Thames Tideway Tunnel: Hammersmith Pumping Station – highly constrained working Open Access

The Thames Tideway Tunnel project manages 34 combined sewer overflows (CSOs) along the tidal River Thames. This paper focuses on the works at the Hammersmith Pumping Station site, which is one of the sites that directly intercepts a CSO to direct flows into the deep storage and transfer tunnel system for treatment at Beckton Sewage Treatment Works. The interception of the CSO at Hammersmith was part of the main works contract for the west section. Figure 1 shows the location of the site relative to the whole project and Figure 2 shows the location relative to local landmarks. The pumping station’s catchment covers an area of around 48 km² and it used to discharge over 50 times in a typical year into the Thames, releasing approximately 2 210 000 m³ of untreated combined sewage (Thames Water, 2013).

The main works contractor for the west section of the project was a joint venture between Bam Nuttall, Morgan Sindall and Balfour Beatty (BMB), with primary designer Arup and Atkins (now AtkinsRéalis) joint venture (AAJV), specialist consultant Morgan Sindall Engineering Services (MSES) and Tony Gee & Partners.

Both design and construction were influenced by significant constraints at the site, including the need to keep the pumping station operational throughout the works, the limited area of land available for the permanent works, the close proximity of settled residential communities and requirements regarding the subsequent Fulham Reach development immediately adjacent to the site. The fundamental requirements for the design of CSO interception works are outlined by Fricker et al. (2025) in this issue.

The scope of the main permanent works at the site is shown in Figure 3, which included the following.

• Modifications to the existing sewer infrastructure to divert combined sewage flows into the tunnel system. The pumping station’s inlet channel was extensively modified and included the provision of two new pumping station isolation penstocks.

• An interception chamber, incorporating a tunnel isolation penstock chamber, a secondary isolation gate (SIG) chamber and a tunnel flap valve chamber.

• A circular drop shaft, located in the new boulevard of the proposed Fulham Reach development site.

• A vortex drop tube within the shaft, provided in stainless steel for durability and predominantly encased in concrete. The 3.5 m internal dia. vortex tube was the largest in diameter on the project.

• A connection culvert, between the interception chamber and the drop shaft, designed to accommodate future development structures above and adjacent.

• A connection tunnel from the drop shaft to the main tunnel, incorporating a horizontal deaeration chamber.

The main mechanical, electrical, instrumentation, control and automation (MEICA) scope of works consisted of the following.

• Flow control penstocks and flap valves, including four tunnel isolation penstocks, two pumping station isolation penstocks, two reverse flow penstocks and four SIGs.

• Modifications to the existing motor control centre and human–machine interface (HMI) control systems, instrumentation, telecommunications, cabling, electrical power supplies, an uninterruptible power supply and lighting.

• A new mechanical and electrical kiosk providing centralised monitoring and control, interfacing with Thames Water’s supervisory control and data acquisition and new local HMI control for all the flow control elements.

• Below-ground ventilation ducting system with air treatment of malodorous air.

At this reach of the River Thames, the Hammersmith Pumping Station CSO discharges through two outfalls directly into the river. The flows into the pumping station are from two large relief sewers (the Hammersmith Storm Relief Sewer and the Hammersmith Storm Relief Connecting Sewer, at 2.4 m and 3.2 m nominal internal dias., respectively). The CSO interception structures were designed for flows up to the design flow of 42 m³/s. More information of how design flow rates were derived is available elsewhere (Hon et al., 2017).

During the planning stage, it was decided to intercept the gravity flow upstream of the pumping station for two main reasons.

• Interception of flows upstream allows the tunnel system to accept greater rates and volumes of flow as compared with downstream, which would have been limited to the flow capacity of the pumps in the pumping station. The upstream interception capacity of 42 m³/s provides for greater control of flows in the sewer network and also indirectly controls the number of spills from adjacent CSOs, negating the need for further interception sites.

• Overall energy efficiency in the use of pumps, as the intercepted combined sewage is raised by pumping only once – at Beckton Sewage Treatment Works.

Furthermore, upstream of the pumping station there was better availability of land for the permanent works and, although very constrained, there was working space and access for the contractor’s worksite.

Intercepting flows upstream of the pumping station required further associated works, as follows.

• Provision of a low-flow pumping station to transfer dry-weather flows back to the sewer system. This was required as these flows no longer reach the drain down pumps in the pumping station that used to serve that function.

• Provision of a storm pump exercising system using a separate water supply. This was required because the existing storm pumps no longer operate frequently. Previously, the station was receiving storm flows and pumping to river over 50 times in a typical year. Now that the majority of these are intercepted, the pumps will only be pumping to the river approximately one to three times in a typical year.

This site also has a contingency reverse flow system, whereby reverse flows from the tunnel system can be taken back to the pumping station and then pumped to the river. This contingency provides a facility to further control water levels within the tunnel system in the event of a potential for excessive levels during extreme conditions. This feature is unique to Hammersmith and Greenwich Pumping Stations.

Understanding the hydraulic performance of the hydraulic structures was paramount. Computational fluid dynamics (CFD) and physical modelling were used at all design stages. CFD modelling allowed numerical assessment of the flow at different flow rates and evaluation of design modifications/improvements. Physical modelling was undertaken to carry out additional analysis beyond the capabilities of CFD modelling, including sediment movement and the potential for adverse air entrainment. A summary demonstrating the extent of modelling work undertaken prior to and post-contract award is shown in Table 1.

The initial modelling work was used to establish the required layout and dimensions of the structures for planning purposes, later confirmed in the reference design. BMB/AAJV adopted and further developed these hydraulic designs in conjunction with the permanent and temporary structural designs and construction methodology for the inlet channel, interception chamber and connection culvert. The work resulted in minor changes to the hydraulic surface profiles and the provision of benching to prevent sedimentation. For design responsibilities and the meaning of hydraulic surfaces see Fricker et al. (2025) in this issue.

Physical hydraulic modelling was undertaken for the modified inlet channel and interception chamber, the storm pumping station and the modified low-flow pumping station. Good correlation was achieved between the CFD and physical model results, providing confidence that the hydraulic flow behaviour was understood.

The two sewers supplying the pumping station converge in a 11 m wide, 37 m long and 15 m deep inlet channel immediately outside it. The adopted interception solution required structural works within the inlet channel to turn the flow at 90° through new apertures in the side wall into the interception chamber and low-flow pumping station (11 m wide, 23.5 m long and 15 m deep). This deep interception structure contained all the valve chambers and was within the boundary of the Thames Water Pumping Station compound, allowing ready access from ground level to all areas and mechanical equipment. The link to the drop shaft is by way of a buried connection culvert (4.7 m wide, 5.2 m high and 27.5 m long at 9 m below ground).

The reference design required four flow apertures (1.8 m wide by 2.5 m high) in the connecting wall with the new interception chamber. To turn the flows, a new cross-wall was provided in the inlet channel (Figure 4). This cross-wall also has two new penstocks, which – when opened – allow flows forward into the pumping station wet well where the eight existing storm pumps are located. Flows will also be able to weir over this cross-wall in the case of very high flows or as a safeguard against penstocks failing to open from their normal closed position. Within the inlet channel and the tunnel isolation penstock chamber, a low-flow channel has been provided in the base slab to direct flows through to the new low-flow pumping station during dry weather.

Within the interception chamber, two 1.0 m thick walls were provided to create the three valve chambers. The first wall supports four tunnel isolation penstocks on the upstream side for 1.5 m wide by 3.0 m high apertures, forming the tunnel isolation penstock chamber. The second wall supports eight tunnel flap valves on the downstream side for 1.5 m by 1.5 m apertures, forming the tunnel flap valve chamber. Another smaller aperture in both walls was introduced at the far west side for the reverse flow capability, with two reverse flow penstocks. During the tender process, a requirement for double isolation of the tunnel system was introduced by Thames Water. This was accommodated by adding four large secondary isolation gates (SIGs) on the upstream side of the flap valve wall, covering the full height of the flap valve apertures, thus creating the SIG chamber. The layout of the works and a typical flow stream output from the CFD modelling from the incoming sewers to the connection culvert are shown in Figures 4 and 5, respectively.

During the detailed design, BMB/AAJV assessed historical drawing records of the existing underground structures and carried out intrusive investigations, which resulted in modifications to the plan arrangement. The information indicated that the sub-surface reinforced concrete (RC) walled inlet channel was constructed within a sheet pile excavation that had been left in place and the gap infilled with concrete of unknown quality. To reduce the risk of adversely affecting the existing structure and the new piling works during construction, the position of the low-flow pumping station was moved slightly away from the existing structure and enlarged to optimise use of the available land. This enlarged space was utilised for the MEICA works, stair access and changes to the rising main routing.

The contractor’s detailed design layout for the interception chamber and low-flow pumping station is shown in Figure 6. The layout incorporated the construction methodology of top-down excavation described in Section 3. This final design shows a repositioned low-flow pumping station, the positioning of the secant piles and the existing sheet piles. The layout incorporated the provision for safe access to all equipment and chambers by careful location of covers in the roof slab, ensuring clear vertical access routes. The detailed design incorporated all benching to prevent sedimentation, as determined by the CFD and physical modelling.

All the works had to be carried out within a confined worksite area, surrounded by both residential properties, the existing pumping station and the Fulham Reach development. To manage these interfaces, regular meetings with stakeholders took place. A key issue was ensuring that the permanent works did not clash with the developer’s future works, which included an underground car park and an accommodation block above the connection culvert. In addition, residents were invited every few months to liaison meetings where their concerns of dust, noise, vehicle movements and odour were responded to. To manage vehicle movements, dedicated traffic marshals were employed, utilising a delivery–vehicle system, which streamlined deliveries across the working day, reducing the impact on residents.

One of the biggest challenges that was least well defined at contract award was working out how to safely work in the existing inlet channel without causing disruption to the flow to the pumping station, as disruption would potentially result in unacceptable flooding of the upstream catchment area. Furthermore, the new 15 m deep interception chamber was to be excavated alongside the fragile 1960s inlet channel (Figure 6).

To work safely within the inlet channel, the team needed to understand how flows in the vast network of sewers feeding into the pumping station could be monitored. Thames Water advised that there were 46 weirs within the Hammersmith Pumping Station catchment area. Flow analysis identified 16 of the most influential weirs using three factors: spill volume, spill flow rate and time to arrive at the pumping station. Three types of monitors were installed at each weir, one ultrasonic, one pressure sensitive and a final float switch (Figure 7). This provided redundancy should either the ultrasonic or pressure sensors fail within the aggressive sewer environment. The float switch was a final contingency.

Thames Water already had a network model to represent the catchment area, known as ICM Live. The model was used to predict sewer flow rates, the impact of rainfall on the sewer system and at what point foul sewers would spill into the stormwater sewers. Information from the 16 real-time monitors was used to correlate the predicted model flows to actual recorded flows. Thus, the ICM Live model was finely tuned to the catchment area. Finally, rainfall forecasts from the Met Office were fed into the model to predict flows at each of the 16 weirs and total flows arriving at the pumping station. Installation of monitoring was complex, with the installation at one location (Warwick Road) proving particularly troublesome. For example, the team had to abandon sewer entry on three separate occasions due to gas levels, heavy rainfall and traffic issues. Access involved descending two separate levels within the sewer system, requiring two rescue teams. In addition, traffic management was particularly difficult due to the access openings being situated in busy road networks – entry was only possible during the night.

Once a reliable monitoring system had been installed that allowed the team to predict which days it was safe to work, a plan was needed to create a dry working area within the inlet channel. Flows into the pumping station could not be restricted by any temporary works that were installed. In dry weather, the flow levels are kept at a nominal 1 m depth to suit the stormwater pumps. During rainfall events, the depth can rapidly increase to over 12 m in less than 10 min. A safe working zone of approximately 23 m long had to be created to enable the removal of an existing central ‘cutwater wall’, the breaking out of apertures in the wall on one side of the inlet channel and the installation of the penstock cross-wall and new benching works. Temporary works consisted of two 5 m high bulkheads connected by two 1000 mm dia. flume pipes to control and maintain flow to the pumping station. An additional two 300 mm dia. flume pipes were also installed, primarily to assist during the installation of these temporary works and to remove the requirement for over-pumping at the earliest possible time. The two bulkheads were constructed from a combination of steel walers and vertical timbers. All were relatively easy to handle and timber was adaptable, particularly when connecting to the flume pipes. After installation, no further alterations or adjustments were required for the 4 years it was in place (Figure 8).

In the event of sufficient rainfall intensity, incoming flows would spill over the 5 m high upstream bulkhead and flood the working area. This would have been predicted by ICM Live the previous day and all works would have been stopped during the daily 9 a.m. and 3 p.m. go/no-go conference calls. Once the storm subsided and flow levels dropped, the team would enter the area between the two bulkheads and clean up the detritus – after certain storms, this took months. The detritus was not just non-degradable rags, but also hundreds of tonnes of silt, all removed by shovel (Figure 9).

During excavation of the adjacent interception chamber, extensive temporary works were required to stiffen the walls of the inlet channel and to ensure its structural stability. Two steel walings were installed with a series of circular steel props. The walings also served as runway beams for a 3 t gantry crane, which proved essential for all the low-level works.

The works within the inlet channel required removal of the cutwater wall – a 15 m long, 5 m high and 1.5 m wide twin-tapered block of mass concrete. To reduce noise, dust, vibration and risk of broken concrete blocking the stormwater pumps, the wall was cut into a series of blocks using wire-rope saws and then lifted out through access openings created in the roof of the inlet channel. It took a total of 15 weeks to complete the works.

The low-level wall on one side of the inlet channel was then incrementally broken out for four new apertures and replaced with RC walls with openings, through which stormwater flows would pass into the new interception chamber. To turn the flows, a new RC cross-wall was cast across the downstream end of the inlet channel and two pumping station isolation penstocks were installed. Additional RC was added to the base of the inlet channel, together with additional internal props to stiffen the 1960s structure. Finally, benching and access equipment were installed and the existing roof was removed and replaced with new support beams and slabs (Figure 10).

The works were seen throughout the project as an example of best practice in terms of collaboration with Thames Water. It was essential that communication was maintained, which greatly helped understanding the sewer network and the workings of the pumping station. The foresight to invest and install the network of early warning sewer monitors was in part due to knowledge provided by the Thames Water team. Through the 4 years of works within the highly aggressive working environment, not one injury was recorded and there was no instance when emergency evacuation was required from the inlet channel, other than for emergency drills.

Construction of the deep interception chamber alongside the existing inlet channel – a critical asset for the pumping station – required a very detailed engineering impact assessment coupled with extreme caution during excavation works.

Excavation for the interception chamber would induce out-of-balance lateral forces, due to earth pressure on the north side of the inlet channel. This required carefully designed propping to support the south side of the inlet channel and transfer loads to the south side of the interception chamber. Any excessive movements of the inlet channel could have been catastrophic to managing the flows.

Using the modelling output, AAJV and the Bam Nuttall temporary works team developed a construction sequence and propping scheme that used both temporary and permanent works to ensure that the structural integrity of the inlet channel was not compromised during construction (Figure 11).

Temporary props were installed within the inlet channel, between the existing roof and mid-level props. These were matched by temporary props within the new interception chamber. While this work was essential, it created further congestion in the inlet channel, complicating subsequent modifications.

Before excavation commenced, AAJV analysed the effects of the excavation. Initial analysis was based on reference to the 1960s construction drawings, which indicated that the structure was lightly reinforced with high-tensile steel. Several cores were taken from the existing wall, at various levels, to verify the strength of the reinforcement. The test results showed conclusively that the reinforcement properties were, in fact, closer to mild steel. AAJV revised their entire analysis for excavation of the interception chamber. The design work became more extensive due to the fragile nature of the pumping station. Resolving an issue in one area of the existing structure invariably caused a weakness in another area. Each construction stage was coordinated with the construction team to ensure that it was buildable.

Secant piles were installed on three sides of the interception chamber, 1180 mm dia. male piles interlocking with 1130 mm female piles, to depths of 20–35 m (Figure 6). On the fourth side, adjacent to the inlet channel, seven male piles were installed adjacent to the location where a connection would be made into the inlet channel, which were subsequentially cropped down as excavation proceeded. Along the remainder of this fourth side, a secant piled wall was installed. Finally, a series of anchor piles was cast internally within the interception chamber. These would subsequently be tied into the interception chamber base slab to provide restraint against long-term heave of the structure.

A heavily reinforced capping beam was then constructed, tying into the male piles. Excavation then proceeded to depths of 15 m for the main interception chamber and 20 m to the wet well of the low-flow pumping station. During excavation, five levels of both temporary and permanent props were installed both to transfer ground pressure loads into the inlet channel propping system and for permanent support to the chamber (Figure 12). It is a huge testament to the skill and foresight of the design and construction teams that no significant movement of the inlet channel structure or pumping station was recorded.

Casting of base slabs and internal walls followed excavation, together forming openings in preparation of the subsequent connection into the inlet channel. In common with all the hydraulic structures, the design of the concrete was based on a specific durability assessment of deterioration mechanisms for the particular exposure conditions set out by Tideway. Internally, these included combined sewage and limited dry-weather flow characteristics and abrasion, as assessed by hydraulic analysis. The aggressive environment required extremely durable concrete mixes, which were particularly sensitive to changes in moisture content. The ready-mix batcher initially used had aggregate bins open to the elements, and moisture contents were only taken once at the start of each shift. If it subsequently rained heavily, the mix was affected. One wall pour had to be abandoned and was subsequently broken out and recast. The concrete supplier had insufficient control on the moisture content of the aggregates, which was the main cause of the defective concrete supply. An alternative supplier was engaged, with a batcher that had real-time monitoring of the aggregates.

Within the inlet channel and interception chamber, a total of nine electrically driven penstocks were installed (six 1.5 m wide by 3.0 m high, two 1.2 m wide by 1.2 m high and one 1.0 m wide by 1.0 m high). An innovation in installation of the penstocks was to cast in a stainless steel frame with welded-on bolt sockets into the wall pour. The sockets and frame received the penstock fixing bolts. This arrangement provided the ability to replace penstocks as necessary, beyond their design life of 60 years. Setting of the cast-in sockets had to be extremely accurate and was particularly challenging within the confines of the chamber and the heavily reinforced concrete walls. The team elected to use a precise steel template to set the cast-in inserts to the shutter (Figure 13). Prior to pour, the steel template was removed. The method proved highly effective, with all penstocks installed without issue. This method is recommended rather than the more traditional post-drill and fitting of penstock bolts.

The connection culvert from the interception chamber to the drop shaft comprised three in situ box sections (4.7 m wide, 8.77 m long and 5.2 m deep), constructed within two 25 m deep secant pile walls, internally propped (Figure 14). The units were designed with movement joints to allow for potential ground heave due to future excavation above the culvert for the new development.

The 11 m dia. 35 m deep circular shaft was excavated with a primary lining using a sprayed concrete lining (SCL). Secant piles toed into the underlying clay, providing support through the initial 7 m of Made Ground. Shotcrete was batched on site and extensive trials were carried out to both verify the mix and ensure sprayer competency (Figure 15).

The geology comprised Made Ground, followed by superficial deposits of Alluvium and River Terrace Deposits, over the Thames Group (comprising the London Clay and Harwich Formations), over the Lambeth Group and Thanet Formation over the White Chalk Subgroup at depth. The base of the shaft terminated within the London Clay Formation.

A gantry crane was selected to service the shaft. Due to the confines of the worksite, a beam bridged across part of the shaft to support the crane. Jacks were incorporated under the running rails to enable re-levelling of the rails due to ground settlement expected by shaft excavation. This proved to be worthwhile, ensuring excellent crane operation and reduced maintenance and downtime.

It took a total of 22 weeks to complete the excavation and cast the base slab. A suspended Haki tower was installed as excavation proceeded, to provide a secondary means of escape.

The shaft required a secondary lining and the design for this was non-standard, complicated by the need to incorporate the large stainless steel vortex generator and the drop tube. The design required that the vortex had to be suspended from a ‘bridge’ constructed within the shaft. A vertical concrete plinth had to be incorporated into the shaft lining to support one side of the bridge. This bridge had to be cast with the vortex drop tube temporarily supported until the bridge was strong enough to support the weight of the vortex. More information on the vortex drop design is available elsewhere (Fricker et al., 2025 in this issue; Plant and Crawford, 2016).

Discussions were held with the designer (MSES) to determine whether to slip or jump form the lining. Ideally, slip form should be carried out on a 24 h basis, but the proximity of residents and possible noise complaints was a big risk. The designer advised that, due to the requirement to suspend the vortex generator and drop tube across the shaft, the amount of reinforcement required if a jump shutter was used would be great. The decision was thus taken to slip form on a 16 h shift. As the design developed, it became apparent that, even with slip forming, there was still an extensive amount of reinforcement required. This put all of the delivery team under huge pressure to keep the slip moving, while also fixing reinforcement ahead of the slip shutter and working a disjointed shift pattern (Figure 16). The slip was successfully completed, although significant remedial work was required for concrete repairs.

The next challenge was installation of the 65 t, 21 m long, 3.5 m dia., 20 mm thick stainless steel vortex generator and drop tube, which were fabricated in Cumbria and separately transported to site. The generator was then welded onto the tube and the entire unit was lifted into the drop shaft, temporarily supported by a support table and a series of stabilising anchors in the shaft (Figures 17 and 18). Once in position, a 10 m deep RC bridge was cast across the shaft, from the slip-formed plinth to the connection culvert. The temporary support table was then removed so that the vortex generator and tube were then suspended off the bridge. The final element was to cast the concrete surround to the lower half of the tube, which was made integral with the shaft secondary lining concrete using cast-in couplers (Figure 18).

The 300 m long connection tunnel to the main tunnel was constructed entirely through the London Clay Formation using a SCL primary lining and a cast in situ secondary lining (Figure 19). An innovative shift pattern was used where two gangs worked on weekly rotation, two 11 h shifts per day, from 7 a.m. Monday to 7 a.m. Friday, with a single Friday day shift. This enabled each gang to have 72 h off shift over the weekends. Engineers and supervisors were put on three 10 h shifts per day, with 1 h overlaps to allow time for handovers and completion of reports. The driver was to find an efficient shift pattern that ensured workers remained refreshed and not fatigued. A bonus scheme was set at 18 m/week, which was consistently achieved. This allowed sufficient time to move up services (essential for maintaining good ventilation and dust suppression) and ensure excellent quality control. From day one the team insisted on using water to clean out concrete supply lines (rather than compressed air), an innovation that won the New Civil Engineer Safety Initiative Award.

All tunnels and shafts on the project were secondary lined, primarily to ensure design life and to minimise the requirement for future maintenance access (see Fricker et al. (2025) in this issue). The tunnel system experiences both external and internal pressures (in storm surge situations) and the requirement was to have no longitudinal joints in the secondary lining. Therefore, a full-round shutter was used. Hammersmith was the first site on the project to construct tunnel secondary lining works. Lessons were learnt from previous lining of the 7 km long Lee Tunnel. Extensive research was carried out to locate the most suitable batcher – one that would provide reliable consistent-quality concrete in all weathers (the key requirement being real-time monitoring of aggregate moisture content). Working with the concrete supply company, a mix was developed with a 4 h working life, which would harden sufficiently to strike the collapsible shutter within 9 h. This enabled one pour every 24 h.

The subcontractor (Kern) supplied a 6 m long shutter to produce a 4.0 m internal dia. tunnel secondary lining. The design requirement was to ensure adhesion between the primary shotcrete and the secondary lining. To enable lining of the horizontal deaeration section of the tunnel at 5.0 m internal dia., the shutter was subsequently enlarged by installing inserts.

Pressure washing was carried out to remove any dust/dirt prior to casting the secondary lining. After several 6 m long pours had been cast, cracks started to appear in the crown of the tunnel. Works continued, with various options tried to reduce cracking – none of which were successful.

The mix design had a high cement/powder content, which generated heat during the curing process. This led to early shrinkage of the concrete. As the secondary lining was designed to adhere to the primary lining, the recently cast concrete was unable to uniformly shrink. Due to gravity, the point of lowest resistance was in the crown, and that was where all the cracking occurred. In hindsight, a slip membrane could have been used to allow the secondary lining to uniformly shrink. On completion of the secondary lining, resin injection of the cracks was carried out. Having applied lessons learned from Lee Tunnel, none of the invert remedials that plagued the Lee Tunnel materialised, and the overall quality of the finish was excellent with minimal repair required (Figure 20).

The first 30 m of the connection tunnel from the base of the drop shaft had an enlarged finished dia. of 5.0 m for the horizontal deaeration chamber. This tapered into a 4.0 m dia. tunnel through a tunnel flow restrictor. The vertical ventilation pipe was constructed using a 1400 mm HDPE liner within a steel casing, grouted into position and connecting to the tunnel crown. For more information on deaeration designs, the reader is directed to the paper by Fricker et al. (2025) in this issue, which provides an isometric view of this site’s horizontal deaeration chamber (Figure 6 in Fricker et al. (2025)).

Throughout the construction phase, Thames Water personnel brought their operational and technical expertise to the process, collaborating closely with the project team. Using monitoring information based on Thames Water’s own hydraulic model of its sewer network, go/no-go calls were held between BMB and Thames Water twice a day, to confirm if conditions (weather, sewer levels and flows) were safe for below-ground construction to begin at 9 a.m. and restart after lunch at 3 p.m. Risk assessments and method statements were reviewed by Thames Water’s independent authorisation body for below-ground works, to check that reliable safety systems would be in place and that there were no conflicting activities taking place elsewhere in the network. Access planning meetings for all sites were held on Mondays, ensuring effective deployment of the limited Thames Water resources. All sewer entries, resources and permits were managed by Thames Water using a central database, meaning that Thames Water personnel knew who was entering their trunk sewers: when, where, for what reason and for how long. Working closely with BMB, Thames Water kept an open-door policy, where issues of the day could be discussed proactively between the teams. Except for customer emergencies, Thames Water planned its routine sewer maintenance work around BMB’s works to assist with meeting the project programme. Furthermore, the formation of the Community Liaison Working Group (CLWG) facilitated co-operation and collaboration between Thames Water, BMB and the community in Hammersmith.

The CLWG meeting soon expanded to include representatives from Tideway, the London Borough of Hammersmith and Fulham and St George’s Fulham Reach development. Each meeting highlighted the performance for the reporting period and included key metrics related to environmental commitments. Community engagement grew, and feedback indicated the need for the presence of other key entities that impact community life. This evolution transformed the meetings into a one-stop forum for the community, fostering a collaborative and cordial atmosphere.

A structured commissioning process integrated all systems across the project. The process encompassed extensive systems alignment and testing, preliminary commissioning, system activation, storm testing, final inspections, maintenance and handover of assets from Tideway to Thames Water (see Lewis et al. (2025) in this issue). Close collaboration between BMB, BGEN Ltd (BMB’s control and automation supplier), Tideway and Thames Water was essential throughout this phase, particularly for pump and storm testing events.

Hammersmith Pumping Station was one of the most challenging CSO interception sites on the Thames Tideway Tunnel project. The works were complex, incorporating a variety of disciplines in design and construction. Planning and detailed design was developed to meet the constraints of the small work area, the need for continued operation of the pumping station and the needs of an adjacent development of several apartment buildings. The sizing and arrangement of the hydraulic structures was carried out using CFD and physical modelling, in conjunction with structural design, for deep underground chambers, culverts, the drop shaft and the connection tunnel to the main tunnel.

A range of construction activities was undertaken, requiring careful project management of the interfaces, with collaboration from Thames Water who continued to operate the pumping station without interruption. These included the use of advanced bespoke construction techniques for the vortex drop tube construction, slip-forming shaft construction, SCL and secondary lined tunnels and deep top-down excavation against the critical old inlet channel. The use of temporary flumes to convey flows through this old inlet channel was instrumental for safe working.

A key part of the success was the 6 month planning period prior to starting construction. This gave time for the team (client/contractor/designer) to plan in detail, including developing knowledge of the sewer networks and strategies to monitor flows and work safely without impeding the pumping station. Installation of the sewer monitors was crucial, resulting in 4 years of work without incident within the inlet channel. Construction of the interception chamber adjacent to the existing 1960s inlet channel was critical and was successfully carried out following intrusive investigation and careful design and deep excavation work.

The team had a positive, can-do attitude and problems were quickly overcome. To this day, operatives, staff, the client and designer look back with fond memories of Hammersmith and what was achieved. There were many lessons learned, not least the demonstration that strong collaboration between Tideway, BMB/AAJV/MSES, Thames Water, the St George development and local residents was essential for successful execution of the works. The site was awarded Tideway’s 2019 site of the year and the team received a total of ten monthly and three quarterly Rightway awards for innovation and safety. Furthermore, the contractor was highly commended in the 2019 New Civil Engineer Awards for Innovation in Tunnel Excavation.

The works were brought into operation in December 2024. The second largest combined sewage flows on the project are now diverted to the main tunnel and on to Beckton Sewage Treatment Works. The environment of the River Thames will no longer be plagued by the millions of tonnes of combined sewage previously polluting its waters.

The authors would like to acknowledge Joss Plant (formerly Tideway Hydraulics Lead Engineer, now Senior Associate Civil Engineer Mott MacDonald), James Wood (formerly AAJV Project Manager, now Associate Director AtkinsRéalis), Morgan Anamoah (formerly Tideway Project Manager for this site; now Project Manager, Jacobs) and Sergio Sciamanna (Tideway BIM Manager, Jacobs) for their contributions to this paper.