Three teams shortlisted for £5.7bn White Horse Reservoir

Thames Water has invited three international joint ventures to tender for the £5.7bn main works contract for its proposed White Horse Reservoir near Abingdon, Oxfordshire. The shortlisted teams are WFH JV, comprising Webuild, Hyundai Engineering & Construction and FCC Construcción; BMV+, comprising Bouygues Travaux Publics, J Murphy & Sons and VolkerFitzpatrick; and BBV, comprising Balfour Beatty Civil Engineering and VINCI Construction Grands Projets. The main works contractor will design, build, test and commission the 150 billion-litre reservoir, which Thames Water says would secure water supplies for around 15 million people across the Thames Water, Affinity Water and Southern Water regions. The procurement follows a tender notice issued in January 2026. Thames Water said bidders were assessed on previous experience, financial capability and their ability to carry out major activities including tunnelling and mass earthworks. The current published design includes a substantial tunnelling package linking the reservoir with the River Thames. A 3.5km-long tunnel would run between a new intake/outfall structure near Culham and the reservoir pumping station. Thames Water’s Gate 3 Basis of Design specifies a segmentally lined tunnel with a 6.6m outer diameter and 6m internal diameter. Around 1.4km at the eastern end, where cover is lower, would receive an additional cast in-situ secondary lining, reducing the finished internal diameter to 5.5m. The tunnel would be excavated by TBM from the pumping station towards the River Thames, where the machine would be recovered through the intake/outfall shaft. Precast concrete segments would form the lining, with tunnelling expected to operate on a 24-hour, seven-day basis. Excavated clay would be reused within the reservoir embankments. The river intake/outfall shaft is currently envisaged at around 25m deep with a 14m internal diameter. A second, approximately 450m-long reservoir tunnel would connect the pumping station with the main tower inside the reservoir. This would be excavated conventionally through clay using a sprayed concrete lining rather than a TBM. The tunnel is currently designed with a 7.5m outer diameter and 7.1m internal diameter at the primary lining stage, followed by a cast in-situ secondary lining reducing the finished internal diameter to 5.8m. A further approximately 25m cut-and-cover section would connect the tunnel to the main tower. Unlike the river tunnel, which would operate as a wet tunnel carrying water directly within the lining, the reservoir tunnel would remain dry and accommodate two 2.2m-diameter pipelines, one normally used for inflow and the other for outflow. The tunnel would also provide access for inspection and maintenance and carry power and communications cabling. Thames Water currently plans to install the reservoir tunnel pipework by welding sections within the pumping station basement and pushing the completed pipelines into the tunnel using hydraulic jacks. The pumping station itself is currently proposed as three interlocked 50m-diameter cells formed using 1.2m-thick diaphragm walls. Excavation would extend to around 19–20m depth, with the structure subsequently used as the launch point for the river tunnel TBM. The three shortlisted joint ventures are now due to develop bids for submission in spring 2027, with Thames Water expecting to appoint the main works contractor in autumn 2027. The reservoir is expected to take around a decade to construct and a further two winters to fill, with water currently planned to become available from 2040. Thames Water intends to deliver the scheme through an independent infrastructure provider using the regulated infrastructure model previously adopted for the Thames Tideway Tunnel. The detailed tunnel dimensions and construction methodology are based on Thames Water’s current published Gate 3 design and may continue to evolve as the project progresses through development consent and procurement. Comments: