Vetiver Network International Forum

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#11 2020-12-03 23:44:37

Evan
Member

Re: One or multiple hedgerows?

Fixed link: https://www.vetiver.org/CAM_Mekong_Stab … zation.htm

Vetiver helps to keep those components in place by absorbing the energy of the storm surge and acting as a living blanket to reduce washout??

This is where Andy is on the money. The theory of 'hard' or shaped hedges versus something flexible. Toes may need to be diamond level hard or yielding yet unbreakable.

Besides giant walls, where are successful beach engineering structures? I only ever see vertical concrete, blocks or rocks.

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#12 2020-12-04 01:34:05

admin
Admin

Re: One or multiple hedgerows?

There was no engineering at the toe of the Mekong River work, and because of that it failed eventually, Frankly the Mekong is so powerful there in the flood season I doubt if anything would stabilize that portion of the river, the current there is actually striking the bank at an angle.  The Brazilian beach work is a combination of wooden piles, vetiver and coir matting. You can see the piles in the photos.

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#13 2020-12-04 04:20:59

Evan
Member

Re: One or multiple hedgerows?

I was thinking that worldwide (besides people associated and focused on Vetiver) that there must be beaches with varying methods that are low-energy and low-impact that Vetiver was never integrated in to. Perhaps, like Peter said on the FB group, that a combination of methods are appropriate and Vetiver might be the thing that ties them all together.

It seems like a lot of Vetiver purists try to make Vetiver do all the heavy lifting when it could be the icing on the cake instead.

The piles I would call 'hard', Shantanoo was experimenting with hard yet flexible. Vetiver is almost proven to not always be 'toe' worthy and if conditions in the future become more 'energetic' then something else needs to be integrated.

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#14 2020-12-17 20:11:28

Andy
Member

Re: One or multiple hedgerows?

Great references - working through.

The next obstruction to potential VS coastal site is the relatively narrow beach.

We have the same coastal dynamic around the island. Freshwater stream outflows to the lagoon create coral sand deltas. The same freshwater flow creates passages through the fringing coral reef. Sand moves around the coast through longshore currents created as the lagoon drains out through the passages to the open ocean.

There are now very few deep beaches or dune areas due to development of the outer ring road through dune and wetland zones. Most beaches, away from deltas, are narrow, 10-20m. I've just been trawling through research reports on the use of sand fencing to aid deposition - a mixed bag, always site-dependent and seems more appropriate on deeper beaches.

Looking at the model from Fiji, mangroves are used in the tidal zone as first line of defense, with vetiver used to stablise the upper dune and prevent overtopping. We don't have mangroves - aside from algae little vegetation growing in the lagoon along the coastline.

A recent project at the local harbour is using 1 tonne geotextile sandbags (approx dimensions 1.2m x 1.5m x 0.3m) to provide toe reinforcement. Vetiver planted above the inland row of bags. Area is reclaimed wetland (i.e. not naturally a raised area). It will be interesting to see interactions at the base of the bags as they will be subject to storm surges.

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#15 2020-12-20 19:03:34

admin
Admin

Re: One or multiple hedgerows?

Do you have any photos of the "local harbor" application that you mention in your post? I believe that Mohamad Islam in Bangladesh has been doing some coastal work with vetiver in the Sundarbans - also in West Bengal Sundarbans.

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#16 2020-12-21 22:40:57

Andy
Member

Re: One or multiple hedgerows?

Here's the Avana Habour site (Rarotonga, Cook Islands). A single vetiver hedgerow at 150-spacing above the top line of bags (in front of tires). Planted 2-3 weeks ago as overwash protection.

avana-harbour-132050426-10157699947180812-585369900614761687-o.jpg

Photo: Kelvin Passfield / Te Ipukarea Society

Last edited by Andy (2020-12-21 22:42:32)

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#17 2020-12-21 23:06:47

admin
Admin

Re: One or multiple hedgerows?

Why not plant vetiver into the sandbags. Roots will eventually grow through them into whatever is below. This practice has been used successfully for gully rehab in the Congo.
Screen-Shot-2020-12-21-at-2-05-35-PM.png

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#18 2020-12-22 00:40:35

Andy
Member

Re: One or multiple hedgerows?

The Avana sand bags are geotextile - Elcorock. They're bigger than they look in the photo. Fabric allows water to flow through, but does not allow sand to escape. Not designed to biodegrade - I suspect root holes also unwelcome / might compromise utility.

Here's the manufacturer: https://www.geofabrics.co/products/elcorock

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#19 2020-12-22 18:53:45

admin
Admin

Re: One or multiple hedgerows?

Good point. But it might be worth doing a test some time on one of these types of bags to see the impact vetiver might have. Would vetiver roots grow through them, would they be then better anchored, and they would certainly look nicer!

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