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Regional flood management by combining soft and hard engineering solutions, the Norfolk Broadlands

Regional flood management by combining soft and hard engineering solutions, the Norfolk Broadlands (2014)

Situated in East Anglia, Norfolk Broads (Broadland) is one of the finest areas of wetland in Britain. It includes both open water, the Broads themselves (a network of mostly navigable rivers and lakes), and the low-lying marshland surrounding the tidal reaches of the River Yare, the Waveney, the Bure and their tributaries. These rivers reach the sea at Great Yarmouth. The Broadland Flood Alleviation Project (BFAP) is a long-term project to provide a range of flood defence improvements, maintenance and emergency response services along the tidal rivers within the Broadland. The project has been mainly prepared based upon strengthening the embankments to resist breaching with sufficient crest raising to protect settlement and contrast expected climate change and sea level rise effects.

Case Study Description

Challenges

Norfolk is a low lying coastal county. Sea level rise and climate change are among the major concerns for the specific tidally dominated site. The UK Climate Impact Programme (UKCIP) produced several scenarios for the expected impacts of climate change in the Norfolk County. Attending the latest projections for the year 2080, annual average temperature is almost certainly expected to increase in the area, extremely likely between 1 and 5 degrees Celsius; heat waves, winter rainfall and intense rainfall events are likely expected to increase; sea level is expected to rise about 80 to 90 cm; extreme events are also projected to increase, with higher wave and storm surge elevations, greater frequency of winter storms and higher wind speeds, increasing frequency of flooding events (UKCIP scenarios for the Norfolk County, 2008).

For many centuries, the rivers of Broadland played an important role, transporting goods and equipment for trade and industry. Today, Broadland is still busy, although in a different way. Fifty per cent of the land is used for traditional farming. The rivers continue to provide major inland navigation, which, together with the Broads, provide access to 125 miles of waterway. Recreation and tourism have become very important, with thousands of holiday makers visiting each year. In response, the boat hire industry now makes an important contribution to the local economy. The area’s attraction is closely linked to its diversity of landscapes and wetland habitats that give it a quality found nowhere else in the country. The area is internationally important for nature conservation and in 1988 the whole of Broadland was designated as having equivalent status to a National Park. The flood-banks (about 260 km) provide protection to approximately 30,000 ha of land that lies below sea level. All floodbanks are subject to deterioration in condition. This phenomenon results in a reduction in the standard of defence provided, making them more susceptible to the impacts of floods.

Objectives

The existing embankments have generally been built using the indigenous marshland peats and soft clays. Historic maintenance of defences had not kept pace with the deterioration rate and in the early 1990s they were susceptible to overtopping and breaching by even modest tidal surges. Moreover, the integrity of embankment foundations was put at risk due to erosion of the river banks, caused mainly by boat wash. In 1996 a flood alleviation strategy for Broadland had been prepared based on strengthening the embankments to resist breaching with sufficient crest raising to protect settlement and address projected climate change effects. The first step of the BFAP project is to strengthen existing flood defences and restore them to a height that existed in 1995, taking into consideration SLR and future settlement of the floodbanks in future steps. The project is not expected to prevent all future flooding as a consequence of overtopping, but will significantly reduce the risk of breach.

Solutions

Many floodbanks have settled since they were built or last improved and are at risk of being overtopped by even fairly small tidal surges. This is expected to be exacerbated by sea level rise and the potential increase in frequency of storm events. Moreover, in some parts of Broadland the existing defences are threatened due to erosion of the river edge (rond) by wind and waves, boat-wash, normal river flows and the action of the tide. Although some lengths have been protected by steel or timber sheet piles, much of this was installed over the last 40 years and now needs replacing or removing. The existing infrastructure and their degree of deterioration have been considered not enough to counteract the increasing pressure caused by the combined effect of climate change and sea level rise.

Historically, a large part of the cost of maintaining the flood defences was due to the steel and timber sheet pile erosion protection arrangements installed to prevent the flood banks from being undermined by tidal currents and boat wash. The BFAP sought to replace as much of this hard engineering as possible, with wide reeded ronds (soft solutions), which were effective for that purpose and provided additional benefits appropriate to a national park, as improvements to landscape and ecology. The project follows a regional concept of flood protection which consists of a combination of hard and soft technical solutions implemented in the first step of BFAP:

  • Floodbank Strengthening. This solution is used where the existing reeded rond is wider than 5m or the erosion protection system or sheet piling is in good condition. This involves the strengthening of the existing floodbank in its present location by placing material on the front and/or back slope of the bank. Raising the crest level may also be necessary and this is usually achieved by placing additional clay at the time of strengthening. The material comes from either widening the existing soke dyke or excavating a new one in the grazing marsh. Typically the strengthened banks will have a minimum 2m crest width and a back slope greater than 1m in 3m. Bank crests are designed to be wide enough to allow maintenance access and further topping up if necessary.
  • Floodbank Setback. This option consists of the construction of a new clay embankment, 15m to 30m (setback) behind the existing soke dyke. The actual distance of setback depends on local erosion rates, river depth and the quality of land behind the existing floodbank. Once the new bank has established the existing piling or erosion protection will be removed, the existing floodbank levelled and the new rivers edge profiled to promote a stable rond. This is a preferred solution when the bank might become unstable due to failed piling or an eroding reed rond. Its use is subject to suitable ground conditions and the availability of sufficient material for the new soke dyke construction.
  • Floodbank Rollback. This option is similar to floodbank setback, however, the distance the floodbank is moved inland is considerably less. This approach reduces the amount of land taken but requires additional material to fill the existing soke dyke (for stability reasons). This is a preferred solution when rond/erosion protection is insufficient to allow for just bank strengthening and where ground conditions, topographical features or structures do not permit full setback. It utilises the total lifespan of any existing piling but relies on adequate remaining life.

The project is expected to produce many benefits for the natural environment. The project has been developed in collaboration with the Norfolk Wildlife Trust and other similar institutions to enhance wetland habitats around Hickling Broad National Nature Reserve, including the creation of 55 hectares of freshwater reed-bed. This will contribute to the target required under the Habitats Regulations for losses due to flood risk management schemes on the Suffolk coast.

By June 2014, BAFP has nearly reached the end of the improvement works phase and interventions have been completed or substantially completed in 33 of the 37 compartments, including: (i) floodbank strengthening along 175 km; (ii) floodbank setback along 50 km; (iii) floodbank re-piling along 7 km; (iv) Other erosion protection including asphalt matting and timber poles combined with reed along 20 km; (v) Piling removal associated with setback areas along 14.5 km. In the period 2006 – 2013 the area has been affected by three major flood events. In these occasions the improved flood defences throughout Broadland did not register serious structural damages. The system is designed to contain flood water till a certain level and to be overtopped in case of major flood without breaching. In the strong event of 2013, large volumes of water spilled over many sections of the bank causing only two minor breaches. This performance has been made possible thanks to the interventions implemented within the project.

Relevance

Case mainly developed and implemented because of other policy objectives, but with significant consideration of CCA aspects

Additional Details

Stakeholder Participation

Public participation is an integral part of the Broadland Flood Alleviation Project (BFAP) that seeks to involve stakeholders at every opportunity. BFAP has developed a consultation database that contains details of over 1200 stakeholders. These include special-interest groups, businesses, statutory and non-statutory bodies, as well as over 500 landowners. An open approach has been adopted to stakeholder consultation, encouraging the participation of individuals and local interest groups in the development of both strategic and site-specific proposals. Separate participatory consultation exercises are undertaken in locations where the provision of first-time flood protection for riverside properties and boatyards are planned (DEFRA - Partnership saving the Broads, 2007; hereafter DEFRA, 2007).

The change from vertical piling to more natural river banks has not been welcomed by most boating interests. Piling has provided the facility for casual mooring, added to which there are concerns that piling removal will result in increased rates of sedimentation in the rivers. Action plans for addressing these issues have been addressed, and are working closely with the Broads Authority on the implementation of its Mooring and Sediment Management strategies. Initial public concerns that the project would suffer from the innovative private-public partnership approach due to the need to maximise profit margins have been largely allayed as the partners have shown a willingness to embrace wider benefits. It has, in fact, provided a unique opportunity to integrate flood defence works with other public interest initiatives (DEFRA, 2007).

The flood defences have been designed in order to be sustainable and within the strict financial limits of the Project. The public participation process has been helping to make sure of this, both for the Project overall and each individual scheme within it, by clarifying that each part is:

  • Cost-effective and economically viable;
  • Technically feasible;
  • Socially acceptable, e.g. by identifying the possible impacts on, and gains for, local communities;
  • Environmentally sound, e.g. by identifying environmental gains where possible and by minimising potential negative impacts where they are not.
Success and Limiting Factors

A major success factor for the project is represented by an effective private-public partnership. In 1992, the British Government launched the Private Finance Initiative, a public-private partnership programme, as a way of providing higher quality and more cost effective public services (Marsh, K, Philpot, M, Payne, D, Russell, D - Broadland; a current model of future delivery? 2010.). Through the Broadland contract the Environment Agency has effectively delegated certain flood risk management functions to a private company, Broadland Environmental Services Ltd. This Private Finance Initiative shell company is used to deliver the contract, comprising stakes of 90% BAM Nuttall Ltd and 10% Halcrow Group Ltd (now CH2M HILL). This Consortium is entrusted with improving and maintaining the Agency’s assets, providing emergency services and acting as a custodian for the environment (Ayling, B, Rowntree, J, and Lancastle, B - Broadland Flood Alleviation Project. Paper presented at Defra Conference, 2002; hereafter Ayling et al., 2002).

A key reason for the success of the Broadland Project has been the equality maintained between the two partner organisations (one public and another one private) particularly given the unequal split in financial risk. The choice of partners and the recognition that each requires the other one’s strengths has been key to building a strong team. The strong interaction between the two company members of the consortium and the UK Environment Agency represented the strength and the main successful factor of this project (Ayling et al., 2002).

Despite all the positive sides of the implementation of this project, a massive flood protection intervention in a large area such as the one under consideration has also negative impacts. The main limitations (some of them just temporary) identified could be listed as follow:

  • Temporary disturbance to residential property;
  • Possible changes in land use from the construction of the flood defence;
  • Possible impacts on undefended communities by altering the flooding pattern;
  • Temporary visual effects of works during construction;
  • Temporary loss of vegetated areas;
  • Visual impacts of new, large soke dykes;
  • Temporary disturbance of flora and fauna.
Costs and Benefits

Total value of the contract with the consortium Broadland Environmental Services Ltd. was fixed in 2001 at around 117 million UK pounds. The project is cost limited. This cost ceiling implies that all individual schemes within the project have to be strictly designed to be cost-effective and within the planned programme.

Beside the environmental and social positive effects, the economic cost of the project is expected to be compensated by benefits represented by significant reduction of the losses for the agricultural sector caused by seawater flood events. One of the main characteristics of this project is the consolidation of the flood banks in order to prevent breaches. When a flood bank breaches, the low lying freshwater marshes are submerged by saline water for a long period, as long as it takes to carry out the repairs, possibly several weeks. This is likely to cause long term and thus expensive damage to the agricultural and nature conservation qualities of the land. When overtopping occurs, saline water flooding still occurs but, because the volume of water is much less and repairs to the flood bank are not usually necessary floodwater can be pumped back into the river within 2-3 days, which is usually quick enough to prevent any significant long term damage to the agricultural land. The difference between the damage costs due to breaching and overtopping is one of the benefits taken into account in designing the project. On the cost side of the calculation, there was only sufficient suitable material available locally to increase the bank heights back to the 1995 levels. To increase the bank heights further and totally prevent overtopping, large volumes of construction materials would need to be transported long distances, the cost of which would have far outweighed the benefits.

Legal Aspects

In 1996, the UK Environment Agency began a process to consider the potential use of the Private Finance Initiative approach for procurement of Flood Risk Management services. As a result, the Broadland Flood Alleviation Project (BFAP) was one of only two selected and designated “significant projects with pathfinder status” by the Treasury (Hayman, S, Marsh, K, Lancastle, B – Partnership saving the Broads, 2007; hereafter Hayman et al., 2007). A full description of the nature of the Contract and the procurement process were given in a paper to the 2002 Flood and Coastal Management Conference (Ayling et al, 2002). The key feature is that, within the Broadland area, the Contractor is responsible for providing a specified standard of Flood Risk Management service, including maintenance, improvement works and emergency response. The purpose of this partnership between the public and private sectors is to further the drive for cost-effective delivery of public services through operational efficiencies and innovation, and this is embodied in the bespoke contract form. The Agreement is for a 20 year period, with a requirement to deliver the improvement works between the 2nd and 12th years. Payments reflect the rate at which works are carried out, with no large up-front capital commitment by the Contractor (Hayman et al., 2007).

Implementation Time

Implementation period 2001-2021, 20 years.

Life Time

50 to 100 years.

Reference Information

Contact

Paul Mitchelmore
UK Environment Agency
Broadland Flood Alleviation Project
Tel: +44 1603 226178
E-mail: paul.mitchelmore@environment-agency.gov.uk

Kevin Marsh
CH2M HILL
Broadland Flood Alleviation Project
Tel: +44 1603 226164
E-mail: kevin.marsh@ch2m.com

For the development of the current case study, we gratefully acknowledge the UK Environment Agency, client for the project, and the Broadland Environmental Services Limited (BESL) consortium: BAM Nuttall and CH2M Hill.

Source
Broadland Flood Alleviation Project, UK Environment Agency and technical papers

Keywords

Broadland, dykes, erosion, flood protection, risk management, river banks, setback

Sectors

Coastal areas, Disaster Risk Reduction, Water management

Climate impacts

Flooding, Sea Level Rise

Governance level

Sub National Regions

Geographic characterization

Europe

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