Engineers are poised to start building up massive protective islands along the United States coastline threatened by the Gulf of Mexico oil spill.
Phase one of the vast geotechnical barrier island project involves building huge protective sand berms in front of natural island barriers around the Mississippi River Delta.
Workers are now ready to mobilise after the project secured funding and the US Army Corps of Engineers (USACE) issued relevant permits for work in navigable waters.
£250 million costs
Oil giant BP last week agreed to pay the $360M (£248.4M) cost of building the first six of 24 proposed berms.
An explosion on one of its rigs in April has caused millions of barrels of oil to leak into the sea every day since.
Engineers hope the protective sand berms will make the clean-up easier and effectively shorten the amount of the natural coastline exposed to the oil spill.
Dutch delta technology research centre Deltares and Dutch dredging contractor Van Oord approached the US authorities with an outline idea for the scheme. The USACE then assessed and developed the plans.
The idea is that the berms will provide a hard, relatively easy to clean surface for the oil to settle on. It is much more difficult and almost impossible to clean oil from the marshy wetlands on the Louisiana coast.
The Dutch duo submitted its plan to the US authorities on 6 May. Five days later the state of Louisiana applied to USACE for the emergency construction permit. The USACE granted permission for the first six islands on 27 May.
Louisiana has a 639km long tidal shoreline, although the inlets and lagoons mean that the total perimeter of coastline exposed to the spill is 11,700km.
The wetlands are part of the Breton Natural Wildlife Refuge, and represent 40% of all continental US marshland. Oil has already reached some parts of the wetlands.
“Dredging is not unusual in Louisiana, but it is at this scale and speed”
“The coast guard originally didn’t think the oil spill [around 80km off the coast of Louisiana] would reach the shores,” said Louisiana Coastal Protection and Restoration Authority public information director Chris Macaluso.
Phase one is split between islands to the east and to the west of the Mississippi River.
Louisiana has appointed Shaw Engineering to build the berms.
East of the river, construction comprises two islands - one 12.5km long and the other 29km long (see map). Sand will be dredged via hoppers and pipes from two borrow areas, north and south of the islands.
To the west, construction will create four islands ranging in length from 3.5km to 9.3km and totalling 21.9km.
“It’s tough to get all the parties to sit down and talk about the project in such a short timescale.”
Sand will be dredged from a single borrow area within the river delta and transported over 80km to form the new islands. The six berms will be constructed in front of existing natural islands and will be about 128m wide, 6m high and require over 20M.m3 of sand.
The scale of the engineering effort is vast. “We have never had an oil spill like this,” said a USACE spokesman.“It’s tough to get all the parties to sit down and talk about the project in such a short timescale.”
“Dredging is not unusual in Louisiana but it is at this scale and speed,” added Macaluso.
The USACE had to shift proposed borrow locations because of concerns that dredging so close to the naturally formed islands at the mouth of the delta would alter tidal flows and cause them to erode more quickly. Engineers decided to move the proposed borrow areas from just 1.6km away from the berm locations to a travelling distance of 16km from the east side, and 84km from the west side.
Early indications suggest it will take 90 days to complete this work. The USACE said it could not give a timescale for building the other 18 berms because of the challenge of assessing the scheme and issuing further permits.
- This week BP said an inverted funnel-like cap it installed over the leak was now capturing between 33% and 75% of the spill.