Last month I was fortunate enough to visit the Norfolk Broads, joining 2 million tourists that visit the area every year. However my agenda was rather different to the holiday makers as I was charged with writing about the 20 year PPP arrangement established in 2001 to defend the area from tidal flooding. The article ran in New Civil Engineer on the 26 May and was sponsored by consultant Halcrow. Here is what I found:
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 1700 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 PFI 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 in 2001. The company beat 15 other groups to win the contract and it is formed of contractor BAM Nuttall (90%) and consultant Halcrow (10%).
The rationale behind using a PPP was clear. 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.
The rationale behind using a PPP was clear. 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,” saysBESLtechnical manager Kevin Marsh, who is also an associate director at consultant Halcrow.
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 per cent cheaper. As expected for a 20 year agreement the cost of the works is index linked and the team expect that the outturn cost will be around £140M.
Another financial advantage for the Agency is thatBESLfunds 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 per cent of the agreed value of that work. The other 30 per cent 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 BESLconsists of eight key service elements, under which the mechanisms for payment are set. Essentially 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 of 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 water levels. What we didn’t want to do was start building the banks too high pushing the water upstream into the undefended areas,” says Marsh.
At the end of the two year periodBESLhad a detailed strategy in place to take it forward over the next ten years, which would become the improvement phase. One of the most critical requirements of this 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,” saysBESLenvironmental 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 will attach 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.
Instead the Agency askedBESLto restore the flood defence banks to 1995 levels including allowance for both natural settlement of around 19mm per year and sea level rise of 6mm per year. Incidents of breach areBESL’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.
To date there have been two major storm events, in November 2006 and November 2007, which requiredBESLto send in their 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.
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 have 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 construction manager forBESL, 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 are the most appropriate solutions.
Mitchelmore says that allowing the contractor the freedom to develop the most cost-effective solution is one of the reasons 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 1-2 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 isBESL’s responsibility under the contract. “Obtaining statutory approvals was one of our highest risks,” says Marsh. “There are conflicting interests within theBroads, 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 understandingBESLtakes 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,” explainsBESLenvironmental 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 then feeds in to the design and subsequent planning applications,” he says.
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 2021BESLwill hand the improved defences back to the Environment Agency, unless the Agency choose to extend the agreement, with a planned 10 year maintenance regime in place. 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 theBroadshave 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 and notes that its success could certainly be repeated in the future, especially given the current pressures on public finances. “The Project is a successful working model of an alternative, cost effective means of safe guarding rural communities and offers an essential example of the approach future governments could take.”
The full article can be viewed here: