NEC contracts used to protect 4000 homes in Yorkshire, UK from fluvial flooding

The council used a variety of NEC contracts to procure the scheme. Initially the NEC3 Professional Services Contract (PSC) option E (time-based contract) was used to engage the principal design consultant Mason Clark Associates alongside Pell Frischmann, which provided geotechnical support, and its subconsultant Cowi UK. The first £1.3 million works phase was then let to PBS Construction under an NEC3 Engineering and Construction Contract (ECC) Option A (priced contract with activity schedule).

Finally ECC Option C (target contract with activity schedule) was used for both the £3.9 million second phase and £8.5 million third phase, for which the contractors were a Colas Siac joint venture and nmcn (formerly North Midland Construction) respectively. The council’s infrastructure and facilities team was NEC project manager for all three works contracts.

The scheme involved diverting rainfall run-off from West Ella valley into a new 1.5 km long 1.8 m diameter tunnelled culvert, which in turn was connected via new open watercourses to a new 120,000 m3 flood storage lagoon on the site of a former school. Previously most water flowed into Easingby Drain and then into Western Drain river, which frequently overtopped its banks causing extensive flooding of local properties.

The works included building a new inlet structure at Kerry Pit, which diverts excess flows from Easingby Drain into the new tunnel. At the other end of the tunnel is a new reinforced concrete energy dissipation unit to control flows into a new gabion-mattress-lined watercourse. This links to the existing Western Drain flood lagoon via a new Marr Bridge culvert on the B1232 Beverley Road. A new geofabric-lined watercourse then transfers water into the new, much larger Tranby lagoon, which is fitted with a controlled discharge into the existing Acre Head Drain.

The first phase was for the new Marr Bridge culvert, while the second phase was for creating the new main lagoon on the site of the former Sydney Smith School together with the interconnecting ditch and joint reservoir spillway. The contract included creating high quality sports pitches inside the lagoon, which is technically a reservoir under the Reservoirs Act, for community use in dry weather. The final and largest phase was for the tunnelled culvert together with inflow and outflow structures and the connecting ditch to the new Marr Bridge culvert. A 17t full-face tunnel boring machine called West Ella Worm was used to excavate the pipe-jacked concrete tunnel, which included an intermediate shaft for inlet flows at Tranby Lane.

Work started on site in March 2016 and was completed on time and within budget in July 2020. The project was shortlisted for Climate Resilience Project of the Year in the 2020 British Construction Industry Awards.

NEC frameworks

He says the council has used NEC with great success for civil engineering works, buildings, housing, repair and maintenance contracts and various types of consultancy commissions. ‘In 2008 as the lead authority for establishing the regional YORhub frameworks, we chose NEC for both the overarching frameworks and the call-off contracts. These include the YORcivil framework for civil engineering contractors, YORconsult for consultants and YORbuild for building and housing contractors.’

Cooper says to date YORhub has delivered approximately 1,500 projects using NEC. ‘We have found the contracts promote real collaboration on projects and, with the range of relevant contract forms and pricing options available, are sufficiently flexible to meet the requirements of YORhub’s 90-plus clients. Both the YORcivil and YORconsult frameworks were used for appointing the consultants and contractors on the Anlaby and East Ella flood alleviation scheme, which formed the platform for why this project was so successful.’

He says the council used various NEC contracts and payment options, including project bank accounts, to suit the different aspects of the scheme.

‘The evolutionary nature of the design suited PSC option E. This cost-reimbursable option was used for the design process from inception through to the final design, as well as for supporting the contractors’ design activities. Mason Clark Associates integrated with our delivery team to support client ownership and governance of the project’.

According to Cooper the construction contract options were driven by the scale and nature of the works in each of the phases of the development.

‘This resulted in both ECC Option A and Option C being used. Option A suited the smaller value, lower risk first phase, whereas the higher value, higher risk second and third phases, with greater emphasis on contractordesigned elements, were best suited to Option C with pain-gain share. The use of this form successfully prompted a collaborative approach to delivery.’

Benefits of using NEC

• NEC contracts promoted a partnership and collaborative approach through the design and construction phases, leading to non-adversarial relationships, common incentives, integrated teams and objective assessment of performance.
• The NEC suites’ variety of contracts and payment options allowed flexibility for procuring various delivery roles while retaining the core collaborative principles.
• PSC option E suited the evolutionary nature of the design, ECC Option A was right for the relatively straightforward first phase and ECC Option C was more appropriate for the larger, riskier subsequent phases with contractor design.
• NEC contract forms were familiar to all parties using the YORhub frameworks.