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By Fiona Hamann
October 1, 2017
According to a number of scientific reports, sea levels are rising more quickly than ever before. The Potsdam Institute for Climate Impact Research (PIK) predicted in 2016 that even using the most conservative modelling (of 2C/3.6F temperature rise), the sea levels in New York City could be 60cm higher by the year 2100, and over time, the United States could lose up to 7 per cent of its land.
The same warnings are echoed in a report released by The Union of Concerned Scientists in July 2017: “Many communities have 20 years or less to prepare before rising seas begin to regularly impact homes, neighborhoods, and families. Other communities are already facing this disruptive reality. As global warming continues to drive sea levels higher in the decades ahead, more and more communities will join the ranks of those facing chronic inundation.”
By 2200, millions of people across Asia could be impacted by up to six metres of global sea level rises. To put that in perspective, more than a quarter of the populations of Mumbai, Hong Kong, and Shanghai would find themselves below the water line.
The impact on smaller island nations and states is far more dire. The Pacific nation of Kiribati has already claimed its residents may need to flee their home as soon as 2020. The Cocos Islands, an Australian territory off Western Australia, may be facing similar issues by 2030.
The Cocos (Keeling) Islands are made up of a series of coral atolls located 2750 kilometres North of Perth, midway between the Australian Mainland and Sri Lanka, in the Indian Ocean. It sits a mere ten metres above sea level at its highest point, with most of it population of around 600 people, residing only one to three metres above sea level. It is a popular tourist destination, famed for its sandy beaches and water sports. However, it is also pummelled by the elements, causing severe foreshore erosion.
Aaron Bowman, CEO of the Shire of Cocos and Keeling, explains the particular issues facing the Islands: “Of all of the islands, only two are inhabited. West Island faced threats from severe coastal erosion, with a number of buildings in danger of falling into the sea, while Home Island is impacted by flooding, with most residents living only a metre above sea level.
“It only takes a high tide, a strong swell, severe storm event, and a bit of wind to cause untold damage. Just recently, we had 700mm of rainfall in only three days, and that is a reasonably regular occurrence,” he says.
The Commonwealth Government is preparing to undertake a coastal vulnerability study on the Cocos Islands. The previous report, commissioned around 15 years ago, estimated that the islands had only 30 years to address sea level issues or face the prospect of leaving the Islands for a safer place to live.
Bowman explains the impediments to finding a fast solution: “The remoteness of our community creates further obstacles in terms of the solutions available to us, and the enormous cost to ship equipment and materials from the mainland. A 20-foot shipping container costs $12,500 to ship from Western Australia and an excavator costs around $50,000 each way to ship here.”
The Shire Council appointed Global Synthetics to address the issue using a GeoRock® solution to create one of the largest seawalls in the Australasian region. The resultant sea wall on West Island was completed for around $2 million (AUD) using Commonwealth funding, as it impacted Government buildings. Raising the cost to address the issues on Home Island will need to come from rates, grants, and other revenue raising exercises.
“As a small community, we need to be mindful of managing our budget and utilising any local resources and labour. Our local resources are sand and coconuts. We used both,” says Bowman. “The GeoRock® Solution enabled us to use smaller 1.0m3 bags which we could use with our existing excavators, and we filled them with sand harvested from the shores of our lagoon. To stabilise each bag during the fill stage, we used a coconut.”
The GeoRock® units from Global Synthetics used an anti-vandal layering geo-textile, with UV resistance and higher abrasion and puncture resistance, which was more robust than other geosynthetic sand container (GSC). “We found the solution offered took into account our requirements, from supplying the best quality GSC’s of any, through to understanding the limits of our equipment and budget,” says Bowman. “The solution needs to be the best in terms of longevity, but the Global Synthetics’ solution was also the best value for money.”
The West Island Seawall is made up of 5,350 sandbags, creating an aesthetically pleasing soft armour solution which will last for at least 20 years.
Already, the seawall has been tested by severe weather events, and has proven itself. It has protected the foreshore from further damage, and Bowman believes may have slowed the rate of damage and erosion, and ultimately slowed the Island’s sea level issues: “While I don’t pretend to be an engineer or erosion expert, the seawall has definitely slowed down the impacts of recent weather events on West Island, and we are mid-way through building a seawall on Home Island to minimise the effects of flooding,” says Bowman.
While there are other solutions available to manage the effects of rising sea levels in flood prone regions, such as traditional Rock Revetment Systems, Large Geotubes, or Breakwaters, the GeoRock® solution can achieve results cost effectively and utilises the resources to hand. This is particularly useful in areas short on rocks or with limited natural resources available or in remote locations where the cost to ship in equipment can be prohibitive. Each location does need to be assessed for suitability with a full hydraulic analysis with the design of any flood mitigation system being bespoke according to the particular geological conditions.
rising sea levels
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