Innovative thinking and long term cost efficiency have been driving factors in creating sustainable flood defence solutions on the Norfolk Broads under a 20 year PPP.
Protecting the Norfolk Broads from flooding is a challenging job, but somebody has got to do it. The 30,000ha of wetlands that make up one of Europe’s richest ecological networks sits so close to the East Anglian coastline that tidal surges regularly push salt water up into the freshwater rivers and Broads, threatening to flood agricultural land and occasionally breaching existing flood banks. “It is an unusual flood defence project,” says Environment Agency project manager Paul Mitchelmore.
“Typically you think about defending thousands of properties but this is a project that is about nature conservation and agriculture.” That is not to say that homes are not defended as part of the Broadland Flood Alleviation Project. There are 1,700 properties in the area, many of which will be defended for the first time under the scheme. But the real emphasis is on protection and maintenance of the 260km of flood defence banks that protect 24,000ha of agricultural land and 28 sites of special scientific interest (SSSIs) (see box) which together form the Broads National Park.
It is not just the ecology that makes this project unusual. It is the country’s only tidal river flood defence project to be carried out under a PFI contract and one of only two undertaken by the Environment Agency. The 20 year £117.6M Public Private Partnership contract was awarded to Broadland Environmental Services Limited (BESL) in 2001. The company beat 15 other groups to win the contract and it is formed of contractor Bam Nuttall and consultant Halcrow.
Using a PPP meant the flood defence assets would be improved and maintained over a 20 year period by an organisation with the operational skills to carry out the work in the most cost effective way.
“The vision goes beyond just flood defences and looked at what is the impact on the area’s economy. We are not just protecting properties but looking at critical infrastructure, designated sites, navigation, angling and recreation,” says BESL technical manager Kevin Marsh, who is also an associate director at consultant Halcrow.
“I think we have got best value here. We are on schedule to deliver significant savings against traditional methods”
Paul Mitchelmore, Environment Agency
In the past, the Agency had used traditional forms of contract to repair flood defences but this was not keeping pace with the deterioration. Ten years on the Agency says the pioneering PPP was the right approach. “I think we have got best value here. We have more opportunity for risk transfer, better predictability of expenditure and more accurate programming. We are on schedule to deliver against the public sector comparator which showed significant savings against traditional methods,” says Mitchelmore. Original calculations showed that the PPP contract would be around 10% cheaper. As expected for a 20 year agreement the cost of the works is index linked and the team expects that the outturn cost will be around £140M.
Another financial advantage for the Agency is that BESL funds each piece of work from conception, through design and planning, to construction and completion.
“At this point we get an approval from the Agency that confirms the defence meets the service level and we get a lump sum. The lump sum is effectively 70% of the agreed value of that work. The other 30% is then financed over the remainder of the contract,” says Marsh. “We give the Agency predictability of year on year cost and can tailor our construction work to meet these figures so they get a much more balanced payment profile.”
The contract between the Agency and BESL consists of eight key service elements, under which the mechanisms for payment are set. These consist of monthly payments and lump sum awards, so maintenance works are paid for monthly as is the provision of an emergency response team, but lump sums are awarded for achievements such as completed improvement works, getting planning permissions and completion of the annual strategy.
The annual strategy is a critical part of the process and is used to ensure that improvements are being carried out in the areas most at risk from flooding. These areas are considered as 40 separate flood compartments, which are discrete areas bordered by high ground or flood walls. “We have the ability to juggle the improvement programme so that if something deteriorates we can bring it forward and reduce our risk. Again that is quite unusual but it means that we can still deliver at a steady rate and keep a uniform site and design office workforce,” says Marsh.
Information in the annual survey builds on the extensive analysis that the team undertook during the first two years of the contract. “In the first two years we did a substantial amount of work to confirm the scheme remained viable. We built ourselves a hydraulic model to see how improvements affected the system upstream and downstream. What we didn’t want to do was start building the banks too high pushing the water upstream into the undefended areas,” says Marsh.
“We have the ability to juggle the programme so that if something deteriorates, we can bring it forward”
Kevin Marsh, BESL
At the end of the two year period BESL had a detailed strategy to take it forward over the next 10 years, which would become the improvement phase. One of the most critical requirements was to prevent the incidents of breach of the existing earth flood banks. Turbulence from overtopping causes erosion of the downstream face which eventually compromises the bank to the extent that sections of it are washed away. For agricultural land this can be highly damaging, as the influx of brakish water overwhelms the pumped drainage system maintained by the Internal Drainage Board. Without the pumps water can sit on the land for weeks.
“An event in one compartment in 2007 led to the landowner having a lot of liver fluke the next year,” says BESL environmental manager Jeremy Halls, who is also a principal environmental scientist at Halcrow. Liver fluke disease is introduced to the grazing land by pond snails. The liver fluke parasite attaches to the grass and is then ingested by sheep or cattle with the undesirable side effects of mortality and contamination of the animal products.
Although the Agency wants to prevent incidents such as this, it accepts that it cannot prevent all flood effects.
“Occasional overtopping is something that we have to accept within the Broads. We don’t have the funding to raise all the banks to 1:100 or 1:200 level and if we built all the banks up to this height it would just send all the water into Norwich,” says Mitchelmore.
Restoring flood defences
Instead the Agency asked BESL to restore the flood defence banks to 1995 levels including allowance for natural settlement of around 19mm per year and sea level rise of 6mm per year. Incidents of breach are BESL’s responsibility - unless caused by an unusually infrequent storm event. “A one in 100 year flood event is unlikely to happen during the 20 year contract so there is no point in us asking our contractor to take that risk, which he would then have to be paid for,” explains Mitchelmore.
Setting new standards
Protecting the rich ecology of the wetlands is a critical part of the flood alleviation project.
Approximately 6,000ha of the area is designated for its nature conservation value, including 28 SSSIs, most of which are also protected under the European habitats and birds directives, and the Ramsar Convention on wetlands of international importance.
“There are lots of protected species, notably reptiles, water voles and otters,” explains BESL environmental manager Jeremy Halls. As an endangered species, water voles are fully protected under the Wildlife & Countryside Act 1981, and the Norfolk Broads have one of the country’s largest populations. At the start of the project, the team were physically capturing the voles, driving a couple of miles away and releasing them into another suitable area. “It was labour intensive and caused them stress but we thought it was the only way to deal with it. But we then started to think about other methods to get them to move by themselves.”
Using a combination of cutting back vegetation and draining down the dykes the team encouraged the water voles to seek an alternative habitat.
This was monitored by fitting radio transmitters to a number of animals to follow their movements. “This level of disturbance meant the animals moved away from the flood bank corridor and into the wider marshes within 10 days to two weeks. The stakeholders were satisfied that overall it is a better method than trapping them,” says Halls.
To date there have been two major storm events, in November 2006 and November 2007, which required BESL to send in its emergency response team to tackle breaches in the unimproved defences, one of which had affected the Wherry line from Norwich to Lowestoft. It was repaired within 24 hours. In addition Mitchelmore says that had the team not already carried out extensive bank strengthening and replacement prior to the floods the damage would have been much worse and the repair bill much higher.
“The risk is with the private sector so they can try out lots of techniques”
Paul Mitchelmore, Environment Agency
Thankfully, responding to emergencies is a small part of the role of the site team. The majority of their activities are long term planned improvement projects such as strengthening the existing banks, creating new banks set back from the previous defences, and installation of erosion protection. All earthworks are carried out during the summer and so far the team has strengthened 155km of flood banks, set back another 45km and provided erosion protection to 24km. “In the first two to three years we tried out as many different erosion protection systems as we could think of on short sections of maintenance works to see how they performed and then we were able to use that information to feed in to the bigger schemes,” says BESL construction manager Dan Russell, who is also senior site agent for contractor Bam Nuttall. Erosion protection is only needed in areas suffering from high scour as the underlying philosophy on the Broadland project is to move the banks away from the river and create natural reeded areas that look after themselves. Where protection is required, the team deduced that bitumen matting or gabion mattresses is the most appropriate solution.
Mitchelmore says that allowing the contractor the freedom to develop the most cost-effective solution is one of thereasons behind using PPP.
“The risk is with the private sector so they can try out lots of techniques to achieve this. If it works, great, and if they don’t, then from our point of view they have to sort that out.”
In some cases, for example where sheet piles need to be removed, the team decided to set back the river line creating new flood banks. These are constructed up to 50m back from the original river line and material for the bank is created by digging a new soke dyke behind it. Due to the soft nature of the ground, which is mainly soft alluvial clay, the new banks must be monitored and more material added if settlement shows a drop in crest height.
“We then flood the area between old and new bank and leave reed to grow for one to two years. Only when we are happy that this is well established do we dismantle the old bank and remove the sheet piles,” says Russell.
Under any other type of agreement this method, which can see a new bank take between three and five years to build, would not be cost effective. “We would be under pressure to do it in one hit so the banks would have had to be overbuilt to allow for settlement. Here we can wait and see then top up the bank accordingly,” says Marsh. It also allows the machine operators to become familiar with the challenging ground conditions.
“A lot of the success of this method is down to the skill of the machine drivers dealing with the soft ground. The long term agreement has meant that we could train up local drivers and then keep them,” says Russell.
Each of the improvement works packages requires planning permission, achievement of which is BESL’s responsibility under the contract.
“Obtaining statutory approvals was one of our highest risks,” says Marsh. “There are conflicting interests within the Broads, people like driving their boats, others like angling. There are vociferous interest groups that don’t always agree. We have to understand those conflicts and manage them accordingly.”
To gain this understanding BESL takes an open approach, disseminating lots of information to the public and inviting interested parties into the office to find out more about the project. “For the first few schemes there was a lot of concern about PFI and what it meant, and being in a designated area, Natural England scrutinised our proposals quite hard,” explains BESL environmental manager Jeremy Halls.
This also explains why the first approval in 2002 took just over a year to obtain, but this soon reduced and approvals are now obtained much more quickly - consistently meeting the 13 week target. Achieving this clearly took a lot of effort and was guided by the strategic environmental assessment carried out at the start of the project.
“That gave a number of key objectives based on feedback from stakeholders, and that determined our approach,” says Halls. “A lot of time is invested in taking to people. This feeds in to the design and subsequent planning applications,” he says.
“We have constructed 200km of flood banks in 10 years and there is nowhere that has been done before”
Kevin Marsh, BESL
Looking ahead, the team is preparing for its next major challenge - moving into the maintenance phase of the agreement. All improvements will be completed in 2013 with the remaining eight years spent maintaining the assets. When the contract ends in 2021 BESL will hand the improved defences back to the Environment Agency with a planned 10 year maintenance regime in place, unless the Agency extends the agreement.
Innovation in construction
Contractor Bam Nuttall has been able to develop more efficient ways of working thanks to the 20 year tenure of the PPP project.
“It has enabled us to form long term relationships with hire companies who have been able to then buy in the best equipment for the project, knowing that there is a certainty of work,” says BESL construction manager Dan Russell.
Another innovation was the decision to use a side-grip piling hammer as a means of installing sheet piles, removing the need for a crane to lift these elements.
“Traditionally a crane would hold the pile 5m to 10m in the air with someone guiding it in.
“We wanted to get away from that for safety reasons,” says Russell.
Instead the 25t excavator equipped with a side grip piling hammer can pick up each pile individually and position it at ground level.
A member of the site team will then make sure it interlocks with the previous pile and then it is driven, with the whole process being mechanically controlled.
To date, the team has removed 14km of piles, and reused the material in creating a further 7.5km of new walls. A further 14km of piles will be removed by the end of the contract.
“Steel sheet piles give a canalised appearance, we’d like to get rid of as much of it as we can and replace with a sustainable erosion protection system,” explains Environment Agency project manager Paul Mitchelmore.
Mitchelmore says he is enthusiastic about the project performance to date and the decision to go for a PPP. “The scale of work and savings possible through PFI tilted the financial balance and provided us with a viable means of delivering what we and the Broads community wanted. The fact that the project has a degree of financial security and a foreseeable start and finish date also breeds belief in the local community that works will be done and allows them to make best use of the project,” says Mitchelmore.
On reflection, taking a 20 year view was also considered to be the most appropriate timeframe. Designing schemes with 50 or 100 year life could have over-engineered the area and would not have given the team the flexibility to create the sustainable solutions currently being implemented. In recognition of the benefits of the approach the Agency has highlighted the Broadland Project as a case study in its long term investment strategy (LTIS).
With the improvements phase almost complete, Marsh estimates that to date the Broads have benefitted from up to £90M in investment. “The project has delivered what it said it would deliver and that is key. We have reconstructed 200km of flood banks in 10 years and there is nowhere that that has been done before,” he says. He notes that its success could be repeated in the future, especially given the pressures on public finances.
“The project is a successful working model of an alternative, cost effective means of safeguarding rural communities and offers an essential example of the approach future governments could take,” he says.
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