install the dummy piles was carried out utilising a reaction platform. The Giken rig then used the previously installed piles to generate reaction to enable on-going pile installation. The sheet piling works (undertaken by Sheet Piling (UK) Ltd) commenced at chainage 1,880m which is the junction of the perimeter and the reservoir dividing embankments. A wider toe area had been identified as a turning and laydown area for the storage of equipment. It was also used for the reaction platform for the installation of the dummy piles. The first 100 piles were fed to the rig by the crane at the base of the embankment. Once the radius of this crane was exceeded, the ‘non-staging’ method was adopted utilising a clamp crane and pile runner to move the piles along the crest and to feed the piles to the Giken rig. A 15m long PU32 section pile was adopted being dependant on the chosen method of installation, length of pile and expected ground conditions. The pile clutches were lined with sealant to ensure low permeability through the wall joints. Press-in driving of the piles with the Giken rig was assessed as feasible with hard/difficult driving being a low risk when reaching the London Clay layer. Subject to the approval of the reservoir Qualified Civil Engineer (QCE) water jetting was an option to achieve required toe penetration. [caption id="" align="alignnone" width="1200"] Reaction stand setup excavation - Courtesy of MWH Treatment[/caption] Crest road works The Giken piling method minimised the access width requirement to work on the crest, however some excavation was still required. Using an 8T excavator the crest road was excavated to expose the clay core to allow the alignment of the sheet pile wall with the centre of the core. The base width of the trench was specified at 2m to allow the Giken rig to operate. The top of the core was covered with plastic sheeting to prevent desiccation and protect the clay core from being damaged. Following the completion of the sheet piling works, the trench and crest was reinstated. Site installation of the piles Sheet Piling (UK) Ltd commenced work on site at the end of October 2022, with a planned 10-12 week site duration. The 200T attendant crane was stripped of all non-essential weight in order to maintain the 12T per axle load weight restriction. Once in position on the crane pad a smaller 45T service crane off loaded the initial crane ballast and commenced rigging; once part rigged the remaining ballast was self-rigged. The reaction stand was lifted into position by the 200T crane to the 6m x 6m hardstanding area finished 600mm below the top pile design level. The Giken rig was then positioned onto the reaction stand followed by counterweights. The first pile was then driven utilising the weight of the rig and counterweight as reaction. After the first pile were installed, it became a reaction pile for subsequent piles to be installed. When the rig fully sat on the dummy piles, the reaction stand and counterweights were removed. Once a pile was sufficiently driven and stable the rig releases its clamps from the reaction piles and travels forwards. This ‘self-moving’ system eliminates the need for support by a crane during the piling operation. Following installation of the first 100 piles a clamp crane was utilised as the piling works had exceeded the working radius of the 200T crane. After the clamp crane had travelled along the piles as far as possible inside the 200T crane working radius a track, formed of a temporary pile welded along the completed wall, allowed a handling train to deliver the piles to the clamp crane. Pile verticality was critical as the piles must not exit the puddle clay before penetrating the underlying London clay. During piling verticality was monitored via spirit level. Once completed Sheet Piling (UK) Ltd employed CMCS Ltd to undertake a verticality survey. This included the first five 5 piles and then 10% thereafter, resulting in a total of 32 tests. CMCS Ltd utilised the lancing tubes on the piles that were welded prior to installation. The data reported the tilt of the pile and to what extent, whether leaning towards or away from the reservoir. [caption id="" align="alignnone" width="1200"] Train moving a pile to the clamp crane - Courtesy of MWH Treatment[/caption] Success of piling solution After the first week of initial set up and pressing of the 3 dummy piles, Sheet Piling (UK) Ltd installed 275 piles over the next 6 weeks. The site team completed the work in advance of programme despite difficult weather conditions. The crest of the embankment was very exposed; strong cross winds resulted in several days when piling was prevented, but the team were able to boost productivity to recover lost time. The Sheet Piling (UK) Ltd team de-mobilised mid-December; this was during the weekend of a severe snowstorm with over 6 inches falling over the Sunday night. The MWH Treatment team and subcontractors mobilised additional resources to clear the site of snow, including the 1km toe road, enabling several lorries and the 200T crane to safely leave site. Site demobilisation took place earlier than planned realising 3-weeks’ efficiency on the track matting hire period. After the Christmas shut down, the trench on the crest road was reinstated and an embankment survey was carried out by Derryard Construction to confirm the final ground levels were within tolerance. A post-installation Willowstick survey was conducted which reported that the previous flow path had been cut-of. The sheet pile wall appears to be working as designed by cutting-off the preferential flow of electric current through and beneath the northern half of the sheet pile wall; interpreted as cutting off the seepage flow. The post completion survey confirmed that the remediation works had been successful. Biodiversity The King George V Reservoir is a major wintering ground for wildfowl and wetland birds, including nationally important species. A total of 85 wetland species have been recorded and the reservoir also forms a moult refuge for a large population of wildfowl during the late summer months. Over the course of the project environmental consultants Middlemarch visited site monthly to monitor bird activity and to ensure site works were not affecting wildlife. The site compound took up the space of the sailing club/water sports club car park so MWH Treatment constructed a temporary car park providing sailing club patrons with continued safe parking. On project completion it was agreed with Thames Water that the car park should become a permanent overflow car park. A wildflower meadow is being planted to compensate for the biodiversity loss of the car park. Conclusion MWH Treatment have delivered a very successful project overcoming access, logistic, weather and environmental challenges. The sheet piling cut-off wall achieved the desired project outcome: mitigation of water seepage. The project was delivered early with an excellent safety and environmental performance. Thames Water additionally gained an upgraded toe road and improved protection for critical services. The project also fostered and maintained excellent relationships with neighbours at the sailing and activity clubs.

South West Water’s (SWW) Hingston Down Reservoir site is located on an exposed Cornish hilltop and contains two service reservoirs which supply nearby villages with potable water. Originally there was only one reservoir at the site and there was no way of being able to take it out of service for cleaning, so a Braithwaite GRP storage tank was installed in the early 2000s. As the local settlements expanded, including holiday parks, the temporary tank started to become relied upon during the busy tourist season to ensure adequate water supply throughout the day, so became the second service reservoir, hydraulically linked to the original. Project drivers The temporary Braithwaite tank was only ever intended to be a temporary structure to aid cleaning the original reservoir. It was never designed to be maintainable in the way required by regulations. This, together with the site struggling to provide sufficient quantities of water during the busiest summer months, resulted in the requirement to replace the temporary tank with a new service reservoir with a greater capacity. The replacement structure was to assist in providing resilience to the supply of compliant water to the network; whilst allowing maintenance to be carried out in a safe manner, under the control of SWW’s safe system of work. Programme restraints This project was strongly time dependant. The requirement to replace the tank was only made in the autumn of 2021, and the replacement reservoir had to be in service by Easter 2022. During the winter period, SWW believed the network could be serviced from just the existing reservoir as the main constraint was the feed pump capacity supplying the reservoir(s) and this capacity would be exceeded at the start of the Easter holiday tourist season. Site mobilisation and demolition of the existing Braithwaite tank commenced in December 2021, with RM Penny Group employed to undertake the demolition work. The tank was broken up using a 20t excavator with a selector grab attachment. The GRP panels were ripped into manageable pieces with the stainless steel reinforcement bars segregated for recycling. [caption id="" align="alignnone" width="1200"] (left) The existing temporary reservoir, (top right) the demolition of the temporary tank and (bottom right) the view of site following tank removal - Courtesy of Galliford Try[/caption] Design In order to provide greater storage capacity on site, the Galliford Try design team came up with a novel idea of using a ‘smart valve’ to link the new and old reservoirs together. An existing pumping station supplied the site but struggled to keep up with peak demand. The logic therefore was to now only pump to the new, taller reservoir and use the ‘smart valve’ to release water into the existing adjoining reservoir, keeping the original reservoir within a set of control levels. The new reservoir could then act as a balancing tank whilst also providing supply to the network. Hingston Down Reservoir: Supply chain - key participants Design/construct: Galliford Try Civil & structural design services: Bailey Partnership Topographical survey: Kemp Chartered Engineering & Surveying Demolition & removal of existing tank: RM Penny Group Reinforced concrete works: D Wall Construction Services Ltd Fabrication: Thorne Fabrication Limited Pumps: Pump Supplies Ltd Mechanical items: Teignflex Ltd Mechanical & civil items: Wolseley UK Electrical items: Edmundson Electrical Ltd Wirechairs: Miers Construction Products Ltd Access scaffolding works: RBS Scaffolding Devon Diamond drilling works: 24-7 Diamond Drilling & Sawing Services Mechanical items: Vulcan Industrial Fasteners Aggregates: Hanson Aggregates Construction Products: Jewson Plant hire: Brandon Hire Plant hire: Sunbelt Rentals Ltd Plant hire: Gap Group Ltd Crane hire: Spence Crane Hire Ltd Crane hire: Macsalvors (Plant Hire) Ltd Civil items: Travis Perkins Fuel: Watson Fuels Haulage: Steve Wills Haulage Construction With the Braithwaite tank removed, the Galliford Try civils team moved on site to undertake the preparation works for the new reservoir; including the underground pipe connections. Due to the new site operating logic, numerous pipework connections and modifications had to be undertaken with the inlet and outlet pipes to the reservoir being set within the base slab. D Wall Construction Services Ltd was employed to undertake the reinforced concrete construction works. Weekend and evening shifts were used to ensure their tight programme was maintained and to try to mitigate against the Cornish winter weather. Wind was the biggest issue, the site is located on top of a hill and with all construction having to be undertaken from just one side of the reservoir, lifting formed a large proportion of the construction process. [caption id="" align="alignnone" width="1200"] (top left) Installation of steel reinforcement for new reservoir on existing tank slab, (top right) frost blanket placement as pour undertaken late January 2022, (bottom left) steel reinforcement for tank wall with internal shutter erection and (bottom right) column and wall shutters ready for concrete pour - Courtesy of Galliford Try[/caption] Resources Regular meetings and conversations were held by the site team with key suppliers to ensure they could hit the dates promised and any issues quickly identified and mitigated. A Critical Path (CP) Board was used to itemise each day’s activities by all suppliers, including the suppliers’ off-site activities. All interfaces between different sub-contractors were discussed to ensure nothing got in the way of the day’s planned progress, which also included when deliveries were to be made and how/where they were to be off-loaded. The SWW operational team also became heavily involved in the CP Board review sessions and this resulted in network alterations and availability of water for testing being available exactly when required. Most deliveries were ‘just in time’, often being dropped off the day before, or even on the morning of the day of installation, so when a delivery of straight reinforcement bar was delivered curved, a solution had to be found immediately. Unfortunately, the supplier could not provide replacement steel for a few days, however another supplier located around 150 miles away could get it ready for collection the following day (which was a Saturday). Thankfully a regional member of GT was found with a van who was willing to drive to the supplier early Saturday morning and get the steel to site by lunchtime the same day, thus allowing the steel fixers to keep working to their programme. Time saving solutions Due to the project time restraints and coupled with the exposed site location, a cast in situ reinforced concrete reservoir was chosen, which would provide 406m3 of additional capacity to the existing reservoir. The five-month construction programme had to be cut down to three months in order to complete the works on time and resulted in a construction programme with zero time risk on the critical path. The design and delivery team therefore worked closely together to shorten the overall construction programme and employed the following solutions: Utilising the existing tank slab as blinding for the new structure. Fast-tracking panel design and construction by utilising the Galliford Try in-house panel shop. Working with all aspects of the supply chain for prompt deliveries and reserving manufacturing slots so that when drawings were issued, these could be slotted directly into the supply chain. Hiring in a shuttering system from London to allow the walls to be poured in one go rather than the four pours identified at pre-construction. Working with concrete batching plant to create a hybrid mix design. Working with SWW’s scientific department to deviate from the usual testing regime whilst still ensuring all tests were undertaken as required. [caption id="" align="alignnone" width="1200"] (top left) Steel reinforcement and shutters ready for roof slab pour, (top right) Application of waterproofing pain system to roof slab and top of walls/upstands, (bottom left) placement of stone cover to reservoir roof slab, and (bottom right) the new reservoir is complete and undergoing water testing - Courtesy of Galliford Try[/caption] Embedded carbon and carbon savings are very important to South West Water, so the initial concrete mix design contained a healthy element of cement replacement. This however resulted in delayed curing and it took a full three days for the base slab to cure sufficiently on this exposed site before wall and column construction could start. Due to the crack width and other requirements for a potable water retaining structure a full 100% cement mix was not possible. The delivery and design team worked closely with the local concrete batching plant to create a blended hybrid mix which would set as fast as possible but whilst also meeting the stringent standards required for the structure. This concrete mix turned out to be so good that the lost three days were recovered in the curing time for the walls and roof slab. By far the biggest time saving came from working with South West Water’s scientific department, which saved around three weeks off the initial tender programme. As soon as the soffit was struck, the tank was cleaned with a pressure washer and filled for the initial water test. Samples were taken after the seven day water test was complete and analysed to identify possible areas of compliance failure. It was identified that alkalinity was an issue, (as would be expected with water contact on a new concrete structure) however there was no issue with bacteria, but a slight oil residue was detected. The oil residue was quickly identified as the shuttering release agent and it was decided to empty the tank and refill again for a further seven-day water contact period with the structure. The scientific results which came back following this test were very promising, and it was decided that no further action was required prior to the normal sterilisation and water sample testing which would be required prior to brining the reservoir into service. [caption id="" align="alignnone" width="1200"] View from inside new reservoir prior to initial water test - Courtesy of Galliford Try[/caption] Customer and stakeholder Due to the critical nature of this scheme, official progress meetings were undertaken every other week with communications and site visits from the operational team undertaken several times a week. The local community was informed of the project through letter drops and the resident who lived opposite the site was kept up to date by in-person visits from the site team. The site is located adjacent to a mining heritage site, which is frequently visited by tourist and locals; especially dog walkers. The site team ensured they were approachable and polite and built up a great rapport with several of the locals. Key interfaces were logged by the site’s client liaison officer with summaries fed back to South West Water. It is testament to the site team that not a single complaint was received regarding the construction activities being undertaken on the site and gifts and praise for the works undertaken were regularly received. Completion and handover Water testing was undertaken during a 28-day period of concrete curing which was required before the application of a polyurethane waterproofing system - a South West Water requirement - before the reservoir could be brought into service. The waterproofing system was the last critical path item and was initially booked in with Technique (system applicators) in January of 2022. The application slot was hit by the delivery team and the reservoir handed over to South West Water on the agreed date so that the system could be brought online just at the start of the Easter holidays.

Kerse lies in open countryside approximately 3.5km from the former mining village of Patna in East Ayrshire, some 15km from the county town of Ayr. The newly constructed 3 megalitre capacity, twin cell, treated water storage (TWS) tank serves a local population of 6,500 private customers and businesses. It is situated immediately adjacent to the existing facility and is fed from the nearby Afton Water Treatment Works. Scottish Water’s Non-Infrastructure Alliance Partner, ESD JV (a joint venture comprising MWH Treatment, Binnies and Galliford Try) commenced construction in July 2022.  Water into supply was achieved on schedule on 21 May 2024. Existing facility

The existing single cell, below ground 4.5 ML clear water storage tank dates from the 1930s. It is, therefore, an ageing asset whose deterioration has recently led to some failures in water quality and general lack of resilience in the system. These drivers led to a decision by Scottish Water to commission a £6.5m replacement. Forecast modest rises in local population numbers was a secondary consideration.

Challenges

The principal challenges were:

How to build the new underground tank in a position immediately adjacent to the existing, still operating, facility. Non-interruption to the operation of the existing asset was a primary consideration. Working on the existing ageing network to fulfil the new process pipework. Undertaking testing and commissioning of the new asset whilst keeping the existing asset live and ensuring no negative impact on the network. How to stabilise the ground during excavations to ensure the continued, uninterrupted operation of the to-be-replaced tank and network pipelines. How to mitigate against poor soil conditions - mainly heavy clay - during two winter and spring seasons of heavy rain leading to severe drainage issues. The site was also located adjacent to a number of disused open-cast mines which were situated under a sludge restoration scheme, so continual coordination around access was key. Scope

The contract specified the replacement of the existing almost 90 year-old tank with a 3 ML, twin-celled treated water storage tank to be constructed on the same site, contiguous with the structure of the old tank.

The dimensions of the new asset are 29m x 21.5m x 7m to be covered by a reinforced concrete roof with waterproof membrane.

All aspects of the design of the new tank were undertaken by ESD JV’s design and engineering department. Work started on-site in July 2022. In total, approximately 850m3 of concrete was poured to construct the new structure.

[caption id="attachment_13133" align="alignnone" width="1200"] View of tank with backfill almost completed. Pedestrian crane on the left - Courtesy of ESD JV[/caption] Kerse Treated Water Storage Tank: Supply chain: key participants Client: Scottish Water Delivery contractor: ESD JV Binnies Galliford Try MWH Treatment Geotech design: Stantec UK Tower crane base design: Noble Works Ltd Mechanical design/installation: Dustacco Engineering Ltd Electrical installation: RRC Project Solutions Ltd Soil nailing: Albion Drilling Group Ltd Waterproofing: Concrete Repairs Ltd Underpressure connections: Swan Pipelines Pressure testing: Pressure Test Scotland Ltd Tank disinfection: Panton McLeod Ltd Telemetry: ID Systems UK Formwork: Peri UK Ltd FRC: AJ McAlpine Instrumentation: Processplus Ltd Control valve: CLA-VAL UK Ltd DI pipework: Saint Gobain PAM UK PE pipework: FPP Scotland Ltd Metalwork: HK Gillies Scaffolding: JD Scaffolding Ltd Tower crane: Ladybird Crane Hire Security system: Pointer Access covers: Technocover Ltd Rebar: Midland Steel Reinforcement Supplier UK Ltd Concrete & aggregates: Breedon Group Aggregates: Hillhouse Quarry Group Groundworks

In order to protect the viability of the existing tank, and as a consequence of above average rainfall in the winters and springs of 2022, 2023 and 2024, a complex bulk excavation operation was undertaken which included the extensive use of soil anchors to stabilise the ground.

This solution included some in-depth collaboration from the site team and specialist sub-contractor to design a solution to ensure no current live network pipes (which were only 6m from the top of the batter of the excavation) were damaged during the installation of the anchors. In order to achieve this, the site team undertook a survey of the existing network to establish the precise coordinates of each pipeline.

This allowed for the design to be altered to a smaller length of anchors with a revised slope angle ensuring no pipes would be damaged as part of the TW solution. All excavated material (spoil) was used as backfill for the new asset and also for the existing asset which is scheduled to be de-commissioned and removed with minimal excess being removed from site. In total, circa 10,500 tonnes of material were excavated to construct the new asset.

[caption id="attachment_13134" align="alignnone" width="1200"] (top left) Groundworks nearing completion, (bottom left) tank construction underway, and (right) view of tank interior - Courtesy of ESD JV[/caption] Innovative construction

A hydraulic assessment to decide the level of the tank resulted in the need to bury it underground. Given the damp ground conditions on-site, a water impermeable concrete was used to construct the base and walls. This maximises the lifespan of the asset and represents the best carbon solution.

The heavy clay soil resulted in the rapid build-up of water within the excavated area leading to significant drainage issues. This resulted in some pre-excavation cut off drainage ditches being constructed at the high level of the excavation along with gravel filled silt ditches and fencing installed around the site to mitigate the impact of any run-off. Due to the inclement weather encountered throughout the winter of 2022, this led to some initial delays to the programme.

However, any delays were mitigated by innovative solutions to other tasks. The team at Kerse are proud of their ‘championing’ of the use of an electric pedestrian tower crane. Operated at ground level, this led directly to accelerating the construction programme and a significant cost reduction. The selection of the pedestrian crane, which was initially proposed to be an operated crane via operator at high level, brought significant health and safety benefits by removing the need for working at height.

Also, the site team installed cameras at critical inspection points on the crane which meant all daily inspections could be carried out at ground level by the operator, again eliminating the requirement to work at height. All statutory inspections were undertaken by a third party under a safe system of work which was included as part of the sub-contracted scope.

The additional benefit from selecting this method came from a reduction in carbon output with the initial temporary works reinforced concrete pads (which were due to be in excess of 95m3) and the selection of the pedestrian ground operated crane reducing this concrete requirement to only 8m3 to fulfil the temporary works requirement.

A rechargeable electric mobile elevated working platform (MEWP) was employed, providing further benefits. The use of the pedestrian crane and MEWP significantly reduced the carbon footprint on the project in comparison to using alternative options such as mobile cranes and access scaffold which are commonly used on this type of project. The use of the tower crane to facilitate lifting operations throughout the project, along with the MEWP for high level access, proved to be a time saving, cost effective and carbon friendly solution to our buildability requirements on site.

Another innovation was the temporary works wall truss system employed.

Reinforcement for the walls of the new tank was prefabricated on-site. In itself, this produced significant cost, time and safety benefits. This solution reduced the requirement for access scaffolding to be erected, this being substituted by the MEWP system. In addition, personnel did not have to construct the reinforcement whilst working at height or manually handle the reinforcement and place it into position. Instead, this was achieved via pre-fabrication at low level, subsequently allowing full panel reinforcements to be lifted and installed into position providing further safety, time and cost benefits to the project. Another reason for employing this system was that no additional temporary support system was required to support the reinforcement.

[caption id="attachment_13132" align="alignnone" width="1200"] The almost completed structure before backfill operations - Courtesy of ESD JV[/caption] Telemetry

Throughout the project, there was regular liaison between ESD JV and Scottish Water with weekly and monthly collaboration meetings held leading to a close and productive working relationship on the project mitigating potential delays. All issues and challenges have been met in a collaborative environment.

At Kerse, Scottish Water have introduced a new telecoms telemetry system using 4G connectivity monitoring all instrumentation, including water level sensors, alarms and floats, which replaces the old PSTN line.

This option was the result of a business approach change from Scottish Water to provide either VDSL (fixed line) or LTE (4G mobile) for IP enabled communications. In order to prevent the time and cost involved in installing a VDSL line, a decision was made following a successful survey to utilise a new 4G solution for the project’s telemetry communications.

Current status

Water into supply was achieved on schedule in May 2024. This was followed by reliability testing and sampling by Scottish Water before the facility was declared fit for operation which was achieved on 30 May 2024, with the old asset now drained and ready for de-commissioning.

Currently, a new site access road is being completed and various measures of landscaping, including grass seeding, are underway. A new perimeter fence will also be installed as per SW security requirements.

Towards the end of the project, ESD JV was asked by Scottish Water to undertake the decommissioning and demolition of the now-replaced clear water tank. This was not part of the original scope of the contract. These works will be completed in the summer of 2024.