Works visit to Abberton Reservoir Enhancement project

Carillion Civil Engineering is in the first year of a three year contract to carry out works at Abberton Reservoir to enable the top water level to be raised by 3.2m.  The work is being carried out for client Essex and Suffolk Water (part of the Northumbrian Water group) to ensure security of supply over the coming decades.  Abberton Reservoir is located just South of Colchester in North Essex and was originally constructed in the 1930’s.
Abberton Reservoir looking east

The Reservoir Enhancement Project is part of the wider Abberton Scheme which also involves pumping stations and water transfer pipelines.  Abberton Reservoir is essentially a pumped storage reservoir which receives water pumped from various surrounding rivers including via the Ely Ouse Transfer System.  Water from the reservoir is then pumped to the nearby Layer-de-la-Haye water works where it is treated.  The potable water is then pumped into the network which principally serves areas of South West Essex and North East London.

On Thursday 23rd September a group of a dozen or so members or guests of the Institution of Civil Engineers visited the site to see some of the works that are currently in progress.  The visit was organised by me in my capacity as Chairman of the Essex Branch of the ICE.  Coincidentally I work for Carillion, was in the bid team that won the contract, and was based on site for the first few months of the works.  Work started in earnest on site in April of this year. It is a brilliant project to be involved with – but then I am slightly biased!

The visit started at 5pm with an introductory talk by Carillion Contracts Manager David Hutchinson assited by myself and Essex and Suffolk Water Project Manager Daniel Wilson. Daniel described the need for the project and its wider context then David talked the attendees around the project describing the key elements of the works and highlighting how they fit within the 3 year programme.

Daniel (left) and David (right) introducing the project

The main elements of the works include:

  • Reprofiling of the existing shoreline including removal of the old concrete slabbing
  • Raising of the main dam crest level by filling on the downstream face
  • Construction of 3 new col dams up to 5m high and 1.2km long on the south side
  • Raising of the B1026 Causeway
  • Creating new headlands for a new inlet cascade and the offtake pumping station
  • Raising and refubishing the offtake pumping station
  • Construction of a temporary offtake pumping station to enable the above
  • Raising the existing main dam swallowhole and valve tower
  • Strengthening the existing outlet tunnel through the dam by insitu concrete lining
  • Constructing a new main inlet cascade
  • Constructing various new pumping stations associated with the other works
  • Diverting or installing new raw water pipelines
  • Significant mechanical and electrical works
  • Diversion of a 1.5km length of the B1026
  • Relocation (by others) of the Essex Wildlfe Trust visitor centre

Following the introductory talk and visitors induction the group mounted up in full PPE into two of the sites 4 wheel drive vehicles and set off along the north side of the reservoir.  The group drove from the main offices to the offtake pumping station with items including the shoreline reprofiling, layer pit inlet flume and channel and rye borrow pit pointed out on the way.

At the offtake pumping station we dismounted and – stood on an access platform – David described in more detail the required works and the works in progress.  The visitors inspected the temporary offtake pumping station wet well (a 10m x 10m x 10m high concrete box) which is soon to have its roof slab cast, and the sheet piling for the 1600mm diameter inlet pipeline.  After that they were shown the foundation/base slab for the associated electrical and chemical dosing building which is under construction.

From there the group moved on in the vehicles to the main dam where they drove along the crest road and parked up by the valve tower / swallow hole structure.  David again described the complex works that were required to the struture which were due to start shortly. He also described the ongoing enabling works at the base of the dam including the installation of wick drains, extension of the toe drainage system and construction of the new toe drainage pumping station.

From there the group moved to view the almost completed new Broad Meadows inlet cascade – constructed to replace the existing main inlet which needs to be demolished in order to raise the main dam.  From there – and in failing light – the group returned via the same route to the main offices where the visit ended.

A number of photographs from the visit are included below along with a couple of recent aerial shots covering the two main areas visited.

A follow up ICE evening meeting on the Abberton Reservoir Enhancement project is due to take place next year to which all are welcome.

Overwintering wildfowl at the west end of the reservoir. Offtake pumping station in background

David Hutchinson describing works to construct the temporary offtake pumping station
Recent aerial photograph of offtake pumping station works
Visitors inspecting the existing swallow hole structure
The existing valve tower and swallow hole structure
Wick drains being installed at the base of the main dam prior to filling
Existing main dam toe drainage extensions and pumping station works
New Broad Meadows inlet cascade
Recent aerial photograph of works to main dam
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