Avana Point is to the lower left of this aerial view of the Avana and Muri lagoon. Both areas have huge cultural and historical significance. 18071151
Avana Harbour on the eastern side of Rarotonga has been in the spotlight this week as residents awoke on Monday to find a digger dredging in the narrow stretch of water. Al Williams investigates what this project is all about.
Landowners were hot under
the collar, some concerned about the digger moving silt in
They were not made aware of the operation, and
horrified to see the harbour changing colour with sediment.
After some investigation, it was revealed that what
they witnessed, is a pilot programme in action.
The first of its kind in the Cook Islands.
And the programme has been extended, as a small
stretch of coastline in the harbour continues to suffer from the effects of
storm surges and outflowing currents.
Avana is a location of significant historical interest
as it has been known as Te Avatapu-ki-Avaiki (the Sacred Passage to Avaiki, the
ancestral homeland of the Polynesian people).
Rarotonga resident Ngatuaine Maui in Avana, the Passage of Traditional
Navigators, writes, the Avana site highlights the outstanding ability of
ancient Polynesian navigators to sail long distances across Te Moana Nui a Kiva
(the Wide Ocean of Kiva) using traditional navigation systems.
“The knowledge and skill of navigation possessed by
the Polynesians far exceeded those of Western nations at the time.
“It is believed that as many as a hundred voyages to
Aotearoa (New Zealand) were made by vaka (traditional double-hull canoes) from
“There are even accounts of voyages made from French
Polynesia and the Marquesas to Avana before continuing on to Aotearoa.”
Two engineering reports supplied to Cook Islands News,
one updated in 2022, show the site also has significant interest among environmental
Te Ipukarea Society commissioned the reports.
Technical director Kelvin Passfield says the Society
was looking for a pilot site as the technology has been successfully trialled
Now the Society is looking for funding to assist with
similar schemes in the outer islands.
National Environment Service (NES) is the regulatory
body for projects that may have an impact on the natural environment, and its
director Halatoa Fua says coastal protection is a key component of
environmental compliance of which NES assesses the impact and the necessary
That includes Avana.
The first step for NES is to understand the full scope
of works to determine the environmental impact, before approval is given and an
engineering report is submitted to the Rarotonga Environment Authority (REA) to
An Environmental Impact Assessment (EIA) permit is
then issued which requires an EIA report, and 30-day public consultations for
the REA to consider.
it comes down to at Avana is the use of geotextile bags.
Geotextile bags (also referred to as geo-tubes,
dewatering tubes, or erosion control tubes) are used for large shoreline protection, erosion control, dewatering and
sludge removal projects.
Geotextile tubes are cost-effective solutions for
containment, dewatering, desludging, and shoreline protection.
It’s 20-year-old technology, but it’s efficient,
The Avana project, launched in 2020, has two main
To prevent further erosion of the area to
the south of the jetty built under the Japan Grant.
To demonstrate a more environmentally
friendly version of seawall protection than the current practice of using
The area is scoured by wave action, especially during
high tides or stormy weather. The project involves the partial excavation and
removal of the existing bags full of coral rubble and sand, which are a legacy
from the Japan Fund wharf project.
The existing foreshore protection was “clearly non
effective against erosive forces of waves and high seas”.
“If this section of land is not provided further
protection, it is likely that it will continue to erode, with the consequential
loss of the small shelter constructed landward of the beach, as well as the gradual
erosion of the land used for recreation and boat launching, further landward,”
according to the engineering report.
The new ElcoRock geotextile sand bags, about 80 of
them, have been extended 45 metres along the shoreline.
They are supported by a geotextile matting placed
underneath the bags, to help prevent undermining of the ElcoRock bags by wave
On the landward side of the ElcoRok sand bags, native
vegetation provides a second level of defence against coastal erosion.
The alternative form of protection, basalt boulders,
such as have been commonly used in other parts of the coast line in Rarotonga
However, supply of these boulders is becoming more
difficult due to injunctions placed on some land where these are being sourced.
The engineers point out that in addition, a number of
these boulder revetments have caused erosion to adjacent properties, as well as
scouring of the lagoon beach floor seaward of the boulders.
When these walls fail, as has happened in numerous
locations, including the Vaimaanga Hotel site, the boulders are left littering
The geobags have
been attached to a filling frame, and filled with the material inside the
existing bags at the site.
project budget is approximately NZ$60,000, including all materials, equipment
hire, and project oversight.
the main project benefit is the reduction or cessation of coastal erosion at the
Avana location with the added benefit of shoreline beatification from the
planting of native vegetation, which will also help control erosion.
The project also
allows the opportunity to assess the effectiveness on Elcorock geobags. They
may be particularly practical for the Northern Group, where there is no access
to basalt boulders locally.
The fact the bags
are light and easily transported is a big advantage over one tonne boulders.
The cost of high quality geotextile makes the system comparable in cost to rock
structures when suitable rock is available in close proximity to a site.
“So for this site
there is probably no cost advantage in using the Geobags in place of boulders.
“However, if this
project demonstrates the suitability of Geobags for the outer islands, it
should be a significant cost saver for erosion control in those locations that
do not have the choice of using basalt boulders.
“There is also the
advantage of not having to mine boulders from sensitive inland areas, with the
associated environmental impacts of the quarrying and transport of boulders to
the erosion site.”