Dredging can unlock a valuable raw material
Limerick's picturesque Fenit Harbour is the test bed for geotube dredging technology
Just as Dickie Attenborough and Steve McQueen had to invent ingenious ways to dispose of spoil as they worked on tunnels through which to escape Stalag Luft III in The Great Escape, so dredging work requires ingenious solutions to find alternative uses for the spoil it creates.
Although tiny by world standards, Ireland's ports and their dredging requirement are a microcosm of global activity, as a balance is sought between economic and environmental concerns.
It's recognised that the potential for using what's been dredged in the past may not have been explored as well as it might have been, and the country's Department of Agriculture, Fisheries and Food has changed its dumping-at-sea licence application form to reflect the fact. It says: "The dumping of dredge spoil at sea is only acceptable when other means of disposal are ruled out for ecological or sound social or economic reasons. Even so, for ecological/environmental reasons, the dumping of the waste may not be permissible in all cases."
That puts Ireland between a rock and a hard place. Its dozen main commercial ports form the conduit for 99% of the country's imports and exports, with an annual value of up to ¢120bn ($170m). Dredging is obviously vital to sustaining that, so how to use the material it produces?
At the tiny Fenit Harbour, to the west of Limerick in the country's south-west, a capital dredging project is being planned that it's hoped can be linked to maintenance dredging in the future. The clever part is the use of geotubes, into which dredged material with at least 40% solids content is pumped. The water flows out through the tube walls, and the remaining sediment forms the basis of, in this case, a new breakwater and protection against coastal erosion.
Geotubes were used extensively to create protection from storms and the base of beaches for residents in the Amwaj Islands, an artificial island development in Muharraq, Bahrain. The island perimeter uses 30km of 13m-circumference GT 1000 geotubes to create the perimeter, which was then infilled with more than 20 million m³ of sand and stone.
Sheehan, Harrington and Murphy advocate geotubes as a potentially-viable solution providing a means of using the dredged material sustainably not only to prevent at-sea dumping, but also to make the most of economic benefits secured by not having to quarry and move rock that would otherwise be needed. They say: "This research may be applicable to a variety of sites around Ireland once the coastal structure being considered is within pumping distance of a port or harbour with a dredging requirement."
IADC president Koos van Oord believes it's part of his industry's challenge to develop innovative solutions. He says: "In an island nation such as Ireland where dredging is essential, the search for more cost-efficient means of achieving coastal security, as well as port development, can be combined by using, rather than disposing of, dredged material."
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