Over 40 houses in Harlow, Essex are now protected from internal flooding during a 1-in-20-year flood event following successful completion of an NEC-procured flood alleviation scheme. The project won the Small Project of the Year award in the 2018 British Construction Industry Awards.
Client Essex County Council and its delivery partner Ringway Jacobs engaged contractor Topbond to construct a flood bund and main flood storage area for the scheme under a £400,000 NEC3 Engineering and Construction Contract (ECC) Option C (target contract with activity schedule).
The 150m long, S-shaped flood bund was built from a combination of site-won and imported fill within Kingsmoor playing fields at the foot of rising woodlands south of Harlow. Measuring up to 30m wide and over 2m high, the bund was designed by Ringway Jacobs to attenuate 7500–8000m3 of flood water at peak storage capacity. Nearby properties had experienced significant flooding in recent years from overland flows and overloaded surface-water sewers.
The bund has a compacted clay core and cut-off trench, and the side slopes are dressed with topsoil and seeded. Turf reinforcement matting was installed across the spillway to reduce the risk of excessive erosion during overtopping, while a reinforced concrete basin at the lowest point of the storage area was built to provide drainage via a fixed-orifice plate.
The council also separately commissioned minor works in the protected woodlands upstream of the bund. These were to attenuate high-velocity, overland surface water flood flows that occur regularly during heavy rainfall as well as to help capture silt before it reached the piped drainage system. The works included desilting two ponds and building eight small, leaky dams with local logs.
The Kingsmoor bund works were undertaken as part of the NEC-procured Essex Highways programme, a bespoke 10-year framework contract between Essex County Council and Ringway Jacobs. Commenced in in 2012, the framework has played a major part in delivering the council’s capital flood alleviation programme, which has seen over £13 million schemes completed to date.
Council project delivery manager Dave Chapman says, ‘We have used ECC Option C on many different projects over the past 4 years and found the NEC target cost arrangement works really well. It gives us the ability to reject or renegotiate prices that we have queried, but it also gives our contractors the confidence of knowing there is a clear and transparent process for supporting and implementing any changes to the NEC works information.’
He says the NEC early warning process is also a major benefit. ‘On the Kingsmoor contract, there were early warning notifications for things such as bad weather but also for the fact that some of the material being excavated from the site was unsuitable for constructing the bund. This enabled the project team to source additional fill material without causing undue delay to delivery.’
He adds that the NEC obligation for parties to work in a ‘spirit of mutual trust and co-operation’ means the council has generally enjoyed collaborative relationships with its contractors. ‘This in turn has led to more efficient delivery on our flood alleviation schemes’.
Benefits of NEC
- Transparency in ECC Option C gives clients full control over pricing but also ensures contractors are fairly rewarded for changes.
- NEC early warning process means issues are flagged up at the earliest opportunity to help ensure successful delivery on time and on budget.
- NEC obligation for parties to work in a ‘spirit of mutual trust and co-operation’ promotes collaborative working leading to more efficient delivery.