Supply Chain - Mapping & Modelling - Topographical Surveying

The River Lyd Pumping Station is consented to abstract up to 40 Mld from its intake source at Lifton, Devon during November through to March, pumping raw water approximately 7km to Roadford Reservoir. The pumping station was last used on a full operational basis during the mid-1990s and the original equipment had remained in a shutdown and non-operational state up until the point of the upgrade works. The existing electrical switchgear was deemed to be life-expired and beyond the state of any possible refurbishment. The primary driver for the scheme and the scope of works was to upgrade and re-commission the pumping station for operational use at full output design capacity. During the course of the capital works project, a temporary works scheme was implemented in order to maximise operational use of the available pump sets while the capital build was in progress. Background The pumping station is configured with six Pleuger-type QN borehole pumpsets supplied by Flowserve Ltd and which had been previously refurbished by the manufacturer in the intervening period, and the pumps were maintained in storage at Roadford Reservoir. Four pumps are sized at 5 Mld and two at 10 Mld, providing for a combination of flows up to 40 Mld. The discharge from the common pump manifold is to the 900mm diameter rising main to Roadford Reservoir operating with a system pressure at 11 bar. At the works, two surge anticipation valves protect the pipeline in the event of failures and resulting critical surge conditions. Downstream of the common pump discharge manifold, and within the section of pipework that forms the washout connection at the river headwall, are two pressure transducers which have been installed to provide high pressure alarms and initiate pump stop in the event of an adverse operating condition and to afford protection to both pumps and also the rising main. From the common discharge, manifold flows leave the site through the existing 900mm rising main and are measured by a new Siemens electromagnetic flow meter installed as part of the refurbishment works. Eel screens Prior to the upgrade and re-commissioning works of the pumping station, a separate contract was undertaken by Galliford Try in 2021 to replace the river eel screens. The scope of works in this respect was to make the connections between each of the eel screens designed and manufactured by Andritz Ltd and a new air-burst cleaning system. The air-burst compressed air system is a self contained package plant designed and built by Quantum Engineering Developments Ltd with its own local control panel and PLC which control the cyclical cleaning of each of the eel screens. Local alarms are initiated at the LCP and key alarms are relayed back to the main plant MCC as required. Duty/standby screw type air compressors are installed, supplying a single air receiver with operating pressure at 9 bar. There are six air lines that connect with its respective screen and the control of air is via electro-pneumatically operated valves installed at the air compressor skid. Flexible 50Nb air hoses are installed in ducts and connect each piped outlet with a connection to the eel screen. Within the pump chamber a piped manifold of manual isolating valves and air hoses has been installed to provide for the connection to each eel screen. [caption id="" align="alignnone" width="1200"] Airburst package plant - Courtesy of Galliford Try[/caption] HV & LV electrical works The scope of HV electrical works required the re-establishment of the HV supply to the site and these works have been undertaken by National Grid to provide a new 1250 kVA supply to their existing substation on the site and inclusive of new interconnecting HV cabling from their primary substation. A new transformer of required capacity has been designed and manufactured by Wilson Power Solutions under supply to Enerveo who have completed the site HV installation. The LV side of the transformer is connected to a new form 4A Type 3 MCC which has been designed and manufactured by Galliford Try. The build incorporates the six soft starts for each of the existing 190kW and 110kW pumpsets. The incomer is rated at 2000A and busbar 2500A. Phase failure, surge protection, and transformer protection are incorporated within the build. There are common controls section, distribution board feeders, 110V and 24V supplies. Plant control and surveillance is managed by a Schneider Electric PLC and HMI which are built within the C&I section. Water quality monitoring A containerised suite of raw water quality instruments has been installed in accordance with the requirements set out in South West Water’s Technical Standard for Intake Protection & Raw Water Monitoring. The respective quality parameters measured are colour, turbidity, ph/temperature, dissolved oxygen, and ammonia. The sample is drawn from the River Lyd by a pair of duty/standby Grundfos JP sample pumps and which are connected to the river headwall by means of dedicated ducted 25Nb flexible sample pipes. Actuated GF ball valves within the piped discharge local to the pumps allow for the sequencing of the duty/standby changeover, air scour sequence and back wash of the sample lines during the changeover cycle. Flow monitoring to the instruments is by means of inductive type flow meters. The control, monitoring, alarm initiation and operator interface is via a local control panel complete with HMI and PLC. River Lyd Pumping Station: Supply chain: key participants Principal contractor & designer: Galliford Try Pumpsets: Flowserve Ltd Flow meters: Siemens PLCs & HMIs & switchgear: Schneider Electric Eel screens: Andritz Ltd Air-burst compressed air system: Quantum Engineering Developments Ltd Generators: Aggreko UK HV transformer: Wilson Power Solutions HV installation: Enerveo JP sample pumps: Grundfos Software development & automation: Galliford Try Rising main: Kier Group Instrumentation: IFM Electronic Instrumentation: Partech Instruments Capital works delivery Before any works could be undertaken, significant tree and overgrown vegetation clearance had to be carried out at the entrance to the pumping station and along the lengths of the access paths and tracks that connect with the top of the site and the existing HV substation. GPR, topographical and ecological surveys were undertaken to establish conditions. There then followed a programme of dismantling works to remove the original GRP kiosk housing the 1990s MCC and transformer. The programme of civil works provided for the construction of reinforced concrete bases for the new 1250kVA transformer and air-burst package plant respectively. Installed on these bases are new GRP enclosures that provide the necessary protection for this equipment. A third GRP kiosk has been installed as the enclosure for the new MCC which utilised the original constructed base slab and trench albeit extended for the larger switchgear build. Elevated concrete piers have been constructed for the container housing the raw water quality instruments and with due consideration to the known risk of flooding at the site. The new enclosures required the submission and approval of a planning application. New ducts and drawpits have been installed to provide for the routing of pipework, HV and LV cables. The scope of mechanical installation works principally involved the re-installation of the refurbished Pleuger pumpsets and the associated pipework connections to the existing delivery manifold and rising main; the installation of the new airburst eel screening compressor skid and its hook up requiring a new air distribution system within the pumping chamber to supply each of the individual eel screens. The scope of the electrical installation works has been principally the uprating of the original 1000kVA supply to 1250kVA. This has required two new HV supply cables to be installed from the primary substation to the River Lyd site. A new HV transformer from Wilson Power Solutions and switchgear from Schneider  Electric has been installed to make the HV connection. The new Form 4 MCC has been designed and built as the replacement switchgear incorporating the most up to date electronic components and compliance with SWW Technical Standards. The software development and automation works has been carried out by Galliford Try. [caption id="" align="alignnone" width="1200"] (left) River water sampling container on flood prevention supports, (middle) Aggreko UK duty, primary assist and secondary assist generators, and (right) Generator flood prevention as design by the design team - Courtesy of Galliford Try[/caption] Temporary works During the period of the capital works build, and with continued falling level in Roadford Reservoir, Galliford Try was asked to put in place a temporary system of operation for the six installed pump sets using standby generators and temporary switchgear. Working with Kier Group, Galliford Try took charge of the works at the pumping station and Kier Group the rising main to Roadford Reservoir, responsible for checking, filling, flushing and pressure testing the pipeline; mindful that the system was last used in 1996. The original remit was to have the temporary plant installed and connected to allow the existing six pumps to operate by the 1 November 2022. All parties achieved their objectives, however South West Water was unable to obtain approval from the Environment Agency (abstraction permit) in the same timescale. This did however provide more time to allow Galliford Try’s capital works team to incorporate process elements of their capital build into the temporary works (flow meter replacement, air-burst compressed air system, telemetry and online operational water quality instruments). This has provided South West Water and the Environment Agency with a more robust pumping arrangement and water quality monitoring regime. Although the pumps and temporary works operation is scheduled to the end of March 2023, there is the possibility of an extension until the end of May 2023 which is being discussed between South West Water and the Environment Agency. Completion At the time of writing (April 2023) the capital works completion has been achieved insofar as it can be until such time as the temporary works operation has finished and the equipment removed off site. Following on from this, final landscaping will be completed along with those works required to complete all permanent connections to enable the pumping station to come back into operation from the beginning of November 2023.

Tunstall Reservoir is located approximately 5km to the north of Wolsingham, in County Durham. It is an impounding reservoir retained by an earth filled embankment with a central clay core. The dam is approximately 25m high and 300m long. The reservoir was previously used to feed a water treatment works located at the toe of the dam; which is now decommissioned. The reservoir is now used for amenity purposes and to provide environmental compensation flows to the downstream valley. Following a Statutory Inspection under Section 10 of the Reservoirs Act, a number of measures in the interest of safety were recommended by the Inspecting Engineer in order to ensure the safety of the dam. Section 10 of the Reservoirs Act

Following a Statutory Inspection under Section 10 of the Reservoirs Act, a number of measures in the interest of safety were recommended by the Inspecting Engineer in order to ensure the safety of the dam. These recommendations involved the following:

Recommissioning the existing siphon that used to feed the works and was no longer in use had to be intercepted and provided with a new route in order to provide additional drawdown capacity to the reservoir. Repairs to the lower part of the spillway where the existing blocks were damaged. Filling an existing tunnel within the dam structure. [caption id="attachment_18531" align="alignnone" width="1200"] (left) Condition of the spillway blocks prior to the works and (right) new concrete slab with stainless steel protection to the joint - Courtesy of Esh-Stantec[/caption] Siphon re-commissioning

Various options were considered at the concept stage in order to restore the use of an existing siphon that was abandoned in the early 2000s when the treatment works were decommissioned. The preferred option involved the following:

A siphon discharge chamber to break the siphonic effect. This was decided given the uncertainty about the existing system and the significant difference in levels in the downstream leg. Thus, the water would flow by gravity between the chamber and the outfall. This discharge chamber also functions as a thrust block to restrain the thrust acting on the new gate valve that has been installed immediately upstream of the chamber. The use of the existing settlement tanks to retain the water and aid to the settlement of suspended solids. A penstock chamber has been provided between the tank and the new discharge point to retain the water for a day before it is discharged into Waskerley Beck once the majority of the sediment has settled. Routing the new pipework away from the areas of the embankment that present the most valuable Waxcap habitats. Waxcap mushrooms are rare as they are restricted to grassed areas that are not grazed, and are locally protected in Durham. [caption id="attachment_18533" align="alignnone" width="1200"] Tunstall Reservoir dam - Courtesy of Esh-Stantec[/caption] Spillway repairs

The original Victorian spillway structure is formed by sandstone blocks bedded in concrete. However, the Inspecting Engineer identified that the majority of the blocks in the lower part of the spillway presented signs of wear and tear and needed replacement.

The proposed solution consists of four new reinforced concrete slabs that have been placed over the existing spillway, except the most upstream slab where blocks had to be removed to tie-in with the existing structure and avoid a step. An expansion joint was necessary in the centre of the new slabs. The flexible sealant in this joint has been covered by a stainless steel plate that has been designed to protect the sealant from the predicted high velocities expected in the flows and reduce the maintenance requirements.

A number of groundwater relief drains have also been incorporated into the design in order to capture the emerging groundwater at the lower part of the spillway and both reduce the hydraulic load on the new slabs and improve the long-term reliability of both the new concrete and the remaining sandstone blocks. These discharge to a new headwall in the bank downstream of the end of the spillway.

[caption id="attachment_18535" align="alignnone" width="1200"] Tunstall Reservoir spillway - Courtesy of Esh-Stantec[/caption] Tunnel infill works

When the dam embankment at Tunstall was completed and the filling of the reservoir began, significant leakage was observed through the eastern abutment. A concrete cut-off wall extending into the hillside was constructed in 1879 which significantly reduced the leakage rate. Nevertheless, as some leakage continued, a tunnel and shaft were constructed downstream of the cut-off wall, and an 18-inch cast iron diameter pipe was installed inside the tunnel to capture the leakage and convey it to the treatment works.

Following the Section 10 inspection of the dam in February 2021, a number of Measures in the Interest of Safety (MITIOS) were raised recommending works to address the leakage and the stability of the tunnel. One of these IOS measures recommended to fill the tunnel whilst providing some drainage, as a result of the concerns about its structural integrity and the potential risk to the integrity of the dam embankment and the spillway in the event of a collapse of the tunnel.

The project team scoped and contracted a ground investigation (GI) in Autumn 2022 to investigate the leakage paths into these tunnels.

Based on the findings of the GI and the review of the reservoir levels, it was concluded that the cut off wall is in good condition and that the main flow path goes around the concrete cut off wall. There is also a strong correlation between reservoir levels and the recorded flows, which decrease significantly when the levels are 6 m below the top water level (TWL). This was observed again during the construction works, as the water level was kept 6 m below the TWL for health and safety reasons while there was work ongoing in the tunnel and the spillway.

[caption id="attachment_18544" align="alignnone" width="1200"] (left) View in the unlined section of the tunnel (notice the beams across the soffit) and (right) view of pipe inlet and partial headwall (notice standing water on the invert) - Courtesy of Esh-Stantec and CC Informatics[/caption] Various options were considered during the Concept stage. The option of not filling the tunnel was disregarded as it would not eliminate the potential risk to the integrity of the dam embankment and spillway channel. Filling the entire extent of the tunnel was considered, however it was not preferred due to the significant constraints associated with it. These constraints include the difficult access and requirement to work in a confined space, potential land ownership issues, the presence of a SSSI immediately to the east of the abutment, and the increasing depth to the tunnel as it continues beyond the spillway. For all of these reasons, it was agreed with that filling the extent of tunnel beneath the dam and spillway would be sufficient as that would eliminate the risk to these structures.

Three possible fill materials were considered:

Cement grout was discounted due to concerns of potential pollution as a low viscosity mix would be likely to mix with groundwater and filter through the rock, causing a pollution incident. Foamed concrete was discounted as a result of the potential constraints to place it at the furthest point inside the tunnel, and the remote location of the site and access within the site would further complicate the timely delivery of concrete. Expanding geopolymer foam was selected as the preferred material as it reduced the risks associated with grout and foamed concrete; and it had successfully been used by Esh-Stantec in the delivery of other projects.

The expanding geopolymer foam was deemed to be more cost-effective than the alternatives as it offered significant savings to the installation process, because:

It avoided the risk of pollution and therefore any mitigation works to stop grout leakage; Simple installation from a mobile compound, avoiding the need for complex plant and equipment; Geopolymer mix materials delivered to site in barrels, allowing for easy storage and transport within the site. Installation from the surface via boreholes every 10m along the line of the tunnel. Lower carbon footprint that cement based alternatives. [caption id="attachment_18545" align="alignnone" width="1200"] (left) View of the geopolymer in the tunnel, and (right) view of the pea gravel stop end - Courtesy of Esh-Stantec and CC Informatics[/caption]

The filling was undertaken via a number of injection holes that were drilled from the surface at 10 metre intervals, and expanding geopolymer was injected via these injection points. The progress on site was as follows:

A pre-drilling survey took place to confirm the condition of the pipe in the tunnel ahead of the works. Eleven injection holes were drilled along the dam embankment and across the spillway. Prior to the injection, after the drilling had been completed, high resolution cameras were used in each injection hole and a drone survey was carried out to confirm that there was no damage caused to the pipe and that the expanding geopolymer would not enter the pipe. Pea gravel was introduced through the final injection point in order to create a mound that would stop the advance of the geopolymer and prevent it from blocking the pipe. The use of the gravel mound avoided the need to carry out works inside the tunnel with the associated risks of working in the confined space. Once the project team was satisfied that the drilling had not cause any damage to the pipe, the injection began, advancing at 10 metres per day on average. [caption id="attachment_18534" align="alignnone" width="1200"] Overview of the siphon diversion route in preparation for the works - Courtesy of Esh-Stantec[/caption] Tunstall Reservoir MITIOS: Supply chain - key participants Principal designer & contractor: Esh-Stantec Esh Group Stantec UK Geopolymer injection subcontractor: Geobear Ltd High resolution cameras & drone survey: CC Informatics Confined space entry specialist: MRS Training & Rescue Ground investigation: Ian Farmer Associates Topographical survey & laser scan of tunnel: Academy Geomatics Ltd Pipework modifications: UTS Engineering Steel fabrications: JHT Fabrications Ltd Conclusion

The contract has been delivered by Esh-Stantec and the recommendations in the interest of safety made by the Inspecting Engineer have now been addressed. The siphon will provide additional drawdown capacity to the reservoir in the event of an emergency, the damaged part of the spillway has been repaired to a satisfactory standard, and the potential risk of collapse of the tunnel has been removed.

West Hallington Reservoir is a Northumbrian Water Group (NWG) asset situated 1km to the northeast of the village of Colwell in the Tynedale district of Northumberland. The reservoir was constructed between 1884 and 1890 for Newcastle & Gateshead Water Company for the purpose of municipal water supply. The reservoir was built adjacent to the earlier East Hallington Reservoir and operates as a non-impounding structure. It has a maximum depth of 12.1m, a capacity of 3.3Mm3 and a surface area of 50 hectares at the Full Supply Level (FSL) of 155.1m AOD. Scope of works An inspection carried out under Section 10 of the Reservoirs Act 1975, identified that the reservoir had insufficient drawdown capability, and thus needed to be increased such that the reservoir level can be drawn down by 4.8m in 8 days. Mott MacDonald Bentley (MMB) developed a design solution which utilises two 700mm diameter siphons on the west embankment to operate at a combined flow rate of 3.2m3/s. The new siphon pipeline, alongside a temporary pump arrangement and the existing scour pipes, will meet the required drawdown capacity. The siphon flows will be conveyed across a stretch of adjacent field which NWG has purchased. The flows will then either percolate to ground or gravitate to the Coal Burn and eventually to the River North Tyne. Detailed design and engineering challenges Hydraulic analysis MMB has designed and constructed over 25 siphons for various water companies in the UK. The siphon arrangement was analysed using an in-house design spreadsheet, and demonstrated that the siphon would break when the water level dropped 3m below top water level which was deemed acceptable. The siphon location was moved to the west embankment due to concerns about stability and leakage through the south embankment (the original proposed location of the siphon) and because it was easier to access this area of the site. [caption id="" align="alignnone" width="1200"] Summary chart from the reservoir drawdown hydraulic analysis - Courtesy of MMB[/caption] Pipes and thrust restraint Hoops stresses within the DN700 mild steel siphon pipes were checked and a DWI Regulation 31 coating specified. The stainless steel pipe supports were analysed for bending and shear and concrete thrust blocks were designed for the system test pressures. The pipe wall thickness was reduced from 10mm to 8mm as an efficiency. The pipework arrangement drawing was uploaded into the federated model in BIM360 to check for clashes and when installed on site was found to fit perfectly. Ground investigation and geotechnical analysis Following the original construction of West Hallington Reservoir (between 1884 and 1890) the Resident Engineer Charles Henzell wrote a report to the Institution of Civil Engineers describing the works and detailing a number of challenges which included: Areas of soft book leaf marl overlaying harder boulder clays on the route of the embankment needed to be excavated. Embankments sinking or slipping and the toe of the slope reinforced with concrete walls, sheet piles and additional stepped embankments. Springs in the vicinity of the works. [caption id="" align="alignnone" width="1200"] (left) Cable percussive borehole rig on the crest of the embankment and (right) scaffold decked area required for rotary bore works on the slope - Courtesy of MMB[/caption] A desk study and intrusive in situ ground investigation (cable percussive and rotary bored boreholes, standard penetration tests (SPTs), piezo installation, lab testing) were carried out to classify and determine the thickness of the superficial and solid geology along with groundwater levels, identify any contaminated or aggressive ground and determine the engineering properties of the native soils. Slope stability and ground bearing pressure checks were carried out to ensure large plant would not compromise the stability of the embankments. The clay core and embankment material of the Pennine-type dam was found to be very silty and exhibit poor engineering qualities and so was disposed of, and a source of good quality puddle clay and Series 600-2C material was found locally at a brick factory in Birtley, Gateshead. This was installed in compliance with the test and inspection plan (T&IP) to a good standard. Thankfully the three springs in the west embankment mentioned in the Henzell report were not encountered. [caption id="" align="alignnone" width="1200"] Extreme weather conditions during the construction stages: (left) winter 2022 and (right) flooding from Storm Babet (October 2023) - Courtesy of MMB[/caption] Temporary works A borehole at the toe of the embankment on the dry side indicated the presence of water-bearing sands and gravels and so interlocking sheet piles were specified that punched through the sands and gravels into the underlying clays and so cut off groundwater flows into the excavation. A Portadam supplied and installed by OnSite Central was employed to provide a dry area to construct the intake bay. The Portadam was erected in the wet by operatives wearing buoyancy suits, and then pumped out and an excellent seal was achieved. The Portadam also allowed plant access around the pipework whilst the stone pitching was reinstated. Flood risk assessment A flood risk assessment (FRA) was carried out to support the planning permission and, as due diligence, to ensure MMB would not flood a property by accident. The assessment looked at the extent of flooding during operation of the siphon along with fluvial, surface water, groundwater and finally reservoir flood risk due to an uncontrolled release (which of course the siphon is designed to help prevent). The FRA concluded that:

The maximum modelled flood extent from a drawdown of Hallington Reservoir is in agreement with the flow path identified by the Environment Agency in the long-term flood risk map and no communities are shown to be at risk due to the proposed drawdown. As periodic testing of the reservoir drawdown will occur during dry periods, it is not considered that a drawdown of West Hallington Reservoir at this location would increase flood risk elsewhere.

Synchro 4D MMB chose SYNCHRO 4D from Bentley Systems during the latter stages of the design process. SYNCHRO 4D is software that enables MSP/P6Programme to be linked with a Revit model and to run a construction simulation. [caption id="" align="alignnone" width="1200"] A screen dump from the SYNCHRO 4D simulation - Courtesy of MMB[/caption] The simulation highlighted a number of pinch points when materials must be delivered or when water levels must be lowered or raised and helped drive efficiencies. SYNCHRO 4D was also useful for explaining the construction process to the client, to site operatives and to visitors. Solar power The mechanical equipment associated with the siphon is housed within a high security kiosk. Due to the remote site location, the cost of a permanent power supply for the kiosk building services was prohibitive. A solar powered solution has been installed utilising roof mounted PV cells, DC/AC converter and battery storage. This sustainable solution provides sufficient energy for lighting and heating within the kiosk with negligible running costs. West Hallington Reservoir: Supply chain - key participants Construction delivery partners: Mott MacDonald Bentley Feasibility study & ARPE: Stantec UK Ecological surveys: OS Ecology Ltd Temporary water barrier (Portadam): OnSite Central Ltd Large diameter pipes: Powerrun Pipe-Mech Ltd Electrical/instrumentation installation: Intelect UK Large diameter valves: AVK UK Ltd Large diameter valves: Glenfield Invicta Valve actuators: Varley Hydraulics Ltd Stonemasons: Stuart Marley Ltd Steelwork fabrication: AJ Engineering & Construction Services Ltd Steel fixing: D&N Reinforcements Ltd Kiosks: Technocover Ltd Bespoke steel access cover: EJ Solar panels: Green Leaf Engineering [caption id="attachment_9915" align="alignnone" width="1200"] Solar panel display - Courtesy of MMB[/caption] Construction: Problems, successes and lessons learned? Intake bay The intake bay was located along the Small Burn which originally ran across the middle of the reservoir and was diverted into the adjacent Coal Burn in the 1880s via a DN375 clay gravity drain. The ground around the intake bay was found to be poor and was excavated down to competent sub-grade and reinstated with 340 tonnes of gabion stone and 60 tonnes of Type 1 capping material. As this area is normally under a 5m depth of water it was inaccessible during the ground investigation stage. Pressure testing As the DN700 pipes are fabricated from coated mild steel, a Type 1 pressure test (water loss method) was required. All bolts had been tightened using Hytorc© equipment and the torque readings recorded in the T&IP, but achieving a pass proved difficult due to sunny weather. A temperature rise on the above -ground pipework led to a pressure loss of more than 0.2 bar in the water filled pipe voiding the test on a number of occasions. Eventually cloud cover enabled a valid test; one of the only times a site team has prayed for the sun to go in! [caption id="" align="alignnone" width="1200"] Siphon intake bay constructed within a Portadam barrier supplied and installed by OnSite Central - Courtesy of MMB[/caption] Stone pitching Reinstatement of the original stone pitching (to resist wave action) took seven weeks longer than planned; mainly down to availability of stone masons. Productivity increased as the works progressed and the three man gang went from replacing 3 to 5m2 per day. The stone pitching was reinstated to a good standard, but it was felt that the detailing around one of the pipe supports would be built differently next time. The 2,500m perimeter of the reservoir had been faced with stone pitching down to original ground level; installation of which in the 1880s without an excavator and selector grab must have been a job and a half! Ecology Prior to the construction works, NWG employed OS Ecology to undertake trapping for white clawed crayfish, a native species that is in decline due to the introduced North American signal crayfish. No white clawed crayfish were found within West Hallington Reservoir but three were trapped within the adjacent East Hallington Reservoir. A pied wagtail nest was spotted by eagle-eyed site workers next to the engine of an excavator. The excavator was withdrawn from service until the eggs had hatched and the fledglings left the nest. [caption id="" align="alignnone" width="1200"] Reinstatement of the stone pitching - Courtesy of MMB[/caption] Testing, commissioning & conclusions The siphon is designed to operate above a water level of 152.5m AOD and to self prime above a level of 154.1m AOD (TWL = 155.1m AOD) and so the All Reservoirs Panel Engineer (ARPE) requested that during the testing and commissioning stage, MMB should demonstrate the following: That the siphon can be primed between the water levels 152.5m AOD and 154.1m AOD. That the siphon can self-prime above a water level of 154.1m AOD. That the Full Supply Level of 155.1m AOD can be achieved. The water level rate was restricted to 300mm/week and any seepage through the clay core will be monitored in future via a flow measurement chamber. During operation of the siphon, receiving watercourses and culverts were monitored at a number of locations to ensure scour or carriageway flooding were recorded and the test halted if required. The works were completed within budget (final NEC3 contract value £3.3m, £60k gain pot) and on time. The original compliance date of 31 September 2023 was extended to incorporate obtaining the Section 166 agreement and a new date of 30 June 2024 was agreed with the ARPE. [caption id="" align="alignnone" width="1200"] DN700 siphon pipework during installation - Courtesy of MMB[/caption] Leaving a legacy Northumbrian Water is very keen on creating community projects and “leaving a legacy”. MMB widened the access from the main road and provided three passing places as the access route is used by both residents and members of the fishing club. Looking ahead Northumbrian Water are investigating another 10 reservoir sites that potentially require siphons, and so Mott MacDonald Bentley hope to use the good practice and experience learned at West Hallington Reservoir on other schemes in the future. A Northumbrian Water Engineering Briefing Note for siphon design and construction is also underway, which captures all the learning and good practise and will sit alongside the newly published CIRIA 813 Siphons in Dams: Design, Installation, Operation, Management and Testing.