2Atolls just aren’t like large continental countries where engineering grew up. We need a new set of engineering solutions specifically for the unique conditions on atolls. Atoll Engineering should build our resilience, reversing the broad-scale damage the ‘old engineering’ has caused in the past. And we need it now – the islands have run out of time.

Atolls are Different !

In the Pacific Region, we are now experiencing unprecedented rates of damage and even loss of islands and their surrounding ecosystems. There are many reasons for this including increasing urbanisation, poor waste management and climatic factors. But the most preventable of factors concerns our engineering choices, particularly along our coasts.

Approaches to engineering on atolls should not just be a case of spinning out the same old approaches developed and used elsewhere. Attached harbours, conventional seawalls, groynes, filled jetties and causeways can be toxic to atolls, and some don’t work every well in big countries either. Engineering on atolls needs to be fresh and relevant to the real situation on the ground. And on the atoll things are very different to what we find in big countries: we need a new bag of tricks.

Nui pic.2In countries like Tuvalu, this has never been more urgent than it is now. We have serious ecosystem-wide problems with pollution, broken seawalls and gabions, and have lost 2 Funafuti islets in the past few years. What could be better for supporting Tuvalu’s calls for the international community to action on Climate Change (here and here), than getting our own resilience at home to the best state it can be. By getting our ecosystems back to resilient states, we will have the best chance of weathering and recovering from every-day storms through to disasters and climate change.

What Conventional Engineering Ignores

Atolls are ‘living’ systems. Although that is not strictly true, the main reef platform and islets themselves are made of dead skeletons of animals, plants and protozoa that used to be alive. All of the rest of an atoll is alive now. Thinking of atolls as ‘living’ will lead to a better understanding of how they function.

This is in marked contrast to continental land masses, volcanic islands (such as Samoa) and raised reef islands (such as Niue). Countries like Tuvalu, Kiribati and Marshall Islands have no rock base on which to depend. And many others have have a combination of islands so at least some of their land area is in the same precarious position (e.g. Cook Islands which has some atolls and some volcanic land).

Living atoll islands rely on a constant supply of sand and gravel being manufactured on the reef, the reef platform and in the lagoon. This image shows three important sources of gravel and sand for Funafuti.

imageCoral Gravel & Sand

The first of these is the coral rubble and sand manufactured on the outer reef slope (from just under low tide to maybe 30m) and in patch reefs (akau) in the lagoon. The corals grow between 1 mm and 10 cm per year, depending on species and richness of the plankton supply. It also depends on how polluted the water is. An over-supply of nutrients (from sewage, fertilizers, leachates off the land) or excessive turbidity (cloudiness) of the water can slow corals down or kill them. In urbanised islands like Funafuti the cover by corals has decreased as soft-bodied algae (see below) have taken over in the nearshore lagoon areas.

imageimageCorals can be deposited as banks like Bebe Bank deposited in 1972, and from there some of it can be ground to sand… slowly. Coral can also be directly made into sand through the actions of parrotfishes that bite into the coral to feed. The scrape marks in the coral (image right) are from parrotfishes. One of the most important corals in the formation of islets is Pocillopra verrucosa which is incredibly slow-growing but very stony and forms long-lasting strong rubble banks on the ocean side of islands.

Baculogypsina spaerulata7Forams

Foraminifera (or ‘forams’) are found everywhere on atolls and there are many species. These are single-celled organisms that multiply by dividing and produce a hard calcareous (limy) skeleton that forms our sand. The most important foram from a sand-supply perspective is Baculogypsina which grows on the reef platform on the ocean side of islands and sometimes dominates the beach sand even on the lagoon side.

Once storms have built the rubble banks on the reef platform the core of an island is built. After that waves wash the skeletons of forams towards the shore on the ocean side and then transfer the collecting sand by longshore drift all the way along an island till it wraps around the tip, enters the lagoon side and is then transferred along the island – also by longshore drift – during the westerly season. The foram sand then appends to the rubble bank and starts to build the island lagoonwards. That is why our islands are made of rubble on the ocean side and sand on the lagoon side. How much they grow has a lot to do with supply, distribution and finding ‘sweet spots’ where waves, currents and winds are not too strong to wash them elsewhere.

imageimageCalcareous Algae & Shellfish

This mostly includes green and red coralline algae like Halimeda and Lithothamnion, and small shellfish that have limy skeletons. They grow on the outer reef, on the reef platform and in the lagoon. Those that grow on the reef platform probably join the forams and coral sand that gets moved into the lagoon to form the beaches. The materials formed in the lagoon do not generally make it up from the lagoon floor to be added to the beaches on the lagoon side, but instead form part of the lagoon floor sands.

Stressing the Supply & Distribution

Any stresses on the growth of these materials stops production (pollution, turbidity, acidification). Any engineering in the way stops distribution (seawalls, filled jetties, groynes). Both of these things are now happening on our islands and we can expect – in the long run – to see a nett loss of island area if the islands cannot find enough sand and rubble supply to stay ‘alive’.

Adding to that, materials that used to be part of the island’s resilience (kind of a resilience stock-pile) are now gone (storm banks, beach ridges, rough reef platforms). They were removed by people seeking building materials.

image

Images below: The need for living islands to move. This is a graphic of how sand generally moves around islets during the seasons. The sand acts like fat buffering against waves. During one season, the sand acts as protection for the vegetated part of the islet by being sacrificially moved to the other end of the island by wind, waves and currents. When the weather changes and the prevailing winds swap to the opposite direction, the sand is moved back, again protecting the islet sacrificially. The same sand moves back and forth with minor losses and additions from year to year. Any structures placed in the way can stop the migration, or worse, shift the sand out to deeper water where it can be lost to this system and leave the islet more vulnerable to the elements in the next year.

imageimage

Atoll Engineering that Actively Builds Resilience

Long before climate change bites, we could see significant losses of atoll integrity just from poorly designed developments. We urgently need a new approach to engineering on our atolls. The new engineering needs to be based on real, on-the-ground information and not depend on ‘what works elsewhere’.  Its no longer going to cut it (not that it ever did) to have experts from elsewhere coming in and doing the same kinds of things they do at home.

The main interventions we need right now are:

  1. Increase public (and government) understanding of issues and approaches: People generally do not understand how the atolls work and a lot of the old traditional knowledge that may have helped in the past is not being passed to the younger generation. Organisations interested in raising public consciousness on the resilience of atolls (e.g. NGOs) would provide an excellent service to the country.
  2. Studies needed for getting it right: Much of the coastal works done in the past have been done in the blind. Based on assumptions that just are not true for atolls we have seen staggering damage. We need to know more about the specific maintenance, growth and movements of islands; how beaches change during the seasons; what our wave climate is; and more about our currents and tides. Not in general, but what is actually true for each particular island. Some computer models into which this information is placed might provide an opportunity for better informed choices when it comes to developments – they might be used to show us what a new development might do to an island system. For example, getting Lidar information will prove to be far less expensive than dealing with disasters if we get it wrong. Some of the bigger donors like World Bank, Asian Development Bank, UN could develop these studies to inform all future work.
  3. Enhance or recover natural resilience: This means reinstating or improving natural systems that used to protect the atoll islets. This is the cheapest type of intervention because if done right, there is no further need for maintenance. In other works once restored, these systems should be self-repairing and self-adjusting, just as they used to be. This includes restoring beach ridges, tree cover and beach sands and rubble banks. This kind of approach would be best for outer islands where damage has not yet progressed too far.
  4. Augmented resilience: This would be applied in Funafuti and other capital islands throughout the Region where the natural systems may be too far gone to restore. In Funafuti it is now highly unlikely we will ever be able to restore the natural sand supply for the capital islets of Fogafale and Tegako, so the Funafuti Masterplan suggests some structures to build Core Resilience. Structures could include breakwaters and sewage systems that essentially provide ecosystem services (protection, nutrient removal) that the atolls cannot provide because of the large human population. The idea of making an island part artificial is not really new and is happening everywhere the natural no-maintenance ecosystems can no longer cope (e.g. all of the world’s major cities and harbours have engineered resilience).

In the wake of Cyclone Pam there are many donors and other agencies in Funafuti seeking to contribute to recovery and resilience-building for the future. This brings with it lots of funding with the potential to either get it right, or cause lots of damage. We are now seeing in Tuvalu for the first time, millions of dollars that could see disruptive engineering placed on all the islands and lead to long term degradation. Or we could be seeing a new wave of projects that will enhance our resilience. Its up to all of us to get it right.

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