Last update: 09 February 2008

Project questions or comments?  Please e-mail Stuart Terry

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VanOordlogo_frompdf_sm.jpg (3819 bytes)Equipment

Van Oord Equipment List

  • Trailing suction hopper dredger (TSHD) x 2, equipped with state of the art positioning systems

  • Multicat type shallow draft coastal tug/workboat for handling and connecting the floating pipeline to the hopper

  • Seagoing survey vessel for echo sounding

  • Personnel boat for crew changes & general shore-dredger movements

  • Monitoring buoy x 2, to ensure local water turbidity levels don't exceed pre-set limits

TSHD "Waterway"

Overall length

97.7m

Moulded depth

7m

Hopper capacity

4,900m3

Dredging depth

28m (max)

Speed (loaded)

13.2 knots

TSHD Waterway arrived in Poole on the 15th December, when the Volvox Scaldia was demobilized.

TSHD "HAM 311"

Overall length

94.5m

Moulded depth

6.3m

Hopper capacity

3,510m3

Dredging depth

29.6m (max)

Speed (loaded)

11.5 knots

TSHD HAM 311 and Waterway will be working together to replenish Poole's beaches.  

TSHD "Volvox Scaldia

Overall length

85.8m

Moulded depth 6.3m

Hopper capacity

2,548m3

Dredging depth

28m (max)

Speed (loaded)

11.2 knots

The Volvox Scaldia was used to replenish Swanage beach.

Beach work (moving and levelling the sand pumped ashore) has been sub-contracted to Ovenden Civil Engineering

Method

A pipeline (sinkerline) approximately 750m long x 700mm diameter is floated into position and then sunk to the seabed during replenishment work. 

At the seaward end the sinkerline is coupled to a 36m flexible riser pipe section, followed by a 100m flexible floating pipeline.  With assistance from the multicat, the dredger couples to the floating pipeline via a bespoke coupling ball-joint system.

At the landward end the sinkerline is fitted with a steel flange from which sections of shoreline pipe (approximately 12m long) can be coupled to discharge sand to the required locations.  Y-pieces with valves can be introduced to the pipeline to direct the loads to different areas of the beach.

Sand bunds are pushed both toward the seawall (for protection) and towards the shoreline to retain the new sand on the beach and avoid losses to the foreshore.  The sand/water mixture from the pipeline flows in between these bunds where it settles on the beach, with the water returning to sea.

Measuring quantities pumped ashore

There are two factors to take into account when estimating the quantity of sand reaching the beach.  The amount we claim as pumped ashore is recorded by the dredger and we have to allow for a "bulking factor" of 1.2 due to the material being mixed with water in the hopper.  For instance, if we're told that 3,000 cu.m. has been pumped from the hopper it would equate to 2,500 cu.m. actual material dredged.

We then allow for an estimated 20% of that 2,500 cu.m. being lost to the foreshore during pumping, so only 2,000 cu.m. might be left on the beach.

These figures provide guidelines.  Beaches are independently surveyed on a daily basis, comparing levels and widths to a baseline survey carried out before work commenced, and in that way we get a far more accurate idea of how much sand has actually been delivered.

During the project Van Oord ran trials for a newly developed method of monitoring flow & volume through the pipeline.

 Nick Cull, Borough of Poole

Waterway (click to enlarge image)

HAM 311, courtesy of Van Oord

Volvox Scaldia, courtesy of Van Oord

 Phil C.D. Smith, Poole

 David Robson, Borough of Poole

 
   

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