As climate change brings sea level rise and extreme weather with greater frequency, increased investment is essential to protect people, property and the environment from the risk of flooding.
The 20-year Broadland flood alleviation scheme provides a range of flood defence improvement, maintenance and emergency response services in the environmentally sensitive Norfolk Broads. Some 7,000ha is protected by law as a designated national park and wildlife habitat. Farming and tourism are also important for the local economy, and the defences shield 1,700 properties from flood risk.
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Video produced July 2010
BESL staff give an overview of the project
When weighing up its options for managing the region’s increasingly vulnerable flood banks and erosion protection infrastructure, the Environment Agency opted for a private finance solution ahead of conventional contracts as it offered better value for money.
Secured in 2001, the £140 million contract has almost reached its midway point. Its remit is to restore protection to 1995 levels, guard against breaches and cope with rising sea levels and settlement.
By engaging Broadland Environmental Services (BESL) – Halcrow’s delivery partnership with BAM Nuttall – in a longer-term commitment, the contract enables planning and delivery to be carried out at an optimum commercial level. Costs can be spread more evenly over the contract period, generating financial and efficiency savings of up to 20 per cent compared with a conventional approach.
As part of the phased improvement programme BESL has upgraded over 110km of existing flood banks and constructed over 40km of new flood embankments, providing protection to 14 previously ‘undefended’ communities. The strengthened defences were put to the test in November 2007 when a huge tidal surge overtopped the new banks.
Halcrow is responsible for engineering design, environmental monitoring, statutory consents, stakeholder consultation and post-construction evaluation.
Halcrow has developed an ISIS hydraulic model to aid design and predict the effects of proposed improvement solutions on the Broads’ water levels. This is being used extensively to forecast flooding and overtopping in the system, and to understand the resulting impact on flood risk.
As part of the BESL team, Halcrow carried out extensive stakeholder consultation when undertaking the strategic environmental assessment. This involved contacting over 1,400 groups and individuals, and generated an unprecedented 25 per cent response rate. Engaging directly with stakeholders, the team developed a series of environmental objectives to address issues of public concern, which have in turn guided BESL’s approach.
Halcrow is also responsible for detailed pre-planning consultations. Given the number of stakeholders and the protection required for national parks, building trust, confidence and understanding of the flood defence work is a primary challenge. Halcrow developed a series of regular liaison and briefing meetings with key stakeholders, meeting at intervals to suit their particular remits. This significant investment in relationship building reflects positively on the client, and demonstrates our willingness to develop constructive partnerships. Importantly, this proactive approach has enabled around seven major applications to progress through the planning system each year.
Comprehensive environmental monitoring underpins the project, with Halcrow’s specialist team setting new standards in mitigation measures to protect water vole, bat and reptile populations.
This long-term project enables innovative flood defence solutions of various scales to be trialled and fully evaluated. In a first for the UK, new flood banks have been constructed up to 100m behind the deteriorating defences – a variation of managed retreat adapted for tidal rivers.
These setback areas have formed part of a major dredging disposal strategy, developed in partnership with the Broads Authority. Dredged material is levelled out, with channels formed to promote reed bed growth – boosting erosion protection and wetland habitats.
The site’s soft ground conditions – alluvial clay and peat – give rise to significant challenges for engineering design and construction. Innovations in ground investigations techniques include the development of rotary core drilling and associated soft ground testing.