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Geographical Research News - Why building seawalls is generally a bad idea on small islands

24 Mar 2021 11:10 AM | Anonymous

By Prof Patrick Nunn

Patrick Nunn is Professor of Geography at the University of the Sunshine Coast. Patrick is a member of RGSQ and of the Society’s Scientific Studies Committee.

For decades, communities in the Pacific Islands have been building seawalls along eroding coasts to try to halt erosion. This tendency has been supported by aid donors like Australia who often regard it as self-evident that these kinds of hard-engineered solutions should ‘work’ on islands just as they apparently do at home. New research by Professor Patrick Nunn and two colleagues from France suggests this is wrong – and that building seawalls along small-island coasts is neither an effective nor a sustainable solution.

Many seawalls in iconic places (like capital cities) on small islands are donor-funded and donor-maintained. The maintenance gives the illusion of effectiveness and so these seawalls are emulated by rural communities across the Pacific and on islands elsewhere. In rural locations, seawall construction is often funding-dependent. There are many examples where seawalls are built only along the most severely eroded parts of the coastline but the sea at high tide simply comes around its ends and floods the land just like it did before (Photo 1); the seawall is useless. Many rural seawalls collapse after a year or two and, lacking funds for rebuilding, often remain in a state of disrepair (Photo 2). The Pacific Islands are said to be “littered with the remains of collapsed seawalls”, a similar situation to that on Caribbean and Indian Ocean islands. Seawalls are short-term adaptation options for a long-term stressor. One wonders whether it would be more sustainable right now if small-island nations were encouraged to focus on the relocation of vulnerable populations to less vulnerable locations … rather than building expensive and labour-demanding solutions like seawalls that do not last.

Photo 1.

The seawall at Nasauvuki Village, Moturiki Island, Fiji – the water goes around its ends every time the tide is high. And seawall construction has greatly damaged the nearshore marine ecosystems, meaning Nasauvuki residents can no longer find shellfish and other foods there.

Photo 2. 

At Navunievu Village, Bua, Fiji, shoreline erosion began to be a problem in the 1970s, so the first seawall was built. After this collapsed, erosion continued, so a second seawall was built in the 1990s, which also collapsed. Today the rising seas are eating away at (and regularly inundating) the coastal plain.

Navunievu residents have responded by making a rule that every new dwelling house built in the village should be built upslope, something that will see the community move upwards over the next few decades – a fine example of autonomous adaptation.

Photos courtesy of Patrick Nunn.

Reference:

Nunn, P.D., Klöck, C. and Duvat, V. 2021. Seawalls as maladaptations along island coasts. Ocean and Coastal Management, 205: 105554



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