Weighing the alternatives to protect the Cooks from coastal erosion: what’s next?

The port of Avana, east of Rarotonga, was within the highlight this week as locals awoke on Monday to search out an excavator dredging within the slender stretch of water. Al Williams investigates what this mission is.

Landowners have been scorching beneath the collar, with some frightened concerning the excavator shifting silt into the harbor.

They weren’t made conscious of the operation and have been horrified to see the harbor change coloration with the sediment.

After an investigation, it was revealed that what they witnessed is a pilot program in motion.

The primary of its variety within the Cook dinner Islands.

And this system has been prolonged, as a small portion of the port’s shoreline continues to endure from the results of storm surges and outflows.

Avana is a spot of serious historic curiosity because it has been often known as Te Avatapu-ki-Avaiki (the sacred passage to Avaiki, the ancestral homeland of the Polynesian folks).

Ngatuaine Maui, resident of Rarotonga, in Avana, the passage of conventional browsers, writing, the Avana web site highlights the distinctive skill of historical Polynesian navigators to navigate lengthy distances throughout Te Moana Nui a Kiva (the huge ocean of Kiva) utilizing conventional navigational programs.

“The data and talent of navigation possessed by the Polynesians far exceeded that of Western nations on the time.

“100 journeys to Aotearoa (New Zealand) are believed to have been made by vaka (conventional double-hulled canoes) from this web site.

“There are even accounts of journeys made out of French Polynesia and the Marquesas to Avana earlier than persevering with on to Aotearoa.”

Two engineering experiences supplied to Cook dinner Islands Information, one up to date in 2022, present the positioning can also be attracting appreciable curiosity amongst environmental teams.

Te Ipukarea Society commissioned the experiences.

Technical director Kelvin Passfield mentioned the corporate is in search of a pilot web site as a result of the know-how has been efficiently examined elsewhere.

Now the Society is searching for funds to assist with related applications within the outer islands.

The Nationwide Setting Service (NES) is the regulator of initiatives which will impression the pure setting, and its director Halatoa Fua says coastal safety is a key a part of environmental compliance that the NES assesses. impression and the required mitigation measures.

This consists of Avana.

Step one for NES is to grasp the total scope of labor to find out the environmental impression, earlier than approval is given and an engineering report is submitted to the Rarotonga Environmental Authority (REA) for examination.

An Environmental Influence Evaluation (EIA) allow is then issued, which requires an EIA report and 30-day public consultations to be reviewed by APER.

At Avana, it comes right down to the usage of geotextile baggage.

Geotextile baggage (also referred to as geotubes, dewatering tubes, or erosion management tubes) are used for giant shoreline safety, erosion management, dewatering and sludge disposal initiatives.

Geotextile tubes are economical options for containment, dewatering, emptying and shoreline safety.

It is 20-year-old know-how, however it works, says Passfield.

The Avana mission, launched in 2020, has two predominant aims;

• To forestall additional erosion of the realm south of the pier constructed beneath the Japanese grant.
• Reveal a extra environmentally pleasant model of levee safety than the present apply of utilizing basalt blocks.

The realm is eroded by wave motion, particularly throughout excessive tides or stormy climate. The mission includes partial excavation and elimination of current baggage crammed with coral rubble and sand, that are a legacy of the Japan Fund wharf mission.

The prevailing foreshore safety was “clearly not efficient in opposition to the erosive forces of waves and excessive seas”.

“If this part of land isn’t protected additional, it’s prone to proceed to erode, with the resultant lack of the small shelter constructed in the direction of the seashore land, in addition to the gradual erosion of the land used for recreation and boating launch, farther landward,” in line with the engineering report.

The brand new ElcoRock geotextile sandbags, about 80 of them, have been prolonged 45 meters alongside the shoreline.

They’re supported by a geotextile mat positioned beneath the luggage, to assist forestall the weakening of the ElcoRock baggage by wave motion.

On the land aspect of the ElcoRok sandbags, native vegetation offers a second degree of protection in opposition to coastal erosion.

The choice type of safety, basalt boulders, as generally utilized in different elements of the coast line in Rarotonga, have been eliminated.

Nonetheless, the availability of those rocks turns into harder as a result of injunctions positioned on sure lands the place they’re extracted.

Engineers level out that as well as, quite a lot of these rock revetments have brought on the erosion of adjoining properties, in addition to the scouring of the underside of the lagoon seashore off the rocks.

When these partitions fail, as has occurred in lots of locations, together with the Vaimaanga Resort web site, rocks litter the seashore.

The geobags have been hooked up to a filling body and crammed with the fabric inside the present baggage on web site.

The mission finances is roughly NZ$60,000 together with all supplies, tools rent and mission supervision.

Engineers conclude that the primary advantage of the mission is the discount or halting of coastal erosion on the Avana location with the additional advantage of shoreline beatification by the planting of native vegetation which will even assist to regulate erosion.

The mission additionally makes it doable to judge the effectiveness of the Elcorock geobags. They are often particularly useful for the Northern Group, the place there is no such thing as a entry to basalt boulders regionally.

The truth that the luggage are mild and simple to hold is a giant benefit over the one ton boulders. The price of a top quality geotextile makes the system comparable in value to rock constructions when appropriate rock is out there close to a web site.

“So for this web site, there’s in all probability no monetary profit to utilizing Geobags as an alternative of rocks.

“Nonetheless, if this mission demonstrates the suitability of Geobags for outer islands, it ought to present vital value financial savings for erosion management in areas that haven’t any alternative however to make use of basalt boulders.

“There’s additionally the good thing about not having to dig boulders from delicate inland areas, with the related environmental impacts of quarrying and transporting boulders to the erosion web site.”