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Project Focus: Abberton Reservoir enlargement

The £140M project to enlarge Abberton Reservoir in Essex has seen its capacity expanded by 58 per cent and has secured water supplies for decades

The enlarged Abberton Reservoir takes in water from the River Ouse in NorfolkThe enlarged Abberton Reservoir takes in water from the River Ouse in Norfolk

Perspectives

Heidi Mottram, Chief Executive, Northumbrian Water Group: “I think everybody knows how precious water is and how Essex is one of the driest parts of our country. We’re delighted to have delivered the Abberton Reservoir expansion project on-time and on-budget and as a result secured water for our customers in Essex for many, many years to come.”

John Devall, Water Director, Essex & Suffolk Water: “It is fantastic news for our customers that Abberton Reservoir is now full and it represents 23 years of detailed planning and hard work to get to this point. We are incredibly proud of how this essential project has been delivered in a sensitive way that also vastly enhances this internationally important wetland and provides lasting community benefits.”

by James Brockett

Essex & Suffolk Water has successfully completed its major project to increase the size of Abberton Reservoir, work that will help secure water resources in Essex for generations to come.

The £140M project has swelled the maximum capacity of Abberton – south of Colchester - from 26 billion litres to 41 billion, a 58% increase. With the water level raised by 3.2m, the reservoir is now around 17 metres in depth at its deepest point.

The programme of work included an expansion of the Ely-Ouse transfer scheme, which takes water from the River Ouse in Norfolk, via the River Stour and two new pipeline sections, to Abberton. It also involved painstaking environmental work to preserve the environment, since the reservoir enjoys triple status as a Special Protection Area (SPA), a Site of Special Scientific Interest (SSSI), and a protected ‘Ramsar’ wetland site because of its bird life.

The scheme was conceived in the 1990s because of the supply-demand deficit for water in Essex, which is the driest county in the UK. However, many alternatives were explored before the project took shape, explains Jim Jenkins, Abberton Programme Manager at Essex & Suffolk Water, which is part of the Northumbrian Water Group.

“We’ve got a steady growth in population, fuelling demand, and it was identified that we had a need for more resource in the area,” says Jenkins. “We started off by doing a brainstorming exercise, and from around 200 suggestions, produced a list of 16 schemes that were viable in one way or another. For example, one of the options we looked at was desalination by reverse osmosis, which we looked at quite seriously, but at the time it was a very expensive option.”

The list eventually boiled down to three options: build a brand new reservoir, embark on an aquifer storage and recovery (ASR) scheme, or enlarge an existing reservoir. The first option was seen as economically unrealistic without partnering with another water company, while aquifers in the region were judged unsuitable for ASR; so the third option was chosen, with Abberton preferred over E&SW’s other reservoir, Hanningfield.

“Once we’d finally decided on Abberton, the next thing we needed to decide was how much we’d raise the water level by,” says Jenkins. “It was clear that if we wanted to raise it by more than 4 metres, the amount of work required would have put the price up exponentially – we would literally have had to build a wall around the reservoir rather than use its natural contours. So we concentrated on fractions of a metre between 3m and 4m, and it turned out that 3.2m was the optimum in terms of cost versus yield.”

Environment-conscious design

However, the reservoir’s SPA status meant that the company had to satisfy Natural England, the governmental advisory body, that the new reservoir would have an equal or greater amount of water that was 0-1m in depth – a crucial habitat for wading birds. The design incorporated pools and ponds around the reservoir edge to fulfil this requirement, while concrete edging was removed to give a more natural look. A significant section of water, west of the B1026 road which divides the reservoir, was also set aside for further environmental improvements and the creation of additional marshland with the aim of attracting birds to roost and feed in this section. By blocking off a culvert under the road, the project has effectively split the reservoir into two, with this Western section retaining its initial water level.

Extensive environmental studies and consultation were also required for the expansion of the transfer scheme to get off the ground. In order to win the license to abstract more water at Denver on the River Ouse, the project team had to carry out environmental impact assessments on the Great Ouse and in the Wash, a process which took around ten years.

“The Abberton scheme was basically in three parts,” says Jenkins. “The first part was getting the variation in the abstraction license for Denver, which would allow us to take the extra water. The second part was the improvement in the transfer scheme - the rivers, pipework and pumping stations to get the water down here - and then the third part was enlarging Abberton reservoir itself.”

The transfer scheme itself was a multi-stage project. A pre-existing channel carries the abstracted water as far as Kennet, near Newmarket, where a pumping station needed to be increased in capacity to cope with the additional water. From there, the water is pumped to the River Stour. A new pipeline was required parallel to the river, because the upper reaches of the river were incapable of carrying the extra flow; a new abstraction point and pumping station was then created at Wormingford lower down the Stour. Finally, a new pipeline was required running from Wormingford to Abberton.

Planning challenges

Procurement for the schemes saw MWHT appointed to the job of upgrading Kennet Pumping Station, which involved the installation of two 40mld (megalitres-per-day) pumps and one 70mld pump. Farrans Construction won the contract for the two new pipelines – both around 16km long and made from 1200mm welded steel - and also the work to build the new pumping station at Wormingford. Carillion Construction won the contract for enlarging the reservoir itself.

Planning permission for the project was granted in 2009 and construction started in 2010. Because of the large scope of the project, there were four planning authorities involved, and 123 non-standard planning conditions were attached to the permission. These included restrictions on the time of the year certain work could be done, and restrictions on which work could be done simultaneously, in order to protect bird life. All the gravel for the project had to be sourced from the site itself, for sustainability reasons and to minimise heavy vehicle traffic to the site.

Stakeholder management efforts for the project was extensive, with consultation exercises ongoing from an early stage and community benefits, such as a brand new birdlife visitor centre, built into the project. Newsletters were distributed regularly to residents, while an Abberton Liaison Group was formed, with regular meetings to keep interested parties informed of developments. This group had 20 members, including representatives from local parish, county and borough councils, interest groups such as landowners and ramblers associations, and wildlife organisations such as the RSPB and Wildlife Trust.

The construction phase saw a million cubic metres of soil and 250,000 cubic metres of granular material moved around the site, giving some idea of the scale of the project. Major works were completed in 2014, ahead of schedule, and the cost of the project (£140M) was below the original amount approved by the board for the project, which was £150M. In mid-March this year, the reservoir was finally declared full when it reached its new top level of 21m AOD (above ordnance datum) up from the original reservoir top level of 17.8m AOD.

The completion of the project is a moment of great satisfaction for Jenkins, who after being involved in the plans from the very start, has worked as full-time Programme Manager for the Abberton Scheme since 1999.

“I’ve been involved on the Abberton Scheme right from the beginning, and as Programme Manager I’ve been working on the scheme full-time for 15 years. I’ve taken it from the inception, through the various design options, the planning, the public liaison, and I was on site during the four years of the construction. From my own point of view, it’s the culmination of a career - you couldn’t ask for a better project. The variety, the scope of the work: there won’t be another project like this for a long time, and I’ve been fortunate to be with it from start to finish.”

Topic: Water resources
Tags: reservoirs , water resource management

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