Maccaferri embankment protects wildlife lagoons

David Crowther takes a look at work currently under way at The ’WING’ project at Rutland Water.

Here, Anglian Water has created a network of huge artificial lagoons as part of a major project to ensure continuity of water supply to nearby towns and cities whilst at the same time, preserving wildlife habitat in one of Western Europe’s most important wetland nature reserves.

Rutland Water is by surface area, the largest reservoir in England and serves Northampton, Corby, Milton Keynes and surrounding areas with their water supplies.

It is also a “Ramsar” site - a designation given to wetlands of international importance; as well as a Site of Special Scientific Importance [SSSI] and a special Protection Area for migratory and indigenous birds.

In anticipation of increased demand for water, Anglian Water embarked on the GBP117m WING project in 2008, to raise storage capacity and treatment/pumping facilities at Rutland Water.

Carillion were appointed to create a wetland habitat of nine shallow storage lagoons totalling some 85 hectares in area.

Two of the lagoons were created by installing dams in the reservoir to impound water if levels fell, but the remaining six were constructed on adjacent farm land.

The land based lagoons were created by building earth retaining bunds up to 5m in height, partly above existing ground level and partly below.

Artificial islands were formed within the lagoons to encourage plant growth and to provide a variety of water depths for wading birds.

Almost 400,000cum material was shifted by Carillion in a balanced cut and fill process which retained all material within the site.

Where the proposed water level of the lagoons was above the existing ground level, it was felt that additional protection of the earth bund walls against wave erosion was required.

So large are the lagoons that wind blowing over the water can raise significant wave action, strong enough to risk scour damage to the leeward earth embankments.

With this in mind, Carillion installed Maccaferri Enkamat A20 erosion prevention matting on the waterside embankment slopes.

Enkamat is a high performance, flat-back, three-dimensional matting made of polyamide monofilaments pre-filled with bitumen bound mineral filter of 2-5 mm stone chippings.

At 22mm thick and with a weight of 20kg/sqm, Enkamat A20’s composition and solid mass provides an immediate erosion protection.

Its open, woven texture also allows vegetation to grow through its structure, resulting in a naturally vegetated slope within a few months.

Enkamat has been widely used on river or canal banks, lakes and reservoirs throughout Europe and is designed to be resistant to the wave action caused by small ships and pleasure craft passing by.

Its composition allows it to withstand high water velocities immediately after installation and become progressively stronger as the vegetation becomes established.

Enkamat A is supplied in 4.8m wide rolls and is readily placed in the required location in ’top-to-bottom’ arrays, usually with the help of suitable lifting plant.

After installation, the matting is secured with steel pins with the ends of each matting run retained within a small ’ditch’ cut into the head and toe of the banking.

A microclimate highly favourable to germination forms underneath Enkamat , accelerating vegetation growth.

Over 12,000 sqm Enkamat has been installed at the Rutland water site and further quantities have been specified for shoreline protection projects at Grafham Water, Pitsford Water and other sites at Rutland Water.

Throughout the project, mitigation of environmental impact has been of paramount importance.

According to Anglian Water Project Manager Steve Swan ’The success of the WING project means that Anglian Water will be able to fulfil its obligations to supply fresh water to its customers as well as continuing to provide a wildlife habitat worthy of its world class status’.

Construction of the Rutland Water lagoons began in 2009 and was staggered so that impact on birdlife was minimised.

The final lagoon should be completed by the end of 2012.