Marine experts fear wetlands will suffer if the berms fail to catch enough of the Gulf of Mexico oil.
Engineers this week expressed doubts about the ability of the Louisiana barrier island project to protect sensitive wetlands from the Gulf of Mexico oil spill.
The first phase of the project, approved last week, is designed to protect the wetlands at the mouth of the Mississippi (NCE last week). Construction of the islands is due to start this week.
Designs for the plan were submitted on 6 May and the first six islands were granted approval on 27 May. Such rapid approval has concerned experts.
However, engineers have said that the scheme could be flawed and might be a misguided overreaction to the environmental disaster.
“It’s not clear there is an overall strategy,” said University of New Orleans earth and environmental science professor Denise Reed. “It feels reactionary and seems the construction was as much a political decision as a technical decision.”
“It feels reactionary and seems the construction was as much a political decision as a technical decision.”
Many agreed with the general principle of the scheme, which involves building up existing islands with sand berms to create a hard surface for oil to settle on. The system is also designed to funnel oil-bearing water into areas between the islands to focus clean up efforts on smaller areas.
Reed said the idea of trying to restrict water flows entering and exiting the wetlands has its complications because the water will be passing through at very high speeds. The high water speeds could make it difficult to capture the oil using traditional methods such as booms.
University of Southampton coastal zone management expert Simon Boxhall warned that the operation could fail because the berms are only designed to collect oil washing up on their surface.
“A lot of the oil will be distributed throughout the water column and not on the top,” he said.
Boxhall also suggested that the scale of the solution was disproportionate. The plan involves building six berms in front of existing natural islands east and west of the Mississippi (see diagram). They will be about 128m wide, 1.8m high and will require over 20M.m3 of sand. However, 18 more berms have also been proposed.
“It’s like using a sledgehammer to crack a nut,” said Boxhall.
Reed also questioned why only one size of berm is being used instead of designing it around existing conditions. This could require different sized berms for different locations.
She also questioned the logic of choosing to build the six phase one berms first.
The US Army Corp of Engineers (USACE), which issued the construction permits, responded by saying that the islands had been carefully chosen because in these locations the berms are deemed to cause the least disruption to the tidal circulation. They will also protect the wetlands most imminently at danger from the oil, said the USACE.
The USACE reviewed the berm size and made an alternative suggestion which involved extended the berms outwards, so that they had a 1:50 gradient.
However, the State of Louisiana was confident a steeper and shorter slope with 1:25 slopes would suffice.
USACE head of Regulatory Branch Pete Serio said it would review the impact of the barrier islands before deciding whether to issue permits for the remaining islands.