Project

Dredging and sandfill for the construction of Cardiff Bay Barrage.

Location: Cardiff – U.K.
Quantity: 3.500.000 m³
Client: Cardiff Bay Development Corp.
Contractor : Dredging International
Period: October 1994 – October 1999
Value: 25,90 mio Euro.

Scope of work

Dredging
Reclamation

General Information

The Cardiff Bay Barrage is one of the largest investment and engineering project undertaken in the U.K.
The 1.1km Barrage impounds the rivers Taff and Ely, creating a 500-acre freshwater lagoon with a new permanent waterfront of 12.8km.

Cardiff Bay has a tidal range of 14m. At low tide the Bay was inaccessible for almost 14 hours a day with only the vast exposed mudflats visible. The factors have severely limited public use of the Bay an development of the surrounding land.

Description of the works

Dredging commenced in mid October 1994 and was divided into six main areas of operation.

Removal of up to a 15 m layer of alluvium, which was then dumped at a designated site three miles away in the Bristol Channel. This exposed the under laying gravel substructure, which was subsequently covered with a layer of sand won by the trailing suction hopper dredgers Jade River, Antigoon and Vlaanderen XX from a site six miles away.

In January 1995 the Bigg Boss continued the dredging operation on the Barrage’s main embankment, working its way southwards to where the closure cill for the Barrage was situated. The embankment was then constructed with a series of sand, gravel and rock layers of varying grades, with armour stone applied to the tidal face.

In Autumn 1995 Big Boss commenced working in the area where the locks, sluices and fish pass will be constructed. Here, Dredging International created a massive temporary structure – a 1km long, semicircular cofferdam, extending out into the Bay some 500m.

The extreme tidal range in the Bay was the principal controlling factor on the dredging operations but, in view of the close proximity of residential areas, noise minimization was also a major consideration. Noise levels were systematically monitored to ensure that they did not exceed the statutory limits. The work was carried out on a round-the-clock basis for the duration of the project but vessels had to be regularly relocated depending on the tide state or noise constraint at the time.

Dredging International made a number of modifications to Zenne to reduce its noice emissions.

Main Equipment

Trailing Suction Hopper dredgers: Vlaanderen XX, Antigoon, Jade River
Backhoe dredgers: Bigg Boss, Zenne