Project detail - Boskalis Westminster UK
Facts and Figures

Client
Associated British Ports Southampton

Period
2013

Location
Marchwood, Hampshire, United Kingdom

Contractor
Boskalis Westminster Limited

Vessel selection
0m65m
Cork Sand

Hopper and transportation barges

Marchwood Channel Widening

This project involved the removal of material over a 900m length of the western edge of the navigation channel in Southampton Water opposite berths 104-106. The channel was widened by around 30m at the existing maintained dredge level of 12.6m below Chart Datum (CD). The total volume of material dredged was approximately 270,000m³.

The Solent is a major shipping route for passengers, freight and military vessels, as well as a recreational area for water sports, particularly yachting. It is sheltered by the Isle of Wight and has a complex tidal pattern, which has greatly benefited Southampton’s success as a port because it produces a ‘double’ high water, extending the time which a vessel can transit the channel. With the increase in size of both cruise and container vessels that are regularly visiting the Port of Southampton, the Marchwood Widening Works, an early phase of the major capital works planned for the Southampton Approaches, were a critical element allowing container and cruise ships to operate safely at the port.

The project involved the removal of material over a 900m length of the western edge of the navigation channel in Southampton Water opposite berths 104-106. The channel was widened by around 30m at the existing maintained dredge level of 12.6m below Chart Datum (CD). The total volume of material dredged was approximately 270,000m³.

The material dredged varied from soft mud/silt to medium stiff clay. A stable slope was designed based on soil samples taken before the project. This combined a 1 in 3 from the toe of the slope at 12.6mCD to -5mCD in stiffer material and 1 in 6 thereafter to the existing seabed level at approx. -0.5mCD, in softer alluvium.

Project delivery was strictly time bound. To prevent disruption to the salmon migration season, works had to be completed by the start of April, otherwise significant environmental monitoring works would haveto be undertaken, efficient and effective operations were therefore critical.